compression test

[SR]

right then ,probably gonna make myself sound a fool now ,but here gos,the test i did on splitty motor averaged 50-75psi all 4 pots,but it was 15/20 yr old gauge,pump up type ,noy dial guage, since then ive taken engine/box out and got a new gunson tester , mainly to test the trav engine, so connecting power can i do the test on a cold engine ,will a make a lot of difference not being at normal; temp,thanks for looking ,A.Dullard

[mu0u207b]

Its best to do it on a fully warmed up engine as the reading you will get on a cold engine will not be accurate. The heat of the engine expands the piston rings so to raise the pressure fully hot, u wud get a low reading on a cold engine. Bit of a pain really specially if your not intending on going anywhere and you want to save a bit of money on petrol costs!!

[Matt]

If it helps i did a cold compression test on the trav (with a rebuilt engine ~10,000 miles ago) the cylinders that didn't have the blown head gasket were about 140psi

[SR]

nice one matt , will give it a go

[Matt]

oh, that is an engine bored out by 40thou too, 12g202 (bog standard) head

[bmcecosse]

No harm doing it cold - either take the carb off or hold the throttle wide open. The readings may not be the best - but they will show if there is any difference from cylinder to cylinder - which is what really matters !

[Matt]

i did it with the carb on and the throttle closed (well at idle if you know what i mean) with the other 3 plugs in

[bmcecosse]

Noooooo !! The throttle must be held wide open to let it get air - and all the plugs out to let the starter spin the engine as hard as possible. Obviously a good fully charged battery - or jump leads from another - is a good idea. You don't want the starter 'flagging' when it gets to the last cylinder. Do it again !

[Pyoor_Kate]

Uh.

My compression test doobry comes with instructions which say to perform the test:

- Fully warm engine
- All plugs in except cylinder being tested

Does not mention the state of the throttle. At the moment I can't envisage why it'd need the throttle open....

[Cam]

Well........ you don't NEED the throttle open as at those revs (very low) it can draw air in quite easily, but an open throttle makes it even easier but I doubt it would make much difference practically.

I personally would take the plugs out of the other cylinders just to make life easier for the starter, but again it makes no difference to the cylinder on test.

A warm engine is best as then everything is at working temp and the rings have expanded properly.