Poor Compression
 

1952 8BA. New Pistons, rings, wrist pins, has adjustable lifters. Was running fine. Started having a power problem and tapping sound. Also had occasional backfire through exhaust (not through carb) Suspected a stuck valve and ran a compression check.95-110 for cylinders 2-8, #1 was only 35 lbs. Opened the top up and valve operation looked OK, removed head and pulled Exhaust valve assembly. Lapped valve in case it was something not allowing the valve to close. Re assembled, adjusted both exhaust & intake valve. After assembling, disassembling and assembling again I am still hearing the sound and have no compression in #1. I enjoying chasing and solving the problems but would appreciate your input. Thanks

Re: Poor Compression
 

I haven't heard it used for cars but my plane mechanic uses a special compression tester on my plane that allows compressed metered air into the cylinder when it's at TDC. If there's a problem cylinder, he can tell if it's leaking past the rings or either of the valves.
Would noise be of a frequency similar to a lifter tapping? Sounds like the exhaust valve on #1 and the only thing I can think of is a sticky guide.

Re: Poor Compression
 

Did you check for broken valve springs?....Look closely, they're sneaky little devils....

Re: Poor Compression
 

I tore #1 exh. valve apart, inspected "closely", even squeezed the spring in a vice to look for any hidden cracks, lubed and reassembled. both hand turned and starter cranked with it opened up to see if there was a snag somewhere. I am baffled.
Thanks for the thoughts...

Re: Poor Compression
 

You need to do a leak down test.

R

Re: Poor Compression
 

It sounds like a stuck open exhaust valve or something is under the valve.

Re: Poor Compression
 

That was my plan. Stepping back for a couple of days to let the "fog" clear. Two days in my 90+ degree shop really inspires a guy to grab a tall glass of iced tea and "reflect" before proceeding.
I am in a part of Arizona where a snow flake brings out National News Teams.

Re: Poor Compression
 

A 90+ degree shop inspires me to grab a different sort of tall glass to reflect!! Wonder if pouring some Marvel Mistry Oil down the carb when it's doing this might result in a change? You could enjoy you're "tea" during this quick little test. Engine assemblies act differently when their in your hands on the work bench than when they do with 1000* exhaust blowing past them.

Re: Poor Compression
 

Thanks Kirk, will try the MMO tomorrow.

Re: Poor Compression
 

Hard to do on a flathead! but I was shown a method for checking overhead valve heads for a leaky valve. Pour a small amount of kerosene into the ports and see if it leaks out. It is amazing how a valve and seat can look perfect and leak with this test. Know this won't work on an in-block valve and seat, but it shows you how difficult it is to visually tell if there is a leak.

Re: Poor Compression
 

Maybe slightly off topic but maybe not. When my plane was getting a compression test (horizontally opposed, air cooled) with the valve covers off. If he came across a low cylinder that was leaking through one of the valves and would have required a $1000 repair...he would take a rubber mallet and tap the rocker arm on the valve side and 100% of the time in the last 18 years, the leak stopped. It doesn't take much of anything to make a valve leak slightly. In the OP case...I don't think there's something tiny under the seat...I think there's something that's binding the valve.

Re: Poor Compression
 

Thanks, I will keep you posted.

Re: Poor Compression
 

You don't say if it was bored. If not, any of the cylinder's ridge that wasn't completely cut away it will cause the top ring to bind/break or break the next land in the piston.

Lonnie

Re: Poor Compression
 

Ronnie is correct. Easy way to check each cylinder. You will need to bring
each one to TDC.

https://mobiloil.com/en/article/car-...-leakdown-test


http://www.hotrod.com/articles/cylin...akdown-tester/

Re: Poor Compression
 

Not Bored, no ridges. The new pistons worked fine for about 300 miles now. It appears that the #1 exh. lifter is "lazy" and hangs up at the top of it's stroke not remaining seated on the cam. I will try some MMO on it for a couple of days and if that doesn't loosen it up I will pull the valve and lifter (again) and deal with whatever is hanging it up.
Thanks for the input. I am still going to fabricate a tire valve and an old spark plug for a leak down tool. Even if I never use it, it will look cool in my "What's that used for" custom tools box.
I will keep you posted.

Re: Poor Compression
 

You need more than a tire valve and a spark plug shell to do a leak down test.

R

Re: Poor Compression
 

OK, I will research some more. Thanks

Re: Poor Compression
 

OK I splurged and found one on Amazon Prime for less than $30 with free shipping. Saved me a couple of hours trying to make one. Thanks for your responses.

Re: Poor Compression
 

Bent valve?

Re: Poor Compression
 

That's the name of the nag I'm putting my money on.