Thanks, Barney...I'm printing this out right now as reference. :)
BTW...if you hear of anyone who wants to do some horse trading with an MGA
for an early B in great shape (64), let me know. :P That is highly
unlikely but, I'm gonna be gunning for an MGA before the end of the year,
and I should finish this B up within the month. It will be a good show car
when I get done: early B, original engine, 54000 miles, and the only thing
that isn't original is that the battery is in the trunk and it is negative
ground. heh
Anyway...Keep up the good work! :)
Thanks!
Blake
At 04:39 PM 7/25/98, Barney Gaylord wrote:
>
>On Fri, 24 Jul 1998 23:33:17 -0500 (CDT) "Blake M. Wylie"
><bwylie@hiwaay.net> writes:
>>Anyone ever put the oversized throttle shaft in your SUs? If so, how do I
>go about doing that? I've pulled the SUs off my 64 in order to rebuild
>them, and I need to do something about the throttle shaft. It's got some
>good play in there, and would definately be a problem later on. I've heard
>that I would need to probably take it to a machine shop and have them bore
>it out, but I don't know any of the specs or what else might need to be
>done. ....
>
>Yes, I recently did this with my MGA. When I restored the car it had about
>150,000 miles on it, and new standard size throttle shafts got the
>clearance back under 0.005" without machining. Most of the wear is on the
>brass shafts and not much on the throttle bodies. Take the arms off the
>shaft and remove the butterfly. Slide the shaft across until a non-worn
>section is running in the journals of the body, then try to wiggle the
>shaft to determine the clearance.
>
>When my second set of standard size shafts were badly worn at around
>275,000 miles, this test still showed a running clearance of less than
>0.010" around a clean part of the shaft. So I recently drill out the
>bodies and fitted the oversized shafts. Maybe in another 1/4 million miles
>it will be time to bush the bodies.
>
>You don't need a milling or boring machine, and you don't even need a
>reamer. What you do need is a drill press with a mounted vice to hold the
>throttle body, and a 5/16" straight rod or drill bit, and a letter "P"
>drill. The standard shaft size is 0.310" diameter to run in a 0.3125"
>diameter journal. The oversize shaft is 0.320" diameter, so you need to
>drill the body out to 0.323" with the "P" drill. The trick for proper
>alignment is to set the throttle body up in the machine vice using the
>5/16" rod or drill as a pilot to get the throttle body exactly straight and
>centered under the drill chuck. Then you put the "P" drill in the chuck
>and slowly run it through the body to get a clean hole just 0.010" oversize.
>
>After drilling the body you have a choice of also drilling the arms
>oversize or reducing the diameter of the shaft extending outside of the
>body back to standard size. I chose the latter, because I had a small
>lathe handy, and I would be able to re-use the arms later if I bush the
>bodies and return to a standard size shaft. Install the shaft in the
>throttle body with the butterfly screwed in place. The exact location of
>the drilled journal through the body is not very critical, because the
>screw holes in the butterfly are oversized. This is why you can just drill
>the body and not have to use a reamer or a boring machine.
>
>First install the butterfly screws loosely, then rotate the shaft until the
>butterfly is closed and touching the wall of the throat all the way around,
>then tighten the screws. Then you mark the shaft where it exits the
>throttle body on both sides, and also measure and mark for the correct cut
>off length. For most applications the shaft will be longer than necessary
>on both ends and need to be cut off. Then remove the shaft, cut the ends
>to length, and use a lathe to reduce the diameter of the shaft extensions
>back to 0.310 like the original shaft. If you don't have a lathe, you
>could drill the arms to fit on the oversize shaft.
>
>Last step is to cross drill the shaft to accept the pins that retain the
>arms. Use the original shaft as a guide to get the angle(s) correct for
>the cross holes. It is important to get the new holes drilled exactly on
>the centerline of the shaft so the holes will line up with the holes in the
>arms. If you miss the center by more than a couple of thou, you will have
>to drill one of the holes oversize or out of round to get the pin
>installed, in which case you run the risk of having the arm work loose later.
>
>When you get it reassembled the butterfly should touch the throat all
>around when it closes, and it should close and open easily without
>sticking. The original type butterfly screws have a split tip so you can
>spread them open like a split rivet to keep them from getting loose.
>Alternatively, you can use plain tipped screws and install then with a drop
>of thread adhesive. Do be sure these screws are locked in place. It's not
>nice to have one fall into an intake port.
>
>When I got the new shafts installed, the carbs back on the car and tuned
>up, it was so satisfying to once again have a car that would idle properly
>and consistently at the same speed every time when I let the throttle up.
>And I no longer have to adjust the mixture rich to compensate for the air
>leaks around the shafts at idle, so now it also doesn't have to run rich at
>higher speeds. If you do not have a drill press and you are cost
>conscious, you only need to farm out the job of drilling the bodies and
>fitting the arms. The rest you can do with hand tools.
>
>Barney Gaylord
>1958 MGA with an attitude (and a nice clean idle)
>
>
>
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