We have added this page to cover some of the basic procedures that should be followed when rebuilding a gearbox and what to look out for as early signs of failure.

GOLDEN RULES OF GEARBOX REBUILDING

1. Always replace any circlips with new ones when rebuilding the gearbox. These are available from your local dealerships for your relevant make of bike. Paying as little at £8 for 6 circlips can save you a bill for a whole gearbox!!
2. Always check all gear dogs and teeth at every re-build. If something looks worn, chipped, dented, cracked, or heavily discoloured replace it!! If unsure seek an experts opinion. See section below for further details.
3. Always, if possible, check the gearbox shifts cleanly up and down the box before sealing up the engine cases!! If this is not possible at least check with the cases dummy built together, before the engine goes back into the frame!
4. Always check for excessive wear on selector forks and selector drums, also check selector fork pins.
5. Always make sure that the main gearbox bearings are not worn out. This is usually characterised by feeling ‘lumpy’, or excessive lateral play while turning by hand.
6. Always make sure there is not any excessive ‘play’ in the selector mechanism, especially on older bikes which have a lot of linkages and rollers. If there is large amount of lateral movement at the pivot points or rollers allowed to move around rather than just rotating, gear shifting can become erratic and the result can be a damaged gearbox.
7. Always make sure that sliding gears move smoothly along the shaft and engage correctly with the gears either side. If possible ensure that the cross drilled oil holes in the shaft line up with any holes in the selector fork groove of the gear.
8. Always make sure that all fixed gears rotate freely but without excessive side play. If the gear runs on a splined or plain bush, make sure these are within tolerance and aren’t discoloured which can show signs of over heating due to an incorrect clearance. If a gear has a bronze bush which is heavily worn get it replaced!! We will manufacture and fit new bronze bushes if you send us the gear!!
9. Always make sure that all plain washers and splined washers aren’t dished, this can be caused by overheating or just after many years of use. A dished washer will take up clearance which will lead to seized gears. Again a few £££’s for some new washers can save a much bigger bill!