George---Yes, it's strange that nothing was found in the head gasket area, when
the cylinder pressure on adjacent cylinders were low. But that seems to be in
the past??
Best now to go back over your work. Check the lash, and look for a broken
(outer) valve spring.
You can check your fuel pump volume and pressure by following the Bentley page
on this. Clogged fuel filters can be the culprit for engine hesitation, at
speed. (This usually starts off as a drop in power, then the misfire, as one
carb float bowl can run out before the other)
All said, it's probably the old Pertronix that's the bad guy. A check here
would be to pull of any one plug wire at the sparkplug and hold it close to
ground. Run the engine at the "misfire speed". The spark jump should be
regular. I'd do this easy test on some different plug wires, just to be sure.
Go from there...
Dick
-----Original Message-----
From: George Loriot
Sent: Wednesday, September 3, 2008 9:42 AM
To: 6pack
Subject: [6pack] pertronix?
Hi Listers
I have a 76 tr6 with pertronix ignition and I suspect the pertronix is sudenly
giving me trouble. I just did some head work on it, since it began running
rough and a compression test showed 2 adjacent cylinders with very low (15
psi) cranking pressure. I thought it was the gasket between the cylinders,
but it wasn't obvious that the head gasket was blown after i took it apart.
So anyhow, I had the head milled to about 8.3 c/r (3.495 head thickness and
had the valves and seats ground even though they looked good. The machinist
did a 3-angle valve job while he was at it. Valve guides were nice and snug.
Is this the beginning of shipwright's disease?
So I reassembled it, following torque specs and torque order in Bentley, got
150 psi on all cylinders, and it started right up. Nice boost in power (thanks
to all who suggested the milling) and ran better than ever. For a short time.
Then, at one run up to 3000 rpm (light load) it started to miss badly. Kept
missing, when the engine is warmed up. And the boost in power seems to be
lost. Checked the valve lash (when cold) and it seemed fine. Timing is 10
deg BTDC at idle (the vacuum retard is disconnected) and advances when revving
it up. But it misses under load, so I can't really check that the pertronix
is still working then. Has anyone had something like this happen with
pertronix? Suddenly fails when the engine heats up?
Gas feed could be the problem, I guess. The fuel pump seems to be working, I
replaced it a couple of years ago. Does anyone know how to test it? Maybe I
should recheck the vavle lash tomorrow, just to be sure.
Any help from the wisdom of the list would be greatlyu appreciated.
George Loriot
1976 TR6
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