Help With Compression Test Levels

sticky nicky · Postby **sticky nicky** » Fri Apr 29, 2011 11:22 pm

Hi,

I have a '93 1.8Ltr and I am getting a compresion test done and was wondering if someone can tell me what level I should expect to see from the results if everything was normal. The car has done 225K.

Thanks

Postby **NitroDann** » Fri Apr 29, 2011 11:52 pm

brand new is about 200psi, you dont want to see a lot lower than 150psi (this is just about a drop in power as a fraction ie; 150/200 is 3/4 original power) Assuming you manage to do better than 160 or so your golden, a large variance in pressure indicates something like a valve problem or something.

Dann

geofiz · Postby **geofiz** » Sat Apr 30, 2011 1:53 am

Nicky,

A compression check is a good start, and as Dann said, a large difference between cylinders, or a pair together that are low can help diagnose the problem. To confirm a cylinder head / gasket problem, you can't go past the radiator pressure test and chemical test. They pressurise the cooling system,and have a liquid setup that chnages colour in the presence of CO, a major component of the fule burn process. If it changes colour, you know you have combustion gases in the cooling system, which confirms a head gasket problem.

Russell

xmx106 · Postby **xmx106** » Sat Apr 30, 2011 9:25 am

1.8 compression test, figures taken from enthuasiast workshop manual.
12.8 kg/cm2 = 182 psi @ 300 cranking RPM
9.0 kg/cm2 = 128 psi is acceptable with no more than 2.0 kg/cm2 = 28 psi difference between cylinders.

sticky nicky · Postby **sticky nicky** » Sat Apr 30, 2011 6:54 pm

I had my compression test done and 200 psi on three cylinders and 195 psi on the other.

That sounds surprisingly good compared to what xmx106 was saying it should be, I guess I should be pleased with that shouldnt I considering the high Ks on the clock.

Postby **NitroDann** » Sat Apr 30, 2011 7:10 pm

Sounds like it was very good. Just needs 15psi of boost now and youll be set.

Dann

geofiz · Postby **geofiz** » Sat Apr 30, 2011 10:39 pm

Those don't sound bad at all.

xmx106 · Postby **xmx106** » Sat Apr 30, 2011 11:10 pm

Next question did you find out where you lost the coolant and the cause of the white smoke when you start up cold.
Those compression pressures are excellent, no problems there, shows how good these engines are.
Some guys have reported 215 psi.

sticky nicky · Postby **sticky nicky** » Sat Apr 30, 2011 11:38 pm

Hi guys,

Yeh apparently I was loosing coolant from the lower radiator hose due to a faulty seal around the clamp which he found by doing a pressure test. The white smoke is almost non existant on start up now. In KYP's opinion it is probably due to a faulty oil ring on the cylinder with low compression and/or faulty valve stem seals which Im not too worried about at the moment, my main concern was the loss of coolant and whether the two were related.
So all in all I am happy that I dont have a huge job to do at the moment, the cars running great. I guess in time if the smoke gets worse I will have to do something about it.
Time to get my road/track tyres which I had put on hold

manga_blue · Postby **manga_blue** » Sun May 01, 2011 1:06 pm

That's good news.

Just for comparison, I did a compression test on my NA8 before dismantling the motor because of a buggared crank. At 175,000kms it held 187 on 3 cylinders and 183 on the 4th. After dismantling and cleaning, the bores and pistons looked absolutely new - you could still see all the original honing marks on the bores. All the rings were still within new factory assembly tolerances.

I'd say that if yours is reading 200psi then you've got no worries about pistons and rings for a long, long time.

Mr Morlock · Postby **Mr Morlock** » Sun May 01, 2011 6:33 pm

whatever way you look at it 225k is well into old age- 18yo. Cars wear out but if it is running well and safe and not breaking down then go with the flow. Many owners never see 100K on their cars - traded or sold - long before they start to do major maintenance.

Postby **NitroDann** » Sun May 01, 2011 6:47 pm

Thats because they dont do the minor maintenance.. or they bought an astra or vectra..

Dann

evil_weevil · Postby **evil_weevil** » Wed Jun 29, 2011 9:36 pm

I did a comp test on mine last night...105 - 110 across all 4.......

Postby **NitroDann** » Wed Jun 29, 2011 9:41 pm

sounds like you did it wrong. Do you have a really strong battery? And did you hold the throttle flat on the floor? And were all of the plugs out the whole time?

Dann