rm125p (93/94/95) crankshaft interchange.

[lukeyrm12593]

My son who is 15 has been riding a 93 rm125 at our local track for the last couple of years,and its is now time to refresh the top and bottom end.Upon stripping the bottom end weve found the crank is out of spec and and the journals where the main bearings sit are worn so badly that the bearings just fall off-lucky we found it when we did before anything bad happened.Our problem is that finding a crank for a 23 year old rm125 has been a bit of a problem,no one does an aftermarket one (we are in the uk) and the one we have cant now be reconditioned.So my question is do any cranks from the later rm125 fit,as this would open up our options on finding a secondhand rm crank to recondition.Looking at rm125 cranks up to the year 2000 they look very similar but i need to be sure before i part with any money,and my poor lad is getting withdrwal symptoms from not riding!,thanks in advance

[Sandblaster]

Let me see what I can find...

[lukeyrm12593]

That would be great-thankyou!

[Sandblaster]

Unfortunately I don't have any cranks for that year range that I can measure and post for you.
However.... Your crank that has a bad bearing journal, is that all that is wrong with it? Just a bad journal?

[lukeyrm12593]

Where the main bearings sit on the ends of the crankshaft,the shafts have worn so the bearings just slide off,they both have a lip or a ridge where they have worn so the new bearings arnt an interference fit as they should be,i ndidnt think it would be so difficult to find a good crank, hence needing to open up the choice we have of finding one by hoping a later model may be the same.

[Sandblaster]

We have had other crankshaft bearing journals fixed.
You can go to a Industrial Plating Company (Not decorative chrome).
Look for a place that plates hydraulic cylinders, ect.
They can grind the bad bearing journals so that they are round again, then they will plate them slightly oversize.
Last, they will the precision grind them to the correct finish size.
Another option is a dry plating service that can plate the journals while it is on a lathe.
Or, go on to eBay and see if a seller of a newer crank will give you all the dimensions you need for a comparison.
Hint, send them a picture of your crank with dimension on it for comparison.
It will make them more likely to spend the extra time.
Something like this..

[Sandblaster]

Whatever you find, please let us know so we can pass on the knowledge

[lukeyrm12593]

Will do many thanks for having a look for me and for some good tips!.