[6pack] Carbon on top of pistons - engine experts please help!

[Sally or Dick Taylor]

Andy--- If removing the external oil feed line to the rockers reduced
the oil consumption, then oil is, or was going down the valve guides.
You didn't mention if these were renewed when the rest of the engine was
overhauled in '05. If not, then this could be in order. While the head
is off, disconnect a couple of the valves and see if you can move the
stems from side to side. I would compare the valves where the deposit
was heaviest, to the piston where it is the lightest, to see if there's
a difference in looseness.
 There is data on the amount as shown in the Bentley Manual. (I think
it's .020 max.)

It is  not  easy to clean off the carbon deposits that have formed on
the piston tops. You don't want the hard carbon from flying into places
where it could lodge and later harm a running engine. Obviously it's
better to remove the pistons for this chore.  (This is what I did and
used a hand drill motor and a three inch brass rotary brush)

I have tried different methods of softening and soaking this carbon with
little success. (Dams of lacquer thinner, gasket remover, etc) Wooden
spatulas were useless.

I don't know if removing this carbon will stop the run-on you are
experiencing. Having a working anti run-on valve, as in the later TRs,
is the best solution. Short of that, keep the engine idle speed as low
as possible.

Dick

 From: apackard68 at comcast.net

I had engine run-on issues prior to my restoration project, so while the
engine was on the stand, I pulled the head to look for carbon deposits
on top of the pistons. I found significant deposits on five of the six.
I used to run an external oil feed but stopped after going through oil
at a fast rate (ring problem?). When I removed the oil feed, oil
consumption was greatly reduced but my run on problem was present. 

What remedy do I have available to a) clean the pistons and b) prevent
the problem from happening again. I'm assuming that if my engine is put
together and broken in correctly, the external oil feed should not
contribute to additional oil consumption. BTW, the engine was rebuilt in
late 2005 with new pistons, rings, bearings, etc for .030 over bore.
Thanks in advance for advice you can share. 
Andy