Motorcycle Repair: Hondamatic Seals, crankcase pressure, houseofmotorcycles

Question
Mr. Bill:

I have a 1983 450cc Hondamatic and the transmission (to chain) seal is leaking.  Manual is no help so can you advise how to change and is it a big task?

Answer
Bob, I assume you are referring to the transmission output shaft, which carries the front sprocket....?

http://houseofmotorcycles.bikebandit.com/honda-motorcycle-cm450a-1983/o/m2132

It is hard to tell from the images above, whether or not the seal has a retainer lip in the center or not. If you know that you will have to change it, buy the seal and look at the mounting edge surface. If there is a raised rib on the center of the seal, it generally fits in a matching groove in the crankcase, which means the cases will need to be split to replace the seal. If the outer edge is flat and smooth, then you may be able to pry out the old one and install a new one w/o case separation.

Driving the seal in squarely is best done with a proper seal driving tool or at least something like an appropriately sized piece of PVC pipe to keep the seal square with the hole, as you push it in.

There is a double seal set on that shaft, so you will really have to do this carefully, if going in from the outside.

Be sure that the engine isn't creating extra crankcase pressure because of a blocked/pinched breather hose for the crankcase vapors. That will cause oil leaks at seals and gaskets, unnecessarily.

Bill Silver