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  1. #1
    Join Date
    Oct 2004
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    Southern Highlands NSW
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    Default Throttle spindle buh material?

    I intend to fix a carburettor base that has a worn spindle bore.
    There are no bushes as standard in the zinc-alloy casting, so I will need to bore it oversize for newly made bushes.
    I bought some acetal which is a type of plastic, but can find no reference to it being used for this purpose.
    Does anybody know of a reason not to use it for this job?
    The spindle is brass.

  2. #2
    Join Date
    Nov 2008
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    North Brisbane. Qld. Australia
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    70
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    Default

    Maybe Nylatron?
    Nev.

  3. #3
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    Sep 2005
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    Bendigo
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    Default

    I repaired a carb when I was much younger and used a plastic but had no idea what type of plastic it was, result was not the best as the plastic swelled when exposed to petrol.

    Looks like acetal should be suitable for the job but I have no first hand experience with it.

    https://www.industrialspec.com/images/files/acetal-pom-chemical-compatibility-chart-from-ism.pdf

  4. #4
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    Sep 2008
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    Riddells Creek, Vic.
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    831

    Default

    Normally an oversize shaft is used when the body is worn, they used to be available for common vehicles. I made a piloted reamer to suit a +.010" shaft for a HQ Holden carburetor once.

  5. #5
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    Quote Originally Posted by droog View Post
    That's the sort of effect I'm worried about. Hopefully acetal is more stable than the stuff you experienced.
    Thanks for the link, which is reassuring.

  6. #6
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    Quote Originally Posted by SurfinNev View Post
    Maybe Nylatron?
    Maybe?

  7. #7
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    Quote Originally Posted by Techo1 View Post
    Normally an oversize shaft is used
    I have a standard sized spindle, but anyway the hole is worn very bigly.

  8. #8
    Join Date
    Mar 2011
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    Southern Flinders Ranges
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    Default

    I’ve reamed and bushed a number of SU’s in the past, I always used brass, but I’ve also seen them done with bronze (something of an overkill)
    I wouldn’t put any form of plastic into a carb body as a butterfly bush, if the fuel doesn’t eat it deform it or somehow otherwise get at it, the heat likely will.

  9. #9
    Join Date
    Oct 2008
    Location
    Cairns, Q
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    Default

    Quote Originally Posted by nadroj View Post
    Maybe?
    FWIW when I built the Blanchard spoke lathe some years ago I used Austlon for the low speed lightly loaded rocker bearings at the suggestion of one of the local bearing suppliers. However, he didn't warn me that this type of bearing material can absorb quite a large amount of atmospheric water in the Cairns climate (hot and humid in summer), and swell. The manufacturer's literature warns of this, and offers advice on working around it, but, of course, I did not read this until some time later - as they say in the classics "when all else fails, RTFM!" The rockers are about 600 long, the pivot pins 10 mm diameter.

    Even with the 600mm leverage the rockers now require considerable force to move by hand; they need to move freely in use. If I ever want to use the machine again (unlikely), I will have to dismantle the carriage and try to remove the four pivot pins - two on each rocker frame - without causing any further damage, and ream the Austlon bushes back to their correct size.

    I don't know how Austlon compares with the equivalent grade of Nylatron in this regard, but if you decide to go that way, check moisture absorbtion characteristics first. A stuck throttle could be embarrassing.

    Frank.
    .

  10. #10
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    Nov 2017
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    Adelaide
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    Acetal should be reasonable for this application.Acetyl is resistant to alcohols, aldehydes, esters, ethers, glycols, hydrocarbons (petrol, engine oil), agricultural chemicals, weak acids and alkalis.

  11. #11
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    Quote Originally Posted by racingtadpole View Post
    I always used brass, but I’ve also seen them done with bronze
    I'd rather not use brass against brass (or bronze).

  12. #12
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    Quote Originally Posted by franco View Post
    I used Austlon for the low speed lightly loaded rocker bearings at the suggestion of one of the local bearing suppliers. However, he didn't warn me that this type of bearing material can absorb quite a large amount of atmospheric water.
    Sorry about your failure. You must have been cross with the supplier that recommended a nylon type material for that job.
    I was surprised to learn that it absorbs water.

  13. #13
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    Quote Originally Posted by Creedy View Post
    Acetal should be reasonable for this application.Acetyl is resistant to alcohols, aldehydes, esters, ethers, glycols, hydrocarbons (petrol, engine oil), agricultural chemicals, weak acids and alkalis.
    Sounds promising.
    I will give it a try.

  14. #14
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    Oct 2008
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    N.W.Tasmania
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    Default

    As far as I am aware most if not all nylon materials absorb water.
    Lots of carburettors used brass bushes on presumably brass shafts. They did eventually wear, but usually lasted many years first. I would imagine that Acetal, (Delrin) would be ok as would Teflon if you can score a bit to try. Good luck!

  15. #15
    Join Date
    Nov 2007
    Location
    melbourne australia
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    Quote Originally Posted by nadroj View Post
    I'd rather not use brass against brass (or bronze).
    Why not? Is there a galling issue? I love Delrin (acetyl), but I wouldn’t use it in contact with petrol.
    Chris

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