How to tell if crank seals are leaking?

[pgiganti]

I have a '72 Yamaha CT2 175 that I'm restoring. I've gotten it to run, but it occasionally dies just outa nowhere. Runs fine otherwise, sometimes for long stretches of time and miles. Someone has suggested that I may have a leaky crank seal(s).

What are the symptoms of leaky crank seals in a two stroke that's running? How do you diagnose this positively other than putting new seals in? Is there some sort of compression test you can do? If so, what do you look for when you're testing?

Paul

 

[_JOE_]

The proper way to check is a leak-down test.

Usually a leaking clutch side seal will mimik rich jetting causing plug fouling and excessive spooging. A leaking ignition side seal will mimik lean jetting usually resulting in high idle rpm or engine damage.

The problem you describe sounds more to me like an ignition issue.

Do you have the service manual? If so you can use a multi-meter to test the ignition. Sometimes you can find a component out of spec on a cold system, sometimes you have to run it till it quits to find what's wrong.