XT600 5th gear wear, a solution
I have fitted 3YF 5th speed gears to my 2KF, tested it for a short ride and found no issues yet. Time will tell if there are faults in the execution and what the life will be.
This is the second repair to 5th gear. 32000 km ago, before i had 'cracked the code', i fitted early gears 5Y1 and 1VJ. Not only did they last poorly, they wrecked the new 3AJ oil pump, put fine scratches on many working surfaces.
I have learned so much since then, thanks to many posts here, especially XTKlaus, and to guys like martyn biker who sent the 1st proper parts list i have.
1st, a little history: the 1983 XT600 34L was a development of the 550, code 5Y1. By 1986 the next significant model change was the 1VJ, and already there was a new 5th gear with that code. 1987, '88 and 1989 saw more changes including revised primary ratio and pressure oil feed . 1990 brought paired 2JT gears with fewer teeth.
A combination of these, but i suspect predominantly different use, dampened the 5th gear issue. Hard riders migrated to other brands. Yamaha 'milked the cow'.
The 1st XT 660 3YF developed from 600 got new gears. I can't find were they were used in a 600 before the 4PTA of 2000. The 600 4PTB ended 2002? Odd, maybe that engine lives on in another model. Belgradia?
The 3YF 5th gears are 1.5 mm wider than all previous gears. The casing of 4PTA has a changed part number suffix, '00' to '11', indicating changes.
I believe the bearing housings in left hand casing were machined to accommodate wider gears on longer shafts.
Modifying the earlier housings similarly is possible, but there may be an easier, cheaper way:
I have yet to figure out how to add text after placing photos, so may have to post this and add to it afterwards.
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