Throttle shaft D4-5T Pony

I think I would try looking for another carb before building parts. At the rate I see pony motors being converted to direct start there should be plenty of candidates out there. Don't know what the market might be for new shafts???

I ended up making a new shaft. What I found in the process of getting to the point I decided to build the shaft was interesting. I found the bushings are available from CAT and so is a throttle shaft with a changed part number that is supposed to supercede the original. The bushings a fine but the throttle shaft I have some issues with. I first made the tooling to align correctly the stop assembly to the flat on the shaft when pressed together. The plating on the shaft looked to be a nice gold as if the shaft were brass plated. When I drilled the hole for the roll pin to stake the alignment I found it was not plated but brass. Thus a new steel shaft, like the original. I did take advantage of the dimensions I could take from the new shaft as well as the original and a “good” one I received.

I made the new shaft from a length of 1/4” oil hardening drill rod. The screws that hold the butterfly on are 5-40 and one does need to ream the bushings to size for the new shaft.

I made a drawing for the shaft and milling tooling. I can e-mail or post depending on interest. I did not make a drawing for the assembly fixture but can describe the procedure to make one using the old shaft as a pattern. I would not describe this as difficult project if you have access to machine tools but I doubt I would want to pay someone to do the work.

Below are some pictures of the process and one of the D4 and some other projects.

I have the carburetor reinstalled on to the D4 but have not been able to get the pony to run at high speed. More adjustments to the carburetor are required. More time once it stops raining for a while. At least I found the magneto works.

Part Nos.
Shaft: Original: 9B4977, New: 160-5208 -- Brass
Bushing, Stop side: 9B4783
Bushing, Blind side: 9B4779

Geoff

Good pictures and good stuff. Thanks for posting.
My only concern would be using the drill rod which I find rusts quite readily.
I think I would stick to the brass or maybe a stainless.

I will agree with you on the use of stainless shaft. The material I used was material I had. I can see some advantage to stainless. I am not that familiar with the availability of turned, ground and polished stainless shafting but it is worth investigating.

The reason brass is not the correct for this application is fretting. The failure mode of the original shaft was wear all the way around at the brass bushing on the stop assembly end. There was also a groove worn into the shaft by the spacer washer.

In general a properly designed shaft and bushing combination are done when the shaft is significantly harder than the bushing. The can be seen by the differences in the coefficients of friction between steel on brass and brass on brass. Machinery’s handbook shows the coefficient of friction for steel on brass as .35 (clean) and Mark’s Mechanical Engineers Handbook shows a coefficient of friction for brass on brass of .88 (clean). For comparison Rubber on dry pavement is about .88. The concept of using a brass on brass combination in what amounts to an un-lubricated state, not a desirable combination.

If I were to remake the shaft I might look into stainless.

Geoff

You must be another "Mechanical Engineer" (so am I) from Cal Poly to.
I wouldn't worry about the coefficient of friction on a shaft that size and only used as linkage. There are also some pretty neat plastics available for bushings.
Can't really knock the brass either. (only lasted some 50 years. LOL)
Either way, steel equals stuck due to corrosion, think that is concluded.
McMaster-Carr has the precision ground ss rod starting at 1/8" dia. (not sure what the throttle shaft dia. is)
Neat project😄 😄

P.S. What is the GOTSLOCO company??

The original shaft was steel. The replacement I purchased form CAT was brass.

The tractor has few hours on it relative to its age I don't understand the shaft wear at all.

I am and engineer by training, BS Agricultural Engineering, Cal Poly SLO, BS Mechanical Engineering CSU Chico.

I no longer work in engineering due to the changing nature of design in the last twenty years. I saw the changes CAD would make but was not in the right place. I worked for 2D AutoCad company that refused to up grade in a world that expects 3D Solid modeling and won't train.

I use my engineering background for my hobbies restoring trucks, tractors, and Trains.

http://sprr.calpoly.edu/index.html

GOT is my initals
SLOCO is my location

Geoff