Corsa No Compression on 3

For 0 bar on cylinders 1 to 3....buy a new compression tester!

You will always get a reading, even with no rings at all (assuming the pistons are going up and down!) of at least acouple of bar. (30psi)

Tim..

I'd say the camshaft isn't turning.

maybe the crank has snapped?

The message from "Dave Plowman (News)" contains these words:

Not now he's taken the cylinder head off, no!

Let me guess. The cylinder that had compression is at the cambelt end of the engine and the other three had none. The camshaft has snapped between cylinders one and two.

check that all the pistons go up and down

All the pistons go up and down and the camshaft is not snapped. I tried the compression tester a couple of times on all cylinders and go the same readings

next step is to establish what is leaking. I would do this before removing the head using air pressure and finding where it blows out. As the head is off you will have to resort to older methods. pour some thin oil (like 3 in

1 for instance) around the edge of each piston, the oil should very slowly leak away, if it falls straight past the cylinders that had low compression, then you probably need to dismantle the bottom end and replace at least the rings (this is very possible if the engine has been severely overheated, but not really common. with the head on its side on the bench, pour petrol into each inlet port and see if it leaks straight into the combustion chamber, dampness appearing round the valve is normal, but a flow is not. Do the same for the exhaust valves. If all these tests are ok, then the head gasket was massively at fault or the head has severe cracks in the combustion chamber.

A thought, when you did the compression test, did you have the throttle wide open or shut?

mrcheerful

Are you sure the valves are ok, turn the head over an fill the combustion chamber with petrol, if any seeps past the valve into the exhaust and inlet chambers then you do probably have slightly bent valves or badly burned valve seats.

You could also set all pistons to the middle of their stroke and but some very thin oil in each cylinder to check if you have any rings installed.

You said at the start of this thread that you bought a faulty corsa, what was you told about the fault or history of the car.

One last thing, check your comp tester on another car, just to confirm its working ok and you have not diagnosed your car with a faulty tool.

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Thanks mrcheerful and Paul. I will give that a go. To answer your last question mrcheerful the throttle was shut. Paul I will try the compression tester on another car just to confirm. Also the history of the car is I bought it of ebay for not a great amount. The gentleman I bought the car of said it was running and he took it to a friends garage to have the scratches and blemishes removed. A little while later he got a call from the garage to say the car would not start. The bloke has 100% score on ebay and when I met him he appeared genuine so I have no reason to disbelieve him. He also said he replaced the timing belt. I believe that was before the problems started to happen. The head appaers to have been off before as on the camshaft housing the sealer was coming out around the edges. Also the was a stud and nut missing from cylinder head on the inlet manifold side. One thing I forgot to mention in the post the forth cylinder (the one that had compression) has a lot of carbon on the top of the piston and the cylinder head. Don't know if that means to much. Thank you to all that have posted your advice it is much appreciated.

Then the exercise was pointless. If air can't get into the cylinders how do you suppose they can generate any compression?

Even with the throttle 'shut', some air can be drawn past it, as cars can run at idle.

I did the test as per the Haynes manual and it didn't mention holding the throttle open. Can you then tell me how I got 13 bar on the forth with the throttle shut?

ROFLMAO. Are you telling me that when you close the throttle that it creates an airtight seal?

No more than I can tell you how you got nil on the other three. Nothing about your story makes any sense and if three cylinders really did have zero compression it would be glaringly obvious why.

Yes, you must fully open the throttle when testing compression. You may have got compression on one cylinder only due to an air leak on the that cylinder only (unlikely) or, more likely, the other three cylinders have bent valves.

trying to test compression with the throttle shut will give lower figures than with the throttle open (on a runable engine)

I suspect that your engine originally had a simple ignition fault or something like that, successive 'mechanics' have meddled and it is all a right mess.

Do the leakage test as outlined earlier, replace the bent valves (my best guess), reassemble properly, retime carefully, then check your compression, then find why it won't run.

Sealant between the cambox and the head is the correct method of sealing on these engines, the quantity sounds excessive though, you shouldn't normally notice the sealant until you dismantle the engine.

mrcheerful

Of course not or an engine wouldn't be able to idle but it reduces the compression gauge results by between a third and a half on an average engine which makes the test pointless.

Ok I see your point I should have had the throttle open. The ignition system was tested. All the spark plugs sparked and the timing is correct.I will do the tests to the pistons and cylider head as described earlier as it is a nice day today and will post the results.

Test complete oil went very slowley around the edge of each piston and no petrol leaked out the valves. The head gasket appears to be in pretty good nick. No odvious damage. There is a little rusting on one of the rings in it but only very small. Is it worth getting a head from a scrappy or replaceing the head gasket and bolts and re testing the compression? Thanks again for all the replys. I am a laptop / PC engineer by trade so if at any time I could return the favour by offering advise please ask.