Final drive/crown gear question

[fbenach]

Hello,
while checking my transmission and changing the bearing on it, we decider to give a quick check to the final drive inners... noticed that the crown gear has started to have a little "play" and will have to be replaced someday (not today thankfully).
Now, as long as those are quite expensive and more expensive to get down here (I live in Costa Rica) I was wondering about the possibility of using a crown from an R80 or R45, which were more common back in the days... and might be possible to get here as an used part...
A friend of mine has also a ´69 R75/5 complete final drive... good condition...
Anyways, it might not be the way I will go, but I was wondering if someone has ever done that before... does the bike gets faster? weaker?
What do you say??

take care!!

[Barry]

does the bike gets faster? weaker?

Yes.  Different models had different final drive ratios. Look on your final drive adjacent to the drive shaft fill plug and you will see the the ratio stamped in the casting in the form 31/9 which is the number of teeth on the crown wheel and pinion respectively.  Any replacement should be the same ratio otherwise the speedo will also have to be changed.


Although there was some variation in different markets an R75/5 drive ratio is likely to be a 32/10 where as  your drive ratio is likely to be a 31/9.  An R45 would be 35/9.

[tvrla]

 What Barry said! I have heard that the 32:10 is a good ratio for the R65.

However, a little bit of play would tell me a bearing is possibly getting worn. If it's not the bearing, then the  gears should be re-shimmed.

It's unusual to hear of problems with these final drives. They're one of the most rugged parts on the bike.