Thursday, April 24, 2014

Some photos for Sarge

Nothing exciting, just some crankcase photos.

Friday, April 18, 2014

Lift graph for 4V Desmoquattro cams using strada inlet cam as exhaust cam

I thought I'd post a graph here for a conversation that I've been having with someone about using the 4V Desmoquattro strada inlet cam as an exhaust cam.  I haven't tried this personally, but have been told it works well.

In the graph, you can see the exhaust cams on the LH side.  The yellow curve is the G, the corse exhaust cam used from 1992 (888 SPS had it too) until the last of them in 2000.  They obviously liked it.  The 916/999SPS exhaust cam (blue), while having much less duration, has a fairly similar shape and compared to the pink strada exhaust curve, is completely different.  The strada is much slower opening, with what is called an asymmetric profile.  The point of this graph, the red line, is the strada inlet cam being used as an exhaust.  Profile wise it is very similar to the SPS up to peak lift, although it doesn't hold the peak or closing profile as long.  But much better than the strada exhaust, and the SPS cam set does work very well.  It's not a straight fit, the closing lobe needs to be narrowed and the opening rockers need some grinding at the feet.  But well worth the effort given the cost and complete unavailability of the SPS cams.

How much input the SPS inlet has over the strada inlet in comparison I don't know.  The extra high lift duration of the SPS inlet is something the specs don't show on their own, and that sort of extra area under the graph can only be good.  The orange curve is the 748RS '506' cam, shown because there's some on Ebay at the moment and duration wise they only have 5 degrees more than the SPS and 11 degrees more than the strada.  They do have a lot more lift, and are quite aggressive acceleration wise.  But if you kept them to around 10,000 rpm, not the 13,000 or so they would have seen trying rather vainly to keep the Japanese 600's in sight, they won't be too destructive I'd think.

Doug Lofgren's cam page has more info on them too, with cam doctor graphs.

Saturday, April 12, 2014

Timing belt pulley positioning on belt drive Ducatis

There's a thread going on one of the forums about replacing belts, and the point of marking the belts has been raised.  I made the comment that I found the marking of belts an over complication of the procedure, but some people do find some comfort in it.  In particular for locating the vertical camshaft correctly (vertical inlet on a 4V), due to the load the vertical inlet closing spring places on the camshaft when the cam is at the correct position.  Coupled to the fact that on most of the 2V models the vertical cam pulley has a surround covering it and making it hard to get a good hold of it.  I can understand the issues this brings to those who do this very infrequently.

So, to confuse people further, I thought I'd introduce another method to bypass this.  I did teach this method to a previous workmate, who them went and bent some valves, so if you don't understand it, don't use it.  But it seems pretty simple to me.

The timing shaft pullies traditionally have 4 holes in them, and the locating dot on the outer edge.  See the picture below:

In this instance, the locating dot is lined up with the mark on the primary drive cover.  This denotes the engine is at TDC firing on the horizontal cylinder, which is the master position for most setting procedures.

As the timing shaft turns at half crank speed, it rotates 180 degrees for one crankshaft rotation.  From the RH side the crankshaft rotates clockwise and the timing shaft rotates counter clockwise.  Vertical TDC firing is 270 crankshaft degrees after horizontal TDC firing, or 135 timing shaft degrees.  If you look at the above, you can see 4 holes spaced at 90 degrees, and conveniently located at 45 degree spacing either side of the locating dot.  This means that the second hole clockwise from the locating dot is 135 timing degrees from horizontal TDC firing, and as such, it's a locating dot for vertical TDC firing when aligned with any of the aligning marks on the primary drive cover or camshaft surrounds.  As below:

On the engines with adjustable cam pullies, these holes aren't present.  But of the three locking screws that hold the halves together, one is in the correct position.

The locating dot still gives the position anyway.  On the 2V pre DS motors, when the timing shaft dot is at 3 o'clock, the vertical camshaft dot will be at 4:30.

On the later 4V Testastretta and 2V DS style engines with the 20 tooth pullies, the small holes are still there.  But there are many larger holes, just to confuse the issue.

And, as always, when done, the locating dots on the timing shaft and all cam pullies must align with all the correct marks once set back to horizontal TDC firing.

Sunday, April 6, 2014

Fitting a 2003 onwards 696/796/800 6 speed gearbox into a pre 1998 600/750

One of the motors I have in bits is a 600SS motor, which came from the bike I sold the original engine from Minnie into.  I actually sold more of this engine last week, just to make it harder for me to pointlessly waste a heap of money rebuilding it.  This was mostly due to a mock up of the bits I had done the week before, trying the 68 mm stroke 900SS crank (a narrow one) to see what happened.

There was contact in a couple of places between the crank webs and the cases, at the inside of the starter drive idler gear boss in the LH case, and in a similar position on the RH, with a casting ridge that I'm guessing would be for an oil gallery.  So I can't really cut either out, meaning the crank would have to be relieved at the outer edge, which reduces the most significant section of balance weight (furthest from the centreline).

The same section of crank web also hit the timing shaft on the RH side, where the later model timing shafts don't have a locating ridge.  The pre 98 small blocks have a timing shaft that is shimmed between the cases to locate it, unlike the big block or 98 on small blocks where the shaft is held against the LH bearing by the timing gear.

The bottom of the 600 cylinder did just clear the web, with the underside of the piston quite a distance away.  And the rods cleared the timing shaft.

And the 620 pistons I was going to use (it was going to have 750 heads, similar chamber to 620 and much larger than the small chamber in the 600 heads, which I had sold anyway) stick out a bit, but a thick base gasket shaped spacer would fix that.  The 6.5 mm stroke difference between 620 and 900 (61.5 mm to 68 mm) would suggest the spacer would need to be 3.25 mm thick.

Anyway, I digress.  The point of this was trying to put a late model small block 6 speed into pre 98 cases.  The complete 6 speed box I bought from Ebay was from an M696.  The easiest way to show why it wont drop in is with some photos.

Input shaft:
The input shaft has a larger nut on the clutch end, like all other late model boxes.  So you'd need a bigger nut and possibly to do something to the clutch hub to accommodate it.  The length of the clutch snout looks to be the same from threaded end to first gear.  I didn't notice any difference there, but I didn't measure them.  I might do that.  6 speed at the top.

The LH end of the input shaft has an extension that goes through into the recess which the clutch pushrod passes through.  As the pre 98 doesn't have the clutch pushrod passing from left to right, there's no need for the extra snout, and no room in the LH case for it anyway.  It has to be removed, and I figured the drop saw would take care of that.

Output shaft:
Not a great deal of difference here.  The shaft outside of the LH bearing is 10 mm longer on the 6 speed, but you'd just turn the sprocket around to fix that.  The only other thing I noticed is that, while both shafts are 25 mm diameter at the sprocket spline, the 6 speed wouldn't slide into my 600 cases like the 5 speed did.  Maybe it just didn't want to be there.

Shift drum:
The shift drum is the biggest issue, with quite significant differences.

The RH bearing area is much smaller diameter on the 6 speed (1 arrowed).

The RH end of the 6 speed drum has the 6 groove snout (2) for the sprung detente lever the later bikes use.  You can see at the bottom left of the snout that one ridge is missing its top, that's neutral.  The sprung detente lever at the RH end of the shift drum was introduced with the 916 from memory, and every new model since has adopted it.  The sprung ball detente at the LH end of the shift drum is now only for neutral, so there is only one corresponding groove in the LH end. 

The neutral light activation has gone from a 2 wire switch that is pushed in by the lump on the 5 speed drum (3) to a single wire switch that is earthed by the drum itself.  The light brown covering on the drum, with the space at the (3), is an insulating coating that keeps the earth circuit open at all times except for when the drum is in the neutral position.

The difference in the shift fork groove pattern is obvious, so clearly you can't use a 5 speed drum.

I had various thoughts for overcoming these issues, from cutting and shutting the end of the 5 speed drum onto the 6 speed drum to making a spacer ring and welding on a switch pushing lump and cutting off the detent snout with the drop saw.  Attempting the shut once the cuts were made is the only way you would be able to determine if that was a viable option.  If not, you have two scrap shift drums.

But you still have the issue of the LH end to deal with.  The LH end of the 5 speed shift drum shows the old style detente grooves.  You would have to machine these into the 6 speed shift drum to use it, which for me starts to make the whole thing much more of a hassle as I don't have a mill.  One option around this is to use a non RH snout detente style shift drum from a pre 916 big block as a starting point, ie, 851, 888, 900.  I'm sure I have one of these around somewhere.  I did compare a 900ie shift drum, which does have the RH snout detente, and the grooves appeared to be functionally the same.  They weren't as smooth flowing, with a step at each transition point, but all appeared to do the same thing at the same setting.

So I didn't get any further with this fitment.

The other issue I have with the concept is that while a 6 speed is nice, the niceness comes from the ratio spread.  The 5 speed ratio spread is 2.59, the 6 speed is 2.67.  The big block wide ratio 6 speed is 2.88, a comparatively much bigger change.  To overcome this there is the possibility of having another gear made for 6th, either 1 tooth bigger on the input or 1 tooth smaller on the output.  The 26/24 ratio gives an 8% gap between 5th and 6th.  27/24 gives an 11% gap, 26/23 12%, with a ratio spread of 2.78.  That makes about a 3 tooth on the rear difference between the top gear ratio of the 5 and 6 speeds.  The shape of the current teeth determines if the 1 tooth idea will fly.  The input shaft gear will be the easiest to make, as the output shaft gear has a shift fork groove on it.