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Thread: Throttle spindle buh material?
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8th Dec 2021, 07:09 PM #1Mechanical Butcher
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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.
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8th Dec 2021, 07:24 PM #2Most Valued Member
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Maybe Nylatron?
Nev.
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8th Dec 2021, 07:45 PM #3
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
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8th Dec 2021, 08:19 PM #4Golden Member
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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.
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8th Dec 2021, 09:23 PM #5Mechanical Butcher
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8th Dec 2021, 09:24 PM #6Mechanical Butcher
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8th Dec 2021, 09:27 PM #7Mechanical Butcher
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9th Dec 2021, 10:22 AM #8Most Valued Member
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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.
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9th Dec 2021, 11:06 AM #9Golden Member
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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.
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9th Dec 2021, 03:04 PM #10Intermediate Member
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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.
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9th Dec 2021, 07:25 PM #11Mechanical Butcher
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9th Dec 2021, 07:31 PM #12Mechanical Butcher
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9th Dec 2021, 07:46 PM #13Mechanical Butcher
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9th Dec 2021, 09:22 PM #14Diamond Member
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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!
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10th Dec 2021, 07:06 PM #15Most Valued Member
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