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    Alum. pistons and steel cyl. liner. Would appreciate any advice on the best way to get the rings to seal. Having a problem with low compression.
    • CommentAuthorgbritnell
    • CommentTimeMay 11th 2010
    Hi Craig, In most cases if the cylinder is round and the rings are properly made and fitted the compression will be good from the start. That's not to say that it won't improve with some time on the engine but you need good fits to begin with. Another thing you could check would be the valve seating. If you're sure that the piston, bore, ring thing is good then I would check the valves. Sometimes we overlook another part of the equation when trying to diagnose a problem. What kind of engine are you referring to, a single, a multi a hit and miss, and what is the bore size? Do you know what the compression ratio is? If the ratio is low it won't seem like there's much compression.
    Assume rings are cast iron on a steel liner, if that is the case, it will take some time to wear the liner into the proper shape.
    Try using break in oil, and no synthetic at all, Shell does one break in oil, Steel liners seem to take longer to wear in than cast iron, I guess they will last longer.
    Some engines will not develop a lot of compression no matter how much we try, check as George recommends all other possible leak areas, valves are a good place to start.
    Have you measured compression, use a small indicator to measure compression, place some oil in the piston and measure again, does it increase, then rings may be the problem ?

    The engine is the Silver Bullet. The compression is about 20 psi on each cyl. I suspect I may have air leak around the valve cage of the intake valves because I am getting some spitting thru the carb. The rings are cast iron. Compression ratio should be 6 to 1. Will pull the head off (again! ) and look for the items mentioned in the comments I have gotten.
    • CommentAuthorgbritnell
    • CommentTimeMay 12th 2010
    Craig, usually I try to suck on the intake port or exhaust port to see if the valve is leaking. I know sometimes that's hard to do but the only other way I know how to do it is like full sized practice and fill the combustion chamber with kerosene. If it leaks you have a problem.

    In the same engine I had a similar problem, guess what the leak was between valve cages and head, I made them as advised in plans in Silver steel, but the issue was they are sharp and have to be guided into the head with a lot of care ( which I didnot) and there was a small gap created in the head, and it was leaking under pressure.
    Solution made a new head and valve guides assembled them correctly second time and voila it is a nice runner now.

    Best of luck.