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Compression in 1940 346 engine

Started by Hilarius, March 08, 2013, 06:28:54 AM

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Hilarius

Hi everyone!

I purchased a 1940 75 model Cadillac a while  ago and the seller stated that the engine had been completely overhauled about 5000 miles ago. The rebuild included among other things 8 alloy valve seats, and 16 new guides, valves and springs
I am presently restoring the car, the body is off, and I thought it a good idea to take a look at the engine while it is well accessible. I made a compression check with the engine cold and found that there was a noticeable difference in the readings, especially at the two rear cylinders on the right side.
I thought that maybe the clearance between lifters and valves might be too small after the refacing of the valves, so I took out the lifters checked them on the bench and found them OK as well as the clearance between them and valve stem ends. I also took off the right hand head and turned the engine so I cold look at all the valve seats with a mirror and found them all shiny all around. With the engine reassembled I made another compression check and the readings are as follows.
Left cylinder bank        Right cylinder bank

Cyl.#   Cold    Hot           Cyl.# Cold    Hot
   1     6,0     5,4                 1      7,0   5,2   
2     6,2     5,5                2      7,0   5,1
3     6,7     4,6                3      5,3   4,4
4     6,0    4,5                  4     5,8     4,0

Even though a difference in pressure remains, I cannot explain the decrease of pressure with the engine hot, when it should be the other way around. It doesn’t burn oil, the exhaust vapour is clean, neither blueish nor gray/black. There is enough oil in the pan, so the oil film on the cylinder walls cannot have been washed away for lack of oil, and the starter turns the engine well.
I am not really looking forward to taking out all the valves to grind them to their seats.
Any other ideas for the cold-hot difference???

Hilmar.
Hilmar Schneider #26898
1930-162, "353", 4D-SDN-7P
1940-7567, 2D-CCP-2/4P
1948-7519X, 4D-SDN-5P
1952-6019X, 4D-SDN-5P
1973 Mercedes 107R, 2D-CCP-2P
2015 Cadillac SRX, 4D-SDN-5P

Steve Passmore

Hilmar. I though you had gotten over believing what the seller had told you? Iv seen the pictures of your headlight buckets remember :D
Steve

Present
1937 60 convertible coupe
1941 62 convertible coupe
1941 62 coupe

Previous
1936 70 Sport coupe
1937 85 series V12 sedan
1938 60 coupe
1938 50 coupe
1939 60S
1940 62 coupe
1941 62 convertible coupe x2
1941 61 coupe
1941 61 sedan x2
1941 62 sedan x2
1947 62 sedan
1959 62 coupe

Dave Shepherd

My same old recommendation, do a leak down test for a better diagnosis.