The mystery of low compression

[Horsepoor]

Problem:
Apparently, low compression in the number one head. Engine runs fine with the compression screw in but as soon as it is screwed out, the number one cylinder misses badly and only fires occasionally.

Engine facts:
New GTC 20/2 down rated to run at 850 rpm.
The number 2 cylinder runs fine, both at high compression and at low compression (screw out)
Piston rings properly installed at 180 degree off sets with the next layer at 90 degrees.
Valves set to machine shop before engine ran and tappet clearance set at .008
Injector pumps set to fire at 26 degrees before TDC
Bump clearance set at .052 and verified as accurate.
No noticeable leakage heard nor detected when engine is slowly turned over / cranked.
Number one compression change over valve examined, seals look good and spring loaded cylinder appears to be functioning properly.

Suspect areas:
I wonder if the injector might some how be malfunctioning. The fuel used is jet fuel. I plan on swapping out the injector and seeing if the problem goes away.
I wonder if the cylinder head cavity could have been cast larger than normal? I plan on measuring the volume by carefully pouring in a measured among of oil. Does anyone know the standard volume?
I wonder if there is some feature on the design or maintenance of the compression change over valve that might cause low compression.
I have a standard compression tester for gasoline engine with the screw in spark plug type head, which will not work here. Tomorrow, I am going to look around town to see if I can buy a diesel compression tester cheap.

Do any of the members of this distinguished forum have any ideas or suggestion for me to run down?

[kyradawg]

Peace&Love, Darren

[listeroidsusa]

Check your exhaust temp. If one cylinder is noticably cooler than the other the problem is usually the injection rack adjustment on the cool cylinder. Turn the clevis on the cool side in a half turn and see if it helps. Keep doing so until the exhaust temps are the same for both cylinders. This is a common problem with the twins.

Mike Montieth

[Horsepoor]

Tks Mike,

Couldnt get it to run with the screw out but with the number one screw in temp was 400F and 375F on the number two with the screw out. It should have been the other way around I should think, but I will experiment with the linkage just to see if it helps. Tks

[Horsepoor]

Yea, now that I think about it, nothing stopping me from running both at high compression and getting the tempertures to ballance out exactly by adjusting the linkage. Then I can see if the number one will run on low compression after I am certain of the ballance. Good suspect area. Tks

[cujet]

I saw the engine run. It sure seemed to me like the number one cylinder was low on compression. However, it may be something else. I was thinking about all sorts of things. Maybe the valve is being held open a bit too long? Maybe CC volume? Maybe injector? Just guessing.

Chris