Hugh :
My guess would be worn intake valve guides instead, with the majority of
the oil going through #4. The pitting would be detonation under cruise
conditions, caused by the octane-lowering effect of the oil. The
increase in 'wet' compression is probably caused by the oil taking up
part of the combustion chamber, in effect temporarily increasing the
compression ratio. It's unusual for rings to wear that evenly, and even
ring/cylinder wear would not explain the increased oil in #4 and #6.
In any case, it's a lot easier to change the valve guides. You may even
be able to temporarily add valve stem seals without removing the head,
both as a band-aid and to verify the problem. You'll need an airline
and adapter to pressurize the cylinder and hold the valve up while you
remove the spring, install the seal, and replace the spring. I don't
know the sizes for a TR6 offhand, but I was able to buy 'teflon' type
seals over the counter at a local speed shop, given the guide od and the
stem od. About $1/each.
Randall
Hugh Fader wrote:
>
> Hello,
>
> I have just completed a compression test on my 72 TR6. The test was
> performed using a screw-in compression gage, with the engine hot, and with
> all plugs removed. Here is the data.
>
> Cylinder/Dry psi/Wet psi/Plug Condition
> 1/100/115/brown, dry
> 2/100/117/brown, dry
> 3/105/115/brown, dry
> 4/105/110/oily, pitted
> 5/107/113/brown, dry
> 6/101/110/brown, some oil
>
> The car burns oil. Smoke is blue in color. It seems to be worst at cold
> start and when accelerating or shifting. I have not been able to have
> someone observe engine braking yet. Starts easily and runs strong.
>
> My diagnosis is even wear of piston rings causing blowby. This is based on
> the even numbers and consistent increase in wet compression. I don't know
> what to make of the pitting on cylinder 4 plug. The previous owner had
> diagnosed valve guides, but I'm not sure how.
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