Compression test results after cambelt failure

[chris1roll]

Wondering what the opinions are on this?

Car is a 1989 Gplate Volvo 744 with the 2 litre B200E engine with 82k on it.
The 15 year old cambelt stripped 7 of its teeth on the way home from buying it, with my long suffering wife driving it behind me in the C70.
The crank did [at least] 320 degrees on its own, ending up roughly 40 degrees behind the crank, and the engine kept running - just, with some horrible pinking and detonation noises.
I think I could hear some clinking when restarting it to move it somewhere safer (it was not in a nice poisition, weighing up possible more engine damage v possible written off car I went with the former and moved it)

Opinion oddly divided on if the engine is interference - some people have had bent valves, others reckon they have tested it with the belt off and could spin the crank freely.

I retimed it and put a new belt on to see, and the engine starts easily, runs on all four cylinders and revs up cleanly, however I think there is a metallic clink that wasn't there before.
I can't test drive it as it is now currently uninsured and I sent off the form for sorn (God knows why you can't do that online with the new keeper slip)

This morning I idled it up to operating temperature and did a compression test (twice, in fact). All plugs out, WOT, Battery on jump from my current daily so that wouldn't be a factor.

No1 - 170
No2 - 195
No3 - 155-170 (was inconsistent over a few attempts. I haven't tried the teaspoon of oil yet)
No4 - 195

Then I checked the valve clearances. sadly my smallest feeler gauge is 0.05...
Specs are 0.30-0.40 cold and 0.35-0.45 warm The engine had been off for probably 3 hours before I did this.

1E 0.35
1I 0.50

2E 0.40
2I 0.45

3E 0.35
3I 0.50

4E 0.35
4I 0.45

So 1 and 3 Inlet clearances are larger which corresponds to the cylinders with lower compression.

My thinking is that if a valve(s) is very slightly bent - just enough to lower compression but not affect idle, then it won't be seating properly, so will sit fractionally lower than before and the clearance between the shim and the cam will be larger. The largest clearances I have measured are on the inlet valves on cylinders 1 and 3 at 0.50mm which are the ones with the lower compression.
Not exactly conclusive though?

Removing/replacing the head to check is not a big job on these, I'd just rather be able to put the money the gasket set would cost towards the new rear lights and exhaust it needs. However what I don't want is for a slightly tweaked valve to work harden and drop off destroying the engine if a couple of new valves lapped in and a headgasket kit is needed.

Thanks.

[Smint]

Confess i thought all those B 20 engines were non interference, it was certainly the case with the 200 series.

[Boosted LS1]

I'd suggest you buy a leakdown tester and you'll need a compressor. That'll give you a proper diagnosis and may save you from lifting the head. It's a very useful tool to have.

[stevieturbo]

Likely worrying over nothing.

[E-bmw]

As above, a leak down test will help, as could another compression test.

Having said that, it sounds like you have been lucky/found that the engine isn't interference.

[chris1roll]

Thanks,
Yeah I probably am worrying over nothing.
I don't have a compressor, so I wouldn't be able to do a leakdown test without more investment.
Nobody I have spoken to has said 'ooh better get the head off' so I think I'm going to do the valve shims, and get it back on the road.

[TwinKam]

Personally, I would leave the shims for now, run it for 1,000 miles, and then check them again... adjusting as necessary.
If the valves have been 'kissed', they could equally straighten themselves out over that time, closing up your previously carefully set clearances...

[DVandrews]

TwinKam said:

Personally, I would leave the shims for now, run it for 1,000 miles, and then check them again... adjusting as necessary.
If the valves have been 'kissed', they could equally straighten themselves out over that time, closing up your previously carefully set clearances...

That’s possible, depending on how well the guides locate the valves, but each bending moment as the head hits the seat will fatigue the stress point created by the clobbering, one of the likely outcomes could be losing the head of the valve with predictable carnage, I would have a leakdown test unless you are certain the engine is non-interference.

Dave

[TwinKam]

DVandrews said:

TwinKam said:

Personally, I would leave the shims for now, run it for 1,000 miles, and then check them again... adjusting as necessary.
If the valves have been 'kissed', they could equally straighten themselves out over that time, closing up your previously carefully set clearances...

That’s possible, depending on how well the guides locate the valves, but each bending moment as the head hits the seat will fatigue the stress point created by the clobbering, one of the likely outcomes could be losing the head of the valve with predictable carnage, I would have a leakdown test unless you are certain the engine is non-interference.

Dave

Just to be clear, as the thing is running fine, and the valve clearances are only just out of spec, I don't think that there has been any 'clobbering' in this instance, and that any 'kissing' would have been of the near-miss, Hooray-Henry, mwah mwah dahling, variety!

[DVandrews]

For what it’s worth I dont think that there has been any contact either, but as a matter of principle to expect a bent valve to right itself with no commensurate risk is foolhardy. As it stands it’s just speculation either way, unless you know what the valve clearances were before the belt event you can’t be sure how much they have moved. I’ve seen too many engines wrecked through uninformed assumptions or carelessness.

Dave

[stevieturbo]

Oddly this list says interference. I had thought most of the Volvo's were not

http://yourcarangel.com/2014/07/interference-engin...

https://roadsumo.com/interference-engine-list/

https://www.volvoforums.org.uk/showthread.php?t=27...

https://www.volvoforums.org.uk/showthread.php?t=11...

[richhead]

if its running on all cylinders then unlikely to be a bent valve, stop worrying

[chris1roll]

Realised I never came back to this.

I Bought a cheap endoscope for £20 (that turned out to be surprisingly good) and poked into the cylinders. It had in fact hit all 4 exhaust valves.
After a bit more thinking I pulled the injectors (k-jet so direct into the head above the valves) and turned the engine over while videoing the valve stems.
None of them looked bent, so decided "she'll 'dog on' " completed a full service+new injector seals and just went for it.
Done about 750 miles in the six weeks since I got it back on the road with no problems.

Not many cars that can continue to run and drive with the cam 40 degrees out, hit 4 valves in the process, and survive!