Not been on here a while, but some may remember my trials and tribulations trying to get this old bike back up and running:

http://www.trialscen...-gears-damaged/

http://www.trialscen...y-gear-removal/

http://www.trialscen...9-crank-damage/

…and some more…

Anyway, the engine is ON THE BENCH with a genuine intention to put all the many bits back together, and I can’t recall where these things go:

Well, I’m pretty sure they go between the main bearings and the crankshaft seal carriers, can anyone confirm? And if so, why??!

But what puzzles me is that there at least two different thicknesses of these shim things and I’ve no idea what I’m “shimming”. Note that the picture is all the shims from two engines…..

Thanks for any pointers

- Steve

Edited November 28, 201213 yr by andy
Fixed broken embedded image

yes that is where they go, and they are to locate the crankshaft in the right place. You will need to understand shimming to put that motor together without damaging it

OK…. So any clues then?! I have rebuilt quite a few engines but none have this shimming method.

Here’s where the shims go:

So looks like they hold the main bearings to prevent any creep sideways/outwards as the engine temperature cycles.

Which would suggest…. That the crank bearings need to be fitted with zero clearance against the crank. Or???

Edited December 1, 201213 yr by thedktor

yes the bearing inners rest against the crankwheels on both sides. The shims are to hold the crankshaft in the right spot so the conrod runs in the middle of the crank pin.

Be careful you don't bend the crankshaft during assembly of the bottom end. This is a common mistake whe rebuilding motors that have a crank that can be adjusted side to side and it causes the primary drive gear teeth to bind at the tight spot. I suggest that once you get the crank in the middle, you make sure it is straight before deciding what shims to fit for final assembly.

The motor was made to use 0.5mm thickness gasket material for the crank seal carriers and the centre gasket.

OK thanks feetup. Any tips for how to actually do this then as obviously the bearings are not free to float so will need some "persuasion" to move and find the right position.

Cheers, Steve

fit the bearings to the crankshaft first by heating the bearings. When the crank is cool (some people put it in the freezer to get it nice and cold) heat the casings to fit each side, one at a time. That will minimise the side loading on the crankshaft. If there is too much resistance when the bearing outers are being fitted into the cases, pull them into place with a puller rather than pushing on the other end of the crank.

Work out the positions for where you want the bearings to go before you start, so the bearings end up at the right spot in the casings. Once you have worked out the position, you can use the seal carrier as the stop for how far to insert the bearing.

One way to do this is to use the old gasket and the chosen shims.