crank seals

[leaglen]

What are the symptoms of bad crank seals?

[KDXGarage]

Left side = air leak

right side = transmission oil going into the crankcase and fouling plugs, appearing super rich

[KickassKX125]

^ you forgot to mention what an air leak causes!
An air leak causes a lean condition

[stevied645]

and makes the bike rev up if its worn bad enough

[KickassKX125]

^ And that!

[leaglen]

Thanks.

[gaz]

after reading all these posts I now suspect its what is happening to my '05 kx250. I have a lot of oil coming out of the kips vent pipe and exhaust. Its enough to leave a small pool of oil the next day, my kx125 never leaked this much oil even when running rich. Fouling plugs and blowing heaps of smoke. Still all this after leaning of the main and using top clip of needle. Can seals be replaced without splitting the case? Never ventured this far before into the motor. The motor itself is good. Heaps of compression, easy to start and still goes ok. I am going to confirm this with a leak down test.

[leaglen]

Could be. Mine just ran rich, and smoked alot on top end. It would also blow some oil out of the crancase vent tube when it was hot and idling. Nothing I did with the carb would stop it. If it is bad enough you might see a drop in crancase oil. Mine was a 1974 f9 350. I could replace the seal without splitting the case. Don't know about the kx250.

[stevied645]

you need to split the cases to replace the seals.

[gaz]

D@mn, guess I'll start the strip down on the weekend. Thanks 645

[gaz]

ok, I did a leak down test, it wasn't that hard, apart from the pump I already had it cost about 20 bucks to make. Blocked the exhaust port, power valve vent and adapted a tube valve to the cylinder inlet port. Took out a reed so nothing was in the way. Put the piston to TDC. Pumped up to 6psi then sprayed with detergent and water over everything and found some leaks but easily fixed. Retested and no leaks but found the test leaked away in less than two minutes. This is bad. I put some soap/water across the crankcase vent pipe and so as I start pumping it blows bubbles even before a solid reading on the guage. I assume air is escaping through the right side seal into the transmission and out the vent. Have I done this right??? I cannot find any other leak. Any opinions?

[KDXGarage]

gaz, did you ever adjust the air screw or change the pilot jet?

Is your transmission / clutch oil level lower after running the engine (riding) for a while? That is an easier way to check on losing oil into the top end.

[gaz]

yeah, main from 160 to 155, pilot 50 to 45 and dialed in, NFTG (stock) needle 2nd clip to top clip and even tried NALF needle 2nd clip to top position. (NALF stock needle is kx250 '04 but same carby). I was going to try a leaner needle NALG but I have already leaned off heaps and didn't want to go further in case I blow the motor. About the oil level, it hasn't changed much but the amount of oil coming out of the KIPS vent pipe is if concern. I run 40:1 MOTUL 800 and it wouldn't take much oil from the case to change to say 20:1 etc when riding. From the leak test it really points at the seal. I just wanted to know if I had done the test right? The bike was in dismal shape of neglect when I bought it but the motor seemed OK at the time, compression, bore ok etc but typical from a farm they used anything to fix it. I am going to do the bottom end for piece of mind. Its too good a bike to struggle with running half right. I mean you can ride it but take a bag of plugs if doing trails and stock up on pipe packing at home.

[gaz]

Bingo, did the leak down test with motor on the bench (could have done it in the bike but was sure its the seal leaking) with the clutch basket removed and the crank sprocket removed (clutch holder tool worth every cent) so you can see the seal. Pumped up to 6psi again and sprayed the seal with detergent. It was bubbling away straight away. I'll post it to youtube so you can see the movie of it. I dont know how to put photos on this forum. So now its a rebuild. in the mean time I'm putting the carby back to NALF 2nd needle position with 45 pilot/155 main and start from there for jetting. The leak down test is so easy and you can see the results.

[gaz]

Its loaded on youtube and search with: KX250 crank seal leak test. It goes for about 20 secs. Motor is pumped up to 5-6 psi although it will leak almost immediately. I sprayed detergent/water mix on the seal and as you can see the leak is severe. Motor is now in the shop getting a new wiseco crank/bearings/seals (crank rebuild is the same cost as a new non OEM crank ) after I stripped it to the point of splitting the case. This saves labour costs. Oh yeah the bird noises in the background are pet rainbow lorikeets! I'll stop now as I seem to be running this thread, just passing this info on.

YouTube - KX250 Crank Seal Leak Test