----- Original Message -----
From: "T.R. Scratchings" <wob@dandrade.freeserve.co.uk>
To: "Richard Taylor" <tarch@bellsouth.net>
Sent: Monday, September 15, 2003 4:10 PM
Subject: Re: Barking Heads
> Be sure when you replace the guides to ream and then hone them to size.
Too
> many heads I see only get the latter,
> so the valve can be waggled in the guide convincingly, but of course
there's
> a tight spot where the guide enters the head.
> A 5/16" tapered hand reamer and corresponding Flex-hone don't cost much.
> Jon Wood
> ----- Original Message -----
> From: "Richard Taylor" <tarch@bellsouth.net>
> To: <fot@autox.team.net>
> Sent: Monday, September 15, 2003 3:04 PM
> Subject: Barking Heads
>
>
> > Group,
> >
> >
> >
> > Here's the next wrinkle in the old "barking carburetor" syndrome. The
> original
> > problem turned out to be that three exhaust push rods had off-set their
> > respective rocker arm sockets. I figured that I had over-revved the
> motor,
> > put them back in place and entered the HSR Historic Race at Road Atlanta
> last
> > weekend. During practice Saturday, my motor did the same thing, but this
> time
> > at a carefully monitored 5500 rpms.
> >
> >
> >
> > My friend, Neil Estes, and I pulled off the rocker arm rack and found
that
> all
> > four of the exhaust valves were sticking convincingly. We pulled the
head,
> > hand-drilled out the valve guides with a 5/8th drill bit, reinstalled
the
> > head, it ran fine and took second place in the race Sunday (as the lone
> TR-4
> > in a class of MGB's).
> >
> >
> >
> > At the Saturday night refreshment session, the collective wisdom was
that
> the
> > initial displacement of pushrods was caused by over-heating, not
> over-revving;
> > that the bronze guides had expanded within a steel head and deformed
> inwardly
> > against the valve stems and that this deformity remains after the head
has
> > cooled.
> >
> >
> >
> > The motor had 17 races on it when it first had this malady so too-tight
> > fitting valve guides is probably not an issue and, yes, I was having
> cooling
> > (over-heating) issues when the problem first occurred. I never
associated
> > that with sticking valves.
> >
> >
> >
> > What is the collective experience of the group with heat-expanded valve
> guides
> > which lose their memory when cooled. Quite frankly I am quite
comfortable
> > trusting my Saturday night drinking buddies' thesis, but a second
opinion
> > might help us all.
> >
> >
> >
> > Thanks,
> >
> >
> >
> > Richard Taylor
> >
> > TR-4
> >
> > Atlanta
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