Oh Wise Ones,
After becoming frustrated with a fouling spark plug, and with summer top
down driving coming up, I decided to fix the problem once and for all. So,
this morning off came the head of my restored TR4A with only 5000 miles on
it. I need your help in reading the tea leaves (carbonization).
Number 1 piston is the culprit. In the chamber there was plenty of
carbonization, but the top of the piston was very clean. I could still read
the etchings on top. The exhaust valve was dark brown, but the intake valve
was heavily carbonized, probably a 1/16 inch or more.
On Number 2, 3 and 4 it was exactly the opposite. The top of the pistons are
carbonized but the chambers are clean (relatively speaking). The intake
valves are dark gray, and the exhaust valves are light tan to almost white.
It was progressive, lighter the color of the exhaust valve the heavier the
carbonization on top of the piston.
>From the manifold side looking into the valves no 1 intake looks medium
gray, while the other intake valves have some "sludge" on them, especially
around the base. On the exhaust valves no 1 looks black while the others are
light gray.
A compression check before tear-down showed all four cylinders alike at
about 190 PSI. Putting a squirt of oil in during the test showed no
difference. I don't have the equipment to do a leak-down test. As you might
guess tuning the carbs is a nightmare, and cold starting is a pain. I'm
running a stock cam, Petronix ignition in a standard distributor, Lucas
Sport coil, and NGK BP6HS plugs on 91 octane. I've tried going to BP4HS on
no 1 without much better results. I've put a Gunson Colortune on all four
cylinders and the spark looks fine.
All of the cylinder liners look fine, and the cross hatching is still
evident. I pulled the lifters and the cam looks great.
Someone suggested that the oil sealing ring on no 1 piston might be bad.
But, before I take the next step and drop the sump I'd like to get some
feedback on what you think. Obviously the head goes into the shop on Monday.
John in San Diego
'67 TR4A IRS
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