Dear list,
I promised to post my findings on the head gasket experiment.
A couple of weeks back I was bemoaning the fact that I had another blown
head gasket on this engine. It was the second blown gasket since I've had
the engine (1994), but the first blown gasket since a recent valve job (last
5K miles).
The unit is a 1589 bored + .060"; ported and polished mkII head that has
been over-milled by a succession of unknown owners; 270 degree cam; stellite
valves; and flat-top pistons. Performance is fairly respectable, but the
high compression caused run-on, and presumably, blown head gaskets. This
time I cc'd the head and found the CR to be about 13.5 to 1. A little
excessive for the local 93 octane.
When I pulled the head and de-coked it all appeared normal. I did not remove
the valves.
I had decided to try doubling the head gasket in an effort to lower the
compression, but keep the easy breathing features of the ported head.
Several of you advised me to try the fibre-type Federal-Mogul Payen gaskets
instead of the copper gaskets I had been running. The gaskets are very
nicely made and are chunky at .050" prior to installation. They have a red
bulgy process running the length of the gasket on the sparkplug side where
John Twist suggests laying in a piece of thin copper wire to help effect a
seal on the B-series engines. I guess they engineered this bulgy line in to
do just that. I used two MGB gaskets and replaced all of the head studs and
nuts, as the old ones had been stretched a few times.
Upon reassembly, it started right up and ran nicely for about ten minutes. I
let it get fully warm and when I shut it down, there was no run-on as had
always been the case before. Later, when I started it up again, it dropped a
cylinder and would barely run. Uh oh, I assumed I had wasted two more head
gaskets. A compression check revealed:
No. 1: 130 psi
No. 2: 0 psi
No. 3: 135 psi
No. 4: 135 psi
Number two seemed a little low... I assumed a stuck valve. Sure enough, when
I got the rocker cover off, the number 2 exhaust valve spring was compressed
and I could measure the tappet clearance with a dime... turned on edge.
Sigh, this was unexpected. I wonder if I've bent a valve? Well, I'm not
messing with it anymore tonight. I'll pull the head again and see about
replacing the valve. Any suggestions or words of encouragement will be
appreciated.
I think the jury is still out on the double-head gasket business. I wanted
to run it a thousand miles or so before horning in, but this new wrinkle has
de-railed that for awhile.
Happy holidays to my fellow Americans. I hope you fellers across the pond
aren't still sore about that tea-in-the-harbor business.
Regards,
David F. Darby
Ozark Uplift, USA
http://www.mgbexperience.com/mgz
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