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2000 rm125 crank seal question

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Hi all. First post here. This is technically my first 2 stroke dirtbike but I've been lurking a ton to read up.

Just bought a 2000 rm125 that doesn't run. I removed the jug and piston to learn that the previous chowderhead had installed the piston backwards, destroying the ring and slightly scoring the cylinder wall (arrow on the piston not pointing to the front). I bought a wiseco piston and decided to replate the cylinder.

I tore the power valve out today and it was pretty well coated, not caked, with black sticky oil (but it still moved freely). I learned from a similar post that this can either be caused by a blown right crank seal or just running too rich. (to my knowledge, the pipe and jetting are stock so I don't think its the latter)

The crank seems good. No up and down movement, but a little side-to-side wobble which is apparently normal.

Anyways, how should I go about determining whether crank seals are bad? Should I just slap the bike back together and assume the gunk in my power valve is just from blatant disregard for scheduled cleaning? Or should I investigate further? If so, how do I check without being able to run it? Would the bottom of my crank be full of oil after sitting for a while? Would my silencer be all gooped up from all the oil? Would my gear oil be milky? Is there a quick way to be sure whether the seal is good or bad?

Any help is appreciated!

-Greg

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Only way to know for sure without splitting the cases would be a leak down test. For the price of the seals you might as well replace them, you don't need to split the cases to replace them.

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Thanks for the reply.

The fiancee just bought me a compressor for christmas. Might try the ~ $20 leakdown test.

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Only way to know for sure without splitting the cases would be a leak down test. For the price of the seals you might as well replace them, you don't need to split the cases to replace them.

What he said!! It's a very small investment. Replace the seals and you know that they are good after that.

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What he said!! It's a very small investment. Replace the seals and you know that they are good after that.

I guess I'm a little hesitant to remove the flywheel, clutch basket and primary drive gear to do this job.

I guess I ought to just man up and do it.

While the jug is off, is there any benefit to splitting the case? Or is it just as easy to do the crakshaft seals with the cases together?

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I guess I'm a little hesitant to remove the flywheel, clutch basket and primary drive gear to do this job.

I guess I ought to just man up and do it.

While the jug is off, is there any benefit to splitting the case? Or is it just as easy to do the crakshaft seals with the cases together?

It's easier to change them with the cases split but certainly not worth the effort of splitting the cases for the difference.

Check main bearings and big end of crank bearing for play. If they are good no need to split the cases.

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I just did the crank seal job on my RMX. Not a big deal at all, don't be afraid to dig in if you have to. I suggest you put it back together and run it. If your clutch side crank seal is bad it will run like absolute crap and it will smoke on biblical proportions. Drain every drop of oil from the gear case, then carefully measure exactly how much you put back in. Run the bike for about 10 minutes, drain and re-measure the oil. Mine burned 11cc in 7 minutes...obviously a bad crank seal. Its a simple test requiring no special tools and you can have some confidence if that is your source of splooge. All for the price of a quart of oil. Good luck.

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I just did the crank seal job on my RMX. Not a big deal at all, don't be afraid to dig in if you have to. I suggest you put it back together and run it. If your clutch side crank seal is bad it will run like absolute crap and it will smoke on biblical proportions. Drain every drop of oil from the gear case, then carefully measure exactly how much you put back in. Run the bike for about 10 minutes, drain and re-measure the oil. Mine burned 11cc in 7 minutes...obviously a bad crank seal. Its a simple test requiring no special tools and you can have some confidence if that is your source of splooge. All for the price of a quart of oil. Good luck.

Plus add the price of - time to tear out and replace. Compared to - do it now and don't worry! Plus you'll save the cost of a quart of oil if it leaks.

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How do you get the left crankshaft seal out without splitting the cases? The right side is easy but the left side doesn't really have anything you can grab with a hook and no room to pry. How do you guys get the left seal out?

Thanks!

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You can also check the crank seals by looking in the bottom part of the magneto case for a little pool of gas or oily residue. This isn't foolproof but it can help.

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