CU engine - Mega low compression

[skred]

Hi folks. I did a compression test on my air cooled van earlier tonight and to my surprise my readings were :
Cyl 1 - 10 -15psi
Cyl 2 - 110 psi
Cyl 3 - 80 psi
Cyl 4 - 110 psi

The engine was cold and put a few drops of oil into cylinders 1 & 3 to see if they would increase but they didn't. which I think points to either valves or the head gasket? Is there any significance in 1 & 3 being opposite each other both having low compression?

Cylinder 1 looks to be in a bad way but if someone has had a similar thing before, where do I start with fixing/repairing? Does the engine have to be dropped if a valve is stuck?

[ajsimmo]

Engine out, tinware off, heads off, valves out, inspect, repair/replace as necessary. Also barrels off, check rings (as 1 is very low, a drop of oil in the bore shows up worn rings but not broken or missing ones!).

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[sarran1955]

Hello,

Does it start and run OK ..

Can you do an oil pressure test..

When were the valve clearances last checked..

I'm assuming it is all standard.

The bad news is that the motor will probably have to come out..

The good news is that if it is still running, then it can be overhauled with little stress..

Aircooled bliss..

Cordialement,

[skred]

Yup seems standard and the engine runs and idles away fine although it is massively down on power. I did wonder if the lack of use has caused a valve to stick so I was thinking about letting it run for while. Might this unstick a valve?

I will have a look at the valve clearances but I was obviously under the wrong impression that the hydraulic lifters meant the valves weren't adjustable.

Oil pressure test?

Looks like it's time to learn how to drop an engine!

[sarran1955]

Hello,

Yup seems standard and the engine runs and idles away fine although it is massively down on power. I did wonder if the lack of use has caused a valve to stick so I was thinking about letting it run for while. Might this unstick a valve?

No, but it won't do any harm to run the engine..it may help to reseat ( a bit) the valves..

I will have a look at the valve clearances but I was obviously under the wrong impression that the hydraulic lifters meant the valves weren't adjustable.

Learning curve ahead..

Oil pressure test?

Yup.. if your oil pressure is ok, then it will avoid splitting the crankcase..

Buy a gauge..

Do this:

https://www.youtube.com/watch?v=3nqUWst2XRo" onclick="window.open(this.href);return false;

Cordialement,

[skred]

Today I managed to get the head off but the cylinders were firmly attached so, taking it all off in a oner, i used the rubber mallet to break the seal but for reasons I still don't understand, the rubber mallet broke cylinder 1 barrel. D'oh! Hopefully, I can buy one cylinder rather than four? Any ideas?

Other than the newly created problem, I still have the issue of low compression and hopefully some of you guys might be able to see a problem with the head pics. There is quite a bit of hard carbon fouling around both heads (but evidently not creating an issue on cylinder 2) and the discolouration of the right hand valve on cylinder 1 - any indication here? The same valve stem is pretty badly fouled from the top of the head. The only other potential problem I see is I took the piston rings off and the gaps are quite significant - top ring gap 1.0mm and
lower ring > 0.7mm - hugely out is it not?

As always, I appreciate all your responses.

Heres some pics all:
Ring gaps -


Head condition



Uh, depressing

[skred]

I've removed both cylinder heads from the engine for valve work and I notice that they have metal ring head gaskets for each of the four cylinders. I thought this was just for watercooled engines, not the Aircooled one. When I removed the gaskets, 2 of them had impressions showing they were deformed, more oval than circular (you can see this about 40 degrees round the cylinder on the pic). Can anyone clarify if replacement gaskets should be fitted or whether I can just do away with them and lap the cylinder to head instead?




Last question, any checks I should do of the engine other than check end float when the block is stripped this far back?

[multisi]

You need the metal ring seals. New ones should be fitted.

[ajsimmo]

VW heads use the sealing rings. AMC heads omit the rings and lap in the barrels.

[skred]

Thanks. Heads have just come back from the shop (one exhaust valve, couple of guides, and a thread insert) so ring gaskets on order for refitment this week I hope. I've read a lot of threads on the merits on calculating compression ratios on a rebuild but as I'm just replacing like for like on what seems like a bog standard engine I'm not going to get involved in it.

[davidoft1]

Vw discontinued the head gaskets, no need to fit them

[ajsimmo]

Vw discontinued the head gaskets, no need to fit them

I haven't seen that service bulletin. Do you have a reference?

Afaik, If you have VW heads, fit the sealing rings. If you have AMC heads, no rings needed, just lap the barrels into the heads.