Vintage Dirt Bike Q & A

Hello,
Finally getting around to getting my bottom end put back together. Curious on the left hand crank seal(ignition side) as to how deep the seal should be seated? Flush with seal lip or deeper? I believe I may have driven it too deep. It is currently 5mm deeper than the seal lip face as I thought it would seat sooner. I have a spare OEM seal and willing to remove and replace. Thanks for any advice.

I've always installed my Honda seals flush with the case edge. 5mm further in is a lot for a 7mm-wide seal - it may not be seating on much case metal.

If your seal is now touching the bearing - as it might be - that could be a real problem. The inner bearing race may wear away the inner seal lip, and more importantly the seal could be blocking the oil passage down from the LH transfer passage, which would starve the bearing for oil. I really hope it didn't affect the bearing cage. Does the crank move freely, without noise?

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

Thank you Ray, knew I could count on you. I should have known better and taken measurements prior to install. The seal I removed was slightly deeper than flush as well as damaged. The crank still moves smoothly with no noise however with resistance that wasn't there prior to installing that seal, which makes sense it being up against the bearing. I have not moved the crank around alot due this resistance and realizing my mistake. I'm hoping no bearing cage damage as well, but dont believe there will be as I was not driving it in with excessive force. I will pull the seal and replace before continuing on with the assembly.

Thanks Again

Erik

Erik,

No problem, glad to help - I wish I had better news for you. On these motors, as soon as a seal's outer shell makes 100% contact with the case metal, you should be good to go. Your bearing cage is probably fine, but obviously check it once the seal's off.

When I was rebuilding my MR motor (nearly identical crankcase), I took photos of everything right after it came apart, which came in real handy later on. The pocketed bearings and seals were no big deal, but the unpocketed ones - especially the RH countershaft bearing - were a different story.

The LH crank bearing cage came apart on my CR, it's a miracle the crank didn't punch it thru the cases. I never did find the rivets.

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

Yikes. I did the same, took lots of photos. Works well when combined with the shop manual. I was able to find all OEM bearings and seals, and had the crank rebuilt and balanced, so I hope I have done everything right as I dont want to have go through that search and downtime again.