41 LC no cylinder compression

[Paul K.]

Well, I do not have a stuck valve like I thought in one cylinder that has so little compression it will not produce 20lbs of pressure. All other cylinders have 125psi. The valves in the suspect cylinder are both opening and closing OK when I look at them through the spark plug hole. I believe they are seating as they look like they are resting in a similar position as the good cylinders when closed. I have also gently pushed down on both valves with a screw driver while cranking the engine and feel both valves seating. Sooo... maybe I have a hole in the piston? or... a chipped valve? I put some 40wt. oil in the cylinder and cranked with no compression change. Now there is some compression and vacuum but very little felt when I put my finger over the spark plug hole while cranking. This motor was rebuilt and has few miles since the rebuild. Should I pull the intake next? What is a Ford valve pry bar?

Thanks!

[Guest imported_V12Bill]

Could be a broken ring or carbon holding a valve ajar. If it were a hole in the piston you would have a lot of blue smoke out of the exhaust. Is the car road worthy? If so take it for a few spins around the block and see if it clears up when it has had a chance to exercise and warm up.

[Paul K.]

Thanks Bill, I do not think it is a ring either, there is no blue smoke, It acts like an intake valve as I am also getting backfire out of the carb. The valves look (from what I can see) like they have full lift and are closing fully when I compare them to the other cylinders. I was careful to oil up the cylinders and turn the engine over by hand before starting. I haven't driven the car yet because of the backfire. Your thought about the carbon sounds like a possability like the penetrating oil I squirted in the cylinder dislodged some carbon. I have never worked on a flathead before, but it looks like I cannot get to this through the intake and will have to remove the head or both. Thanks again, Paul

[okdave]

i would pull the head on the low compression side. i had the same problem with low compression and it was a warped aluminum head which caused head gasket to leak. a machine shop should be able to level out a warped head. depending on how long heads have been on they may be difficult to remove. i removed all head nuts and started engine--that compression broke head loose. earle browne has new style head gaskets.

[peecher]

If you are getting backfire thru the intake you probably have an intake valve that is either partially burnt( not likely) or is not seating due to carbon build up on the stem. The only way to check this is to remove the cylinder head. You really can't do much thru the spark plug hole. If the valve is indeed just stuck running the engine while adding a little detergent like Rislone or Marvel Mystery oil thru the caburetor might free it up?