how do you perform a compression test?

[Tidy Max]

as title says really!

whats the dealio!

[D7AKE]

Easy, get a compression tester take 1 plug out at a time fit the tester, remove the coil lead, crank the engine... hey presto compression reading!

:thumb:

[Tidy Max]

alright! if i crank the engine.. does that just mean turn the ignition key, but obv it wont start because the coil lead is removed? cheers matey, i believe this will be your first bit of rep!

ooo green blob!

[Lee H]

Also you should ideally do it on a warm engine with the throttle open.

[paul james]

You don't actually run the engine when testing, just turn the bottom pulley by hand - i think!

[Lee H]

You don't actually run the engine, just turn the bottom pulley by hand - i think!

You'd never register compression doing it by hand lol Needs to spin at about 200rpm so can only do that on the starter.

[paul james]

:) ah right, I've never actually tried it myself! Always just taken the head off to look to see whats wrong instead.

[Tidy Max]

the engine isn't connected up to any fuel line or anything you see, its just fixed in the car at the moment, im going to hopefully be rebuilding it anyway. i would have just checked out of interests sake to see wether the rebuild had been worth while!

cheers for the advice!

[Stuart]

take all the plugs out, ensures it wont start and the best chance of a consistent result

[Will F]

Like stu says, all plugs out, remove any fuel bits (relay) and do it with the throttle wide open.

[mowgli]

you should do a dry test first, ie: stick the tester in the plug hole & crank it on each cylinder. then a wet test. basically squirt a drop of engine oil down each bore, and do the test again... then you will see two sets of figures.
if the first set of figures aren't much different to the second, then the engine is pretty good. if there is a massive difference, then its strip down time, and when you've done that, take the engine to bits.......

[nova_saloon]

turn it over withj finger in spark hole, if there is poof, you have compression!

[craig green]

turn it over withj finger in spark hole, if there is poof, you have compression!

Hardly accurate. Using the comp terster will measure what compression there is & highlight which cylinder (if any) is low/high. I would expect a fooked engine to still have compression unless there is a large hole in a psiton or similar. :thumb:

[nova_saloon]

Hardly accurate. Using the comp terster will measure what compression there is & highlight which cylinder (if any) is low/high. I would expect a fooked engine to still have compression unless there is a large hole in a psiton or similar. :thumb:

i know it was a joke, just seemed funny at the time. But another thing you can do is on a air compressor they have a little attachment on the gun that shows you the pressure (usually on a tyre inflator. if you can attach that in to the hole (seen it done before) you can get a rough reading of the compression!

[mowgli]

i know it was a joke, just seemed funny at the time. But another thing you can do is on a air compressor they have a little attachment on the gun that shows you the pressure (usually on a tyre inflator. if you can attach that in to the hole (seen it done before) you can get a rough reading of the compression!

Christ!!!! you'd get a more accurate reading with a condom over the exhaust!!!!!

[MK999]

Christ!!!! you'd get a more accurate reading with a condom over the exhaust!!!!!

Anyone got an inflation size chart I can use for calibration?

[Tidy Max]

Christ!!!! you'd get a more accurate reading with a condom over the exhaust!!!!!

lol lol lol