Mike:
A distinct possibility is that you have the wrong valve springs or
valves in your rebuild. If the valve is too short or the spring is incorrect,
the springs can stack solid at maximum lift and then something most definitely
will break! In this scenario, the rockers are not bad, they are being
asked to do the impossible, and they give up after a while.
Make sure that you can slip a 0.010" feeler gauge between each and
every coil on your valve springs on both the intake and exhaust valves when
they are at maximum lift.
Another less likely possibility is that the valves are hitting the
pistons near TDC due to a cam phasing issue, but you would probably have
noticed an unusual idle and other symptoms immediately the first time you drove
the car if the cam was mis-phased enough to cause the valves and pistons to
touch.
I would expect the piston to break long before the rocker did, but then it's
British, so you can't be sure =;-)
Cheers,
Vance
-----Original Message-----
From: YeOldEd@aol.com [mailto:YeOldEd@aol.com]
Sent: Thursday, August 28, 2003 2:46 PM
To: 6pack@autox.team.net
Subject: Sheared Rocker Arm (again)
Only 1000 miles on the engine since overhaul, and I just sheared my second
rocker. (Not in the same position). I don't much believe in coincidences, and I
haven't been over 3000 rpm yet. I know it's an easy fix, but I'm nervous of
going more than 10 miles away from my garage! This is on an all-stock 1972, and
oiling to the rockers appears to be OK. The affected valve moves freely in the
guide. The pushrod looks straight to me.
What do you guys think. Just lousy luck, or do I have a badly cast set of
rockers? In case I decide to change them all, who makes the best quality engine
parts?
I'd appreciate other listers' experiences in this area.
Thanks.
Mike N
CC75088L
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