Cylinder Compression Test

[JamesT5]

Hi

I've been out today and done a cylinder compression test (after finally working out how to use the tester) :dunce:

I followed the normal advice, a warm engine and 3 tests per cylinder with at least 5 'turn overs' on the ignition/starter motor.

I got my girlfriend to sit in the car, open the throttle and keep it down whilst cranking the engine over 5 -6 times per test. I did the 3 valve tests one after the other quite quickly, so cylinder 1 was tested 3 times, then I moved to cylinder 2 and tested that 3 times and then on to cylinders 3, 4 and 5 testing in the same fashion.

The results thankfully were pretty consistent across all 5 cylinders although cylinder 3 yielded slightly better results but by no more than about 5 -10%.

The following shows the results in PSI. I had to interpret the gauge as it kind of goes from 50 then the next number is 72 so I had to count the lines in between, and I figured each line represented about another 3 psi on the guage........

Cylinder 1

1st Test = 56
2nd Test = 59
3rd Test = 59

Cylinder 2

1st Test = 56
2nd Test = 56
3rd Test = 56

Cylinder 3

1st Test = 62
2nd Test = 59
3rd Test = 59

Cylinder 4

1st Test = 56
2nd Test = 56
3rd Test = 56

Cylinder 5 Test

1st Test = 56
2nd Test = 56
3rd Test = 56

Somewhat reassuring is that all 5 cylinders are showing roughly the same results, which tells me that if the valves are wearing, they're at least wearing at the same rate. But to be honest, I think as the results are fairly uniform across all the valves, everything should be ok.

I did however, notice a very small amount of oil on the spark plugs that wasn't there when I took the last set of spark plugs out.

Regards

James

[Wally Dog]

Could the oil be valve stem oil seals?

[JamesT5]

What's slightly worrying is that I've seen another Volvo website thread that says pressure should be 150 - 180 psi. :worried:

[bubba_1986]

They are very low figures mate, would get valves check out asap

[JamesT5]

They are very low figures mate, would get valves check out asap

Stupidly the car runs lovely now since I've changed the coils. I'm wondering how much power is missing if the valve pressures are only about a third what they should be!

[Kingsford G]

Stupidly the car runs lovely now since I've changed the coils. I'm wondering how much power is missing if the valve pressures are only about a third what they should be!

Will b down quite a bit mate.It would b burning oil and lots of smoke if it was the rings so thats a good news.Nothing to do wiv valve stem seals as mentioned above gotta b valves.B prepared to have new valves fitted as u may find deep pits in them so best to replace.

[V70 Graham]

Hope it's nothing too serious.

[oblark]

Try doing the compression test again but this time put a small amount of oil in the bores, If the readings stay the same then it`s the valves, If the readings go up it`s the rings.

[960kg]

Hi

I've been out today and done a cylinder compression test (after finally working out how to use the tester) :dunce:

I followed the normal advice, a warm engine and 3 tests per cylinder with at least 5 'turn overs' on the ignition/starter motor.

I got my girlfriend to sit in the car, open the throttle and keep it down whilst cranking the engine over 5 -6 times per test. I did the 3 valve tests one after the other quite quickly, so cylinder 1 was tested 3 times, then I moved to cylinder 2 and tested that 3 times and then on to cylinders 3, 4 and 5 testing in the same fashion.

The results thankfully were pretty consistent across all 5 cylinders although cylinder 3 yielded slightly better results but by no more than about 5 -10%.

The following shows the results in PSI. I had to interpret the gauge as it kind of goes from 50 then the next number is 72 so I had to count the lines in between, and I figured each line represented about another 3 psi on the guage........

Cylinder 1

1st Test = 56
2nd Test = 59
3rd Test = 59

Cylinder 2

1st Test = 56
2nd Test = 56
3rd Test = 56

Cylinder 3

1st Test = 62
2nd Test = 59
3rd Test = 59

Cylinder 4

1st Test = 56
2nd Test = 56
3rd Test = 56

Cylinder 5 Test

1st Test = 56
2nd Test = 56
3rd Test = 56

Somewhat reassuring is that all 5 cylinders are showing roughly the same results, which tells me that if the valves are wearing, they're at least wearing at the same rate. But to be honest, I think as the results are fairly uniform across all the valves, everything should be ok.

I did however, notice a very small amount of oil on the spark plugs that wasn't there when I took the last set of spark plugs out.

Regards

James

There is nothing wrong with the engine!!

The main thing is the cylinders are all within 29psi of one another

I doubt it would start at that low pressure if it were correct.

You are doing something wrong but you are consistant with what you do as it as it shows.

Although the proper pressure should be 165/ 180 or whatever it does not matter what the pressure is as you are checking them all at the same time, same temperature and the same way.

Find what you are doing wrong (are you pressing the button to release the pressure so returning the reading back to "0" each time between tests??) and that will restore your trust in the motor, you won`t get the same values per cylinder as often as you have if something is wrong, engines don`t wear equal, as the cylinder at the waterpump end is cooler so will wear more. The in between cylinders will give more psi in general as they run a similar temp. unless a valve is burnt but then it will give more than 29psi less.

[Kingsford G]

Tbh wiv valves leaking tickover is a lumpy ish.R u actually sure the gauge is good and accurate?What was the reason for the test anyway?

[960kg]

I don`t think he has pushed the button on the compression tester to release the previous test pressure before the next test so that is why they are all practically the same!

[JamesT5]

I don`t think he has pushed the button on the compression tester to release the previous test pressure before the next test so that is why they are all practically the same!

Thanks for the input here, it's actually very helpful as I've never done this test on a car before.

Ok, I'll try and clear up some of the questions above to see if it helps....

The reason for the tests is to rule out any damage left behind by the misfiring issue (I've now resolved). I was putting a lot of strain on the engine by running on 4 cylinders and now I've fixed the problem I wanted to make sure I hadn't damaged a valve or valves. The compression tester was new out of the packaging this morning so I am assuming it's not faulty etc.

Just to confirm I did release the pressure valve fully and set the meter back to '0' each time, without fail so that should rule out any errors on that front. I was very methodical with the way I conducted the tests to ensure the results were as accurate as possible.

I made sure also that the fitting for the spark plug hole was screwed in square on (not cross threaded), and that it was tight enough to stop any air escaping.

I've just had the thought though as I type this, I took all 5 spark plugs out at the same time and then conducted the tests, and I'm wondering did 'pressure' escape through the other spark plug holes to the cylinders or would that not make any difference?

The only other possibility is that the little screw type thing that surrounds the pressure release valve wasn't tight enough and pressure was escaping when the valves were pumping air in. I will say though I did get this as finger tight as possible and it didn't seem to want to turn any tighter.

Also, I've ruled out misreading the unit type, i.e. psi, bar etc. There is 2 scales, that both run along side each other. One is psi and the other is bar. It was peaking at 4 bar which would coincide with the psi of around 55 - 60.

Ok, so that's the variables considered. Any thoughts?

Thanks for your help everyone...

Regards

James

[JamesT5]

By the way, there is absolutely no sign of blue smoke, burning oil from the exhaust or burning oil smells at all. The emissions from the exhaust smell like normal healthy petrol fumes. The 'acid test' will be to get it down to my local ATS Euromaster and get them to run an emissions test. If the emissions are within normal levels then there's little or no oil burning going on. I've been watching the oil levels on the dipstick, and it doesn't seem to be going down either which is good news.

As for the trace amounts of oil I found the spark plugs, they were worse on spark plugs 1 - 3 but less so on 4 and 5. Also, note that the oil wasn't on the electrodes but on the rim below them that's between the electrodes and the thread, (thinking I should have taken a photo or 2).

[Kingsford G]

Each cylinder got its own compression so no escape from other cyls.Does the car pull well?There is deffo some mistake in reading mate.

[JamesT5]

The car pulls off nicely. The only thing I would say is that there is a slight (and I mean slight) judder when I'm in say 5th gear at 5 and applying the throttle. Other than that the car runs like new.

Must be my readings aren't accurate.

Regards

James

[Jamest5r]

If you put a "1" in front of them figures there perfect :)

[JamesT5]

If you put a "1" in front of them figures there perfect :)

There's a thought! :)

[Kingsford G]

Yr car is fine mate from what u saying.adder is something else.Wiv a compression leak on a tick over u could notice a bit of missing if none present thats fine.

[claymore]

You need to get your terminology right mate, your posts are really hard to read and understand.
I can't see why you would want to do a compression test after a missfire to be honest with you.

[JamesT5]

You need to get your terminology right mate, your posts are really hard to read and understand.
I can't see why you would want to do a compression test after a missfire to be honest with you.

Unfortunatley I'm not a mechanic and have zero mechanical vocabulary and therefore terminolgy doesn't really come to me, I just have to go with what I can with the knowledge I have. I'm trying to learn from more knowledgeable people and offer back whatever I can.

Anyway, if there's nothing wrong with the engine and it's my readings that are out then happy days. :B_offtopi :Handshake

Regards

James

[jbconno]

Stop flapping get back to enjoying your car ;-) If its running well then its running well, leave it alone and have fun with it.

[960kg]

Unfortunatley I'm not a mechanic and have zero mechanical vocabulary and therefore terminolgy doesn't really come to me, I just have to go with what I can with the knowledge I have. I'm trying to learn from more knowledgeable people and offer back whatever I can.

Anyway, if there's nothing wrong with the engine and it's my readings that are out then happy days. :B_offtopi :Handshake

Regards

James

Good for you that you are trying to learn and do things yourself with the motor. You have to learn to ignore any quips and just absorb the facts!

At least you did one thing correctly and that was although there is something wrong with the readings you did it consitently wrong so giving the readings as nothing wrong toward with the engine.

[spesh]

where abouts in mid wales are you James? im travelling back to swansea from scotland soon and i got a compression tester in my car, dont mind popping in give you a hand, think im just about competent to do a compression test :-)