Help!! Blaster Internal Crankcase Leak???

[dericsdad]

Have a '03 Blaster. it started burning gear oil about 4 races ago... smokeing bad when full and smelled like burnt oil (Not 2-stroke oil). It was starting to loose power, so redid the top end and replaced the crank seals. Went to .080" bore, everything else is stock except for FMF fatty pipe, reeds, reed spacer. It was running really hot and pinging on break in so jumped from 165 main jet to a 340, and raised the pilot to a 35. Still pinging and hearing spark knock at mid throttle... And now noticing it is blowing smoke and burning gear oil again. Only about 1-2 hours run time, if that.

Pulled engine out and did a leak down test, wouldn't hold at all. It is all coming out the gearcase breather! Hold my finger over the breather and it holds pressure. Rechecked crank seal, pressure tested with the gearcase cover off, and the crank seal is fine. The crank has a little endplay, but the bearings feel tight. I can hear the air leaking from somewhere under the balance shaft area...

Has anyone had an internal crankcase leak on a Blaster before??? Like to the inside of the transmission???

[dericsdad]

Just looking for some advice before I split this thing looking for a needle in a hay stack...

[JAG Motosports]

It's not that uncommon. You have to split the cases and lap them. A crack or a break where the balancer is, also common. Check the crank while your there. Really shouldn't be any end play. Also make sure you don't have more than .025 play between the thrust washers and rod.

[dericsdad]

Thanks!

I definitly found it! A spot about 3/8" long between the case halves was leaking. The yama bond was all brown from oil and not stuck like the rest was.

No cracks, and the case halves look smooth and flat, no gouges or scratches.

Someone has definitly had this split before. And they polished up the crank with emory cloth or something. It's nice and smooth but fits loose with no press fit into the pto side crank bearing. It does fit snug in the flywheel side though.

The crank otherwise looks okey. Big end bearing feels okey. Can just barely squeeze a .025" feeler guage in between the thrust washer and rod. So I think it will be fine, I'll just throw some new crank bearings in it I think.

I'll bet I can pull out the 340 main jet and go back to around a 270 or 280 when I'm all done now...

[JAG Motosports]

glad ya found it. It may not of sealed because it's not flat. I'd check it just to sure.