Compression tester fittings sizes

[594rmm]

Who can tell me what size fitting I need for a compression tester as it seems all the ones for sale are metric although the Gauge reads in both, it mentions m10 etc etc Thanks for any advice

[philthehill]

14mm is the size of compression tester adapter where it fits into the plug hole for a Minor.
I can recommend this type of compression tester:-

http://www.ebay.co.uk/itm/Draper-Petrol ... Sw34FVHmqZ

Absolute accuracy is not so important as being able to compare cylinder compressions.
Phil

[oliver90owner]

I have always used a rubber bung - a couple fit virtually all plug holes and it is obvious if leakage occurs - but most of my testing has been on kero burners, over the years. Plugs were metric from a long time ago (virtually after NPT was dropped). Try 14mm, if you must have a threaded tester.

[594rmm]

Thanks for all your help, bought the draper one

[594rmm]

One other question, what should be approx a decent reading for a 1098cc by using the compression tester

[amgrave]

Warm the engine then remove all spark plugs (mind they will be hot). Place a brick or similar on the throttle pedal. Attach the gauge to each plug hole in turn and spin the engine on the starter for a few seconds till the gauge is at it's highest reading and note the PSI readings for all four. A good engine will give up to 190 PSI but these gauges are not accurate. Repeat the same test but this time give a squirt of oil down the plug hole just before you do each one and again note the readings. This is the important thing, the difference between the dry readings and the oiled ones if the readings seem low. Once you have done the complete test come back on here and we can advise.

[594rmm]

Thanks for your advice can it be done from cold as I'm not too keen on starting it as i think the head gasket has gone its running but very very badly

[philthehill]

To determine whether the cylinder head gasket has failed the compression test can be done cold.
If the head gasket has failed - the readings on one or two cylinders will be greatly reduced.
Phil

[oliver90owner]

If one does not have a compression tester, but do have a compressor, one can check compression, on a comparative basis, by timing the pressure drop of each cylinder.

One can easily tell if any excess leakage is going past the rings or valve seats, etc by simple observation.

RAB