What can effect compression results

[pwayzjellyroll]

I tried searching, but to no avail. I want to do a compression test, to see how my motor stands before I start anything else. What can affect the numbers that come out? I have an oil leak right now that will not be fixed until next weeked, a new timing belt going on, new plugs and a fresh oil change. Will any of these numbers change after I do those things? Should I wait to perform the test or is it alright to go ahead and do that now. A point in the right direction or an answer is appreciated. Thanks - Alex

 

[Cs4g63]

None of those things will affect a compression test.

 

[95blackGsTurbo]

None of those things will really affect compression. Do a leakdown test. It will let you know if your rings are leaking or you have a burnt exhaust valve or the headgasket is starting to go out. Compression is just a basis of what the motor is like. You can do one but the results won't change unless your timing is off or something like that.

 

[Locke]

Things that will cause compression to be low on an engine would be:
Worn/broken rings,
Broken ring lands,
Headgasket leak,
Cracked crankcase or head,
Bent valves,
Damaged valve margins,
Damaged valve seats,
Uneven buildup or deposits on valve seats,
Cams way out of time,
Broken valve springs, retainers, or keepers.

Things that would cause it to be high are:
A lot of carbon buildup.

Other things that could cause compression to be off if you worked on your engine:
Improper crank/rod combo,
Incorrect pistons,
Bowl porting,
Wrong HG thickness,
Head surface machining,
Shim without gasket,
WAY to much gap on rings.

Pay attention to the manner in which compression raises during the test. It can help lead you to what may be wrong, if there is something wrong.

There is no reason not to do the compression test now.