compession test?
 

i had one of my r/c buddies,bring his savage over today and i noticed he had anew engine .asked what was up,replyed he was having trouble geting it to run(noob)so he took it to the lhs,and compession tested it said it should hold 60psi cold,it didnt so they talked him into a new engine,to me it does not make sense that a cold engine,thats broke in could hold that kind of pressure,warm maybe.needless to say i dropped said junk engine in one of my trucks.after about 10 minutes of tuning his junk engine is ripping around my yard,pullin wheelies,idling,and runnin at temp.

RE: compession test?
 

whats the question? colder engines have more compression as do new engines

RE: compession test?
 

He got ripped off but maybe not intentionally. It's useless doing compression tests on engines this small because of the dead volume inside the compression tester which is huge compared to the volume of the combustion chamber. High exhaust timing will also drastically reduce the compression figure shown too. An ABx engine that's still got a pinch will hold compression almost forever whether hot or cold. I tried it with a well run in (~30 hours running) plane engine and simply gave up after 45 minutes.

The only thing that's important is how quickly the compression leaks away but even this is hard to judge. Basically if you can turn an engine up against compression and still feel resistance for a few seconds then it's fine. Even at idle a car engine is only up against compression for about .01 seconds.

RE: compession test?
 

was not really a question,it was something i was curious about ,so i put it out there.it was something i have never heard of being done.just trying to learn and if you dont put stuff out there you,ll never know right.after thats what these forums are for.thanks downunder thats what i thought as well