November 2006
As my engine is a 984 it is an accumulation of selected part that not always wanted to fit together as they are coming from different engines so I ended up with some interesting problems. It gave my some trouble but nothing is to difficult to sort out if you just want it enough and never give up
First up was to shim the gearbox. When I was disassembling the gearbox I found that it was all wrong. Both the in shaft and the out shaft had wrong axial clearance. Same thing with the selector drum. On top of this the forks were not centered on the selector drum so I had to start it all from scratch.
The first thing to do was to install the out shaft and assembly the crank case half’s just to see how much axial play I had. Then disassembly, do the same thing with the in shaft, and finally with the selector drum.
When I had done that I know how much shim I had to add or remove. I still did not know were the shims had to be added or removed so to find that out I added shims equal on left and right side of the shafts and the selector drum just to get the proper play. Then I assembled the crank case again with the out shaft, selector drum and the forks for the out shaft and tried to measure how good/bad the forks were centered. Disassembly again. Do the same thing with the in shaft, selector drum and the forks for the in shaft.
Finally I had the figures so I know how much I had to add and how much the shafts had to be moved sideways to center the forks properly. Now it was just a question of taking all the shims that I had and try to find a combination of all the shims so it all worked out nicely. Easy if you have a complete shim kit. Unfortunately I did not have all the shims that I needed so it ended up with a lot of work with fine sandpaper to get the shims to the size that I needed.
That is an easy one and it should not give any problems, or should it? It is just to install the smallest shim available, measure the axial clearance, decide how much preload I wanted on the bearings and calculate the shim size. Ducati sell shims in sizes from 1,90mm to 2,55mm in 0,05mm step.
When I disassemble the engine I checked the preload and found it to but 0,36mm. That was with almost 20 000km on the engine so it must have been something like 0,50mm when the engine was new. This is way to much as it should be 0,15mm.
The engine had originally two 2,25mm shims. Simple mathematics made me think that if I installed shims that were totally 0,35mm thinner then the original I would all be good so I need a total of 4,15mm shim. (2,25mm+2,25mm-0,35mm)/2. That gives 2,075mm per shim and that was what I had. 2,10mm.
I assembled the crank case again, this time with the crank only and with the smallest shim 1,90mm. I tried to measure the axial clearance and found it to be more or less nothing. How should I be able to find the correct size of the shim if I could not measure any backlash?
I was thinking that Maybe I did not install the bearings properly in the case so I decided to remove the bearings and the bearing holding bushings again. I measure the bearing holding bushings and found out that they were not as deep as the original bushes so it was a reason that it was a bit tight so I could relax and reinstall the bearings and the bushing and continue with my measurement.
I took an old shim and spent a few hours with sand paper to make it a few tenths of a mm smaller to I had a starting shim. Everything went together again and I could measure it properly. I finally ended up with using two 1,95mm shims and got a preload spot on 0,15mm. Just like I wanted. Perfect!
It was only one problem. The smallest shim that I had was 2,10mm as that was what I expected to use, top this up with the fact that it takes at least a week to get the new shims if I order some so I ended up with some more hours with a sand paper to get the shim down from 2,10 to 1,95mm.
I quickly realized that the longer stroke crank shaft together with my customized Carrillo rods did not work out. The rods were hitting both the crank case and the timing shaft. It needed some more thinking. I was sending some mails to the forum at www.speedzilla.com and got some advices from BCM Ducati and some other engine builders with ideas how to solve the problem.
It ended up with some machining of the timing shaft and a few hours with the Dremel on the crank shaft. Ducati cases are good as it is a lot of meat in them so it should not affect the strength of the case to much. The timing shaft was taken down about 3 mm in diameter and it all turned out with a good healthy clearance at about 1,8 mm that should be enough.
