Carb/Throttle Shaft Wear

I

Ironhorse

Well-known member
I have to believe that someone like George, Rick (BillieandMillie) or Lurker Carl have run across carb bodies with excessively worn throttle shaft bores and have performed the machining necessary to fabricate install a bushing. Other than this problem, there aren't a whole lot of reasons why the Cub carburetors can't be salvaged for years to come as long as they aren't cracked or overly warped. How 'bout it guys?... :wink: I have one that I don't think a new shaft is gonna' fix...have you surgeons pumped new life back into these ageless wonders?... :) I'm thinking about attempting it here shortly and wanted to see if anyone else has and if you were succesful.

Thanks!!
Gary
 
Most of the time, the bulk of the wear is on the shaft and a new shaft fixes things up. Have you tried a new shaft yet to see how much wear there is in the carb body?
 
Hey Jim, I used a like new shaft out of a different carb, slipped it in the bore and it seems to have excessive wear. I've seen rebuilt carburetors (not for Cubs) that had been machined and fitted with bushings and figured it could be done but don't know what material they were made out of.
 
Ironhorse":2n4mtarn said:
I have to believe that someone like George, Rick (BillieandMillie) or Lurker Carl have run across carb bodies with excessively worn throttle shaft bores and have performed the machining necessary to fabricate install a bushing. Other than this problem, there aren't a whole lot of reasons why the Cub carburetors can't be salvaged for years to come as long as they aren't cracked or overly warped. How 'bout it guys?... :wink: I have one that I don't think a new shaft is gonna' fix...have you surgeons pumped new life back into these ageless wonders?... :) I'm thinking about attempting it here shortly and wanted to see if anyone else has and if you were succesful.

Thanks!!
Gary
Click to expand...

Yes, I've seen it... It was the very first thing my mentor showed me! The subject was a single cylinder engine which is much more likely to have the problem. The first problem is finding the original center before boring to prepare the body for the bushing so the butterfly fits properly. The wear will be on the side toward the engine so centering it up will have to be done using the opposite side.

The choice of material will depend on which element will cause the least problem upon future wear. Would you prefer to replace the bushing or shaft later? Denzil used brass for the bushing which matched the shaft. Strange thing is that the harder side will suffer the most wear because foreign grit will imbed in the softer material. I've seen oilite bronze bushings in furnace blowers cut steel shafts completely through.
 
I just finished putting new parts into the carb for the '51 and was thinking about bearings/bushings. The throttle shaft on mine is brass, and the choke shaft is steel. The carb body is aluminum, I think.

George's point about boring the true center of the hole makes sense. If the hole is egg-shaped resulting from differential wear, finding this center is possible but the margin of error is pretty small. If I were to attempt a bushing in a carb, I would probably bore the shaft hole well over-sized. Then I would set the bush in JB Weld or a similar gas-proof epoxy. Grease the shaft and butterfly plate and reassemble the shaft in the carb. Allow the butterfly plate to move the shaft into the correct position. As the epoxy hardens, but before it is fully hard, operate the shaft and see if the shaft opens and closes freely.

Will this work? I have no idea, but it sounds good.

An alternative might be to drill and tap 3 holes in the carb body where the shaft is supported. Say 4-40. Put set screws into the holes and you could adjust the hole center to be spot on. Once the bushing is centered, fill the space with epoxy. It will lock the set screws in place and seal the area around the bushing. It is a little more work than the previous option but it should work.

It would be easier to machine an adapter to mount some other, readily available, carb to the manifold. Maybe a side draft SU, or ...

I suppose all things are possible to the person that does not have to do them.

Rick (brainstorming includes the bad ideas) Dulas
 
Allow the butterfly plate to move the shaft into the correct position. As the epoxy hardens, but before it is fully hard, operate the shaft and see if the shaft opens and closes freely.
Click to expand...
This brings up a good point. Even when we do a rebuild with the new IH kit, once the new shaft is installed and the plate is screwed to the shaft, we should wiggle the plate into position before it's tightened down completely. Whatever repair is done to the hole, the plate offers a tiny bit of forgiveness because of it's oversized screw holes. It can turn clockwise/counterwise, plus up and down. Not a whole lot, but alittle.

Rick
 
Actually, re-bushing throttle bodies is a very common rebuild practice. Some high end kits even come with the bushings, sometimes aluminum (for aluminum throttle bodies) or bronze for steel bodies. Shops that rebuild lots of carbs have special counter bores for the process. I've re-bushed them, just being as careful as I could, to get the hole centered. Not always perfect, but always worked out fine in the end. Folks like George (with a milling machine) have a real leg up on the rest of us on this one.
 
A friend of mine used JB Weld on the shaft of his John Deere lawnmower.

He put grease on the carb shaft and then fill in around it with JB Weld. He said he would twist the shaft back and forth at times while the JB Weld set up. The grease and twisting keep the shaft from setting up with the JB Weld. His lawnmower runs good and he hasn't had any trouble with it sticking around the shaft.

Just another idea.
 
Ya' gotta love these technical discussions...brainstorming sessions...bright minds at work using common sense and good old American (and sometimes Canadian :wink: ) know how to develop solutions for just about anything "Cub". Its how some of the best ideas have gone from principle to paper to production whether its one idea or the combination thereof. I imagine that its the same type of people that are keeping them running and working today that came up with the idea of the "Cub" in the first place...hmmmmmm...don't mind me guys...I'm just thinking about the years of experience in this forum that are available to anyone and everyone at the touch of a finger and that less than 20 years ago, folks would have been forced to pry information out of a less than willing technician at a dealership unless they were one themselves...my hat's off to all the willing participants for sharing theire knowledge...now if we could just get our nations leaders to do the same thing... :lol:
 
Using a flat nose punch you can close up the hole by peining around the hole lightly a little at a time till its small enough. Its a quick backyard fix when there's no other options available.

So why do these wearout? Its lack of lube and maintence...so when you change the oil and grease the tractor give that carb shaft a shot of oil when you lube the genny too...all the linkage should be lubed just a little.



When reassembling the carb shaft put some moly on it and work it in.

Moly

Eliminates all wear

Moly works into the small pores of the metal on both mating parts and wears against itself thus no metal to metal contact thus no wear.

Reduces Friction

Since there is no metal to metal contact when using moly its eliminates all drag reducing friction.

Fights corrosion

Using Moly fights corrosion "no rust"

Moly stays wet and were were you put it.


I use moly on everything;

On engines when assembling on the piston skirts and cylinder walls and rod and main bearings, valves and valve guides, cams and cam lobes too.

They also offer an engine additive a transmission additive which can be used in differentials too.
 
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