Question about Chevrolet Venture
How to fix lost compression in two cylinders
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Posted on Jan 02, 2017
Per the Ford manual, the acceptable range is 155-195 PSI. It sounds to me like you don't have a compression issue with this engine (without knowing the exact readings for each cylinder). Normally one cylinder being higher than the others, but still within spec, would not concern me a lot. Had one been much lower, then I think that might be cause for concern. There could be many reasons for the one hole being higher. If the engine hasn't been rebuilt in a long time, there could be carbon deposits in the compression chamber. There are many chemical fixes for this availble at your local parts store. If the engine is running fine with no pinging or detonation, I'd just continue to enjoy your classic ride (I own a 1971 Challenger converitble with a 440-6 pack, so I understand the joy of a classic car!).
Good luck and please let me know if this helps!
Posted on Oct 10, 2008
I have changed a few cylinder heads under warranty for this type of problem. The exhaust valve guides wear, this causes the exhaust valve to seat badly, giving low compression. if one cylinder compresion reading is more than about 50 psi below the others, then this warrants head removal. It is quite a job, due to the fact that the camshft id chain driven. If you are up for it then once the head is removed, poor liquid into the exhaust ports and see if it leaks out through any of the exhaust valves.
Posted on Jul 23, 2009
Lost of compression is due to either leaking head gasket, valves not closing and seal properly or piston rings are worn and need replacing. One can tell if you have bad head gasket, oils contaminated by water when looking at dip stick, bad valves cause some smoke and run rough, worn piston rings will cause lots of blow-by and will cause white smoke heavily and also runs rough. Being 1968 original motor and never have been rebuilt will probably have over 100k mile will be needing tear down and rebuilt. Rebuilt it correctly will get another 100k plus. being 1968, doing your head and valves job or replacing head gasket if that is the problems and you can get by it. worn rings, I would rebuilt it completely instead repairing one or two cylinder unless you plan to get rid of it.
Posted on Aug 07, 2009
OK!... did you do a cylinder 'leak down test'?.. .if not, do it! If any 'unacceptable' leakage, have the head REDONE! NOW!.. you must BE SURE the valve timing is accurate!... Go to www.hmaservice.com and register( Vehicle by VIN). Afterward, you have access to shop manuals, service bulletins, wiring diagrams, etc. about your vehicle.
Posted on Oct 04, 2009
The fault may very well be with the tester itself: The compression tester should have a check or "HOLD" valve which causes the needle on the gauge to REMAIN at it's highest recorded point. For example, my 1993 Isuzu Rodeo had a compression of 160 psi. The gauge "holds" the needle at the measurement UNTIL THE VALVE IS RELEASED-(mine had a button that needed to be pressed to release the pressure) then there will be a slight discharge of the pressure contained within, the needle should drop back to zero, and THEN you should be able to remove the tester. What I am getting at is if the pressure drops that fast, I think the "HOLD" valve on it may be defective, OR the tester is not properly sealing on the combustion chamber (stripped threads?). Might be worth buying another one for 20$ just to be sure.
A four cylinder engine, you say? Very rarely will you have ALL of your cylinders exhibit the same pressure loss symptoms. How did the other three cylinders test?
Here are the components required for a running engine to fire:
1-good spark (adequate voltage, good plugs/wires)
2-dedicated fuel supply (fuel pump with adequate pressure)
3-timing (slack in timing chain/belt?)
If the timing belt broke or maybe even jumped a tooth or two, it COULD cause DAMAGE to your engine-pistons hitting valves-if it IS what they call an "INTERFERENCE" engine.
Hope this helps.
Posted on Dec 31, 2009
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