Air Leak -crank seal repair

[77vettejeff]

Any vintage bike mech's there? My bike is leaking air bad. Lean-out is causing it to rev on it's own after starting. It can run at appox 4-5k rpm's steadily if I almost completely close-off the mouth of the carb with my hand! Is it possible to replace the crank seals without splitting the case on a '75 yamaha dt125? For left side, I'm hoping to pull the armature and take a look to see if this is possible. I think I've pretty much ruled-out all areas of leakage other than crank seals or main case seal. Occationally, if the bike misfires, I see exhaust leaking from the left side cover. This can be observed with the point plate cover off.
Any help would be greatly appreciated. Thanks, -Jeff

 

[TimberPig]

Yes, you can change them without splitting the case. You have to pull the entire flywheel and stator out on the left side to access the seal. On the right side, the primary gear has to come off, and normally the clutch as well. That will give you access to the seals, which can then be pried out with a seal removal tool, or very carefully improvised with a screwdriver or a couple screws and a pair of pliers. Once they're out, clean the bore, inspect the bearings to ensure they're not damaged, then drive the new seals in square to the bore, being careful not to damage them. Reassemble and you're done, provided there's no other leaks.

 

[77vettejeff]

Good news, thanks for the reply.

 

[77vettejeff]

Is there a special puller for the armature? Is it pressed onto the crankshaft?

 

[TimberPig]

Yes, you need a flywheel puller designed to thread into the flywheel threads, and push on the crankshaft end. The flywheel sits on a taper, and cannot be removed without damage with anything else. Good news is they aren't very expensive.

 

[77vettejeff]

I got it off and the left crank seal replaced. That was definately the problem. The seal was trashed. The bike runs good now. Thanks.