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After taking my bottom end apart, i found that some of the dogs on the gearbox I had were quite rounded. I have bought I better used box that I planned on using, but had some questions;
1) I see that the first gear on the Mach 1 is 17t vs 16t on the other box I have. Would it be a benefit to use the Mach1 input shaft w the taller 1st gear for track use?
2) Are there other differences that I should be aware of between the boxes?
3) I have read the shimming thread, but I have found no real info on service limits on the shifter forks. Mine look mint, should I just presume that they are good to go?
4) Can the circlips on the input shaft be reused or should they be changed?

Anything else I ought to check while in there?

Hi,

I hope that you are a man of infinite patience, as you will need to be! First you will need a torch and a long screwdriver to check the engagement through the cylinder mouth. Make sure that you grease the crankcase centre gasket to make all the assembly and disassembly easier.

Shimming is an exercise in the art of the possible, and a compromise. After setting the end-float on the shafts, you need to check the engagement of all the gears, you want the dogs to engage fully with their neighbours, but not over-engaged; you do not want the gear that is stationary is being forced over. Check also that the gears next to the bearings cannot move sideways out of engagement.

I would re-use the circlips if they are good, but it may be sensible to have a couple of spares if you can get them. If the forks look good then they probably are, they are not a part that wears badly (AFAIK). Other people will chime in here with their experiences.

Good luck,

Colin

The best bit of advice there is to be patient and to (lightly) grease the case gasket. I assembled and reassembled mine about 4 or 5 times before I was happy with everything.

I think I would replace the circlips even if they look good. They are cheap and you’d kick yourself if one did fail.

Ian

Yes same as above with luck about three goes will get you there, remember to tighten the cases up pretty firmly the first time to squash the gasket down to fitted size (and grease it of course) as Colin said make sure none of your gear engagement is TOO tight. Take the patience tablets now . Cheers George

The Forks are about 4.4mm thick when new and I would change them once below 4.2mm. You can reuse clips by reshaping them back, but if the circlips have lost their "spring" and don't snap snuggly into the groove, then replace them. Check they are in the groove well with an eye glass, if they are spinning around then they are to loose.....if in doubt replace.

Regards Nigel

...and yes use the taller 1st gears from the Mach 1 in the race bike, it will help with the gear change from 1st to 2nd. The std N/C 1st to 2nd is a big jump, when compared to the W/C ratios.

Nigel

I have read that the 5 speed drum fork tracks are not particularly well engineered so a little axial play in the drum shimming is better than being too close a fit. %th gear is reputed to be a fast wearing gear or weak .

Thanks for all the replies. I will then use the Mach1 1st and change the rest and measure up the forks.
All this talk abput gaskets has me wondering as mine were assembled w/out a centre gasket. And all my [limited] experience from later Ducati belt twins have told me to get rid of the centre gasket. Is it normal to retain these on the singles?

Some people do dispense with the centre gasket and use sealant. Personal choice!



Cheers,

Colin

It all depends on if? or not? the engine was previously shimmed up with a centre gasket......for example having the crankshaft shimmed with a gasket in place to zero endfloat it would then excessively preload the main bearings by leaving the gasket out. Personally I have never built a widecase engine without a centre gasket ( I only grease them and never had a leak yet).
Cheers, George