At 12:45 PM 11/13/98 +1000, Neil Cotty wrote:
>....
>Anyway I tried backing my ignition off to 14 degrees btdc. I still have
some pinging but it's significantly reduced - but 'oh my gosh' I no longer
appear to have 'flat spots' in the rev range, it's powering through the
trouble spot (1800-2900rpm) and singing above 4000.
Have you checked the cam profile? A member (maybe several) in our local
club has a hot cam in his 1800 engine, and it seems to like spark advance
in the range of 0 to 5 degrees BTDC with a strobe light. I think that
translates into a static timing of less than 0 BTDC, meaning something
slightly after TDC. If you have a non-standard cam profile, the timing
numbers in the book aren't much of a guide.
>....The compression in my cylinders ranges from 146-148 from 1-3 and it's
about 140 on #4. The HT lead on number 4 and the plug cover & plug appear
to be extremely hot (at idle & after driving) compared to the other three
cylinders.
Pretty good compression readings. You may have a loose connection causing
arcing inside the boot on #4 plug. You nay also have a bad wire. Check
the resistance of the plug wires with an ohm meter. Solid wires should
have zero resistance. Carbon wires should give about 6000 ohms per foot of
length.
>.... could it be something to do with the lower compression in that cylinder?
No.
>A valve problem?
Not likely, as the compression is good. Check the wire and the wire
terminal inside the boot.
There is just a remote chance that it may be a bad spark plug. Try
switching the spark plug with another cylinder and see if the heat problem
moves with the spark plug.
Also check to see if the head itself is getting especially hotter in the
area of the #4 spark plug. If the water jacket gets partially plugged with
rust or mineral deposits the lack of circulation at the back of the block
or head may cause a hot spot there.
Keep us posted,
Barney Gaylord
1958 MGA with an attitude
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