Thread: Throttle spindle buh material?

Originally Posted by jack620

Why not? Is there a galling issue? I love Delrin (acetyl), but I wouldn’t use it in contact with petrol.

I've read that the only type of metal that can bear against itself for an extended time is cast iron.

Have you had a bad experience with Delrin exposed to petrol?

Probably true but the bushes are a wear part, like wheel bearings, ball joints and uni joints. Only carb I can think of that doesn’t have brass bushes on a brass shaft is a Mikuni, and that’s because it doesn’t have a butterfly. SU, Stromberg, Holley, Carter, Weber, and Delorto all use brass bushes bearing on brass shafts.
I wouldn’t be so worried about the contact with fuel vapour, DuPont data sheet for Delrin acetal says 120 degrees, if your carb is over the exhaust manifold or turbo if so equipped you will exceed that and potentially wind up with a throttle you can’t shut because the bushes have turned to chewing gum. There’s a reason why the carb manufacturers don’t use plastics….

What sort of carb is it, and what’s it off?

It's a Zenith on a Land Rover that's over half a century old so no surprise there's wear on the spindle and non-bush (zinc alloy).
A thick insulator sits under the carb.
I think I'll go ahead with the acetal as an experiment, having bought some.
I've come across plastic bushes in restored carbs before.

Originally Posted by nadroj

Have you had a bad experience with Delrin exposed to petrol?

No, but I've not tried it. I just found a chemical resistance chart and it seems to handle petrol well.
I'd still use brass for the reason racingtadpole gave.

Interested to see how it goes, let us know

OK, but a high mileage report isn't likely to happen.

I went through a similar exercise

https://metalworkforums.com/f303/t20...bushing-carbys

After 4 years you might think I could provide some feedback on suitability of material.

Sorry. Very little progress on this project.

John

I did wonder if a phenolic based bearing product such as turcite would be suitable, but a quick search of its properties found nothing about its reaction to solvents and fuel products.
If you have time, maybe dropping some easily measured samples of your choice into a jar of fuel for a week or three might give a clue to the risk of swelling.
Bill

Originally Posted by GuzziJohn

I went through a similar exercise
https://metalworkforums.com/f303/t20...bushing-carbys

Interesting, thanks.
Did you rebore the spindle holes?

Originally Posted by nadroj

Interesting, thanks.
Did you rebore the spindle holes?

If you mean the carb body, there were existing worn out factory bushes. These were removed and the new material installed.

John

Originally Posted by GuzziJohn

If you mean the carb body, there were existing worn out factory bushes. These were removed and the new material installed.

John

That's a good feature that the Zenith doesn't have.

Blast!
I butchered the carb body by not having it set up accurately enough before drilling.
Back to the drawing board.

Buell XB motorcycles have a throttle body with some sort of plastic bush that the US guys have found can be replaced by trimming these bushes available from McMaster in the US.
They are made from PEEK (polyetheretherketone).

https://www.mcmaster.com/6627k411

That's interesting. I never heard of PEEK plastic.

A couple of problems:

- The size would have been too large for the Zenith.

- McMaster-Carr won't sell to Australia.

My father did a couple of SUs with brass for his Vanguard ute back in the 60s.
It had a TR4 engine.
No probs as I remember, I inherited it when he carked it and used it to tow my lightweight mini to the track.
H.