Vintage Dirt Bike Q & A

Greetings,

Have an MT engine sitting on the workbench and a newly painted frame waiting to receive it. Getting a flywheel puller tomorrow since I see (and ray pointed out from a picture I posted) that one of the coils appears to be huffed. In addition, although I can account for the sticky oil and grime around the fly wheel being deposited there by the chain through a chip missing in the housing directly adjacent to the front sprocket, it seems a prudent person would also check out the crank seal while they have it apart to make sure it's good. Now the question: It occurs to me a reasonable way to test the seal while the engine is on the bench is to carefully pressurize the tranny through the vent on the backside of the case, and see if: a) it holds pressure and b) if the left side crank seal weeps as a result.

Assuming that makes sense sense, what should the test pressure be? I know the crank/head assembly is around 6 lbs, so, is that what I should pressurize it to?

Any input would be greatly appreciated.

Al

If it were me, I'd just replace the LH crank seal (p/n 91202-357-003, still available from Honda) while the flywheel's off - you'll definitely have to do it eventually, might as well be now while it's easy. If you want to test the RH seal while the motor's on the bench, I'd suggest sealing up the clutch cover and spraying some soapy water around the seal where it meets the crank, then lightly pressurize the gearbox as you mentioned (3-5 psi should be fine, no real need to go higher IMO). It's kind of a backward test, but if you get bubbling at 3 psi the seal's definitely bad, and if it holds 60% or more of the original pressure for a couple of minutes or more w/no bubbling at all, the seal should be OK (depending on how many hours are on it, of course).

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Thanks!