First Generation Firebird-L Mailing List
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The engine probably was rebuilt by someone with a rudimentary knowledge of
what they were doing. We have all been there. The nut and 'half-moon'
under it that goes with each rocker arm should always stay with that rocker
arm that they started with. If someone rebuilt it, they could have mixed
them and with each part having different wear patterns, there will be a
stress that would be harmful to the rocker arms. If they grabbed something
off of the bench that looked the same, but was for another GM or a Ford, the
'half-moon' might have been the wrong size and this would cause the stress
to break the rocker arm, also.
Over-rev in my experience has caused bent pushrods, bent valves and broken
rods or pistons or blocks, but could cause damage to a rocker arm, I
suppose.
A different cam with too much lift or a larger than stock base circle and
having the lifters not adjusted correctly would cause the bent valves, bent
pushrods and broken springs, and again, could possibly cause a broken rocker
arm (poor pistons).
A valve spring that was too weak for the lift would cause valve float that
would be similar to all of the above problems, also.
The fix for the most likely problem would be to replace all rocker arms and
hardware to new or switch to a roller tip with new hardware. I run a full
roller valvetrain 400, but the taller valve covers are rather much a pain.
Another problem is the engine could have several collapsed lifters or wiped
lobes that resulted in little or no oiling to the rocker arms. This in
itself could cause the type of heat and stress to do the damage you wrote
about.
Since you are going to be this far into valve train damage checking, you
might want to pull the intake off and check for collapsed or broken lifters
and look at the lobes to see if they are all still in equal lift condition.
With something that was in this much of a bind, the likelihood of lobes
being wiped flat and lifters with pieces missing or broken is pretty good.
If it was driven very far with wiped cam lobes, the steel off of the cam
floating around in the oiling system would leave the engine needing a
complete rebuild with a bore job, valve job, crank turning, all new pistons,
all new bearings, a new oil pump, etc...
What broke was not a common problem. Look very closely and expect the worst
scenario if you are buying. Anything that is not wrong is a bonus.
Rusty Allison
----- Original Message -----
From: <[EMAIL PROTECTED]>
a friend has a 400 motor that he is thinking about selling,runs strong. I
pulled the valve covers off just to check condition and there are several of
the pieces on top of the valves-retainers?? the ones that look like upside
down cups? that are cracking around the edges,one had cracked all the way
and slid down to the base of the springs..what causes this?weak springs,over
size cam,over revving? is it serious? this motor was supposed to have been
rebuilt at one time..thanks,Larry
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