The Stovebolt Site Forums The Shop Area Engine Shop Compression check question?

Recently did a compression check while working on the engine. The numbers were:

1 122
2 120
3 104
4 128
5 120
6 128

Number 3 is very low compared to the others and spec. Anything to be done about this to fix number 3? I see there are re-ring kits out there that allow you to replace rings and main and connecting rod bearings. With a head job and a re-ring kit do you think number 3 would improve? Can the re-ring be done while the engine is in the truck? Thanks! Searched for re-ring and nothing.

David

How do you know it's rings and not valves ?

I would say unless you have a problem such as a big miss or an oil burning problem, the best idea would be to leave it be for now. I have seen the kits too but if you go that far, you won't know what sizes are needed until it is all torn apart.

I don't. That is why I said rings, bearings and head job. I really would like to not have to pull the engine. If it came to that I would probably drive it the way it is until I needed to find another to replace it (engine).

You didn't say if you got those numbers by just doing a dry test or after a wet test. Try squirting some oil in the low cylinder (you should do all cylinders) and check it again. If the compression comes up more than a couple of lbs you could have a ring problem. Otherwise it is likely a valve problem and can be fixed without overhauling the entire engine. The rule of thumb is that more than a 10% variation between cylinders indicates a potential problem. As truckernix stated if it generally runs OK it's not a major issue for now.
Fred

Dry test but I am going to redo the test dry and wet (for #3). It would be nice to just be a valve problem. I have read here on the dry vs wet testing and the meanings of both.

The other cylinders look so good, too bad number 3 is off. Seems to run pretty well though.

Don't mess with it. Drive it until you find your replacement engine.

I agree with leave it alone if that is the only symptom. Does it idle smooth? Check for blow by at the oil fill with the engine idling. Does it smoke out the tail pipe? If all that is good it will last for a long time.

It is currently down now waiting on the Stovebolt/Weber carb swap. It did idle well with no smoke before. Just leaking fuel all over the place from the old carb.

Be sure the valves are adjusted properly before doing the compression test. A slightly tight adjustment could account for your low reading, or even a little carbon buildup on a valve seat. Try a "cylinder leakage test" where you put air pressure into the cylinders with the transmission in gear and the parking brake set with the piston at top dead center on the compression stroke. Listen for leakage at the carburetor, tailpipe and crakncase to tell where the compression is escaping. Also check the radiator for bubbles, indicating a head gasket leak or cracked head. Repeat the above procedure for all the cylinders.
Jerry

Thanks Jerry and all!

That motor looks a little too nice to run and get all messy! It is a very good looking truck!

Bought it for a driver though. Alot of the hard work was done by the PO. Tom Langdon's carb setup came in today and will go in tomorrow. Door latches were replaced and adjusted today. All services done last week. Needs new tires bad. Will replace shocks and tires next. Been searching on radials. Maybe some Fenton headers and dual exhaust after that. Then gauges......

I can't wait to drive it after the carb is replaced.


David

I rebuilt my 235 in the '53 (inframe),the first thing that I did was a complete valve replacement because I had one that was broke.The only thing that I noticed was a slight, rough, idle until I tried to adjust the valves and found one that wouldn't adjust.
When I finally got to the rebuild, after a broken piston, I pulled the head and pan and went to it.It took me the better part of two days to complete,from tear-down to fire-up.
Just watch your fenders when you are moving parts from engine bay to garage.