Quick question

[philtoms101]

to those of you who have ever done there own compression test before, I need to check out my head gasket and i've just bought a compression testing kit (£11 quid on ebay new).

Just to double check, screw the bung end into the spark plug socket, and then turn the motor a few times on the starter motor, but not letting it actually catch and fire up. Rinse and repeat three times for each cylinder to try and get an acurate as possible reading. Any to to add that i have missed out ?

Also what i'm looking for is not so much as a lbs/inch reading but the difference in the reading between all four cylinders, anything more than about 10lbs difference is bad news.........is this correct

Just want to double check her as i got to take the Mrs away for her birthday and i don't want the car breaking down on me, enroute and the head gasket had been suggested as the problem !!

Cheers,

Phill

[skyshack]

Take all plugs out together not one at a time or the compression load from the cylinders with plugs in will slow it down giving low readings. Disconnect ignitition pack from loom so it doesn't spark over to earth inside the coil which can damage the insulation. When tuning it over make sure it does the same number of compression strokes on each cylinder to get consistant readings - 5 or 6 is OK to get a good reading. It's quite easy to hear each stroke. Floor the throttle fully when turning it over or you will only part fill the cylinders and get low readings.

142psi min pressure with 14psi max diff between cylinders. Any that are low put 2-3cc (teaspoon full) of oil in though plug hole and crank over to distribute, then re-test compression. If it improves up to 140psi+ it's rings and you can get away with them down to about 100psi on one or two pots. If it doesn't improve it's either valves or head gasket. Two adjacent cylinders with the same low reading and no improvement when tested with oil is almost 100% going to be HG between those two bores. If HG on any cylinder has gone other than between bores you should see bubbles in header tank if you warm engine fully with rad cap off. You would also expect to keep finding air in rad header tank as it blows water out to the expansion tank and though HG but the air under pressure so it expands as system cools preventing water being sucked back in. Lots of people only find the HG has gone and the engine very poorly when there is no water left in the rad even though the expansion tank that they have been looking at every week is still full. If it's not low on adjacent cylinders and there are no bubbles it's a fair chance it's valves.

[philtoms101]

Skyshack,
Pretty darn impressive response, I think you have covered everything

Thanks for the advice,

Phill

[G'boy]

Also you should do the test with the throttle fully open

[philtoms101]

Well i've done the test with the throttle fully open, as per Skyshacks instructions, thanks for those mate

Not good i'm afriad, i got 155ftlbs, 155ftlbs, 115ftlbs, and 0ftlbs, the plugs on the higher compression cylinders, looked like the had been run at little lean and the other two were caked in crap, like she had been running rich !

But that is about right for a head gasket failure, from what i understand (lower compression meaning fuel is being wasted). There also appears to be a small amount of oil in the coolant header tank.

So any recomendations on replacement gaskets, i'm going to do the whole upper set, Manifolds etc.. any suggestions on group a quality replacement, I see the trust head gaskets seem to be popular on the board, are they any good ?

Still we found out before she did anything to nasty, ah yes whilst i'm at it can anybody recomend somewhere i can send my head of to be skimmed, to ensure a nice snug fit for my new HG !!?

Cheers,

Phill

[w00dy2009]

hi there ive just done a compression test on my ca18det which is only firing on 3 cylinders. on the one that isnt firing the no.1 piston there is only half the compression compared to the other 3. any ideas?

ive also checked why it isnt firing by checking spark and fuel and i dont seem to have any problems there.

hopefully find out soon anyway as the engines nearly ready to come out.

[arry]

What figure did it produce?

Have you tried a wet test?

[w00dy2009]

um cant remember the exact figures i did the test a couple of weeks ago. but i know the piston that was down was at 60psi i think and the other 3 cyclnders where just under double that.

and no i didnt get to do a wet test. but ve started taking everythng out now and the engines coming out this weekend so ill find out what the problem s when i strip it down.
im in no rush anyway as the cars off the road but i just found it strange that its not firing on that piston at all.

cheers for the help

[arry]

If it's got fuel and spark, the reason it won't catch is because it's got bugger all compression