> I have a dilema and am hoping the wisdom of the list will come up with the
> answer. My 1969 MGB motor burned a hole in in the exaust valve of # 3
> cylinder back in December... After removing the head I
> discovered the exaust valve in # 3 cylinder burned trough.....AGAIN.....
Herw's some possibilities-
-Coincidence. 2 bad valves, or heads with bad valve seats.
-Poorly adjusted valve clearences. 14-15 Thousandths on MGB exhausts,
if memory serves.
-Worn rocker or shaft for that valve position, allowing the clearence
to change under operation.
For these 2, it would be the case of too little clearence not
allowing the valve to close all the way, which lets hot exhaust gas
blast past a small area, and torch it away.
-Air leak, causing #3 to run lean. This could be in the manifold,
gasket, carb, etc. (I think the dist vacumn line fitting is closest
to #3, if it were leaking, that would lean #3)
-Lean adjustment on rear carb.
Lean conditions can be checked with a colour-tune (see-through spark plug),
or by checking the coluor of the plugs in operation. (Standard manual
descriptions/pictures) Lean conditions result in a hotter burn, with
extra air to act as a cutting torch.
-Poor or blocked cooling passages in the block, allowing hotter temps
in that area, causing similar conditions to those above.
________
/___ _ \ Roger Garnett (Roger-Garnett@cornell.edu)
/| || \ \ Agricultural Economics | "The South Lansing Centre
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