The Stovebolt Site Forums The Shop Area Engine Shop Compression Test - Need advise / '37 1/2T

Before working on the electrical system, I decided to check the compression of the engine with a leak down tester.

Context: a ’51 era 216. Parked running (according to my Dad) in ’69 and never run again. Last June, filled all cylinders with Marvel after draining all the oil.

Last week: pulled all the plugs and turned the engine by hand. Turned over easy with no sticking.

Leak down test:
front cylinder – 100 PSI in = 64 – 72 PSI on the cylinder side (depending on where I held the engine by hand). Good sign for the rings, the air pressure itself forced the engine to roll over after TDC.

2nd cylinder – 100 PSI in = 16 PSI on the cylinder side. We had the same thing on the next 3 cylinders.

What the heck?

Went back to the 1st cylinder to verify the gauges and couldn’t get the results we had at the beginning. Couldn’t get the leak down to go above 20 PSI. [Insert bad words here]

Borrowed a compression set: throttle wide open – no compression on any of the 6 cylinders.

Next steps?:
1. Verify valves are not being held open by the rockers
2. Remove the head and inspect.

I am looking to those with more experience here for more ideas before I remove the head. What are your thoughts?

Thanks,

If it were mine, after freeing it up I would get it running. Then after getting some run time on it, then I would do the leak down and compression test, and see what I got.

Are you sure you were on TDC compression on all the cylinders during the leakdown test? The pistons come to the top twice in a 4-stroke cycle, once on "overlap" between the exhaust and intake strokes with both valves slightly open, and again one turn of the crankshaft later with both valves closed.

Watch the valves on a cylinder as you rotate the engine, and when you see the exhaust closing and the intake beginning to open, go halfway around the firing order and pressurize that cylinder. For instance: #1 valves moving/pressurize #6. Listen for air leaks at the carburetor, tailpipe, and oil filler to determine what's leaking- - - -intake or exhaust valves or piston rings. Bubbles in the radiator will indicate a cracked block or head, or blown head gasket.

Continue around the firing order until all cylinders have been inspected. I suspect you've got some sticky valve guides that are preventing the valves from closing fully. Did you loosen the valve adjustment slightly before beginning the leakdown test, and did you tap the valve ends of the rocker arms several times with a dead blow hammer while squirting penetrating oil on the valve stems? I do that every time I try to resurrect an engine from long term storage.
Jerry

Thanks for the replies.

I am 99% sure I was at TDC. I have the valve cover off, so I watched the exhaust valve open and close, then the intake open and close and then felt for the top of the cylinder through the plug hole.

Thanks for the hammer and penetrating oil idea. I will give that a try later in the week.