Vintage Dirt Bike Q & A

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 Post subject: HELP...RM Bottom End!!!!
PostPosted: Thu Jul 08, 2010 4:13 pm 
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Joined: Fri May 14, 2010 12:03 pm
Posts: 4
Ok, I have a RM50 that needed a crank rebuild so I pulled it apart and got the crank back. Now my problem is I'm trying to get the shift drum in correctly. I have put it in but cant get it to seat in correctly or shift through the gears smoothly. I believe I am supposed to have it in neutral but I'm not sure how to tell where exactly that is. I have a Clymer manual and that thing is worthless for the 50cc models since it concentrates on the bigger bikes (it covers 50 - 400) and doesn't go into detail on the shift drum install anyway.

Has anyone got experience with a bottom end rebuild on the vintage RM's?? Or know a website with good useable info. on a bottom end rebuild??

Thanks in advance!


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PostPosted: Mon Aug 02, 2010 10:27 pm 
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Joined: Fri Jun 02, 2006 11:12 pm
Posts: 159
Location: Salinas, CA
You ought to be able to find the original factory manual for that bike on ebay or even rotting away on the shelves of your local shop. Don't be too shy about asking the service manager if you can buy their 30 year old unused manual for $10.
Once you figure out the gears, make sure also to put something between the crankshaft wheels when you press the cases together so you don't through it out of true, replace the crank seals and bearings even if they look good too.

Lastly, it shouldn't be critical what gear it is in when you put it together. It is really important that it shifts through all the gears right though, otherwise you'll be taking it apart again. Nuetral should be easy to find though. Look for a spring loaded mechanism that somehow causes the shift drum to rotate to detents or clicks. Watch how that mechanism rolls up and down the ramps that it presses against. Neutral will be a halfway stop between 1st and second, the dead giveway will be a different detent holding pattern on the detent mechanism.

Good luck,
Jon


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PostPosted: Tue Aug 03, 2010 1:17 pm 
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Joined: Fri May 14, 2010 12:03 pm
Posts: 4
Thanks for the response.

Well I finally got it back together and running for the most part. The issue was that the shift drum wasn't in the correct possition..not supported as it should have been.

The bike starts on the first kick with no choke but the problem now is that when you give it gas it boggs/cuts out until you let off or you have to keep reving it and it revs fine. If just at idle and you give it gas it will want to stall until you let off. Any ideas as to whats going on. I believe its in the carb since it did that before taking it appart. I did clean the carb throughly before taking the bike apart since it was doing the same thing.

Any ideas what "jet" in the carb could be bad?


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