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i got my ultra shes not running good. its got alot of miles so im thinkin compression. i know from workin on chainsaws 100 is pretty much as low as you can go. what should the range of my compression be? thanks
I'm thinking it should be around 150 for a good tight engine.polarisripper28 said:whats the normal amount??
i looked in the sevice manuel and it didnt say anything.
It has to do with port location which effectivly alters timing. I am not talking about ignition timing but rather event timing (intake charge verses exhaust cycle. If the port is higher/lower, the cylinder will bleed off or retain more or less of the cylinder pressure at cranking speeds. That is assuming that the engines being compared are relatively tight and are not suffering from any other mechanical issues. That is about as simply as I can explain the difference in compression readings in different engines.polarisripper28 said:ya i relize that how come different motors are different psi. because my 81 air cooled ski do has like 150
Back in the day we used to mill the piston skirts on 750cc Kawi triple's to change the port timing,along with porting,those thing's used to haul the mail.tc66nova said:It has to do with port location which effectivly alters timing. I am not talking about ignition timing but rather event timing (intake charge verses exhaust cycle. If the port is higher/lower, the cylinder will bleed off or retain more or less of the cylinder pressure at cranking speeds. That is assuming that the engines being compared are relatively tight and are not suffering from any other mechanical issues. That is about as simply as I can explain the difference in compression readings in different engines.polarisripper28 said:ya i relize that how come different motors are different psi. because my 81 air cooled ski do has like 150
Port location doesn't affect compression all that much, and is not a main factor as to the differences in compression between different engines. Compression ratio is the biggest factor, and port location doesn't affect compression ratio. The compression ratio is the total volume of the cylinder with the piston at BDC divided by the volume of the combustion chamber with the piston at TDC.tc66nova said:It has to do with port location which effectivly alters timing. I am not talking about ignition timing but rather event timing (intake charge verses exhaust cycle. If the port is higher/lower, the cylinder will bleed off or retain more or less of the cylinder pressure at cranking speeds. That is assuming that the engines being compared are relatively tight and are not suffering from any other mechanical issues. That is about as simply as I can explain the difference in compression readings in different engines.polarisripper28 said:ya i relize that how come different motors are different psi. because my 81 air cooled ski do has like 150