At 08:43 AM 8/29/2000 -0700, Stuart MacMillan wrote:
>Wow, I've never seen anything like that either. I actually started out
with the stock pushrods I picked out at a junkyard (sorry, "recycler")
Oh-oh. I think you might start an entirely new thread with that mention.
Not that I'd even blink though. I've never changed a pushrod in my life
before this.
>and I had the same noise. I bought the Crane lifters from VB to see if
they would help, but there was no difference.
Change of pushrods and lifters, and you still have the same noise? For
that I had to go back to check your original post where you said:
> "On the newly rebuilt '68 vintage engine ...."
Now I might suspect lack of oiling on the top side. Oil for the rocker
shaft assembly comes up through the rear rocker shaft pedestal. The oil
gets there from the rear cam bearing. That rear cam bearing must have a
radial oil access hole aligned with a drilling above it in the engine block
in order to pass oil on up to the rocker shaft. I suppose you did have new
cam bearings installed? Also the correct pedestal with the oil passage
drilling must be installed at the rear of the rocker shaft assembly in
order to accept and pass oil coming up through the drilling in the head.
If any of these holes are not in place and properly aligned you get no oil
to the rocker shaft. Of course I could be all off track here, but it's
easy to check. Just remove the valve cover and start it up to see if oil
comes out of the rocker arm bushings as it should.
>It looks like a valve stuck or valve float caused this, is it possible you
over-reved the engine?
Who, ME? Over-rev? ROTFLMAO. I don't recall ever running my stock MGA
1500 engine much past 7000 rpm. I have dropped a head off an exhaust valve
on a couple of occasions while cruising at a reasonable and steady speed on
the highway. And I have had the keeper end of an intake valve stem break
once before (with a three week old new valve), but with no other damage.
With the stock cam, stock dual valve springs, and all stock valve gear I
used to occasionally (well okay a little more often) run it up around 7000
rpm for a few seconds while autocrossing. In that case it makes lots of
raucus noises out the exhaust when it goes into valve float, but that never
seemed to cause any problems, and I've been doing this for at least a few
years now.
OTOH, after installing the new cam with higher lift (more inertia in the
valve gear) it likes to go into valve float at just over 6000 rpm, so until
I get the high performance springs installed I have been casually loafing
around under the 6000 rpm red line. And for this dilligence I am repaid
with the pushrod failure in less than 3000 miles of running, most of which
was casual road cruising.
As to stuck valves, no way! BTDT, and don't wanna BTDT any more. For some
years now I've been using bronze guides. The first idiot machinist to
install these for me just pressed them in and assembled the valves, which
did cause one exhaust valve to hang up with really hard running (but still
no damage). After having to R&R the head again to hone the guides myself I
have learned that lesson well. I may even be a little overly generous with
guide clearance, running around .003" minimum clearance when new, and a
little more later. Just now checking my records, these particular guides
had 75,000 miles on them without incident, and are now running a couple
thou more clearance than when new.
>Were you running stock or ratio rockers?
Yup, stock rocker arms. Just a little extra lift from the cam, getting the
valves up from the stock .356" to .399" intake and .419" exhaust. And no,
there is no interference at the valve heads, as I have ground the necessary
eyebrows in the block for clearance.
>Failure of some valve keepers? ....
Nope. Even the keepers for the valve stem that broke were nicely in tact
inside of the spring cap when the cover was removed, and in perfect condition.
>....
>Barney Gaylord wrote:
>>....
>> Yes. Absolutely got an idea. Look here first:
>> http://www.ntsource.com/~barneymg/grapes/bent_pr.jpg
>>
>> This WAS a brand new set of Crane Cams pushrods. .... notice the end
piece inserts that came loose from the Crane 3-piece tubular pushrods. ....
I'm still open to ideas though, just in case anyone would like to venture a
guess as to cause and effect. And just for the record, since repairing the
engine and installing a stock set of one piece pushrods I have done an
additional 5000 miles of very serious driving, including EIGHT more
autocross dates, and still no more problems.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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