Head gasket question.

[Nelson]

Thanks to all for the good advice.

I sent away the head to have it re-surfaced again as a precaution.? And have now refitted it with a new gasket this weekend.? She's now running sweet as a nut again, purring away on all six, with more than a subtle difference in power.? :D

I have also worked out the cause of the original problem.? It seems that the head gasket fitted during the professinal rebuild although very similar, was not the correct one for the engine.? On closer inspection after posting my original question I noticed that the crush area around each cylinder in the gasket overlapped the edge in the area around the exhaust valves on each cylinder (I.e Was never actually crushed between the head and the block because it overlaped into the combustion area).? This corresponds to the points where the gasket blew.
The new gasket is basically symetrical in the valve area, where as the gasket that blew was smaller around the exhaust valve area.? Once you realise, this is actually visible in the picture I posted previously.
Anyway, something for others to be wary of in the future.

Cheers, Nelson.

[plym_46]

It's not unusual for head gaskets to blow out between the siamessed cylinders.?But your went between the other pairs where the material is thicker, which is different. I suspect you engine man likely did not follow the proper procedure and sequence for torquing the head during assembly,

The head bolts (or studs and nuts if that is the case) needs to be done in the factory sequence which circles out from the center to the ends of the head spreading the clamping forces.? Also the torquing should be done in stages; snug, 35 lb ft, 50 lb ft, and then to 65 or 70 (depending on spec).? Then the head must be retorqued back to final torque folowing the sequence, after it has had a heat cycle.

One thing your post did not mention was whether the head and block were checked to assure they were true.  While the head is off you should check both for a true flat and un warped condition.  If any warpage is present the head needs to be milled to assure a true flant and square surface.  A little more compression doesn't hurt either.  Infact milling the head is the least wxpensive modification you can do to pep up the engine.  When I had my engine done, I had .010 taken off the block, and .040 off the head.  My CR is now about 8.0 to 1, (no head gasket problems in 8k miles.

Also the gasket should be installed dry, although some report good results by putting a light coating of general purpos lubrication grease on the gasket ot block contact side.

[Pandanom]

The head should have been retorqued after the first good run. If it was not, that might account for it blowing between the cylinders like that or if it was assembled dirty. Look closely at the gasket for marks left by grit or dirt. If none of that caused it I would guess a bad gasket. I have a '37 also and have never seen that problem. How tight were the nuts when you took it apart? Are all the studs in good shape? My engine man tells me a washer under the nuts results in better torque.

good luck

[Nelson]

Having noticed a distinct lack of performance and difficult starting on my '37 recently, I did a compression check to find that 2,3,4 & 5 were only 30lbs, with 1 & 6 being 90.
This engine has done 1200 miles since a very expensive professional rebuild. (It was supposed to be problem free for the next 30 years or so.)? The block was re-sleeved, head and crank were crack tested and re-ground, manifolds and conrods were reused, but everything else was replaced with NOS.
Suspecting a blown head gasket, I reluctantly opened it up to take a peek inside.

Anyone seen this before.?(Head gasket is still attached to the head, the gap is greater than 1/8th of an inch ) Was this an installation problem, a faulty gasket, or something else?

Cheers, Nelson.