How do you know for sure when to replace your crank seal??

I was in the process of doing a top end on my 04 CR250 and after talking to the owner of Moto-X-Perts in Lafayette, (IN) about how I have alot of oil coming out of my pipe and that I am fouling alot of plugs he informed me that my crank seal is leaking. I already suspected that was the problem but how do I know for sure thats what it is? After draining the oil in my bottom end and pulling the engine out of the frame I got a good look at it. The oil in the bottom is black but looking down inside the crank from the top end there is no black oil in there at all. I would assume that if it is leaking into the top end there would be some visible black oil in there?

Did the bike run ok before it started spooging and fouling plugs? Usually spooge is associated with rich jetting conditions. I may be wrong as Ive had a leaking crank seal since I tear my bikes down 2 or 3 times a year, but I believe a leaky crank seal (air leak) would cause a lean condition.

it gets sucked in wile your motor is running. and then burnt off. replace it, actully do both sides. they are like 15 bucks each...well worth it.

I haven't had the bike very long but I did take the carb apart cleaned and re jetted it leaner. It had a 440 main which I though was way too fat so I put in a 410 and 35.5 pilot. After that it still had alot of spooge and was fouling plugs even worse. By the way It's got an FMF Gnarly pipe with turbine core II. One thing I did find was that the power valve was way gooped up. The 3 grooves in each of them were completely filled with carbon and I swear the carbon build up was almost 1/16" thick on them.

What oil are you running? I used to run Super M at 32:1 in my CR250, then I switched to 927, and I get a lot more build up. Sure smells good though! (Speaking of smells, I'm using Torco 110 with 927 in the YZ. Man, that stuff is like model airplane cement!) :smirk:

Here are a couple interesting (related?) articles....

Two-Cycle Psycho article

Castor vs. Synthetic (Scroll down to page two and ignore the bad editing.)

If you've already got the thing apart, seems like it would be cheap insurance to replace the seals...

Is this the seal I need (#28) That should be the right one right?

By the way Dougster I run Klotz 40:1. Think I'm gonna change after I get it put back together though.

Use a 100% synthetic at 50/1. No reason to run more oil than that. No reason to use a non synthetic oil. Its 2011.

Use a 100% synthetic at 50/1. No reason to run more oil than that. No reason to use a non synthetic oil. Its 2011.

I might agree if I was running a 2011 bike. :smirk:

I'm still planning to run 927 in the 1981 bikes, especially the air-cooled YZ, and especially since I live in Arizona...

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