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interpret these cylinder compression numbers
kp - 28/8/12 at 07:06 PM

My 1.6 sohc pinto which I got for free, sounds rough and low on power.

I did a compression test and got the following results

cyl 1 =7bar
cyl 2= 8 bar
cyl 3= 0 bar (didn't even move the needle)
cyl 4= 7.5 bar

after a couple of squirts of oil I got these numbers;

cyl 1 =7.5bar
cyl 2= 8.5 bar
cyl 3= 0 bar (still didn't even move the needle)
cyl 4= 8 bar

Haynes says the compression should be 11 to 13 bar. Obviously a serious problem in cylinder 3. Can anyone diagnose what is probably wrong with this engine?

I will be taking the head off tomorrow, what should I look for in terms of damage, aside from the obvious (gasket). I've never done any work on the inside of an engine before.

How much cylinder head rebuilding work can I do in my garage without specialist tools?

jacko - 28/8/12 at 07:20 PM

Before you remove the head are the valve Clarence's set right on no 3 not to tight .
After that its head off and check the valve are ok you can do a quick check by turning the head up side down and putting petrol in the head to see if the valves are ok or leak [ over night ]
After that its piston rings or even a re-bore

balidey - 28/8/12 at 07:20 PM

I wouldn't worry too much about the actual figure, that fact 3 of them are close sounds OK (within reason, I am sure some people will disagree).
But the fact no.3 shows nothing means a major loss of air. So I would first check the plug thread. Its possible its been threaded. You can helicoil it, but thats big,.
It could be blowing past the rings, but the oil usually gives a reading if this is the case.
So I suspect you have a hole.

adithorp - 28/8/12 at 07:30 PM

Hard to say with no's 1,2+4. Did you have the throttle wide open as not doing that could give those readings. Otherwise could be poor seals on the valve seats or poor piston rings.
No3 is fooked! Either holed piston or burnt out valve (usually exhaust). Slight chance of a badly cracked head. If it's not likely to be gasket with a zero reading. Id it;s the valve you'll feel very strong pressure pulses from the exhaust if you hold your hand by it. If its the piston then the pulses will be evident holding your hand over the oil filler. If it's a (big) crack then you won't know 'till you get the head off.

ReMan - 28/8/12 at 07:50 PM

quote:
Originally posted by balidey
I wouldn't worry too much about the actual figure, that fact 3 of them are close sounds OK (within reason, I am sure some people will disagree).
But the fact no.3 shows nothing means a major loss of air. So I would first check the plug thread. Its possible its been threaded. You can helicoil it, but thats big,.
It could be blowing past the rings, but the oil usually gives a reading if this is the case.
So I suspect you have a hole.


I agree
Dont worry about the figures but you def have an issue on 3
Could be a holed piston broken con rod stuck or burnt valve though I'd suspect stuck with a 0 reading thats bad
What engine is it?
What brought you to be checking these figures at all?
Did it break on you or was it bought like this etc etc?

kp - 28/8/12 at 09:08 PM

quote:
Originally posted by ReMan

What engine is it?
What brought you to be checking these figures at all?
Did it break on you or was it bought like this etc etc?


ReMan,

it's a 1.6 sohc pre-unleaded (JA engine code). Block is marked '165'. It came out of a 1989 sierra which was on the way to the scrappers, I don't know why it was being scrapped, but it was running (just about).

Here in Ireland, they were introducing a new super strict (impossible) IVA system back in May, so I rushed to get the locost 'running' and registered before that deadline. I was short of time so I just dropped the pinto in without doing any work to it. The vehicle registration people didn't care about the condition of the engine as long as I could get an engineer to sign off that it was running and 'roadworthy'.

So, the car is registered & running, but the engine sounds rough, takes ages to start, and is low on power. There is also an occasional clicking noise, sounds like a piece of metal being thrown against the rocker cover. But start quickly when warn and doesn't seem to be smoking too much.

[Edited on 28/8/12 by kp]

kp - 28/8/12 at 09:10 PM

quote:
Originally posted by jacko
Before you remove the head are the valve Clarence's set right on no 3 not to tight .
After that its head off and check the valve are ok you can do a quick check by turning the head up side down and putting petrol in the head to see if the valves are ok or leak [ over night ]
After that its piston rings or even a re-bore


That was likely to be tomorrow's question "how do I know if the valves are leaking?"

Thanks

maccmike - 28/8/12 at 09:36 PM

head off and upside down and fill with fuel.

adithorp - 28/8/12 at 10:03 PM

With zero pressure on that cylinder I suspect it'll be obvious what the problem is once the head is off. My money is on a valve looking like a mouse has eaten a chunk out of it.

maccmike - 28/8/12 at 10:04 PM

the mouse might have nicked the entire valve with that reading

craig1410 - 28/8/12 at 10:41 PM

I don't think you will need petrol to find the leaky valve...

Either a holed piston or a chunk missing from the valve or possibly a bent valve stem causing it to stick open. I don't think even MISSING piston rings would leak that much air.

Take the head off and have a look and don't forget to let us know what you find...

chillis - 29/8/12 at 09:16 AM

To have no compression at all suggests a massive failure.

Possibilities are: Valves failing to open - possible but unlikey, Valves stuck partly open/dropped, quite likely, hole in piston also quite likely. Poor plug threads and head gasket failures are likely to cause very low rather than no compression or the gauge needle dropping quickly to zero. Either way it sounds as though you have a significant problem.

omega 24 v6 - 29/8/12 at 11:17 AM

Plug out of cyl 3 and lower in and led ( or small bulb with wirng soldered to it ) connect to battery to light it up, look through the plug hole whilst moving the crank by hand and you should see any piston damage.

As for leaky valves the you get a leakdown tester ( made my own from an old sparks plug ).

Does sound like you have big problems though on cyl3. You don't HAVE to take the head off to find them BUT 99% sure you'll need to have it off to sort the problem out.

kp - 29/8/12 at 01:55 PM

Thanks everyone for all the advise and input.

adithorp said;

quote:

With zero pressure on that cylinder I suspect it'll be obvious what the problem is once the head is off. My money is on a valve looking like a mouse has eaten a chunk out of it.


adithorp was spot-on, it appears a mouse did take a bite out of the exhaust valve. its quite a smallish hole, so I am surprised that there was no pressure at all.

[img]http://www.flickr.com/photos/kenpower/7887292826/[/img]

Anyway, it obviously needs changing. Apart from a valve, what other gubbins are needed when replacing a valve and can I do it without special tools?

Aside from that, everything else 'looks' OK. I did notice that cyl 3 & 4 combustion chambers looked a bit oilier than 1&2.

[img]http://www.flickr.com/photos/kenpower/7887293662/[/img]

Now that the head is off what other jobs are worthwhile doing???

[Edited on 29/8/12 by kp]

[Edited on 29/8/12 by kp]

rusty nuts - 29/8/12 at 06:58 PM

It helps to have a valve spring compressor , you will need at least a valve lapping tool and some lapping paste .You may find that the valve seats need recutting once the head is stripped any decent engine reconditioneers will be able to do them for you. Once the valves are lapped in and the head reassembled it helps to have a cranked spanner to adjust the valve clearances but if you adjust them before refitting the inlet manifold you can get away without one. You will need a torque wrench and possibly a splined bit to fit the head bolts depending on which ones you have