1997 Yamaha wolverine engine rebuilt, now have problem!

[matt290477]

Hello. I have completely rebuilt the engine of my wolverine, due to a defect oil pump. I have replaced pump, crank bearings, rod, oversize piston and new rings, new valves, guides, and seals, new camshaft and bearings, new timing chain. Now, when I start it, it will smoke heavily, for about a minute until it warm, then quit smoking and run well. I have about 3 hours of break-in done, the problem is still present. I have done a leakdown test, no significant leak. compression is 150 psi. i have properly staggered the rings end gap, take care to not overlap oil rings, oil level is correct. There is no oil on valve stem when I look into exhaust and intake port, so i don't think is valves seals or guide. It do not smoke right at startup, it takes few second before the smoke begin. When hot, I can rev it all the way without visible smoke. this is a weird trouble that never happened to me when rebuilding an engine. I'm stumped. Anybody have an idea? What could be wrong?

 

[maim]

when it blew up, did it fill the exhaust with oil? might just be burning it off.

 

[matt290477]

No the exhaust is clear.

 

[maim]

no oil in air box? air filter is not over oiled?

 

[matt290477]

No oil in airbox, no excessive oil on air filter. It smoke badly when started for the first time of the day. After it warmed, no smoke.

 

[maim]

sounds like you have a bad valve seal that is letting oil in when it sits and fills the valve up.

about the only thing i can think of.

 

[grizztracks]

You have good compression so I would pull the head and check valve seals, stems and guides. Check the head gasket and sealing surfaces, especially around and oil ports.

I believe the 97 are air cooled engines so it's not antifreeze burning?

 

[matt290477]

Yes it's air/oil cooled. I will remove the head to inspect, maybe a defective head gasket?

 

[maim]

possible, or the oil passage to the head is missing an o-ring or something.

 

[matt290477]

I had the crankcase splitted and the crank replaced by the dealer. Can they have messed something that can cause the smoke? (plugged oil passage or other thing?) I have done all the rest of the job myself.

 

[matt290477]

A little update : I have noticed if I start it every day, there's no smoke. If I let it sit for a few days, there is lot of smoke for a minute then clear. But It do not smoke right at startup, it takes few seconds before the smoke begin. I think there is a leak somewhere when oil pressure build up at startup then leak into combustion chamber? Can it be a bad head gasket?

 

[maim]

depends where the oil passage is. from the looks of the parts breakdown, it brings oil up to the head along one of the head bolts like the old xt250's used to. i am betting #12 in the pic is missing or cut on yours.


http://www.yamaha-motor.com/sport/parts/home.aspx

go to your bike and look up cylinder head breakdown pic. #12 is what i am talking about. sry not good enough with computers to get the pic up here.

 

[matt290477]

Ok I have removed head and cylinder. Found two thing. First, the oil passage hole is slightly deformed toward the sleeve, nut there is a big o'ring and the head gasket to seal the oil flow?

Also I found some scuff mark in cylinder, it appear to be the piston skirt rubbing on wall. The skirt look polished, the cylinder cross hatch is already gone at some place.

I can barely feel the scratch with fingernail, piston to cyl clearance was 0.0015, maybe it was too tight? What do you think?

 

[maim]

do not have my clymers manual for my atv or bike atm but something is wrong in that jug piston wise. i seem to remeber 0.002 as the clearance for a stock piston on my xt.

looks like you need to dress where the mating surface is so it is nice and flat with a file. i tend to work across the whole surface so that it all stays level. then replace the oring/seal and make shure you use some white grease on it during assembly. will help it slide together and it actually helps the head gasket seal as well. old trick for reusing head gaskets was to coat both sides with a film of grease.