Low Compression on No. 2 & 8

[Johnson]

Spark plugs are dry, I'm thinking valves.....

It's a 1971 302, any ideas on where to get heads at a reasonable cost, or should I just rebuild the ones I have, and as long as I'm doing that I may as well rebuild the motor.

Or anyone have any ideas on how to "unsticky" a valve without pulling the head?

[70_F100]

Have you done a "wet" compression test?

[fordman]

start the truck and let it run. pour transmission fluid down the carb while it runs. dont pour in so much that it dies. keep it running.

[70_F100]

start the truck and let it run. pour transmission fluid down the carb while it runs. dont pour in so much that it dies. keep it running.

I suggest you do the wet compression test first.

That will let you know whether it's valves or something to do with the pistons and/or rings.

If it doesn't improve the compression, then you could try the tranny fluid or Marvel Mystery Oil down the carb.

[Johnson]

What's a wet compression test? I've never heard of that before....

[70_F100]

Squirt some motor oil in through the spark plug holes and check the compression again.

If the problem is the rings or some piston problems, the compression should be better, as the oil provides a little better sealing for the rings during the test.

If the compression doesn't get any better, you've either got a valve problem or a hole in a piston.

[Johnson]

Never mind, I Googled it....

So if my wet and dry compresstion tests are the same, it's more than likely a vavle issue, and if they are different it could be a ring issue....

Is that the right thinking?

[Johnson]

Squirt some motor oil in through the spark plug holes and check the compression again.

If the problem is the rings or some piston problems, the compression should be better, as the oil provides a little better sealing for the rings during the test.

If the compression doesn't get any better, you've either got a valve problem or a hole in a piston.

Thanks, I'll give it a try.....and I need to learn to type faster!!

[BobbyFord]

Loosen the rocker arms enough that the valves are closed and air up the cylinder. Air out the exhaust = exhaust valve, air out the carb = intake valve, air out the valve cover = rings.