[Rob Mc]

My sons 300 blew the spark plug out while mowing. I reinstalled the plug using a helicoil. Another half hour of mowing and the head gasket failed. I sanded the head on a piece of glass and installed a new kohler gasket, torqueing the bolts to 35 ft lbs. Another hour of mowing and the gasket failed again. I found a replacement head, flattened it and installed another new kohler gasket again torqueing to 35 ft lbs. It failed again. I installed another new gasket but torqued the bolts to 50 ft lbs. Kohlers web site said that was maximum torque for a grade 8 coarse thread bolt. I ran the engine and retorqued after it cooled. The gasket failed within an hour. The engine starts easily and runs great. I can see no flaw in the block. What do I do now?

 

[rustyknuckles]

How and where is the gasket failing? Always in the same place? If so, maybe there is a low spot on the top of the cylinder head.... Another thought - any chance your engine is having a lot of spark knock? That could be caused by incorrect point setting (leading to advanced ignition timing) Or maybe too much carbon buildup on the piston top? Has this engine been modified for higher compression (for, say, use in tractor pulling)? The blown out spark plug and the head gasket problems both suggest too much pressure in the cylinder.

 

[dr_evil]

Torque spec on Kohler K-series heads is 25-30 foot-pounds or 300-360 inch-pounds. Tightening them more than that distorts the head and causes the gaskets to blow.

Like Jay says, I'd find a really GOOD straight edge and check the top deck of your block for flatness. Then set the head on the block and slide your thinnest feeler gage, probably .0015 inch all around the mating surfaces and make sure the feeler gage can't be pulled out. You may have distortion around your head bolt holes from tightening them too much, you may need to re-chamfer them or file them down.

 

[mikeduwe]

Run a tap down all your threaded holes in the block and clean them out with compressed air next time you have it opened up.

1+ on checking the timing. I assume the gas is fresh your running?

 

[Rob Mc]

Thanks for the replies. I will do as suggested. The gas is not fresh as the tractor has not run long enough to use a tank in the last year and a half.

 

[mikeduwe]

For good measure, drain the tank and put some fresh stuff in there too...

 

[Rob Mc]

Will do. Thanks Mike

 

[mikeduwe]

Reason I say that is bad gas can knock/detonate, which raises cylinder pressure to the moon and can blow out gaskets or damage pistons.

 

[jcronk69]

Also check that your bolts aren't too long and bottoming out in the bolt holes before they can torque down on the head.

 

[akaothermick]

Mike, just what kind of pressures would bad gas produce, this is a effect that I'm completely ignorant of, and I cant find any threads that expound on this premise, Thanks