Paul,
dare one mention that the 'wet/dry' test won't be as effective on a horizontally opposed engine as it will be on one with vertical cylinders?

On the other hand, use of a 'leak-down' tester makes it possible to determine exactly where a problem lies, be that with the rings, inlet valve or exhaust valve...

As D.A. has pointed out, an intermittent poor running problem isn't going to be connected with low compression.
When that's gone, it's gone for good, despite what those wonder chemical cures may claim.

ken

What's a 'leak-down' test, Ken?

In outline...
< http://en.wikipedia.org/wiki/Leak-down_tester >
and in detail...
< http://www.lovehorsepower.com/MR2_Docs/ ... esting.htm >

A compression test is a very blunt instrument in comparison to one of these.

ken

i get the idea ken, and i think its a brilliant idea!

Depends how you do it Ken. I usually squirt three or four squirts of engine oil in the plug hole, crank the engine for 10 seconds then fit the compression gauge and conduct the second test. At the end of the day the test is only an indicator of why the compression might be low. A strip down will still be necessary but its a good starting point of what to look for.

Now don't you go all Nordic on me, you know it makes sense

Apologies, seems that genetics dictate I mostly do Celtic...

It is possible to make your own leak-down tester and I'm sure once you've realised what an effective tool it is in pinpointing exactly where a problem lies, you would only use a compression tester as a 'first check' instrument.

ken

Friend of mine had an outboard in to repair, running tough as old boots. Top 2 cylinders, no compression, bottom one tons, his instinct said head gasket, between1 and 2, and he was right, but only confirmed after dismantling engine, would a test like that tell you that in theory ?

Hi James,yes it would.What you are doing is pressurisng the cylinder with the piston at tdc,so the valves are closed,thus giving you a sealed cylinder.Now,when you pressurise the cylinder,if the gasket has blown between two cylinders,with all the plugs out,you would hear the pressure leaking into the next cylinder.Also,the gauge would show a pressure drop.

What I had suspected thanks dave

OOOh yer bacon fed Ulstermen may be spinnin in their graves-Red White and Blue through an through

Any way back to post 1
id be looking for an electrical problem for this one

had a spark plug and the screw on terminal had come off ans at certain points that cyl cut out

when you stopped to look all seemed ok