The Ford Barn - View Single Post - No. 7 Cyl never gives evidence of a power stroke on '46 Flathead

ronchamblin · 04-04-2017, 06:46 PM

A friend suggested that the No. 7 valve might be sticking partially open, and suggested that I inject some Marvel Mystery Oil into it. I will try it. However, the following three points allows me to believe that the No. 7 exhaust valve never closes, either because the assembler adjusted the valve on a partial lobe, or there is a foreign object between the valve and the seat, preventing the valve from closing. My belief is because of the following three bits of evidence:

1) With the engine warmed, the open throttle cranking speed pressure test shows all cylinders are 140 to 145 lbs except No. 7, which is 115 lbs.

2) After running engine and removing all plugs, it was found that all plugs were wet with fuel except No. 7, which was dry as a bone.

3) While holding a piece of paper at exhaust, there was a repetitive flick movement toward the exhaust -- presumed to be caused by an exhaust valve being open during piston down stroke.

Therefore, the only conclusion I've arrived at is that the exhaust valve, although moving according to the cam rotation ... never closes. The air drawn into the No. 7 cylinder during the intake stroke as the piston descends comes not from the intake manifold, which has a fuel/air mixture, but it comes from the partially opened exhaust valve, which is only 1/4 inch from the intake valve. A further observation is that the exhaust valve environment actually has a small amount of pressure, thus encouraging air (without fuel) into the combustion chamber during the intake stroke. I might mention that because the adjacent cylinders perform normally on all tests, I can assume that the problem is not caused by a head gasket issue.

What do you guys think? Am I an idiot, or am I probably right?

04-04-2017, 06:46 PM	#52
ronchamblin Junior Member Join Date: Aug 2013 Location: Jacksonville, Florida Posts: 13	Re: No. 7 Cyl never gives evidence of a power stroke on '46 Flathead A friend suggested that the No. 7 valve might be sticking partially open, and suggested that I inject some Marvel Mystery Oil into it. I will try it. However, the following three points allows me to believe that the No. 7 exhaust valve never closes, either because the assembler adjusted the valve on a partial lobe, or there is a foreign object between the valve and the seat, preventing the valve from closing. My belief is because of the following three bits of evidence: 1) With the engine warmed, the open throttle cranking speed pressure test shows all cylinders are 140 to 145 lbs except No. 7, which is 115 lbs. 2) After running engine and removing all plugs, it was found that all plugs were wet with fuel except No. 7, which was dry as a bone. 3) While holding a piece of paper at exhaust, there was a repetitive flick movement toward the exhaust -- presumed to be caused by an exhaust valve being open during piston down stroke. Therefore, the only conclusion I've arrived at is that the exhaust valve, although moving according to the cam rotation ... never closes. The air drawn into the No. 7 cylinder during the intake stroke as the piston descends comes not from the intake manifold, which has a fuel/air mixture, but it comes from the partially opened exhaust valve, which is only 1/4 inch from the intake valve. A further observation is that the exhaust valve environment actually has a small amount of pressure, thus encouraging air (without fuel) into the combustion chamber during the intake stroke. I might mention that because the adjacent cylinders perform normally on all tests, I can assume that the problem is not caused by a head gasket issue. What do you guys think? Am I an idiot, or am I probably right?