2 Strokes Down Under

Hi all, hoping someone here with a little more experience in these matters might be able to confirm what I believe must be a leaking crank seal on the front cylinder of my KR250.

The bike is a low km (4,900) jap import and clearly the engine has never been touched. I've been slowly recommissioning the bike but the focus has been the chassis, brakes etc. as the bike started and ran fine when I bought it, though I must admit I did wonder whether I should've had the engine pulled down for an inspection at least.... And I've certainly read before that many (most / all) two strokes need these changed after prolonged periods of inactivity (which obviously my KR has had).

Anyway, the bike is basically finished and has come up a treat, it looks amazing and I'm very happy with it, except on its first little blast down the road it started spitting oil out of the lower pipe muffler, out the end and out the bolt holes that hold the muffler sleeve on. The oil doesn't appear to be two stroke so it must be gear box oil so I assume I have a blown or leaking crank case seal on the front cylinder. The muffler still has noise suppression packing around the baffle and this is soaked in oil.

So, I'm no engine expert but is this the correct diagnosis? If do I guess I'll start pulling the bike apart again!

Appreciate any advice from the experts.

Cheers, Richard




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1983 RZ350K
1984 KR250A
1985 GSXR750F
1989 TZR250 3MA
2010 Street Triple 675

Can't help with your problem but damn that is a nice looking Kawasaki.

Thanks Geasemeup! It's a lovely little machine, engine is very smooth and the bikes rides be nice on the road.

One thing I neglected to mention is that despite the oil in the exhaust it's not oiling the plug up on that cylinder at all which I thought it would do if a crank seal went?

Any more pics, the front end..

Just took this on my iPhone in the garage now so excuse the quality...

The pipe sounds like its full of fuel due to a leaking float valve and general lack of riding and transport by truck etc. I would be inclined to take top he pipe off and empty it out and refit and give the bike a flogging down the road to blow the rest out. Having said that after 30 years your crank seals will be at deaths door also and with low ks like your bike has then they will let go soon anyway. Smell the transmission oil and if you smell petrol they have already let go.

EPApolice wrote:The pipe sounds like its full of fuel due to a leaking float valve and general lack of riding and transport by truck etc. I would be inclined to take top he pipe off and empty it out and refit and give the bike a flogging down the road to blow the rest out. Having said that after 30 years your crank seals will be at deaths door also and with low ks like your bike has then they will let go soon anyway. Smell the transmission oil and if you smell petrol they have already let go.

Thanks Pat. Doesn't smell like fuel in the pipe and neither does it smell like fuel in the transmission (which I've just changed), plus the oil level hasn't changed up or down. I'll take your advice and remove the pipe to clean it out and then see where I'm at.

Cheers, Richard

My guess is oil. You can keep an eye on the oil level to see if you're losing any.

If the level is slowly dropping, then crank seals would be my first port of call.
As you mentioned - yes, you should have changed the crank seals no matter how few miles it's done. They will probably be nice and hard now.

With the NS400 if this happens then the left cylinder fills up and gives you a compression lock and bent conrod most of the time.

Saw your MVX yesterday.