Very strange compression test results

[D/Dart man]

1964 273 engine. I bought the car knowing the engine didn't run right (price adjustment). I know for sure I have to remove from car and take it apart to figure this one out!
Condition:
1) Engine has been rebuilt probably once in lifetime
2) It does run (poorly). Starts right up with no fuss. No idle, but will run off idle. Very rough running, like a misfire but not.
3) No smoke (blue or white) from tailpipes.
4) No oil in water
5) No water in oil
6) No external engine leaks or signs of trouble
7) Excellent oil pressure
8) No odd internal engine noises
9) All valves appear to be operating normally, full stroke, not stuck. Springs look ok.
10) Push rods look straight

Here is the comp test results:
The low and zero results were rechecked numerous times with two gauges.

 

[Plymouth 65]

Low compression, could be valves or rings. Does it have excessive blow by in the crankcase? 65'

 

[GTX JOHN]

That poor Puppy is Shot!

I suspect you have a bunch of Burnt Valves and
several seriously bent ones at least.

You will know the story when you pull heads off the engine.
Try some solvent it the ports of the heads when they are off
and that should show you a valve problem.

 

[413]

Does it still have adjustable rockers? Check the valve adjustment. If they don’t close all the way then it won’t have compression on that hole.

when it wears the valves get tight and don’t close. BTDT

 

[krazykuda]

It's a four cylinder... Only running on the two front ones on each side...

 

[74 360 dart sport]

Valves not closing all the way

 

[67Dart273]

Google up and try to build your own leakdown tester. If your compression gauge "unsnaps" AKA "quick connector," you can pull the Schrader out and use parts of it. ALSO BE AWARE there may be something wrong with your gauge setup, including a leaking Schrader valve.

 

[D/Dart man]

Does it still have adjustable rockers? Check the valve adjustment. If they don’t close all the way then it won’t have compression on that hole.

when it wears the valves get tight and don’t close. BTDT

I didn't think of that one. I will take a look at the valve lash.

 

[teringer]

All exhaust valves damaged from unleaded gas , as the valve is pulled up thru the seat it removes The clearance at THe valve tip holding them slightly open

 

[Murray]

I agree with#3- shot! But first, on those low cylinders, squirt some engine oil in there and re-test. Does this make a significant difference? If it does, this would indicate worn rings.

 

[cudamark]

Too tight valve adjustments, and/or burned valves.

 

[CRUZE 418]

Buy a leak down tester from Harbour Freight, they aren't that expensive. It will tell you how much leakage you have and by listening , you can determine where. Intake, exhaust or crankcase.

 

[D/Dart man]

A lot of the valves had zero lash, really tight. So I am adjusting them and will do another compression check.
I lucked into a pair of rebuilt heads at a reasonable price with the same 1964 casting number so I will have a backup.

 

[66fs]

Does it still have adjustable rockers? Check the valve adjustment. If they don’t close all the way then it won’t have compression on that hole.

when it wears the valves get tight and don’t close. BTDT

Do this first. .013 intake and .021 exhaust Hot.

 

[teringer]

A lot of the valves had zero lash, really tight. So I am adjusting them and will do another compression check.
I lucked into a pair of rebuilt heads at a reasonable price with the same 1964 casting number so I will have a backup.

That's the first sign the valves are sunk on seats

 

[D/Dart man]

Valves have been adjusted and new compr test run (cold).
Much better results, now the engine should run smoother.
I will run a warm compr test now that it should run better. Curious if the low cylinder will change.

 

[CRUZE 418]

This certainly looks much better, but if you want to really know what the health of your engine is, get a leak down tester.

 

[66fs]

Valves have been adjusted and new compr test run (cold).
Much better results, now the engine should run smoother.
I will run a warm compr test now that it should run better. Curious if the low cylinder will change.

View attachment 1716002728

Get a air line adapter to fit in the spark plug hole and see if you can hear where the leak is. Intake, exhaust, or crankcase?

 

[cudamark]

I'd run that for a while and then do another valve adjustment and compression test.

 

[D/Dart man]

I'd run that for a while and then do another valve adjustment and compression test.

Yes, that is what I'm thinking too.

 

[D/Dart man]

OK, the engine runs like a champ after fixing the valve lash. It is still an old engine for sure but now it runs smooth and will drive. So I can drive it around a bit and see what else needs work without having to pull the engine first.
I tested a few cylinders when it was warm and most readings went up about 10%. Cylinder 8 (the lowest one) was 90 cold, 95 warm, and 115 warm with oil squirted into cylinder.
But I am very happy with a smooth running engine at least!

 

[413]

CHANGE THE OIL TODAY! And don’t use 20/50 Or synthetic. Try a 10/30. This really will help get that left over BS off the rings and help them seal.