Tech Zone > Aircooled RD Tech Help 250cc and Above

Clutch primary gear teeth

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Mary Hinge:
Hi, would somebody be able advise on the difference between a couple of spare clutch assemblies I was given which I believed, although it was a long time ago, both came out of early A/c 350's :-\
I've noticed that one them has 66 teeth on the primary gear & the other has 68 teeth. Intrigued I looked at the parts list and saw that the primary gears actually have different part #'s listed, 280-16150-00 for 68T & 278-16150-01 for 66T. What I can't see/find is anything regarding specific model use, if like the inner hub they're interchangeable and if so what difference would/does the gearing make ?
Thanks  :)

Yes, as you have found, the 250 and 350 have different primary gears, the one on the crank and the one on the clutch basket.  The part numbers show this but you have to count the teeth.  The other clutch components are the same but, the whole clutch and the gears themselves had several updates and revisions so, they don't all match.  Of course, the different gears have to match, the 250 and 350 primary gears are sets and don't match each other.


Mary Hinge:
Thanks for such a quick reply 5port and know I've looked at the part list again I can see that there 2 different crank primary gears listed.
So would you, or anybody else, know what the consequence or any advantage/disadvantage would be if you were to change the 350 crankshaft gear for a 250 21T version and used the 68T drum/basket.
Unless someone says it's a no no for a 350 I was also thinking to make the 68T version useable for a 350 a 21T 250 crank primary gear must more plentiful & cheaper than decent 350 outer drums. Just a thought  ;D

21/68 is 250.  Consequence is higher reduction ratio than 350 by around 10% with increased torque through clutch and gearbox, also making bike undergeared unless final drive sprockets changed.  Also, oil pump plastic gear is different and oiling ratio will change with a 250 plastic sprocket. Plastic tacho sprocket also needs changing.
Quite a few 350/400 bikes run with 250 clutch and suitable oilpump and plastic sprockets.


Mary Hinge:
So guess you meant to type 21/68 as the combo for a 250, making 23/66 the 350 set.
Thanks for the info/insight, bottom line seems to be that they're the same but different :D.


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