Loss of compression

Herald

Hi there, just signed up to find out if someone can answer a puzzle with Z22SE engine.

I have a 2002 Vectra B 2.2 with 110k on the clock. 22 December started engine, ran for about 10 seconds and stopped. Tried to start, but engine sounded like it was just spinning. Local garage checked it and said there was no compression. I assumed timing chain could have broken so removed cam cover to check Timing chain intact and timing correct, checked by position of marked links as well as position of cams. This was late January. Rechecked compression on all 4 cylinders and confirmed no compression. Nothing appeared wrong though. Only answer was to remove head to look for problem. No damage to head gasket. Everything looked ok. Reground valves, but nothing much needed as all ok. Rebuilt head, back in engine with new gaskets, timing and balance chains, as engine was apart seemed daft not to replace. Couldn't see any evidence of wear on old chains though. Engine started and ran without problem. Got back on the road start May, took that long too find time to complete round other work and weather. All runs ok.

So the question is, I did nothing to fix problem, but it appears to have gone away. What caused the loss of compression, and therefore is it likely to recur?

Any clues

HarleyPete

I don't know about the Z22SE (the YH has a cam sensor so it won't run if the chain jumps I believe) but sounds like when you replaced the timing chains you re-timed the cams to the correct position. Might be that the timing chain slipped enough to keep valves open just at the wrong point causing loss of compression. That would be the only thing I could think of that would loose compression on all cylinders.

Dave_Gilbert

Cam chain could have stretched so the valves were open longer and at the wrong time, valve seats could have been slightly damaged n letting gasses escape.

It could be a combination of things.

Did you do a compression test after? if you have all good compression n new chains i wouldnt worry about it.

Herald

Thanks for replies.

I did check the old chain against the new and could not see any difference, either in length or bending sideways to look for wear in the links. From the shape of the cam lobs I wouldn't think the difference in angle would have any effect on compression at the point of firing. That's why I am puzzled. I did check that compression afterwards and that is ok, so as you say I shouldn't worry.

I though like to understand why something has happened and in this case can't see any reason.

I agree the main thing that can cause compression loss is the valves not closing. The only reason I can see for that is the hydraulic dampers got over long / pressurized, but why? And I would have thought after a few weeks they would recover, so compression would return which is didn't. So that doesn't seem logical.

HarleyPete

You wouldn't necessarily notice a stretched chain when laying one on top of the other especially with the length of the timing chain. If each individual link has say ¼ of a mm movement then over the length of the chain when tensioned it would make a difference. I've known a 510 bike chain to stretch 50mm or more over it's length when it's shot. I suppose it's only got to be out by a couple of degrees and the valves might not close completely. To be honest it's the only thing I can think of that would do that to all cylinders.

Dave_Gilbert

A chain on a bike how i was told if you push all the links together so its like 2 straight lines of chain next to each other and measure it. Then pull it as much as you can. The difference should be mm not cm.

but on a timing chain i wouldnt want much movement at all.

HarleyPete

Your right @[deleted] but I have seen them so stretched that they have been that much out. I agree though I wouldn't want that much movement on a timing chain as well.

Dave_Gilbert

Oh iv seen bike chains stupidly stretched. N clicking n bent the sprocket over like a fish hook n we still just turned the sprockets round and pulled the wheel back further hahhaa. Gotta bodge it to ride it as a kid

HarleyPete

Lol that's alright on a pushbike but I've seen it on pretty quick motorcycles as well. Not good when your doing 70 plus on the motorway.

Dave_Gilbert

I dint mean push bikes lol

motorbikes, iv been riding n bodging motorbikes since i was about 13 hahaha

HarleyPete

Lol I see, then you know what I mean then. That's the only thing I can think of that would cause a loss of compression and be sorted by lapping the valves with a new set of chains.

Herald

I find it hard to believe a stretched chain can have that effect, unless it is a lot longer and there is loads of slack. Remember the coloured links all lined up correctly with the marks on the cogs so nothing had moved..

The chain has 76 links, if you assume 0.25mm stretch per link that is 19mm longer. A hell of a lot
Laying the old chain round the camshaft cog it fits snugly, so there is no evidence of stretch. The teeth have not gone spiky as they do when they wear. My experience is with a pushbike. And there I have seen a stretched chain which rides up because it no longer fits correctly. I don't see that with the cam chain.
Using the coloured links as a reference there are 27 links between the camshaft (front of the engine) and the crankshaft. This is the critical part and therefore distance and will define the relationship between the inlet camshaft and crankshaft. If that was 7mm longer that is an additional link, not seen when wrapping the chain round the cam cog.
The gear on the camshaft has 46 teeth, therefore each tooth represents an angle of 7.8 degrees. So hypothetically if could be out my 8 degrees if there was an additional link.
I don't know the profile of the standard cam, but at compression the lobes are on the opposite side and there no evidence of a raised profile on the opposite within a range of 8 degrees.

Based on the above, which is extreme, I find it impossible to think a stretched chain would cause the problem. Therefore I remain puzzled.

evocarlos

the chain is just the media that turns the sprokets its relation ship the the correct timing locations change as time goes by
as the marks get further and further apart as the parts wear/strech
the only way to confirm timing its with a tdc tool and the cam locking tool as its a fixed point that's an interference fit with the cam sprokets bolted directly to the cams
ms paint handy work 🙂

there is a point when one of the cam is to far out and the engine won't make compression
can you remember what your cylinder pressures were book says 140-160 but its 200-210 🙂

HarleyPete

Can't fault your logic @[deleted]. I too am puzzled by the fact that, now you've done the head and chains the issue has gone away. I wonder if it was a combination of the two? The chain stretched enough and the valve seat just not seating enough to keep compression. It's the only thing I can think of that would go some way to explain the mystery. I can see where your coming from with the rotational variance but have to concede that I don't know enough about these engines to afford a better answer. Is 8° enough to cause a loss of compression or even say 4° maybe. Who knows?
I can see where @[deleted] is coming from too, if the sprockets are out in relations to themselves and the crank then that could well cause a loss of compression I suppose.

Herald

Hi Evocarlos Understand what you say and I didn't check with the correct tool. There were some dimensions I found somewhere on the web, but they were way out. When I say loss of compression I am being a little generous, there was no compression. Gauge did not register. I checked in another engine and it read as expected so the gauge wasn't at fault. From my analysis above I can't see there was enough stretch of the chain to end up with no compression on any cylinder.

HarleyPete

Well I suppose the more important thing to look at is that it's not an issue now. Whatever the cause was you've managed to sort it out and have a happy conclusion. You can over analyse things and never find the reason but drive yourself mad in the process. The definite and indefatigable thing is that it must have been related to either the head work, the change of chains or both from where I sit. As to whether it will manifest itself again, well that's an unknown quantity I suppose, lets hope that it's gone for another 100k (potential life of the new chains).