Paul Mitchell wrote:
>Listers,
>
>My mechanic has been trying and failing to fix a persistent
>mis/back-fire on my TR6. Have changed or fixed everything he can think
>of, he reckons that it may be a cracked valve seat. The car pops and
>spits a few times when it's cold, then idles unevenly, and no. 2
>cylinder is apparently cooler than the others. Other than that it seems
>to be fine. Does his diagnosis sound reasonable?
>
>If it does sound fair, then what is involved in fixing it, given that
>while I've got the head off, I might as well prepare for unleaded fuel?
>
Since these heads had the seats ground directly into the head (there
were no inserts from the factory as far as I know), a crack in the seat
means a crack in the head--unless inserts had been installed in a
previous reconditioning. If a seat problem is bad enough to cause
driveability problems, a compression check (or, preferably, a leak-down
test) should show leakage. If it's just a burned valve and/or worn-out
seat, then you might consider having hardened seats installed in
preparation for unleaded fuel. It's probably only necessary on the
exhaust seats, and, given the width of hardened seats, it's not the
easiest thing for a shop to do to replace intake and exhaust, since it
probably would mean that the replacement seats have to be siamesed to
fit (depending, of course, on availability of seats in your area).
The other very obvious thing to examine is flow out of the #2 injector.
If it's partially plugged with crud, it can cause the same symptoms. A
compression check should answer that question. If the compression is
good, and the spark is good and the spark plug is good, you might
consider having the flow to that injector checked and flow through the
injector tested.
Cheers.
--
Michael D. Porter
Roswell, NM
Never let anyone drive you crazy when you know it's within walking distance....
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