resizing swing arm bushings

My bike has been running on a +0.005 oversize swing arm pivot forever. Now I need to replace the bushings in the swingarm, but the ones I have did not come sized for the +0.005 spindle. What is the most practical way to open them up for the oversized pin ? The swingarm is much too big to swing in my lathe.

Thanks

Greg

I normally use adjustable reamers. Any old tractor repair place should have a set. Jim

Sintered bronze or "Oilite" bushings contain pores to hold oil (capillaries).

Conventional methods of machining can "smear" the bronze and close the pores thus making them unable to hold oil.

The proper method to machine is to use sharp carbide tooling.

This is an excerpt from a sintered bronze bearing supplier website:

"Sintered bronze is a porous material, and the thousands of capillaries throughout its structure allow this material to hold and distribute lubricant during usage. If not machined properly, those pores on the surface can become clogged during machining. When this happens, you have converted your self-lubricating part into a solid, non-lubricated material which will require additional lubrication. To properly machine Sintered Bronze, you need to first use Tungsten-Carbide tools whose edges are dead sharp. The nose of the tool should be broad enough to overlap the width of the feed per revolution. A fine feed and shallow depth cut should also be used. Following these guidelines should prevent pore clogging on your part and keep them from failing during operation."

Gidday All.
first a question.
1. ARE the replacement oversize bushes supplied by Andover sintered or solid bronze?.

GJR: as you asked, and Jim advised, the most practical way is to ream them. for best results, the reamer blades must be very sharp, but not so keen an edge as to cause chatter. very dull reamers just rub metal away anyway so sharp is best. the other important bit is to use a pilot extension on the reamer to keep the holes in line.

if you are of a mechanical bent, and if there is access to a lathe, make a pin of any suitable size from 4140 and have it nitrided.
make the bushes from leaded bronze. (LB1 in Aussie) not phospor or leaded gun metal. leaded bronze performs superbly in areas of marginal lubrication.
fit the bushes and line ream to size. minium clearence 1/2 thou, max clearence 1 thou. the nitride case lasts longer than chrome plating.


regarding machining data supplied, this is correct. however this may not be practical as each bush must be then done individually and then fitted. or put on a borer for final sizing. an allowance must also be made then for fitting. and there may be alignment issues.

the most practical method is reaming using very sharp reamer AND a pilot bar. the biggest cause to wear here is lack of lube.
sintered bushes are an industrial, not a precision product. they are intended to function as fitted, and therefore necessarily require wider tolerances.
hope this helps Bradley

I have always cut brass and bronze with the bit/tool with a slight negative rake. Even with a drill I will slightly blunt the cutting edge. To be clear this is not dulling the adge but the negative rake cause the tool to scrape the material away and keep the tool from digging in which is the big risk with when machining/cutting these soft materials.

Copper, on the other hand, is a different animal.

Whilst it might sound like the ultimate no no, I'd put the bushes in your lathe and polish the 0.005" out with some emery cloth. Wash it all out in petrol before soaking the bushes in oil again. You could turn up some bushes in stainless steel and fix up some lube feed tube. The spindle normally rusts down in diameter well before the bushes wear out.

B.Rad said:

1. ARE the replacement oversize bushes supplied by Andover sintered or solid bronze?.

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The swinging arm bushes are sintered bronze, however I've never known Andover Norton (or anyone else) to sell oversize bushes, only the spindle.

Isn't it said that sintered bronze can only be ground to finish. ?
Anything else smears over the granulated structure, and loses its oil-holding lubrication qualities...

Not selling oversize bushes to suit the oversize pins sounds like a flaw in the plan.

Rohan said:

Isn't it said that sintered bronze can only be ground to finish. ?
Anything else smears over the granulated structure, and loses its oil-holding lubrication qualities...

Not selling oversize bushes to suit the oversize pins sounds like a flaw in the plan.

Click to expand...

hello All
this may be so, but apart from the extra cost it sort of defeats the purpose of having sintered bushes.
circumstances may demand that the bushing be re sized after fitting. the most practical method is reaming. therefore a debate over the "correct" finishing method becomes purely academic.

However, sintered bushings are an industrial product, with relativly generous tolerances. They are intended to be used as supplied.
best wishes for a good new year. Bradley

I would hesitate using a bushing that did not need to be reamed to fit. The holes in the swingarm are not all that accurate so making a bushing to fit with the correct clearance without reaming would be pretty tough.

I have fit quite a few pair using adjustable reamers and a cone in the opposite side to hold alignment. My reamers are probably 30 years old but they are still sharp and seem to cut a clean hole without smearing the metal.

The bushings in my swingarm have close to 100,000 miles on them now and are still tight, but I have a small tube running from the oil tank vent that supplies just enough oil to keep the felts wet. Jim

comnoz said:

I would hesitate using a bushing that did not need to be reamed to fit. The holes in the swingarm are not all that accurate so making a bushing to fit with the correct clearance without reaming would be pretty tough.

I have fit quite a few pair using adjustable reamers and a cone in the opposite side to hold alignment. My reamers are probably 30 years old but they are still sharp and seem to cut a clean hole without smearing the metal.

The bushings in my swingarm have close to 100,000 miles on them now and are still tight, but I have a small tube running from the oil tank vent that supplies just enough oil to keep the felts wet. Jim

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Yes Jim, that is the whole point. to do a decent job, as I have said, they need to be line reamed using a pilot. I reckon, (I do not know) that the bore of an unfitted sintered bush will be 4 or 5 thouh over for a one inch shaft. subtracting 1 for the interference and 1 for shaft tolerance, leaves 2-3 thou clearence. too much for a new job. sintered bushes have their place in industry and when used appropriatly perform well. However THEY ARE NOT A PRECISION ITEM.

as supplied, sintered bushes are not a precision item. they cannot be. so when you fit the standard bushes on a standard shaft, the clearence is more than optimum. has to be so.

to get back to the original query, the most practical method of sizing is reaming. I would use the pilot shft as well. nearly have to if only a thou clearence and to keep them in line.

so what you get with sintered bushes is not the best solution possible, but a commercial product that does the job for a while.
So Jim, you are absolutly correct in saying line reamed bushes are optimum. but there must be a lot of owners who have fitted the sintered bushes without needing to ream them and living with the result.

Bradley

I've used down/dirty emery/dowel method then fitted grease zerks and flow grooves. I think ya' all worry warts on this as friction ain't ever going to be an issue with the loads so even dry as a bone the soft bush would just burnish[polish against the super hard spindle about forever, unless of course there was not enough oil or grease on spindle to keep super hard surface pitting and flacking into rust dust. I dare ya to even leave a mark with a file on spindle, so how can sintered brooze? The lube ain't doing anything but chemical oxidation protection to matter. I've had two dry as bones all trapped by swollen rust , yet shock action and ride was fine with routine hard tests. Now don't get me wrong on this friction issue, as oil or grease makes less friction to remove and install. Moral of my tale, if spindle drools oil out below half way, the sintered pours do not leak out enough to protect the hard finish so its a non issue if they are smeared over or not. Now if used in a higher speed device the heat would sweat out some oil to flow and lube. Btw before you operate on the insides might check the bushes are actually round as so soft handling can distort them, which requires more material removed to pass the shaft. Correct my thinking if i'm missing something.