Wednesday, January 2, 2019

A comparison of 2V and 4V Ducati 750 engines

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When I did my 2V cam profile measuring (here), I had the chance to test a theory that I had, being that the cam profiles for the 4V Strada cams - marked A1 - were simply the 2V profiles of the time - the F1 cam that became the R grind used in the 600 and 750 engines from 86 to 02.  Turns out I was probably half right.

The inlet profile looks mostly the same.  The exhaust has a fatter nose for want of a better description, and is more asymmetrical, biased to the retarded side.  I found it a bit odd that they would just use the 2V profile, but while in reality the 2V cam was lacking quite a bit of lift when used with the 41mm inlet valve in the 750 F1, its 9.5mm of lift was more than enough for a 32mm inlet valve (as the 748cc 4V initially had).  Lift required is based on the fact that a poppet valve flow area - if you like the curtain you get around the valve od when lifted - is equal to the valve head area when the lift is 1/4 of the valve head diameter.  So if you have 32mm valve you need 8mm lift.  And 41mm needs 10.25mm lift.  It's a rough guide sort of thing.  By the time they got to the production 748, the inlet valves had grown to 33mm and exhausts to 29mm.

(Thinking back to the above now, after having written much of what follows, I've come to the conclusion that this comparison is flawed from the start.  The 750F1 cam simply doesn't have enough lift for its valves.  Maybe someone on the 4V project at Ducati (Bordi and his team) saw the profile and thought "That's about right for a 32mm valve, I'll have that".  Fair play to them.)

(And another - the 85 750F1 has small 500 Pantah valve sizes, so maybe for them the valve lift was ok.)

To the profile comparison.  Blue and red are A1 inlet and exhaust, green and orange the R inlet and exhaust.



I then wondered if they'd used the P grind from the hot F1 series - Montjuich, Laguna Seca and Santamonica - for the A cam used in the 851 Tricolore Kit and SP series.  But clearly not, the P has much more lift and more duration.

Some time later it occured to me that this meant there were a couple of engines from the same manufacturer with the same bore and stroke using the same inlet cam profile and a similar exhaust cam profile in both 2V and 4V configurations.  Those two engines are the 750 2V and 748 4V, both with bore and stroke of 88 x 61.5mm.

As such, I thought a comparison of 2V and 4V was in order.

In basic engine design, the potential peak torque value is based predominantly on capacity.  There is a measure called Brake Mean Effective Pressure, which is basically torque per cc, and it's somewhat consistant with similar engine designs and a measure of efficiency, both volumetric (how much air the engine can suck in and then trap) and combustion (compression ratio, chamber design).  The actual outright potential efficiency in terms of energy in versus power out is related to the compression ratio, although measures to reduce losses are a big part of engine design these days.

In contrast, the potential peak power value is not capacity based, but air flow based.  Simply, how much air can the engine flow through itself.  This also overlaps with mechanical design and maximum rpm potential.  If you're designing an engine for racing, for instance, you'd start by defining the maximum rpm you're going to use, which is mostly bound by piston speed.  Maximum piston speed is not an enforced limit, but a number that is in reality a development boundary to be pushed and see what happens.  The old "to finish first, one must first finish" kind of thing.  Usually defined as "mean piston speed", which is the average speed over the journey from top to bottom.  The actual maximum piston speed, which occurs about mid stroke, also varies with connecting rod length.  Seems that 30m/s is about the current maximum "mean" used.

With the limits of capacity and maximum piston speed set, the stroke is defined and then the bore defined by that.  Or, in MotoGP for instance, where the capacity limit is 1000cc and bore limit 81mm, those limits give a minimum stroke of 48.5mm, which in turn, if the maximum rpm used is 17,000, gives a minimum mean piston speed of 27.5m/s.

This can also depend on physical properties of components used too, and the limit there, if not specified by rules, is generally cost.  The old "how fast do you want to spend".  As a guide, when Ducati were at the end of the 999 race life, they were revving them to 14,500rpm to try to be competitive.  With a 63.5mm stroke, that gives a mean piston speed of 30.7m/s.  Pistons and connecting rods were not limited by the rules, though, unlike the 1198 era when production parts had to be used.  Through material spec and cost, this effectively limits the maximum mean piston speed indirectly.  This, along with the physical limit of further enlargement of bore size on the Pantah derived 1198 crankcases, is what led to the Panigale engine development.  Bigger bore means shorter stroke, and the shorter stroke was what they needed at the time.

The main secondary variation in terms of possible peak torque production is that the 4V engine has more compression, which realistically is 1/ simply a by product of the required (and better) pent roof combustion chamber design, and 2/ also permitted by that same chamber design with its ability to better resist detonation - ie, a smaller, shallower chamber with valves at a much smaller included angle, large squish areas and a central spark plug.  It is also water cooled, again making it a better high performance engine.  So the generic 4V pent roof head configuration has combustion chamber design advantages you can't get in a 2V without restricting valve size markedly.  The 2V chamber in the 750 engine is a (largely) hemispherical type chamber, which tends to give a deep chamber with much more valve angle than the 4V design simply to get the required valves in.  If you want high compression, you use a piston with a dome that in itself causes issues with flame front travel and increases the potential for detonation.

In so many ways the shallower 4V chamber and flat top piston are just better.

748 chamber on the left, 750 on the right.  748 valve sizes are 33/29mm inlet/exhaust, the 750 is one of my bigger valve heads with 42.5/37mm.  Std 750 is 41/35mm.



Comparing power and torque outputs was the aim of this, so we'll get into it.  Blue is 748, red 750SS and green 750SSie.


The power graph shows the 748 peak power value around 50% more than the 750, at an rpm similarly 50% higher.  This makes sense, as power is defined as torque x rpm.  Same torque at 50% higher rpm will give 50% more power.  If you compare the valve sizes, the 748 has about 30% more valve area.


The torque output, on the other hand, shows some of the implications of trying to spread the rpm range over which the power is produced.  The 2V curves are both generally just rounded curves, whereas the 748 has various peaks and troughs.  This is usually what happens as you widen the rpm range you're tuning for.  At lower rpm, as a general rule, you want things to be longer.

The difference between the 750SS and 750SSie is carburettors vs fuel injection.  The 750 engine with the Mikuni carbs has long inlet manifolds that position the carbs side by side.  The 750 ie engine has much shorter manifolds and throttle bodies arranged at 90 to each other, giving the appearance of a much shorter inlet tract.  In reality, the carb model has short rubbers into the airbox, whereas the ie model has much longer rubber trumpets inside the airbox (much longer on the vertical cylinder) that would mean the overall trumpet to port dimension would not be that much different between the two models.  Keep in mind everything else engine wise - heads, valves, pistons, cams - are the exact same parts.

One thing that is done when you try to extend the power range is to make the inlet shorter.  This helps the overall peak power value, but while it also reduces the peak torque value, it will increase the average torque figure over the wider rpm range and introduce the peaks and troughs.  The narrower the rpm you tune for, the more specific you can be in your tuning setup - inlet length, etc, and that will lead to a higher peak torque figure.  Great for a unique application such as a stationary engine, not so good for general motorcycle use.

There is a great dyno graph that I have never been able to find online - the only place I can recall seeing it in Sir Harry Ricardo's book - from D type Jaguar testing that shows the power curve with inlet lengths varying from maybe 6 to 36 inches.  At 36" the peak torque is well above that of 6", but the rpm range is much narrower.  As an implications and compromises of tuning illustration, it's particularly simple, elegant and quite definitive.  I might have to go to a Uni library and photocopy it some day.

Another point here is that while the inlet cams in this instance are all spec'd at the same timing - 119 degrees inlet centreline, with the exhausts at 106 on the 2V and 112 on the 4V, in reality the 2V would be pretty close to that or even maybe 1 or 2 degrees advanced, whereas the 4V would have all cams retarded to some extent.  We used to find 4V inlets from 5 to 10 degrees retarded out of the box, and when we reset the timing to 108/108 we did sometimes move inlet cams over 20 degrees.  This gives a better shape to the 748 torque curve, as below.  Blue is as delivered, red 108/108.


Incidentally, when this cam first appeared in the 750F1, the timing was 10 degrees more advanced than in the 750 Paso, which makes much more sense to me.  I have read that the timing was changed for "emissions" reasons, which really makes no sense to me as there was no motorcycle emissions testing back then.  I'd speculate it was done for two reasons.

1/ The Paso, with the longer inlet manifolds and Weber carb, had a more midrange orientated power delivery, and retarding the cam timing gave a power delivery more in keeping with what was expected and helped increase the outright power figure.

2/ With the fully enclosed body of the Paso and a compression ratio much the same as the F1 (spec is 10:1 in the Paso manual), even with the oil cooling system I'd think the risk of detonation would have been higher so retarding the cam timing would reduce the midrange cylinder pressure.

By the time the 750SS appeared it had pistons which are the slightest bulge off flat, and the listed compression ratio of 9:1 meant that there was no detonation in sight.  The other difference with the later pistons was that the inlet valve reflief was shallower, so the most advanced I was game to run those cams was 114 degree inlet centreline.  Not sure if you could run 110 on a 750 Paso or not.

Comparing a 750SS with timing at 119 and 114 we get the following.  If we could have run 110 and picked up a little more at the 5500 rpm torque peak and lost a little more over 8000 rpm it would definitely impact the feel of the power delivery, and that may have been a bad thing when you only have 2V motors on offer and people who just love pointlessly revving the snot out of things.


Inevitably, the two previous graphs lead to this one, being 748 vs 750 with more consistant cam timing settings.


Peak torque is almost the same, peak power about the same difference as before.


Yeah, but.....

Frankly, there's more yebits to this story than story.  It was sort of a good idea that has, realistically, taken it in the neck quite a few times along the way.

One could argue that we could make the 750 engine a better one for this comparison by giving it a different cam with more appropriate lift.  Totally negating the comparison, of course.  And its under valved, so lets fix that too.  And the comp is too low compared to the 748.  Luckily, I prepared one earlier.  My 750 engine with 900 cams, 42.5/37 valves and Ferracci 12:1 pistons.  The 900 cams have 12 degrees more duration and 2.5mm more lift.


Even though the cam duration has gone up, the torque curve is still a single peak, typical of the 2V motors.  

But, if we're going to make the 750 a bit better, we can make the 748 better too.  Along the way they had a couple of goes at the 748.  The SP/SPS with its great big old school cams, and the R with the bigger throttles and valves and half big cams.  Neither made a better road bike - it always dismayed me when people who bought 748R came in and claimed their old 748 had more midrange.  Of course it did.  The concept of an homologation special is not understood by many.

748 in blue, 748SPS in green, 748R in red.  Different shape curves, or more importantly, different amounts of torque over 10,000rpm.  Where the power is.  But, the peak torque value is pretty consistant across the 3, as it has been for all the graphs so far.


But (I'm liking these buts), if we're going to improve the 750, we might as well improve the 748 too.  Properly.  That involves bigger valves again - 37/30.5, larger than the 748/748SP at 33/29 or the 748R's 36/30, but reduced cam duration - at least 20 degrees on the inlet and 16 on the exhaust with appropriate lift.  Let's call it a 749.

The totally different exhaust designs may influence the 749 output, but in comparison to the above 748's adding a base model 749 curve in burgundy shows how much better it is.  Again, 750cc so similar peak torque, but the shorter cam duration and bigger valves combine to give better low rpm and high rpm torque compared to the 748.  The valve of good heads and just enough cam.  Although, on the road, it's kind of a boring power delivery.  Having the torque rise more noticeably with the rpm does make them feel more racy.


Power curves show the 749 is much more linear.  I think it'd make a good naked bike motor.


I might stop there.  I've kind of lost the direction of this, which really is just me thinking about it too much.



Friday, December 28, 2018

Closing rocker spring change on the 851.

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One thing about the 851 that has annoyed me for many years is the way it idles - best described as crap.  As a 1989 model it has the early soft closing springs - the springs used to (try to) keep the valves closed as per #5 the picture below.  They're not valve springs in the typical sense, just a helper.



If you run the engine without them, they tend not to idle very well.  Once the revs are up it's not an issue, but at idle too much cylinder pressure leaks past the valve seats.  In use that translates to a lot of misfiring and oxygen and hydrocarbons in the exhaust mixture, which makes it unpleasant to be behind.  Even with the soft "Corsa" springs as this bike had they're not a lot better.

I had hoped that adjusting the valve clearances would fix the issue.  When I first purchased the bike I had given it a big service, adjusting the valve clearances and replacing the original stainless steel collets with steel ones.  The new collets tend to settle (wear) into the shims and valves, so you always need to adjust again once that has happened.  Over the 6,000km I had ridden it in the 3 or so years I had it on the road it had become slowly worse, and parking it for 13 years was the most simple solution.

During the "back on the road" service recently I had found a lot of clearance - most around the 0.20mm range - and 3 pairs of broken collets. Once adjusted though, it wasn't a lot better, still having a fairly ropey idle with a dirty mixture - lots of O2 and HC to really get up your nose.  And that was probably the thing that was annoying me the most now - being embarrassed at how horrible it would have been to be around the bike while sitting idling at traffic lights, etc.

I recall servicing an early 851 years ago at Moto One, pulling the closing clearances down nice and tight and it was nice and clean at idle, so was hoping for a similar result again.  Not to be, unfortunately.  To give you an idea, this is what a dirty mixture looks like on the gas analyser.  5000ppm HC and 5% O2 makes for runny eyes.



I had come to the conclusion the fix was the heavier closing springs fitted from 1991 models onwards.  Confirmation of this came from the early ST3, which had a recall involving replacing the exhaust rocker closing spring with a much heavier part.  The very soft inlet springs stayed as they were, and it took them from having a mixture like the above to the expected clean.

All the later model 4V Strada cam bikes tend to idle very nicely, and I could see no reason why my 851 should be any worse.  It had good leakdown and cranking compression, both of which would indicate satisfactory general health.  And there wasn't a great deal of wobble in the valve guides.

Ideally, I would have pulled the cylinders and heads and fitted the new pair of cylinders and pistons I have, along with 748 heads modified as per the 853 kit procedure and fitted with the heavy springs.  Would have been an absolute treat.  But, I'm not really interested in that sort of thing these days - really, I just want a bike to be able to ride, and the 851 was the only complete, club reg eligible bike I had available at the time.  The time investment required is more than I have available to spend.

The only other option was to swap the closing springs with the heads in place.  I wasn't looking forward to it.  There's a French fellow named Patrick who did his years ago and has been encouraging me to do the same via the 851 forum, but I was still reluctant.  Until the last time I rode it and decided I'd had enough.

So I dug the set of springs I've had for 15 or so years out of the tub and put the bike on the bench.  Everything externally removable has to come out of the heads, as below.  That's the easy bit.



You can see the difference in the springs clearly in a side by side photo.  The original are 2.0mm wire diameter with 7 coils.  The replacements are 2.7mm wire diameter with 5 coils.  Using the spring rate calculator I usually use for fork springs (I think it'd work for rotating coils) and guessing the coil diameter at 15mm give rates of 1.0 and 5.5 kg/mm.  Not sure that I believe that, but the spring rate is proportional to the wire diameter to the power of 4 and inversely to the number of coils.  Thicker wire and less coils both give a higher rate.  In terms of how hard it is to push the rocker down, there's a significant difference.  Let's go with that.



The worst part of the replacement procedure, as it turns out, was getting the springs and rockers back into place and the pins in.  The closing rockers and pins are at the very outer corners of the above photo, and getting in there with limited access - vertical exhaust and both sides of the horizontal with the radiator still in place (frankly, I've had the f#*%ing radiator out of this thing so many times in the last few months that it was not coming out again.  Funny the jobs you absolutely hate) and with everything coated in Motul 300V it was as slippery as the proverbial two eels in a bucket of snot.  I resorted to zip tying the springs in and then poking the rockers in.  There was a fair amount of cussing - you work blue with this kind of job.



I started on the vertical, as I figured the exhausts would be the worst.  As a clarification as to why this is a crap job, the tail of the spring has to go under a lug cast into the inside of the head.  In the above photo, the lug is between the two closing rocker pins - the tails go under one from each side.  The spring tail is behind the zip tie, so you have to pull it down maybe 70 degrees.  It's not a fun job, even when the head is on the bench.  But my home made tool can work an absolute treat.

Speaking of my home made tool, I used it last week on an ST4S head, the frustration of which reminded me after the fact that I was using it wrong.  You'd think I'd remember how to use my own tool.  Ideally, this tool works best from the opposite side - you work the exhaust spring tail under the lug from the inlet side.  There's no access from the vertical exhaust side, so I popped the inlet spring in first from the inlet side then tried the exhaust.  The first one went in so easily it could only give me a false sense of success.  Working around the radiator and thermo fan on the horizontal sucked.  But, overall, it wasn't as bad as I was fearing.

The tool.







Then it was just a case of putting everything back in, and then everything back on (replaced what looked like a leaky timing shaft seal too) and it was time to fire it up and see what happened.  It was a satisfying pile of debris once done.



When I had the plugs out I noticed the vertical was whiter than the horizontal, so I adjusted the throttle linkage rose joints out of alignment to close the vertical throttle blade a little.  I couldn't be bothered doing it properly, it's such a pain access wise with it assembled to a run-able state.  As I hoped, it was idling higher.  At least that was reassuring, the valves were holding compression better.  I didn't replace the eprom first as I had planned, and to my surprise it was a lot leaner than it had been previously.  I guess the holding compression relates directly to trapping more air.  I wound the idle trimmer on the ecu a couple of turns counter clockwise to richen the mixture, and we went from around 1% CO to 4% CO.  It wasn't a lot cleaner mixture wise than it had been previously - it's in the 2500 - 3000ppm HC and 2.5 - 3.5% O2 range around 4% CO, but it idled so much lower and smoother that it was clearly better.

For an eprom I compared the 009B based eprom I was running with the 035 eprom from the 1992 851.  The 89 - 91 bikes all used the 009/009B - the B refers to a software change that Duane told me related to how the engine was "turned off", which was done to improve the life of the starter clutches.  It was done well before my time, and I've never found a service bulletin relating to it.

The 1991 model used the heavy closing springs with the 009B eprom, but I don't recall how they ran.  Don't know if I've ever ridden a 91 now that I think about it.

Comparing the 009B to the 035 gives the % differences as below.  Negative numbers mean 035 is leaner.  Blue along the bottom is RPM, red up the side is throttle opening in degrees.  P7 ecu starts at 0 degrees, which is the lowest TPS output voltage it sees every time the key is turned on.  It's not actual throttle opening, just opening from closed.  The implication here is that if you change the closed throttle position on the idle stop you change the fueling at low throttle openings.  Can be a frustrating system, as the only way to adjust idle speed is with the idle stops as the P7 throttle bodies have no air bleeds.



The 035 eprom is a lot leaner at low throttle than the 009B, and that is the direction I was heading with the eprom I had been running which was my mapping from when I was using an Ultimap UM011 based eprom dropped over the 009B base software with some changes to the environmental trims.  The 009B is also richer on the air temp trims, so in use it will be richer than the above comparison indicates.  I leaned those trims off and reduced the range of them in the eprom I'm running now.

Comparing my eprom to the 035 is as below.  The temp trims on them are much closer.  I made the lower throttle lines the same as the 035 pretty much, and the 035 idle fuel was spot on with the idle trimmer set to the mid point - you remove the top of the ecu and measure the voltage at the trim pot outputs and set them to 2.5V, which is midway between 0 and 5 (oddly enough).  I like to start at the mid point if I can.



The larger positive differences at the top up to 7,000 rpm are for the revised cam timing - closing the inlets earlier traps more air and needs more fuel.  Although after the torque peak, you need less fuel as the volumetric efficiency is dropping faster.  So 8,000 rpm and up it's getting less fuel.  I have the rev limiter set to just under 10,000 rpm from memory, so the point at 10,500 is redundant.

The -100 on the bottom line is simply due to me turning the fuel off on overrun.  You just make the map value 0.

After all this I put it back together and went for a ride.  It was pretty hot here today - 37 degrees - and that may influence how it ran a touch.  Possibly influenced how it started too.  When I turned it on the temp gauge moved off the stop even though the engine was "cold".  I have made the coolant trims at 5 and 17 degrees coolant temp richer from memory, but once running it doesn't need more enrichment as it warms up through the 29 and 41 degree points.  But they do like more fuel for the initial start, and the ecu from 1.6M onwards have a starting enrichment table as well as a coolant trim table, where they have a decaying enrichment that works on rotations since started.

It almost gave me the impression it was a little off a few times, but the more I rode it the harder it was to find any proof of that.  It had a point at 3,500 rpm just off closed throttle that may be too lean, as it shuts down a little there at times, but it's not really an issue.  It really is a lot nicer at low throttle openings, which was the point of this.

I was going to check the idle mixture after riding it in case it'd cleaned up a bit more due to valves seating better with a run, but forgot.

It did cut out a few times as I pulled the clutch in coming to a stop.  Usually that's ignition timing based, but this eprom has modifed spark map breaks that allow more advance at 1000 rpm to try to stop that, and a plateau from 1100 to 1500 that gives you good control of the idle speed with the advance at those points being the same as the original eprom value - 6 degrees from memory.  But I may put some more advance in - it makes them idle nicer if you can add advance without losing control of the idle speed.  That part is annoying as I've never had this bike do that before, and it's another reason to have to remove the seat base to get to the ecu.  Usually more than once.  I'm so over replacing eproms - flashing ecu is so much easier.


And I think the clutch might be slipping.  I'll see how long I can ignore it for.

Sunday, March 4, 2018

Ignitech TCIP4 as a replacement for Marelli Digiplex

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I alluded to this on Facebook, but figured I should put up a bit more info as there's not a lot out there.  It's also a continuation on from this post - Dellorto carb tuning on a Moto Guzzi Sport 1100, with some gearing and ignition rambling - as one of the theories I had on the poor low speed running was it being related to ignition timing.


Many years ago (back in the Moto One days, so 9+) I had a fellow with a Sport 1100 contact me as he was trying to replace his Digiplex with an Ignitech.  The had said it would work, but he failed and gave up from memory.  I asked Ignitech the question again last year, and they assured me it would work.  Like a lot of things, sometimes the only way to prove (or disprove) a theory is to do it.  So I ordered a TCIP4 to suit, which is just a normal TCIP4, not a Ducati / Kokusan specific unit.  It is supplied with a generic connector under the expectation of cutting the original out, but I don't like the point of no return if I can avoid it.

To make sure I wasn't wasting my time I put some terminals on the Ignitech wiring and plugged it in for a test.  Hit the button and it fired straight up, which was a great relief.  I went for a ride and that was good too, so moved on to the making it right bit.



Before I pulled the Digiplex I did some tests to check the ignition timing as was.  I had marked the flywheel with some paint marks, using the teeth on the ring gear.  I had counted them and got 97, which gives about 3.5 degrees per tooth.  I then put a degree wheel on the alternator to be a bit more accurate and that gave the idle at 6 degrees and the full advance at 33 degrees BTDC.

With the Digiplex it appeared with the vacuum hose disconnected (mimicing WOT) to not have a lot of advance under 2,500 rpm, and not a great deal more with the vacuum hose connected.  With the Ignitech you can make up the map as you wish, and a linear increase in spark advance generally gives you a nice feel - no holes or bumps, etc.  Much like good suspension, good ignition timing is often not noticeable in any way.  It just works.

The table below shows what I set the Ignitech map to.  The base advance setting of 12 degrees appeared to correspond with full advance set to 35 degrees, and that gives an idle setting of 12 degrees where it does certainly happier than with the Digiplex.

RPM 1400 2000 3000 4000 5000 6000 7000 8000
Advance 12 18 28 33 35 35 36 36

To connect the Ignitech I didn't want to cut off the original Digiplex connector on the wiring loom, just for retro-ability.  I had no idea where to start looking for the correct connector, as I doubt it would exist outside of oem, so made one from a block of plastic.  It was actually pretty easy.  I measured the terminal spacing and drilled holes as required.  The hole from the back (wire side) was large enough to fit the wire through only, with a countersink on the terminal side to hold the terminals in the loom connector while not allowing them to move back out.  I drilled then filed a slot into the front edge to allow the original loom connector to slot in.  A couple of zip ties seemed like the most appropriate way to keep it all together.




To mount the TCIP4 I bent up a piece of aluminium sheet and fitted it using the original Digiplex mounting holes and rubber bushes.


And that was done.  At this point I gave it back to the owner and he was very happy with the result.  While there's still some low speed jerkiness, it's much less than it was.  Quite amazing, really, how much difference some more spark advance can make.

Personally I think fitting a rear wheel with a cush drive (realistically a 17" from Sport 1100i and V11) would cure that and shorten the gearing a little as well for a nice side benefit.

If you wanted to go further, you could fit a MAP sensor as the version 88 of the TCIP4 has the ability to take a MAP sensor input to allow for a 3D ignition map.  A 3D map allows you to add ignition timing on part throttle, which makes a difference to response and fuel economy.

Saturday, December 23, 2017

Ducati 43mm non adjustable forks 1999 - 2005 ish - The ones with an awful lot of low speed damping.


There's some 43mm non adjustable forks fitted to the smaller engined Monster and SSie from 1999 to 2005 or so, made by Showa and Marzocchi and someone else who possibly makes them under license from Marzocchi (maybe?) that have quite amazing amounts of low speed damping.

The easiest way to recognise them is to strip them and try to get the oil out of the cartridge.  It would appear that the only way for the oil to get out is between the rod and corresponding opening in the top of the cartridge.  A few drops at a time.  I really don't understand that.

As an aside here, after this style fork they went to an externally visually similar (I'd say probably identical) fork which has rebound damping only on one side and compression (allegedly) on the other.  These are the forks in the S2R800, 695 and late 620 and 400 models.

I don't see many of these bikes for fork oil change services, but I did an oil change on a 1999 750SSie a couple of years ago and tried going down to 5 weight oil to reduce the damping.  It didn't really seem to make much difference, and that's as far as I got with that bike.

The oil spec for those forks is Showa SS-8, which I found a spec for on the transmoto.com.au/comparative-oil-weights-table of 36.8 cST @ 40 degrees C.  That's a tiny bit lighter than Maxima 10 weight (32 cST on the linked table, but 37.4 cST in the Maxima blurb), but generally typical for the available range of 10 weight oils.  The Maxima 5 weight is 16.2 cST, which is a big difference that gave little change.

The later non Showa ones are listed as using Shell Advance Fork 7.5 in the 2001 M400/600/750 manual, whose viscosity is 22 cST in the Shell specs.

Many years ago there was a posting on the Ducati Monster Forum from a fellow from NSW who had Shaun at D Moto have a play with his M800ie forks, which would have been of this style.  I rang Shaun to ask him what he had done and he said he'd drilled some holes in the cartridge above and below the piston travel to reduce the low speed damping.

So, recently, when I had a 2003 M400ie come in for some fork seals, I took the oppurtunity to have another go at making them work.

The photo below shows the marking on the inside of the lower leg.  Not sure which company this is.  The cap has a 19mm hex.




removed the cartridges (undo bottom screw) and tried to get the oil out of them, the total unsuccessfullness of which confirmed I had the forks I thought I would.  This is what the cartridge looks like (RH end is the bottom)



The hole you can see at the RH end is where the oil enters the cartridge to fill it on the unlikely occasion it is empty.  This is a non serviceable cartridge, unless you cut it open and then weld it up again.

I made a guess on where I thought the compression valve at the bottom would end and where the piston would be moving, and drilled a couple of holes to allow the oil to bypass the shim stacks.  This is exactly what most adjusters do on adjustable forks - open a hole and allow oil to bypass the technologically superior shim stack via a very technically inferior hole.

Oil flowing through holes is how damping rod forks (old style) work, and that's why they have no low speed damping and often lots of high speed (depending on the diameter of the hole and what weight oil you run).  At some point the hole, which provides no resistance to the oil as it flows through it at low speed, effectively becomes solid as oil is forced through it at increasingly higher speed.  The bigger the hole, the higher the speed at which it becomes a restriction.

The shim stack is very variable and adjustable (if you can get to it) and a much better idea to modify.  If it is any good anyway - if not, you often end up bypassing it with an old school hole.

The holes I drilled were 55mm and 230mm up from the very bottom of the cartridge, as below.



The bottom hole could have been 50mm up I'd think - with the drill bit through the hole you could just feel the end of the piston hitting the bit with the rod fully compressed.  It wasn't blocking the hole though.

The holes shown are the initial 1mm holes.  I used some ti-nitride drill bits and my air drill, which was the only one I had with a chuck small enough to hold the little drills. They drilled through nicely without pressure on the bit pretty much.  The last time I tried drilling holes in some cartridges I broke a couple of drills and it all got a bit messy.  This time no worries at all.

A point to make at this time - after drilling the holes, it's a very wise idea to not move the rod at all if possible.  That oil inside the cartridge, previously impossible to remove, is now very keen to spray out all over you or whatever else the hole is pointed at.  Old fork oil is not a nice liquid to coat one's self with.  You'd almost go as far to say that wearing a hundred ml or so of fork oil is justification enough to throw clothing in the bin.


Once the 1mm holes were drilled I refitted the cartridge, filled the leg with Maxima 7 weight oil (26.7 cST), bled it up and had a assessment of the result.  The low speed rebound was much reduced, and felt somewhat normal-ish. The reduction in low speed compression wasn't anywhere near what I was hoping for, so I went to 1.5mm and then 2mm to reduce it further.  With the 2mm hole the compression felt on what I would call the high-ish side of normal, but much, much less than originally.  Normal is also a relative term - often the Ducati forks seem to have almost no compression damping at all.  The later comp only fork leg has a hole larger than 2mm about 100mm up the cartridge from memory, and no compression damping until the piston has moved down past the hole (the last third or so of travel).  

A couple of points:

1/ The manual calls for 7.5 weight oil, which will have been chosen for some reason.  I used Maxima 7 weight because I wasn't sure what the impact would otherwise be on the high speed damping.  All the hole drilling is concerned with is the low speed.  The high speed will be set by the oil weight.

2/ I'm no suspension expert, nor do I have the skill required to make an assessment of high speed damping and requirements thereof.  So the decision regarding oil weight was more to reduce the number of changes being made, and assuming there was validity in the 7.5 weight spec.  It may turn out that there is too much or too little high speed damping and that a different oil weight would be more desirable.  Or it may have a mismatch and ideally require different weights for each direction, which is impossible to achieve.

3/ This bike is an M400ie commuter, so it's a pretty soft target in terms of making a big improvement without causing problems.  The crappier things are to start with, the harder it is to make them worse.  Well, usually.

In terms of the hole size chosen, it was a guess (I actually think it was the conversation with Shaun, and someone else from somewhere) and trial and error.  You could also vary the number of holes.  A 2mm hole is 4 times the area of a 1mm hole, so you could also try 2 of 1.5mm or 4 of 1mm holes which would effect the low speed similarly, but reduce the impact on the mid and high speed damping.  The 1mm hole will effectively go solid much earlier than a 2mm hole.  As well as being 1/4 the size, the circumference, and hence boundary layer effect on flow, is proportionally higher.  Four of the 1mm holes should work much the same at very low speed, but will give more mid speed damping than 2 of 1.5mm holes, which in turn would give more mid speed damping than a single 2mm hole.

Someone who specialises in suspension mods would have a much better idea of hole sizing.

At this point I had a 1mm bleed hole for the rebound damping and a 2mm bleed hole for the compression damping with 7 weight Maxima Racing Fork Fluid set to 135mm.  The oil height specified in the manual is 80mm, which I know from my previous oil height experiments gives a very aggressive air spring effect.  As I was also going to make a spring rate change, I likewise made an oil level change.

The owner of the bike weighed around 75kg, so I didn't want to go too hard with the springs.  If it was mine, I'd be going at least 0.90kg/mm.  I tend to cut down the original springs if I can, and use a spring rate formula to work out how much I need to cut.

The spring rate calc is (G x d x d x d x d) / (8 x N x D x D x D)

where G is Young's Modulus (material property, 76.9GPa)
          d is the wire diameter
          N is the number of working coils
          D is the spring mean diameter

The original spring is 292mm long, 4.8mm wire diameter, 38.6mm outside diameter and has 22 working coils.  It is a typical Ducati dual rate spring, where it has a tighter wound section with constant coil spacing over each section.  See the top spring in the photo below.  The spring rate given by the formula is 0.606kg/mm for the total spring in its initial travel.  Too soft.



Often, with the Ducati springs, the secondary rate is about what you want, so you cut off the tight wound coils, square and grind the end and away you go.  But, in this case, there are 22 total working coils with 14 open and 8 tight.  The open coils are 10.3mm apart, the tight coils 4.4mm apart.  This means that when the spring has been compressed 22 x 4.4 = 96.8mm, the tight section will be fully compressed and the open section will become the working section.

Unfortunately, by the above formula, the open section being 14 working coils gives 0.953kg/mm.  For a rider weight of 75kg on a Monster that's too much.  Appropriate for an ST, but not an M.  Also, if we have 14 working coils with 10.3mm between each coil the available spring compression is around 144mm.  These forks have around 120mm of travel and you usually have 15mm or so of preload, requiring at least 135mm of compression.  I'd not like to run a spring to within 10mm of coil bind.  So, for this spring, cutting is not an option.  You could cut off less coils, but it would still be a dual rate spring that became a single rate spring of 0.95kg/mm much sooner.

The spring rate I wanted was in the 0.80 - 0.85kg/mm range.  As it happens, the oem rate of an ST series spring is 0.83kg/mm.  I tend to have a few old ST series springs kicking around as I replace quite a few of them with 0.95kg/mm springs, so I grabbed a pair from the old spring stock and checked them against the originals.  As you can see in the above photo, the linear rate ST series spring is 2mm longer than the original Monster spring and preload spacer.

There were a couple of issues I had to attend to to make them fit.  I had to machine about 0.4mm off the spring inner guide (a ribbed plastic sleeve that goes over the cartridge piston rod and inside the spring) to allow the ST spring to slide over it.  Had I used some of the aftermarket springs available I may not have had to do this, but using s/h springs from the pile I have to hand not only recycles a processed piece of natural resource and shares the love, it also knocks about $200 off the job so we can afford a little lathe work.

The ST springs were about 2mm longer than the original springs and preload spacers. The original set up had given 16mm of spring preload as assembled, which I wanted to replicate.  But one issue was that the stamped C plate (see photo below) that holds the spring in didn't sit evenly on top of the ST series spring due to the spring inside diameter.  Well, it didn't sit nicely on top of the original spring either, and the forks had been incorrectly assembled previously 
with the preload tube under the spring as it came apart.  Ideally I needed a piece of the original preload tube to sit on top of the spring under the C plate, so cut a couple of 6mm slices off one of the original preload tubes.  To allow for the increased length (now 8mm over original), I shortened the square aluminium nut that locked the top cap onto the rod by 8mm so that the stamped C plate would sit 8mm higher.  Simple.  Again, see the photo below for the 3 mentioned pieces: nut, spacer, stamped C clip.  Should have put the spacer below the C clip, that'd make more sense.



Back together again, with the bottom on the floor I could almost fully compress the legs with a big bounce of my weight, which seems to be a pretty good test of oil height impact, etc on any fork I find.  It's amazing how much you can feel the impact of 30mm of oil height in a simple test like this.

The top of the cartridge has a recess that a bush on the rod goes into, which when the recess is full of oil becomes a hydraulic bump stop of sorts at full compression.  I though that was kind of cute, although it did spray me with oil a couple of times.




So that's where I ended up.  On the road on my usual road test loop, which is fairly undemanding in a dynamic sense, it felt quite nice.  Before I'd started playing with it (leaking fork seals were the stimulus), the front end didn't really move much. Not too stiff, just reluctant.  Now feels like a normal front end. The owner is very happy with it.  Even though the spring rate is 33% higher, the fact the forks previously didn't move very much due to the excessive damping has lead to them feeling softer and simply more compliant with the road.

It'd be nice to have someone who knows suspension give feedback on the result, as it could undoubtedly be improved upon further.  But, as a simple starting point, and one that's easily repeatable in the back yard, it's pretty good.

Saturday, November 18, 2017

Sunday, November 12, 2017

My revised muffler baffle for Minnie

This is the baffle I knocked up prior to riding to the FOIM.  I realised I was later than I expected at that point, so it was quick.  Not pretty, but very effective as it happens.  Many years ago Mark Harris who was Madaz at that time told me a baffle needs to fully obstruct the linear flow of the gas to really work, but without that obstruction being overly restrictive as such.  The previous one was a shorter tube much the same size with an open end, like a Staintune baffle would be.  It really didn't make that much difference.

Not sure how this will work on the dyno.  Not sure that I want or care to find out.



An end for Minnie's makeover

At the start of the week I had a "to do" list for Minnie to get her ready for the Festival Of Italian Motorcycles today.



"Front brake work?" at the top literally meant "does the front brake work?  With the second front disc adding a corresponding caliper, the demand for front brake fluid displacement increased by 100%.  The original single disc front master cylinder is 13mm, the original dual disc front master is either 15 or 16mm, depending on model.  My 851 had a 15mm master originally, which I replaced with a 16mm (from my Sport 1100i after I crashed it I think).  I was curious to know how it would work with the 13mm, as I'd never tried it before.  My feeling was it would just have a lot of travel and probably some good feel.  But the reality was you could pull the lever back into the bars with little discernable increase in pressure.  Like it had air in it - I spent ages bleeding it thinking I'd screwed that up somehow.  Whereas on the road it gave a lot of travel before it finally started to stop, without a lot of feel as to when it was going to stop.  So, curiosity answered, larger front master needed.  That was Monday's decision.

The 15mm master is 31% bigger, the 16mm 50% bigger.  I went looking for my 15, but couldn't find it.  I figured the best way to find it was to buy and fit a new 16mm master (it worked).  Because the look for this bike is the "coffin" style  masters, I had to buy a new one as the Sport 1100i 16mm now on the 851 is a remote reservoir style.  The new one turned out to be the new style with the larger fluid reservoir, meaning the lovely Chinese billet reservoir caps I'd bought the week before didn't fit anymore.  Great.  And the pivot pin, which is cad pacified (gold zinc) plated on the originals, is now silver and I've spent a heap getting all the fasteners replated so I had to refit the "not so shiny like the rest of the fasteners" original.  Hmmmmmm.  Did have a nice new lever though.

But, it worked.  Funny how a 100% increase in fluid demand is happily dealt with by a 50% increase in delivery.  The very cool floating cast iron discs don't like sintered pads, so I went through my stash of old single pin original pads and found a couple of pairs that were bead blasted and fitted.  Stops better than it used to with the single disc, but with the organic style pads you just don't get that initial bite that I do enjoy so much.  Maybe some new Ferodo Platinums will help.  More money.

So that was #1 ticked off the list.

The speed sensor for the Acewell was the next issue.   With the caliper adapters there wasn't anywhere to fit a little bracket like I had previously.  I liked the little bracket, as it is a serviceable solution (as in you can remove and refit).  My mounting as below is not - double sided taping it to the bottom of the fork leg.  The sort of thing that customers do that annoys me.  I drilled and tapped a thread into the disc carrier and fitted the little magnet and away we went.  Easy.  Compared to the 120/70-17 circumference of 1860mm, the 130/60-16 measured at 1735mm.  But after riding it around with the iPhone zip tied to the handlebar clamp and the speedo app running, I increased the setting to 1760mm (1.5%) to bring the speedo in on the underside of accurate.  #2.


The tacho drive is due to this being an SS engine, which has a cable drive tacho.  I do have a Monster blanking plug somewhere (at least one in an engine), but laziness had kept me from moving it any closer to this engine.  I found a little blue rubber cap that fitted just fine, and it has resisted bailing for quite some time now.  But, I figured I'd make it a little nicer and I like machining stuff, so turned up a little cap and screwed it on with an old cable collar (I always cut them off old cables just in case).

The rocker covers were looking a bit crappy, but I didn't have any paint close to hand that I thought might be a good fit.  Well, I have some gold that is possibly a good match for the Paso rockers covers that I always liked, but didn't think it'd match the rest of the bike.  I didn't want anything bright, but didn't have any shades of real grey so I gave them a coat of cold gal.  With the rocker covers bead blasted and heated with the heat gun the cold gal dried at it hit them, the finish is rather matt and coarse and lighter than I expected, but it's there and that gets it ticked off the list.


This engine has the D on the timing belt covers and the DUCATI on the alternator and clutch covers, so I scraped, rubbed and polished the paint off.  I thought it was a nice little detail.


I needed a new clutch lever and reservoir cap (to match the new original on the brake master) and the master body had a fair bit of scraping along the road damage near the pivot.  I figured the best solution was a complete new master.  Easy.

I was looking for something to fashion a brake line bracket from to hold the front brake hose at the lower triple.  I usually find old horn mounts are good for this sort of stuff, and I stumbled across a nice gold zinc one.  Just lovely.  A quick bend and on.  Another one down.


The last point on the list - frame bolt caps - had me loking for the rubber caps that go into the tubes for the engine/frame bolts, and it took me to a tub that I thought (possibly correctly) contained mostly parts of the disassembled 400SS.  And in that tub, I found the 15mm front brake master cylinder.  Bugger.

At least I know where it is, so now I can lose it again for the next time I want to use it.

To make the inside of the muffler end cap a little less obvious I tried to clean up the inside with some scotchbrite (which didn't work as hoped polish wise), then ran some masking tape around the inside of the outer and the machined end cap.  I had machined the end cap prior to giving it to Ken when he made the muffler so I could fit a baffle as used in the last muffler.  It didn't make a lot of difference sound wise, so I made another with a smaller and longer internal tube and then folded a piece of sheet metal into a u shape and welded it on.  Suitably low rent, and effective I must say.  I don't really know if it's that loud, but the high outlet certainly gets into my helmet.


And today at the FOIM, after a lot of them had left.  I think it might be finished at this point.  

Now I can pull it apart again.