James W. Dunn wrote:
>
> Hello,
>
> I have a problem wtih my 52 MGTD with the spark plugs
> "fouling out". I can't seem to get more than 80 miles on a new
> set of plugs. When i remove the plugs they are coated with a fluffy
> black coating, so I put in a new set and the car runs great for
> another 80 miles or so and then they have to be changed again,
> The engine was overhauled about a year and a half ago with
> many new parts. The car has just been tuned including points,
> condenser, rotor and dist cap, also the valves were adjusted, the
> timeing set and the carbs adjusted. I checked the compression
> and all the cylinders were within normal limits for this engine. The
> engine doesn't seem to use much oil and I haven't noticed any black
> smoke coming for the exhasut pipe. I use champion L82C spark
> plugs set at .025 and even tried .035 with same results.
> Any help greatly appreciated as I'm tired of changing sparks plugs.
>
> Thanks,
> Jim Dunn
> 52 MGTD
> Birmingham, Alabama
Jim,
Although you said the carbs were tuned, I would expect you are dealing
with an overly rich mixture, or incomplete combustion. Regarding the
rich mixture question: in the rebuild/tuneup process, were the carb
jets and needles replaced? I am going to defer to the TD operators
about the heat range of your spark plug.
As far as incomplete combustion goes, are you using the correct "reach"
plug for your head? 3/4 inch or 1/2? And is it correct for your
particular head? There were two different designs of cylinder heads
used in the TD, and the casting change caused a change in spark plug
reach. I'm going to cite Chip Old on this matter: "The simplest way
(to tell which one you've got), although I'm not sure it is foolproof,
is to look for the number which is cast into the top surface of the
cylinder head at the front right corner. All XPAG heads I have seen or
heard about which bear the number 22592 are early heads, which
...require 1/2 in reach plugs. The later heads bear several different
numbers, but as far as I have been able to determine any head showing
any number other than 22592 requires 3/4 in reach plugs." The
"foolproof" way to tell requires the head be removed. Again citing
Olds, "Check the water holes on the head which conduct coolant from the
engine block to the head. If they are oblong (banana-shaped), then you
have an early head. If round, the head is a late one."
Here's why I went through this dialogue. Chip Olds explains, "If a 1/2
in plug is used in a head designed for 3/4 in plugs, the engine will run
but the electrodes of the plug will be shrouded by the unfilled part of
the spark plug hole and will foul rapidly". Hoo boy - does this match
your symptoms, or what! Chip goes on to explain the often dire
consequences of using the longer reach plug in the older head. You
don't want to do that.
Sorry about the length, and I hope this is of some help.
--
*Bill Schooler *Check the MGCC Wash DC Centre Web Page
*Woodbridge, VA *http://members.aol.com/mgccwdcc/
*schooler@erols.com *Editor of The Spark
*69 B/GT, 53 TD *Web Page Coordinator
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