Left Crank Seal

[Joey G]

If the left crank seal was leaking in a 1999 CR125, would I find oil behind the left case cover? Would there be oil on the flywheel/alternator stator or in the bottom of the case?

I have an erratic idle and it is running rich (not a jetting issue). I have ruled out everything but the left crank seal but I do not find any oil in the left side of the case?

Thoughts??

[HrcRacing]

I guess maybe you might get some blow-by but not oil since the crank is separate from the transmission. Try pulling up/down on the flywheel to see if you can detect any play in the crank bearing. If there's any, it's bad and you'll need to replace both bearings and both seals making sure to check the shaft on the left for scoring and the primary shaft collar on the right as well (i.e, it can't seal if it's scored badly).

Of course, the right bearing/seal could be the only one out. If they've never been replaced before, I'd go ahead and take care of it now.

Best of luck.

[minibikedad]

If it's leaking, look very closely behind the flywheel. YOu should see a trace of oil drip. Better yet, remove the flywheel and you should see the oil drip originating right off the crankshaft, making it obvious as to whether it's leaking or not.

Another condition of air leak is erratic idle. if you have a leak, the revs will tend to not rev down as quickly, and sometimes it will idle at low revs and sometimes it will idle at high, sometimes too high, of a rev.

In any case, get it fixed asap, especially if it's as simple as a side crank seal. This $10 part if left unsealed will cost you $400 worth of damage in short order.

[HrcRacing]

I should have been clearer and stated that you might get some blow-by/unburned 2-stroke oil.

Also, keep in mind that if the bearing(s) are bad, just changing the seal isn't going to fix it. Oftentimes, the bearing is bad and that causes the seal to fail.

Best of luck.

[maico450]

If your left crank seal is leaking, you will be sucking air in. This will cause a lean mixture, not a rich mixture. If your right crank seal is leaking you will suck in trans oil. If you have a rich condition, check your reed valve, your airfilter, your choke, your float height, your air screw passageway, your silencer, then adjust your jetting if everything else checks out.

[Joey G]

Thanks guys!

The crank bearings are good. I just replaced the right crank seal. Just wanted advice on the left seal while it is up on the stand.

[minibikedad]

I would definitely replace the left seal too, or plan on doing so in the very short term. The left seal seems to wear out more frequently than the right side.