Lots of exhaust smoke on 4 stroke

Just got a 04 150 4 stroke for 750 bucks. Excellent condidtion, but smokes a lot. Freaked the other owner out and he sold it cheap. I have worked on 2 and 4 strokes before so I did not think it was a big deal. Maybe some piston rings, valves, or a seal.. but I am coming here for more info. The bike still rides strong (compression is good), but smokes like crazy out the exhaust. I checked the valves and they are super tight, no clearance! Could that be causing the smoking?

Now the real Newb question... (kind of embarrasing). I removed the engine cover for the rotor and it was full of oil, to my surprise!! I never worked on a 4 stroke that had oil flow to both sides of the engine. Is this right? Also are there any seals that might be a problem with the oil going up the timing chain and being blown out the exhaust?

I put some oil in it for a test drive and it burns it really fast, but the bike runs good.

The oil has to be getting sucked out of the crank and blown out the exhaust somehow.

Any help or info would really be appreciated.

What bike is it? From what I've read, tightening valve clearances mean a valve job coming up. I wouldn't have thought that would cause heavy smoke though, most likely rings/damaged bore or head gasket. Compression may be fine but what's the leak down like?

Worn out valve guides will cause a lot of smoke without dropping compression.

Worn out valve guides will cause a lot of smoke without dropping compression.

but that would only smoke bad on startup, right? unless it was a REALLY bad leak.

When does it smoke? on start-up, when you rev it, at idle? What kind of smoke is it? Does it smell like oil? Or could it be water vapor? water in the combustion chamber means a head gasket or (worst case) a cracked head/case. I'm not sure of the engine design on the 150, but that's what happened to my old truck, coolant in the oil, turned out to be a cracked case. :)

if it smokes (oil) pretty much all the time, I'd be looking at the rings, or maybe the head gastet. Have you done a compression test? Running "good" is relative, especially since you don't know what it ran like when it was new...

good luck

The rings will expand, so it only smokes on start-up. If it's blue smoke means it's burning oil, I would go straight to valve seals.

It smokes on all the time. Thick blue oil smelling smoke. I was thinking valves too, but am not familiar with this motor. CRF 150.

I will start with valves and the head gasket. As for valve seals where are they?

valve seals are in the head, surrounding the valve stems. The are what prevent oil from draining from the head into teh combustion chamber.

Thanks for the help everyone. I will have at it...

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