Working out a head gasket failure

[Andy Bennett]

Thanks Jeff.
New head is on and settling before final torque up today. Hopefully will be all good for our local village show Saturday.

Andy

[Ruairidh Dunford]

I am sure you will have done this but it may be worth mentioning for others, whenever I fit a new head (particularly one that has been skimmed/ground quite a bit like yours), I sit it on the block without any gasket and lightly press down whilst turning the engine over on the handle.

This allows me to feel any lift, indicating a valve touching.

If the head does not move at all I know the clearance is good, that I can safely fit the head gasket and torque it down.

[Charles P]

Thanks Jeff.
New head is on and settling before final torque up today. Hopefully will be all good for our local village show Saturday.

Andy

And second and third “final” torquing down. 
It’s never fully torqued down until it stops tightening

[Andy Bennett]

Oh bugger, no I didn't do that R. I don't know why as I have seen others comment on it enough in relation to having blocks skimmed and adding spacers if required if pistons are too high but just didn't translate the same logic to the valves/head. I looked at the new one and thought about the depth, but why I didn't put it on the block and turn it over I don't know.
I guess there is nothing I can do now but turn it over by hand but guess I am not going to hear/feel anything and any problems will now show as bent valves and then compression variances/problems, bugger....

[Ruairidh Dunford]

You won't hear anything, but you will loose compression...

[Andy Bennett]

OK, I think I got away with it, assuming it doesn't change when hot.
Squirted a little oil down bores as were dry and of course previously wet so no lubrication present.
Turning over cold (with 3 tightenings of studs to 20lb since yesterday) as I am awaiting a new top hose hopefully arriving tomorrow before refilling coolant.
Compression across 1-4 130, 100, 110 and 120. Appreciating that whilst all over 100 there is a significant variation (noting cold). Repeated twice turning over for 15 seconds to give plenty of opportunity for any crunching.
When the head gasket blew I had 80 on 1 and 4 (engine still warm).
When I last tested (with same gauge) 3 years ago I had 85 to 95 across all.
As I said, more by luck than knowledge, I hope I have got away with it?
I will repeat all when I have run to hot but can the skimmed head really have improved compression that much, combined perhaps with a new gasket and better/flatter head to gasket joint as the numbers seem a little too good?

Andy

[Ruairidh Dunford]

Good news, your head looked to have had quite a but taken off it, let us know how it performs...

[Andy Bennett]

Well. I had a run around the block yesterday and all seemed OK.
We had a trip out today to the local village show. 12 miles each way. It's hillier than my test drive and with 2 of us plus lunch/stove/chairs etc we were fully loaded.
it is more downhill on the way and uphill on the home run. On the way home in particular she was a little rumbly under load (but fine on top speed, I didn 't push but 30 to 35 no problrems) and pinking under load (well that is what it sounded like to me, either that or an extremely loud tappet).

All I did was change the gasket and head, didn't touch the timing.
I will have a little play with timing to see if I can fix, but noting that on my cold tests the compression appeared c30% better than when last tested (c90 to c120) am I right in my understanding that in principle increasing the compression means that I need to retard the ingition a little to regain balance as this would work with my practical experience?
Also noting I am using a bosch distributor so no manual adjustment.

Thanks
Andy

[Reckless Rat]

Your two comments about it being "rumbly under load and pinking" tends to suggest that you need to back the timing off a bit. This is probably because the head has been shaved. I was amazed how much I had to back off the timing on mine when I fitted the HC head. The Bosch 009 dizzy also benefits from having the advance restricted. It's an easy fix.

[Andy Bennett]

Thanks Reckers am pleased to hear that my experience matches yours. I never like unexplained happenings as fixes can be equaly random and unexplained. Rain forecast for today but will adjust timing, retorque studs and find a more challenging loop to run (my wife has suggested I load up with sacks of hen food for added impact) and report back.