Compression test tells how much "PRESSURE" a piston can make. The leak down test is a tool that has 2 gauges and uses a compressor for air. 1 gauge tells how much air is being induced into the cylinder. The other gauge tell how much the cylinder is able to hold. This is leakage. It uses 100 psi of air. So if I am inducing 100 psi and the cylinder is holding 92 psi that is 8% leakage. Most healthy engines will have 10% or less. I always bring the piston to TDC and rollover aprox 1/2-3/4 of a inch. As I have shown many people, Most bad cylinders will test good at TDC but will have excessive leakage just off TDC. This is because cylinders will get a coat of carbon at the top of the cylinder and will make a seal. If the cylinder has any damage the rings will be in damaged area and will show itself. I have performed 2 leak down test in the last week on 2 engines with "GOOD" compression but have high leakage. If you will look for XR2 rebuild here in the questions, you will find one of these engines. This thread is the other. Ditchdocs had 70% leakage on number 1 and when we tore down found the 2nd ring was coked (carboned) up and was pinned into the ring groove and would not move. This was the cause of the high leakage. Feel free to call me if you have any questions.
Got to meet Wrechin2 today!! ... We found some bad news :(
- Thread starter TAzGa
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