Hi all Perhaps the collective wisdom of this group can help cast a light on my missing cylinder. Car is a 1980 MGBGT, cylinder pressures are 170, 175, 175, 180, plugs, points, condenser, rotor arm, cap and leads all new. No obvious fouling on any of the plugs, points at 15 thou and clean. She runs fine for the first run after cleaning / setting gaps, then next time you start up - only three pots firing - HELP.
if you are cleaning the plugs with a wire brush, then that may be the fault, using a wire brush on plugs leaves traces of metal in the porcelain insulator, which then tracks really easily.
Don't discount new components being faulty, especially cap and arm. and leads
is the coil correct polarity.
do the points open to an equal gap on each lobe
are there any air leaks on the manifold or even a faulty servo (if you have one)
First thing though is new good quality plugs and don't touch them with a wire brush. If you ever have plugs that look as though they need cleaning then there is some serious fault. If wet, then dry them with a flame. If lots of deposits and you can't rebuild the engine then get a sand blaster for them.
mrcheerful
Is it always the same cylinder that doesn't work? And what does the plug look like that hasn't fired?
It is not unheard of for new products to be defective. So if it is always the same cylinder that doesn't fire, try swapping the plug and lead with another. If the problem moves, then you need to consider that either the plug or lead is defective. Try swapping the plug with another and see if the problem moves again.
If the problem doesn't move when you swap plug and lead, then you are looking at either the distributor cap tracking (not very likely) or something defective in the failing cylinder. Is oil weeping down the valve guide and fouling the plug, for instance.
Usually this sort of problem is tracked down by elimination of all the things it isn't, until you are left with the one thing that it is.
Jim
Sticking valve?
Ron Robinson
In the Triumph world there have been a lot of crap re-manufactured rotor arms, we recently suffered from one, unfortunately we were on a rally when the ignition died, in the middle of no-where at 2:00 am - the spare was as crap as the original but luckily we had a third NOS one, and all was well. Check your components one by one :-)
Thanks to all who gave suggestions, found the problem in the end, the carbs were wildly unbalanced and full of c**p. Since stripping and cleaning them and setting them up properly the car goes like a train, on all four pots, be interesting to see the effect on fuel consumption.
Thanks again for the help.
Never seen such high compression pressure on a B series engine ! -- I would have expected the dry compression pressures to have been about
150 to 160 psi on engine in really good health.The most likely cause is a broken oil control ring or a problem with the valve guide & seals but it could also be caused by a couple of other simple things.
(1) Check the carb nearest the cylinder float chamber isn't flooding or the cjke sticking on, and remove the plug on the affected cylinder and try determine if it is oil or petrol fouling the plugs. (2) After fitting new points check the points gap on each of the four lobes of distributer cam in turn again after the engine has been running for twenty minutes with new points. (3) check the inlet manifold is not drawing air at the gaskets and also at the core plugs at each end. also if fitted check the servo and anti-ruun on vavle for vacumn leaks.
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