Compression Test Results on a 254

Old Fogey UK

I ran a compression test this morning.

Five cylinders (1,2,3,4,7,8) gave 110 pounds.
Cylinder 6 gave 105 pounds - within 10 percent of the others, so OK.
Cylinder 5 gave 100 pounds so I rechecked it with two teaspoons of engine oil through the plug hole and it then ran up to 115 pounds.

Help please -
Could this be a rings problem ?
Is the compression difference bad enough to investigate further by pulling the head off ?

Plug 5 wasn't noticeably oiled up when I took it out for the test.

 I get a bit of smoke on start up or when idling in traffic for a long period but none under load  and there's no drop off in performance.

Uncle Josh

The difference in compression won't affect running. but a couple of the ring may be stuck a little.  Carefully pour some Sea Foam Deep Creep down the carb at idle, then enough to stall it and let it sit overnight.   Then run it.  I'm running 2 of them (40 Victoria Coupe, and a 46 Pickup) and It's gotta get a lot worse than that before I'd pull the head.

Old Fogey UK

Thank you.

It's a rebuilt motor that was unused for some years. It now has less than 500 miles on it and only has been used on short runs of around 25 miles.

The plugs get sooty very quickly, as does the oil.

So, does it seem most likely to be stuck rings ?

If it does, I'll try the Seafoam treatment, change the oil and see how it goes.

Would an oil additive be useful ?

MikeSheridan

I'd work on the carburetor first. It sounds like you are putting too much gas in the engine. To me, compression would need to be much lower or one or more cylinders with large difference to justify tearing into the engine. 

Old Fogey UK

MikeSheridan said:

I'd work on the carburetor first. It sounds like you are putting too much gas in the engine. To me, compression would need to be much lower or one or more cylinders with large difference to justify tearing into the engine. 

Thanks, I'll also try tuning the carb a bit.

Geoff

Try lowering the float level.  It is obviously running too rich. I agree, leave it alone mechanically.