Bill,
Never happened to me on a British push rod engine, but I would rationalize
your failure as one of the following.... as your push rod was not bent and the
cup/nothing was broken - I am assuming standard lifter and rocker surfaces and
profiles:
1. The valve stuck open for enough time for the push rod to be floating and
therefore side step the tapet
2. The aggressive ? cam profile you are using allowed the inertia of the rod
and valve train to not immediate follow the profile - pretty unlikely
3. The push rod temporarily bent under stress at right rpm due to a natural
frequency standing wave being set up in the rod but did not break - long
enough to pop out.
I would say that 1 is the most likely.
Robert N. Blair 65 Yellow BJ8 rnbmail@yahoo.com
--- On Tue, 10/14/08, WILLIAM B LAWRENCE <ynotink@msn.com> wrote:
> From: WILLIAM B LAWRENCE <ynotink@msn.com>
> Subject: [Healeys] FW: Things that make you go Hmm!
> To: healeys@autox.team.net
> Date: Tuesday, October 14, 2008, 4:46 PM
> ----------------------------------------
> > From: ynotink@msn.com
> > To: healey-bounces@autox.team.net
> > Subject: Things that make you go Hmm!
> > Date: Tue, 14 Oct 2008 23:25:43 +0000
> >
> >
> > On the way to the parts store in my BN1 yesterday I
> had a sudden failure
> complete with popping sounds and power loss and hissing
> noises. I thought I
> had blown another head gasket, but unable to reach my wife
> to bring a tow
> vehicle I limped home.
> >
> > I started to disassemble in preparation for repairing
> the gasket, the head
> and block surfaces if needed etc. but I only got as far as
> the valve cover
> when I discovered the problem. The pushrod on the #3
> exhaust valve had become
> disengaged from the lifter and rocker.
> >
> > I pulled the rocker shaft and retrieved the pushrod to
> discover that it was
> perfectly straight and undamaged. When i reassembled the
> rocker shaft and
> checked valve clearances the setting was correct. (I run a
> 3/4 race Isky cam
> and the recommended valve clearance is 0.018"). I ran
> the other valves and
> found no discrepancies. After reassembly she started and
> ran with no problem.
> I was not revving the engine very high and 4,000 RPM is
> about as tight as I
> wrap it.
> >
> > Despite the noise and the terrible miss there was no
> harm done and the
> repair was pretty simple, but I would like to avoid this in
> the future.
> >
> > Has anyone had this experience? Are there any ideas as
> to what would cause
> this to happen? Is 0.018" enough slack to allow the
> pushrod to jump out of its
> position? I know that some people use bucket lifters that
> might have helped
> avoid this. What lifters and pushrods do they use?
> >
> >
> > Flummoxed!
> >
> >
> > Bill Lawrence
> > Albuquerque, NM
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