Once again, Minnie finds herself without a motor

It's in the box! 

She almost got lucky with the 400SS motor yesterday, but then some idiot decided to give it a leakdown test, exposing an exhaust valve not doing a great job of sealing, and some rings that couldn't be called great team players.

 I'll do a post on building a shipping crate to fit a 2V motor at some point.  I've even got a cutting list.

The 400SS has a similarly forlorn look about it, slumming it with nothing, but the old 600 cases I've had kicking around for years to hold it together.

Christmas Trading Hours

(or lack thereof). 

Monday December 22nd is my last day in the factory until Monday January 19th.

Current "next booking spot' is around March 14 or so, I forget now.

To quote Vicki Smith:

Here's wishing that whatever you celebrate, and however you choose to do
it, that it's everything you hoped for.
Happy Holidays everybody!

Closed September 25 to October 20

As it says, I will be closed from Thursday September 25 until Monday October 20.

Anyone want a hot 750 2V motor?

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Minnie's 750 motor is on Ebay.  It just a bit surplus to my long term plans, with the intention being to put the 400 motor from the SS into Minnie to allow a little 400 playing before ultimately flogging her off.

750 2V motor

I've also listed the 900 crankcases I have, which have been sitting around mocking me for the best part of 10 years I'd say.  Probably longer, now that I think about it.  I bought them to build a 944 or the like for the 851, but we all know how that turned out.

900 crankcases

I've been toying with the idea of selling the 851 too.  It has sat for over 9 years now, and I don't see a time when I can justify spending the time I need to to get it back on the road.  Given it's an '89 model it can be ridden on a club permit this year, and that was luring me to get back on it.  But it needs a full service and tyres and probably more once I get into it.  Given I never walk into the factory without a customer's bike there to work on, any time I spend on the 851 is time not charged out.  It might be more a mental issue than a monetary one, but it's still an issue.

And then there's all the 851 parts I have.

I'm sure I'd regret it, but sometimes ridding yourself of the weight of best intentions left unfilled can be amazingly refreshing.

GSXR fork cartridges in 41mm Showa adjustable forks

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Along the lines of the SC1000 post below, there have been quite a few threads on fitting GSXR 600/750 fork cartridges to the Showa 41mm adjustable forks from the 851, 888, 900SS and M900.  So at risk of driving up the prices of s/h GSXR 750 forks, here's a couple of links.  Appears to be a very good mod, and pretty much drop in* to these forks.

http://www.ducati.ms/forums/57-supersport/149199-gsxr-cartridges-7.html

http://www.ducati.ms/forums/57-supersport/142215-k4-5-gsx-r-750-fork-internals-carb-ss-forks.html

* as long as you aren't too precious about the whole "drop in" thing and can work around a few things to be sorted.

More on the craptacular Marocchi 43mm forks: SC1000, Monster,etc

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 A fellow named Impusive_Duc has started a thread on Ducati MS about the Marzocchi 43mm forks as fitted to his SC1000 and his pursuit to make them better.   He's getting quite carried away with it, something I always enjoy seeing.

http://www.ducati.ms/forums/77-sport-classic/393201-project-100-ohlins-bust-gsxr-cartridges-sc1000-stock-marzocchi-forks-3.html

Some photos from along the way

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My first interaction with Moto Italiano I guess you could say, this 888 on display at the 1993 Melbourne Hot Rod show.  That sign was still around until the end, sitting upstairs on the mezzanine.  It probably went into the bin like everything else did.

March 7, 1995: Trev offers me a bike to take home for the night, a 906 Paso in to be sold on behalf of a customer.  I was going to drop off some brake parts from the shop ute to a mate for reconditioning, so it seemed a good idea.  My first question was "Is it insured".  "Of course it's insured " said Trev.

Hmmmm.

This is what a 906 Paso looks like after it has been wheelied into (unintentionally, of course, on both 'wheelie' and 'into' counts) the RH rear corner of a City of Melbourne mobile works caravan.  Allegedly the noise it made was that of an explosion.  Which is kind of what the front end appeared to have done.

Look at the next photo:

Then try to say "bruised and lacerated scrotum" without smirking.  I can't.

What followed was my first ride in an ambulance and my first time on a trolley being wheeled into an emergency room.  You know those scenes in movies where they show the view of the ceiling with passing lights that someone sees as they get wheeled into the ER?  That's 100% life like, and quite bizarre.

And the first time I had all my clothes cut off on the ER table with the great big "cut everything" scissors.  Cost me my first leather jacket and my TISM "Great Truckin' Songs Of The Renaissance" T-shirt.

And because the ER doctors were:

1/ paranoid about neck injury 

and 

2/ female

the probing for my injuries, done with tenderness around neck level, slowly degenerated into pointed jabbing by the time they'd reached the ball zone.  Given that, by this stage, the level of nadular pain was at hyperventilating levels, the true depth of the evening's deviation from previously laid plans was born out by the stabbing of fingers followed by the ever loving "Does that hurt?"

"Whada you reckon?"

If I had any ability to make my stomach muscles contract at all I might have tried to raise myself up and go them.  But I was helpless, naked and cold.

After they started pumping morphine into me one of the doctors asked if I was feeling a bit spacey.  I think I suggested she call her dealer, as it wasn't kicking in.  Thus began my first interaction with the world of opiates.  It was never something I really enjoyed; while the dopey fog of sleepiness wasn't so bad, the nightmares and itching were.

That night I ended up with 3 stitches in the aforementioned scrotum.  I don't think I'll ever forget the stinging pain of the local anaesthetic needle as they went my nads like a pin cushion, or the sensation of the stitches going in.  And out, and in, and out.  The local removed the pain, but not the feeling.  It's rather odd.

A few days later I woke from my first general anaesthetic with a couple of little wires in my wrist, to hold the end of the (I think) radius in place.  It was quite a weird sight seeing two little pins poking out of my arm.  I expected that a hole in your skin like that would bleed.

A week or so later the stitches came out, a task performed by a male nurse who had, at least, an appreciation of and for the delicacies at hand.  The pins came out a few months later, when I watched a doctor open a sterilised package containing a pair of pliers much the same as I had in my toolbox.  When he couldn't get the wires to move he actually put my hand on the desk and then put his knee on top on it to hold it down, before realising (possibly due to the looks from myself and my mother) that perhaps that wasn't the most correct way of doing things.  Turned out a quick twist was all they needed to free themselves, and then they came out.  Followed by a couple of drops of blood.  Again, I couldn't believe there wasn't a torrent of it.

One thing that came of it was a change in my attitude.  I'd always been a bit of a gunna, while never actually doing anything.  Well, I did manage to finish rebuilding a Monaro a few years before, but up till then I'd pretty much just floated through life without really getting into anything.  So while I had a few weeks off, I came to the conclusion that I should get into something.  And that something became motorcycles.  Although, the way I went about it may seem a little odd, given the surroundings.

Although it did take until the second time my parents got a phone call from an ER saying "We have your son here..." for me to appreciate the impact it had on them.

And I still contend it's one of the better things you can do with/to a Paso.

June 1995: What you get for $8,000.  

Well, it came with all the other parts needed to assemble it pretty much.  A customer was having this resto done, and wanted to bail on it.  At that point most of my friends were getting into property, and over the next 5 years the value of the Melbourne property market generally doubled.  As I sit here 19 years later, the long term impact of that decision is clear any time I look at our mortgage.

Some Saturdays, my play day, I'd go into work and just look at it, wondering how I was ever going to get it finished.  But, by April 1997, I had this:

The colour choice put a few people off, and, to add weight to the general opinion of dislike, it's in one of Ian Falloon's books in black and white (and uncredited).  But I loved it.

I had a preview to how it would ride when I rode Trev's V7 Special (actually an 850GT or Eldorado painted as a V7) in to the 1995 Italian Motorcycle Concourse (November, Lygon St).  As long as you didn't want to do anything too quickly, it was fine.  I'm guessing Trev rode either the SB6 or Mantra (behind the V7), as we were the Australian Bimota importers at that time.  You can see the Monaro behind them, my first love in orange.

And I did find a few years later that you could comfortably scrape the centre stand on the ground without falling off.  It really was a very cool bike, but in the end it was the 6 or so hours it took to clean it that wore me down, so I stopped riding it and eventually sold it.  And I haven't seen it since, although I know it is still around.

February 1996: Bearded up and giving some love to an 888.

March 1998: My Sport 1100i, The first and only new bike I will ever buy.  It's quite a nice feeling removing your own bike from its crate.  Pre modifications and crashing.  And proving I hadn't learnt anything about the benefits of worthwhile investment.  Actually my first official borrowing of money, all $15,500 of it.  I bought it direct from Stolarski, when they were unloading the bikes they still had when they lost the Australian importership.  I could have had a Daytona RS for $18,250 from memory.  In hindsight, I should have found out how much a 900SSie would cost me.  Or one of the last 1997 900SS.  Would have been much more relevant.

It was 20 years ago today........

That I started on this Italian motorcycle adventure.  July 4, 1994.  I had been working on cars with a fellow named Rob (now the mechanical side of Guzzi Spares Australia) and he owned a 907.  He found himself working at Moto Italiano after taking the 907 in for a service and finding they were in need of a mechanic.  Then about a month after he started, the other mechanic left.  So he rang me to see if I wanted to try bikes.  I went and had a look and a chat and then got a call to say that there was a Ducati training course in a bit over a week and if I was interested I should really be there.  I was, and then I was.

The first day was an M900 service, and my introduction to 2V desmo.  I learnt some new stuff (which I promptly forgot).  Day two was a first service on an 888, back in the days when first service meant a full valve clearance service.  Actually, the only difference between a 1,000km service and a 20,000km service (1994 model, probably 15,000km for one year only) was a fork oil change, now that I think about it.  As we were pulling it apart, I opened the throttles, looked down the inlet ports and fell in love.  As an engine guy, it was a most wonderful sight.  I still service that bike.

The training course also coincided with the first 916 in Australia being at the dealership.  I had no idea what it was, but everyone else seemed to think it was pretty special.

Of course, by the first time I had to do valve clearances on a Ducati (a 2V, probably an SS) I stood there with a dopey look trying to remember what it was I was meant to do.  Funny, but I find 2V valve clearances almost therapeutic these days.

I think the first bike I rode after servicing it was a Moto Guzzi T3.  Probably a dark green one.  Compared to the Ducati, the Guzzi were pretty similar to a car in many ways so much of it made sense servicing wise.  But I hadn't done a lot of road riding at all up to that point, and when I got back to the workshop I asked Rob if he could go for a ride on it because there just had to be something wrong with it.  Nope, just a Guzzi.  I did come to love them.  Well, most of them.  Some anyway.

Does anyone know this clutch lever?

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I'm trying to find out here this came from.  Anyone know?

Lovely orange 900SL

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A photo posted by SpikeC on the Monster forum.  Apart from the angle of the black lower section (should be the same angle as the bottom edge of the seat base imo), I really do like this.  Even the gold frame and wheels seem to fit in well.

I do like orange.

Similar colour to my old Monaro, which I repainted Indinapolis orange, and the Eldorado, which was Adlide orange.  I found Adlide orange in a paint catalogue and it was listed as a "fleet colour" from memory.  But googling it shows it's a Torana colour.  Not sure which model though.  Both these oranges changed quite a lot depending on the light.  Deep orange in the shade (like the SS above), much more yellow in the sun.

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Inlet trumpet design and inlet length info from David Vizard

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I've been hanging out a bit lately on the Do The Ton forum.  I quite like the aesthetic side of the custom scene and find some jealousy for the ability of those who do it well, not being overly creative myself.  Although the technical side of it is often rather frustrating, and while many of those involved seem completely oblivious to the consequences of the supreme low budgetness often employed, I just can't get excited about a set of $100 shocks.

Anyway, in the Engines section I found a post with some links to work by David Vizard.  Who is David Vizard you ask?  davidvizardseminars.com calls him "a Race Engine Building and Performance Tuning Guru. Author of many technical books, he now lectures to engineering audiences worldwide ..."  He has done lots of stuff.  The images are found on the Eurospares website.

The two links I found of interest were for inlet trumpet design and inlet tract length, as below.  Best to download the inlet trumpet design page from the link so you can magnify it to see all the detail.

The thing I find interesting about the inlet length diagram is that 10,000 rpm is given as 10 inches, or 250 mm.  There's quite a lot of bikes that are much less than that, and a big part of that is available space.  8,000 rpm is given as 12 inches or 300 mm, which is a lot of length to find on a motorcycle.  I'm sure the "long" manifold system on the Mikuni carburetor 2V Ducati motors is not a lot longer than that.  Maybe I'd better measure it on Monday.
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TPS for Keihin FCR

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Chris at Cosentino Engineering has been making a TPS mounting kit to suit the Keihin FCR carbs when fitted to the KTMs he plays with, which have a TPS fitted as std I believe.  See here for all his bits: Cosentino Engineering

I had Chris send me a kit to see how it would fit to the FCR in the SS and Monsters.  The Ducati FCR fitment is a "racked" pair of carbs, as opposed to the two single carbs the KTM has.  But the TPS fit is much the same.  Although I believe Chris is having some brackets anodised red instead of the usual orange to appease those who like that sort of thing.

The TPS itself is a KTM part and very affordable in the grand scheme of things.  And while I don't have a source for the 3 pin rounded triangular style connector on the end of it (haven't bothered to look, frankly), I do have a very functional set of wire cutters.

One change required to the Ducati FCR set is the accelerator pump arm.  The original flat arm will foul the little nipple that fixes to the end of the throttle shaft, not allowing the throttle to fully close.  Replacing it with a round wire arm (a GSXR part from the FCR diagrams) fixes this issue, and it's not very expensive.  You can see the round wire arm in the following photos.

Some may be wondering why you would want to fit a TPS, and the answer is in combination with a 3D programmable ignition system, like the Ignitech, you can have a spark map with the benefits to fuel economy and response that this gives.  Liam at Fast Bike Gear in New Zealand has written a great expanded Ignitech user guide which includes info on doing this.

 Fitted to Minnie the Monster it looks like below.  Plenty of clearance to the frame and everything else.  The photos are a bit fuzzy, so I apologise for that.  Maybe my lens is dirty.

Fitted to the 400SS, you can see the boss on the inside of the frame that holds the upper fairing mount on a half faired bike.  The mount bracket goes out to the rear, so away from the TPS, but it may need trimming and a shallow head screw.  I was too lazy to try refitting mine to actually check.  The wiring you can see hanging usually runs above the boss, and it was definitely in the way.  This bike is a '93 model, with the battery reversed as compared to the later models, so that may impact how annoying this cable actually is.

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Marzocchi 40mm fork design and impact of oil level on spring rate, Part 3: The crap ones

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It's amazing how a company with such a high end reputation for quality suspension, in many fields, can produce something as crap as these forks.  But, as those in business will understand, if someone asks you to make something, why not.  And clearly, when Ducati asked Marzocchi to make some upside down forks for the Monster and SS range in 1994, the word most emphasised was cheap.  Ie, "Yes, well, they're great, but do you have anything cheaper?"

So what we got were these 40mm forks with a damper cartridge arrangement that is fixed into the fork tubes by the bottom edge of the tube being rolled to fix them.  I've often poked quite a bit of fun at them, but it's not really Marzocchi's fault if it's what Ducati wanted.  As always, it's amazing the crap Ducati have managed to get away with over the years.

Functionally, the forks have normal style rebound damping, but compression damping in the final 1/3 (or so) of travel only.  This leads to quite a bit of initial dive, the sort of thing that catches you out when you grab a handful of front brake at low speed while working through traffic for example.

They were fitted to the Monster (M400, 600 and 750) and SS ranges (400, 600, 750 and 900SS CR) from 1995 until 1999.  I have record of two different dimension springs being fitted, but the overall rate calculates at much the same.  Being way too soft, and two stage to try to overcome it.

My set of these came from Minnie originally, before I fitted some 41 mm Showa non adjustable forks to her.  I did replace the springs at one point, but they've been unused for quite some years now.

I had a little time and curiosity, given my other fork playing, so decided to drag them out and have a looksee.

As I found them, they were fitted with 0.85 kg/mm rate springs fitted with 33 mm of preload and filled with oil to 100 mm.  Why they had 33 mm of preload I don't know, but it seems way too much.  So I tested them again with 17 mm of preload and the oil level set to 140 mm.  The preload tubes in this instance were pieces of 32 mm OD orange electrical conduit.  This is much the same size as the original tube, in both OD and thickness.  With a wall thickness of 3 mm, it does have a noticeable impact on oil level, especially when compared to the Showa thin wall steel tube preload spacers for example.

Then I dug up some original M600 springs from my stash of oldies.  I couldn't find any original preload tubes (long since cut up no doubt), so I cut a piece of orange conduit 120 mm long, which I'm pretty sure is the original length.  This gives 13 mm of preload on the original spring.  The std oil level is 90 mm, so I began with that, then added more preload (another 20 mm piece of orange goodness), then dropped the oil level to 130 mm with the same extra preload.  The orange conduit volume also had an impact here.  I calculated that the 20 mm long piece of conduit added the equivalent of 5 mm of oil height to the fork internal volume.  Which I'm mentioning as I didn't think of it when originally adding it, but later went "ah" when it appeared the air spring rate may have changed a touch.  As ever, it's all the errors you introduce without thinking that catch you out.

And so to a graph.  Blue is how I found it: 0.85 kg/mm spring with 35 mm of preload and oil set to 100 mm.  Black is with the preload reduced to 17 mm and oil dropped to 140 mm.  Red is with the original spring, preload and 90 mm oil level.  Green is with preload increased 20 mm and 90 mm oil level.  Orange is the same as the green, but with the oil level dropped 40 mm to 130 mm.

The orange and black curves show much more linearity, which is what I'm seeing a lot more of with oil levels reduced by 40 or so mm.  The shape of the yellow curve is also influenced by the spring rate, which changes from soft to harder at around 70 mm of compression.  With the preload set to 33 mm, this corresponds to 40 mm of fork compression, or just a bit more than the static sag would hopefully be.  I have found that the static sag load seems to be in the 45 kg range, conveniently occurring around 35-ish mm of compression for the black, green and yellow curves.

If I add the M900ie 'final' curve, with the 0.85 kg/mm springs running 5 mm of adjuster added preload and oil level set to 155 mm in purple, the orange and black look a bit light on at the top end.  Given the black and purple springs are both allegedly 0.85 kg/mm the difference in overall gradient is a bit odd.  I'd probably want to go back up in oil height by maybe 20 mm or so to increase the air spring.

Splitting them up for clarity, first a 20 mm increase in preload with the original spring.  The difference in static sag with this change should be in the region of 15 mm.

Then a 40 mm drop in oil level.  It's only in the last 1/3 of the travel that you'd notice any difference on the road.

The difference a heavier spring makes to the mid travel range is shown in the next graph.  Similar end points, but a difference in the middle of around 8 mm for a given load.  Black is 0.85 kg/mm, orange original.

Ducati Gold Coast special clearance sale

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No affiliation, but Ducati Gold Coast are running a special clearance sale.  some of it is old DP accessories, including some Termi stuff that is now long gone for Monster and SS for instance.  Have a looksee here:

Ducati Gold Coast sale
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Showa 43mm adjustable fork design and impact of oil level on spring rate, Part 2: 748 / 916 / 996 / etc

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Today while I was doing a major service on a 748 I took the opportunity to throw a fork in the rig and see how it compared to the others.  I really wasn't sure what to expect, but was surprised anyway.  It's always nice to be surprised.

While the 748 forks (same as 916 and 996) are also 43 mm Showa adjustable, they differ internally to the M900ie forks by having the long rebound adjuster rod as discussed long ago in the 1000SS fork post.  All 916 on SBK have this style fork (except 749 Dark).  Assembly wise, there is a 100 mm long thin wall steel tube spacer and spring supporting washer below the spring and the usual Showa style preload tube above the spring.  I set the oil level with the lower spacer and washer fitted, as the manual doesn't specifically say to not fit them.  I'm not sure if that's right or not, but it's not mentioned and will result in a lower final oil level and I'm liking that these days.

The 748 forks have an oil spec of 132 mm.  I suspect this one was more like 142 mm before I pull them apart.  I couldn't get an accurate measure as the bottom plastic bush on the preload tube came off in the forks, making it pretty much impossible to get the spring out without tipping them upside down and shaking.  But the level with spring and bottom plastic bush in was about 10 mm lower before compared to after when set to 132 mm.

The spring in the 748 is a linear spring 285 mm long and the rate calculated at 1.00 kg/mm.  I didn't have time to measure it, but the calculation is generally very accurate.  So while it's a bit heavier than the others, it's fitted with only 8 mm of preload with the adjusters at the minimum setting.  Like the M900ie fork, the adjuster range is 15 mm.

To the curves: red is 748 with minimum preload, blue 748 with maximum preload, yellow M900ie as was originally with maximum preload and green is how I set the M900ie fork up at the end.  I don't feel so bad about my M900ie setting now.  Again, the coincidence of unrelated results is quite amazing.

Also again, it amazes me that you can hit (so near to) the same target with such variation in spring rate.  Although the rate variation in this case is a little less than the variation in the M400ie leg.  And the unknown is the variance in internal fork volume once assembled, as the different springs and spacers all contribute sometimes vastly different volumes.

This graph shows the collection of springs as encountered in these reports so far.  For this report, purple and green are the contributors.

One point that just occurred to me is that of fork swaps.  Often you'll read forum threads of where someone has fitted SBK forks to their Monster or other and the poster will be told of how the spring rates will be wrong.  I might even have said it myself.  But the above comparison of the 748 "as delivered" curve and what I decided was a good curve for a M900ie shows once again that, unless you actually check something, you really don't know whether you're talking through your arse or not.

Of course, all of this is separate to damping rates and their influence.  I'm not getting into damping rates at all.  That's completely out of my realm of experience, and it's an area where specialist experience is what matters.
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Showa 43mm adjustable fork design and impact of oil level on spring rate, Part 1: M900ie

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Or, keeping the same title so as to be consistent with the previous playing with forks.

So I got to play with a set of 43 mm Showa adjustable forks from a 2000 M900Sie today.  Well, I'm halfway through it.  I have serviced the forks in this bike once previously, and filled them with 5 weight oil to the spec height of 108 mm.

I thought to start with I'd do the same travel vs load graph (mm across the bottom, kg up the side) as for the Marzocchi forks, and then thought I'd add the original curve for the 43 mm Marzocchi with oil set to the spec height (105 mm?).  Turned out to be a bit spooky, frankly.

Red is the Showa with preload at maximum, yellow Showa with preload at minimum and blue Marzocchi.  Not really what I was expecting, and a wee bit eerie.  Obviously someone at Ducati thinks this is an ideal fork setting.  The difference between minimum and maximum preload is 15 mm, with this translating to 19 and 34 mm of total preload in the assembled forks.

More to come.  It's going to get some 0.85 kg/mm springs (rider 80 kg) and I'll drop the oil to 140 or so mm.

Ok, so on to the more.

I was very surprised by the fact that the air spring effect in the Showa was pretty much identical to the Marzocchi.  Looking at the parts, the Showa has a longer spring (349 mm) that sits at the bottom of the fork around the cartridge, with a long, but thin steel preload tube (277 mm) above it.  The Marzocchi has a shorter spring (249 mm) that sits on top of a stepped washer that itself sits on top of the cartridge, with a thick wall plastic preload tube (38 mm OD, 30 mm ID, about 100 mm long) sitting above (or maybe below, now that I think about it) the spring.  So perhaps it's just the visual weight of the shorter, but thicker Marzocchi preload tube that gives the impression.  Anyway, it was certainly not what I expected.

I replaced the original springs with a shorter, mostly linear rate spring (with a couple of tight coils at one end) which are meant to be 0.85 kg/mm.  I tested them on my amateur rig and came up with the curve below.  At 50 mm compression they average 0.85 kg/mm, but by 100 mm compression they're up to 0.90 kg/mm.  The OEM and ST series springs from the previous Marzocchi report are also included.  The two OEM springs are pretty close overall.  The Showa spring curve starts a bit higher, as it was a touch too long for how I had my rig set up, and also after midnight.  Dimension wise, the Showa spring has less coils (harder), but thinner wire (softer) and they're both 38.6 mm OD.

I fitted the 0.85 springs with 10 mm of preload (adjuster at minimum).   These springs are 282 mm long, requiring longer 335 mm preload tubes.  This is usual when replacing fork springs.  The only springs I know of that come at the same length as the originals are Ohlins, where they generally have a uniform length for a given application.  For the preload tubes I use 32mm aluminium tube with a 1.6 mm wall.  Unfortunately, the original steel tubes have a slightly larger ID, which means, when using this aluminium tube, I have to machine down the plastic end pieces Showa use to allow them to slide inside the aluminium.  The chuck ID on my little lathe is just a touch too small to allow the tubes to slide inside and be held at the machining end, so it's much less destructive to do the plastic pieces.

I set the oil level to 140 mm, thinking this would be a good starting point.  I did check the difference in oil quantity between 120 and 140 mm, so I could make changes based on quantity once the forks were all together.  This saves having to strip them all apart again.  At 120 mm oil height, the fork had 475 ml of oil in them.  Dropping the level to 140 took out 27 ml.  So if I wanted to go back to 120 mm I would just add 27 ml.  Or, conversely, if I wanted to go down to 160 mm, I could just suck out another 27 ml.

So, to the curve for 0.85 kg/mm springs with 140 mm oil height.  Not exactly what I was hoping for comparatively.  Red is OEM with max preload, yellow is OEM with minimum preload, blue 0.85 with max preload, green 0.85 with minimum preload.

I had figured that the 0.85 kg/mm springs would need about 5 mm of preload to give the right sag, which would place them about 1/3 of the way between the green and blue lines.  But the overall result is still a rather high rate of increase in effective spring rate near full compression.  Adding two further curves from the Marzocchi fork report, being the OEM spring with preload increased by 15 mm in orange and oil set to 145 mm and the ST series spring with oil set to 145 mm in purple, shows what I ended up with there.

So we come back to the question of how much load will the forks see?  Peter at Promecha told me that the maximum load (non impact if you like) the forks will see is if the bike is standing on its nose under hard braking with the rear wheel in the air.  And also that you don't spring them that hard, as it doesn't really work that way.  Which makes sense now that I've seen the impact of the air spring.

If we assume this M900Sie weighs 200 kg ready to go, and with the rider weighing 80 kg, plus 5 kg for gear, and taking off 5 kg to allow for the unsprung weight of the front wheel and fork lowers, that's 280 kg or 140 kg per leg.  These forks have around 115 mm of travel.  If we sprung it assuming the springs themselves supported all the load, 140 kg at 115 mm of travel gives a rate of 1.22 kg/mm.  But once we introduce the air spring effect, the required spring rate drops quite a lot.  With the 0.85 kg/mm springs, 145 mm oil level and my planned 5 mm of preload, that load will only give around 100 mm of compression.

How the bike was set up when it arrived, with the preload set to maximum on the OEM springs (the red curve), the same load would have given 95 mm of compression.

So it looks like I need to lose some more oil.  I'm quite disappointed with how this is turning out.  Not at all as I had expected.

Back again after losing some oil.  I sucked out 40 ml of oil, which should relate to 30 mm.  The change is somewhat as expected, as below: purple 140 mm, red 170 mm.  Both curves with minimum preload.

With my intention of running more preload, I made another calculated curve based on adding 5 mm of preload (1/3 of the maximum) and raising the oil level to 155 mm, 1/2 way between the two tested levels above.  The result wouldn't be exactly 1/2, as the change in air spring rate is slightly exponential.  I gave it 60% as a (random) guess, and came up with the curve below.  It's the yellow one.

I haven't ridden this one as yet, but given the chances of me exploring the end limits on a customer's bike during a suburban road test are non existent, I'll have to wait and see how the owner finds it.  The graph below shows how it arrived in red and how it is now in yellow.  There's not a lot of difference to show for my several hours of messing around, but the change in the last 1/3 of travel is what this has all been about anyway.  I would hope it's much more compliant, and less likely to make the big bumps feel big.  If that's not a poor way to describe it.

I got to thinking today that I had seen a fork oil level spec somewhere that always seemed pretty odd.  Turns out it was the 888.  The 888 has 41 mm Showa adjustable forks, much the same internally as the 43 mm forks fitted to this Monster.  The carburetor model 900SS used the same forks as the 888, albeit with the soft crappy dual rate springs in place of what I recall are much firmer, linear rate springs in the 888.  The oil level specified for the 888 is 162 mm and for the SS it's 108 mm, the same as this Monster.  I wonder why there was so much difference?

The 916 oil level is 135 mm, and the manual says "Oil quantity affects fork behaviour at full compression.  Compression load increases or decreases with oil level."  It also gives a minimum level of 150 mm and a maximum of 106 mm.

Which brings us to the end for now pretty much.  I'm curious to try some of the other forks I have kicking around, being the 40 mm Marzocchi and the 41 mm Showa non adjustable forks fitted to 90's Monsters.  Both of these had quite high oil levels specified, 90 mm for the Marzocchi and 80 mm for the Showa.

Plus there was a service bulletin for the M900 with the 41 mm Showa that recommended adding 30 ml of oil on top of the 80 mm spec.  This was aimed at helping the fork performance at full compression.  I'm curious to run them on my test rig to see how they behave, as it just seems like way too much oil.

More rambling to come.  Lucky you lot eh.
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Marzocchi 43mm fork design and impact of oil level on spring rate, Part 3: More fork details

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Just a short update.  I had an S2R800 in today for service and had the forks apart.  While they looked identical to the Marzocchi ones, I noticed that the markings in the inside of the lowers were different.  On closer comparison, it's the brand part that is different, everything else is identical.  I have no idea who makes them, but it is a symbol I see on a lot of these late model forks.  Photos below show them, Marzocchi with 'M' cast logo on left.

I did notice that the RH leg, which is the one I had played with previously, had rebound damping and no compression.  But the LH leg had compression damping and no rebound.  A little for most of the travel, a lot more in the last 30mm or so.  So as a combination they provide both, and that way you can tailor them as desired individually with different oil weights for example.

I added 15mm more preload, using pieces cut from an original spacer.  I'm not sure 15mm is enough now that I think about it, given it had nearly 55mm of sag before we started.  But we'll see.  I also dropped the oil level to 135mm.
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Some photos for Sarge

Nothing exciting, just some crankcase photos.