Originally Posted by Wezz
Hello . Today i got the result of my. Leaktest on the cilinderheads no leaks found .. The gasket. Looks good But before i started the project on my engine i the hoses where a litle hard. Also the machinist said the valves where a little light of collor. So he says there was somewhere a leakage Now im thinking maybe the onder block?? But how can i chek this whit pistons in the engine I chekked the Cilinderwals by eye and i didnt see anything strange Btw cAn u get 159 psi with a cilinder leak ?
After reading Cam choice
, I see you are working on a SBC 305 engine.
If there were a crack in the block, usually this will put oil in the water or water in the oil- or both. This can also cause a lower compression test reading in some cases, but not always.
Often a crack will connect two adjacent cylinders. This can cause an abnormal compression reading in both cylinders.
Sometimes there may be a small crack that won't show up with the engine cold. It takes the engine being heated up before the crack expands enough to start leaking coolant, and to show up on a compression test. But sometimes it won't show up at all.
If the engine is together you can pressurize the cooling system to check for cracks into the coolant passages. If the engine is apart, the best bet is to have the block checked by a magnetic particle inspection process, sometimes called magnafluxing the block. There are other ways to check for cracks but this is used most often on iron castings.
When there's leakage of coolant onto a cylinder, that combustion chamber, both valves and the spark plug will look quite differently than the other cylinders. Often the carbon will be all scoured away, leaving a very clean appearing chamber, with all the carbon having been removed.
If all you are seeing is a bit of a different color to an exhaust valve, I would tend to doubt the block is cracked, but it still should be inspected for cracks to be sure. A visual inspection can uncover some cracks easily, other cracks can be all but invisible to the naked eye.
Any chance you can post a photo of the head and piston tops of the side of the engine that you think might be cracked?