have an older f3 ran for a while, started makin noises and quit running. disassembled timing chain cover, valve cover, found a broken chain guide, and jumped time, i can only get about 40 lbs compression. have retimed (probably incorrectly), does anyone have any idea what that engine should have? is 120 low or average? should it be around 200? dont have a leak down tester but since i have some compression it is safe to assume valves are ok, same reading across all cylinders also indicates a valve timing issue to me, and safe to assume that its not burnt exhaust valves either. Just need a general number to shoot for. thanks for the input.

 

I'm not positive, but I think they are around 160 psi at sea level. The most important factor with compression testing is the range of change across all 4 cylinders though. However, anything above 120 ish and within 10 percent across on an older motor like that is probably ok.

With compression that low though, you probably do have the timing off and your valves are open during the compression stroke. Be careful here though, I'm not sure if that is an interference motor or not. If it is, you are running the risk of the valves making contact with the piston.

Its also possible that you have bent valves. Now might be a good time to remove the vavle cover and see if all valves are fully returing.

 

185 to 190 and you can check the valves to see if they are sealing run your compression test get your readings then add a shot of oil to the cylinders if the compression goes up the valves are good but the rings are going if there is no change then the valves are suspect.