Blow By

Ray64

Ray64

Well-known member
I had a very nice running car before i put a Snyders high Comp. head on it.It still runs great with a lot of extra power.Problem is now it has some blow-by. It is very annoying to the MISSUS.I know about the hose to vent to the bottom of engine compartment.What i want to know is why this happened?Engine has only 10.000 miles on rebuild.Does not burn oil.At least no blue smoke out the exaust.Thanks very much.:confused: RAY
 
:)How were the rings prior to the high comp head being installed?I'd say a bad ring or two? Just my thought, Happy H "A"lloween!!
 
The increased combustion chamber pressure from the hc head is escaping past the rings. Could be the rings were not seated initially or not. In any case, a road draft tube will help a lot. I can smell any A engine from inside a closed car without that tube.
 
Pat I have to respectfully disagree with you. I have no blow by at all and no hose venting under the car. The plugs burn nice and grey, no blue smoke out the exaust. BUT, what did happen it delevouped a bad oil leak. Turns out the rear main babbit delevoped cracks and when I took the cap down pieces of babbit fell out. Rebuild time. Cant win.
 
High compression heads and as a matter of fact anything that changes the how the engine has been operating can and will put different stresses on the parts making weak spots show up.
 
I"m thinking a problem with compression rings. As Mike said, its showing up with the higher compression ratio. Possible cause- Worn or not seated,worn / tapered walls, or rings could be just stuck with either rust or carbon. An easy thing to try is take the plugs out and soak the rings for a few days with a penetrant and or a top engine cleaner. Change the oil before running it afterwards.
 
Have not checked the compression yet, but will today and report numbers.Engine was fine prior to the new head.THANKS RAY
 
I had thought about a new head at one time, but Larry Brumfield asked for my present compression test results and advised not to do it since my engine was apparently too loose to handle a high compression head though it ran nicely.
 
When the new head is installed with a new gasket and tightened to a different torque(probably a higher torque) there will be different distortion in the cylinder walls --this can cause more blowby.

Also the surface irregularities of the different heads will apply different pressures on the block deck changing the bore slightly.

An inside micrometer can be set up in the bore and the block squeezed with your hands causing enough distortion to have it fall out.

If the rings are good they will adjust to the new distortions eventually.
 
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