Diagnose possible Crank seal

[Brett Kerby]

Just checked tranny fluid (73 Gt 250) due to clutch noise and found that I have lost about 400 cc's in about 600 miles. Checked the right side spark plug and it is excessively black and fouled. Left plug is nice and Brown.. I am assumming this is a blown right crank seal would that be a fair guess? Bike is ideling good and did not smoke excessively. Looks pretty straight forward on replacement, is there any hidden problems with this? And how hard is the seal to pull out? I know Billy has a similar problem on his 250, curious as to what he has found....

[advant63]

if it's eating trans oil then it will be the inner seal on that side. that's a crank rebuild. may as well do them all while it's out.


i'd be tempted to carry a fresh plug and drop some heavier oil in the trans

[Barry S.]

The outer seal on the right side is inside the clutch cover and exposed to the tranny oil, I replaced one on a '73 GT250 that I had a few years ago. It can be done, the cases are very sharp where the seal fits in, I chamfered mine to dull it so it would not destroy the seal when pressed in, be sure not to get shavings in the bearing.

[Brett Kerby]

Barry did you use sand paper to chamfer the case? And I am tempted tp drive it some and carry an extra plug, but it doesnt look too hard to change that seal so I am going to order one next week and get busy....

[Barry S.]

I packed around the bearing so stuff wouldn't get in it and used small pin files and sand paper to smooth it out. I ruined one seal before I did it this way, it's still not easy to fit the seal but it can be done. Remember which side goes in when you take it out.