Noise - Bearing replacement?

[Lloyd Boland]

I have a 1976 250 MC5.  I have been told it is the original crank and original bearings.  While racing yesterday I noticed an awful noise coming from what appears to be the lower end.  It is a very loud whining noise that is most noticable after reving the motor and then you turn the throttle off.  As the revs drop, the noise is very noticable.  I have the manual and will be attempting to check the motor out this week before it blows-up.  Need to have it back together in about 4 weeks for the next race.  Any words of wisdom as I go through the process of splitting the cases and checking out the bearings, etc.  I am new to the KTM motor but have split the cases of many cz motors.
Thanks for all input.
Lloyd Boland

[dirtbike]

Well, infact there are some things you need to know.
The crank main bearings is a very special bearing
type named M25. It's easy to split the cases since the outer races only have a shoulder on one side. Then you will have to heat and press the inner races onto the shafts. But the most important thing is that you will need to measure the width in the cases between the bearings, and then the width of the crank. After that you will need to shim the bearings so that you end up with a pretty small play.
Only 0.01 - 0.03mm.

Check this out:
http://www.ktm495.mxbikes.com/81/81-250GS-28.jpg

[Big Mac]

Lloyd - go back about 6 pages, check out "motor rebuild tools" posted by Mick. Some good direction there. Shouldn't be hard to get it all apart, probably just need an expert when it comes to rebuilding the crank. Mac

[Lloyd Boland]

Thanks for the help and the reminder on the "tools".  I think I will try to tear it down this weekend and see what parts will be needed.  I also did a search and reviewed the lengthly discussion on M25 bearings.  All you guys/gals(Lynn) are very helpful to us novice enthusiasts.  Any more suggestions would be greatly appriated, especially any advice on the bearing shims.  

Lloyd Boland
One of only a few SoCal KTM/Penton rides