Coolant in crankcase = no fun
 

So, I went to national enduro this weekend, bike was running fine. During 1st section motor got noisy, and generally just sounded like ass. Pulled to side of trail, noticed cylinder was super hot, pulled the plug and it was white. Popped radiator cap. Dry. Nothing. Dang. So got to watch lotsa bikes zip by while I wait for sweep. there were lotsa lotsa gassers. and just a side note - whoever was on row 78 or so with a black honda crf250. dang you're fast. caught our whole row in 5 minutes. the other guys on my row said he caught them in every section quickly. and a thumbs up top the guy on the old tr5t! and the klr650 :) (he was a couple rows ahead of us, but we caught him in a minute or two..) it takes balls to do a national on either of those bikes...

Anyways, fast forward to now. Drained gearbox, oil looks fine. Pulled crankcase drain. Coolant poured out. Dang. So I'm assuming head o-ring failure. I'm assuming I get to replace: crank bearings, seals, con rod. I have a spare top end so that's going on it. It got really hot so I'm assuming the piston is toast. Theres some weeping coolant at the cylinder head joint near the front head mount. Maybe head cracked. I doubt both inner and outer o-rings failed (there's coolant in cyl and outside cyl).

Bummer.

Sorry to hear...

Pull her down and let her know how she looks.

yeah, well i bought it used, and knew the one crank bearing was starting to get a little loose - i had planned on tearing down anyways eventually to fix it.. guess eventually means now. at least it'll be all new inside, and i'll KNOW what's going on inside, instead of assuming the previous owner had a clue. at least it will be as good as or better than new...

A leaking head o-ring won't cause coolant to get into the crankcase.
Since coolant travels through the lower cases, you may have a center case gasket leaking.

Yes, the leaking head is likely the result of the high temperatures. The head and cylinder should be checked for warpage.

The base gasket seals a coolant passage as well, from the cases up through the cylinder.

Did the bike have a plastic impeller? If so, also the possibility that you lost that and things cascaded downhill from there.

Just an FYI, on the bearings, the '07 uses a two piece roller on the ignition side. This bearing runs a high clearance compared to the ball bearings you are used to on the older motors. You can detect what appears to be excessive radial play but it is normal.

Metal impeller. So Is there a crossover on the left bearing ? I thought it was 6206? And right is 63/28? I know it specs nj206 c3- is it just a switch to a higher load bearing roller? Is case / crank same and 6206 will work?

No 6306 in an '07 motor. Been this way since '02 in 250/300. I don't remember the # offhand but its a two piece roller. You will see when you get it apart, its easier to split but you will have to pull the inner race off the crank and press the new one on. IMO, this is a good setup, lots of hours on a couple 250s with no issues.

Sorry to hear about your bike. Not fun if you're competing. Will you miss many races while you are ripping her down?
Make sure you take some picture and share your finding with us.

my bad - I meant 6206. 09 fiche says 6206. Did case or crank change or why did they go back and forth between that bearing?

that depends on how fast my local guy can build the crank. i have a million things going on today - i can split a motor in about 1 hour. i can reassemble in about 2 hours. i have a local race this weekend, but i dunno if i can get it all together and get parts fast enough...