On Mon, 5 May 2003, Keith Meinhold wrote:
> Pull the plugs out, remove the rocker cover and turn the engine over by
> hand, look at each of the springs to see if there is still a bit of space
> between the coils with each valve full open (down).
Use a feeler guage, there should be at least .040 between the coils with
the valve fully compressed. DON'T FORGET THAT STUFF GROWS A BIT WHEN IT
GETS HOT, so there may be no binding cold but binding when it gets hot. So
.040 cold might be considerably less than .040 when the motor is hot. I'm
not a metalurgist, but I do know that materials have a coefficient of
expansion and I also know that valve springs get fairly hot!
Note: checking the spring coils for binding is a real pain if you are
using dual springs because the problem could be the inner springs binding.
The only way to be sure is to check them with the motor apart. Sorry!
Well, you could use one of the valve spring compresser thingies designed
to be used on a complete engine (Swathmore has these on his web site
recently) to take the keepers off, remove the outer springs, crank the
motor through the entire range and measure each inner then pull those out
and measure the outers and then once you know you don't have binding with
the springs put it all back together and look elsewhere.
> Also did you check your valve clearance before starting the car? If it was
> too tight it could have easily been the cause of the backfiring and the
> broken rocker arms.
Valve clearances that are too tight (i.e. zero lash) cause burned valves
and valve recession.
It's pretty clear that the real problem here is that something is binding
or siezing when the motor gets hot. If the motor is bending pushrods and
breaking rockers, the problem is the valves siezing in the valve guides,
or the springs are binding. It might be an oiling problem (with the
rockers siezing on the shaft), but that's a real "long shot".
> Keith Meinhold
> 66 Marston Avenue
> San Francisco CA 94112
regards,
rml
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