SBC in my 63 chevy - I get consistent readings on other 7 cylinders but number 5 is all over the place. I have tested it wet, dry, etc. its always low but I expected a consistent low number, then a higher number with oil in the cylinder, so I could know if it is valves or rings. Anybody experienced this?
do a leak down test sounds like a valve guide/seat problem some times it hits better than others giving you odd readings or it could be a cam lobe
A leak down tester would show what's going on. With #5 in valves shut position you'll know whether it's intake, exhaust or past rings. Less expensive is the spark plug hole to shop air adapter hose, just thread it in, valves shut you can tell what's going on. Sent from my SM-S320VL using Tapatalk
I just tried that and it wont hold air but I can't tell if it is going past the valves or the piston- how would you know this?
Gotta be going somewhere: - past the rings should show up at the oil fill cap or crankcase vent. - past the intake valve should show up at the carburetor. - past the exhaust valve should show up at the exhaust.
Yeah, I thought there might be a trick I am not thinking of - I am listening, covering, etc but can't tell where the air is going
Most likely One of the 3 Intake side Exaust side Crank case Witch all requires pulling of the head to fix . By chance it could be a lifter on that cylinder is why compression different each time
Embarrassing that I needed such common sense info as "tape up the holes" but I did. That worked and told me I have a bad exhaust valve. Thanks HAMB.
It went between 0 and 90...I couldn't get it to read the same twice All the rest of the cylinders are at 145-150 I am hoping this is good news and that I just need a valve job
Had a great running early 350 in my truck, after I ran it for 20,000 or so miles, I had same problem as you. Pulled heads and found they were "lead heads", not designed for non ethyl gasoline. Got a set of later year 350 heads, with non ethyl compatable valves and valve seats, end of problem.
If the heads are '63 vintage and never updated, I'd pull both heads and have hardened valve seats installed on the exhaust valves. As stated above, the no lead gas kills the older heads. Or update the heads with newer if not concerned with keeping the engine period correct.
Do a used car lot valve job. Take off the valve cover, rocker arm and valve spring on the exhaust valve using an air hold. Use a power drill to spin the exhaust valve. You can reduce the air pressure until it the valve turns and allows you to open the exhaust valve. Having air pressure in the cylinder forces any debris to go into the exhaust system. This can help seat a valve with light rust.
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