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fork links

Hi Guys,

I'm reading in the standards book about the fit between the bushes and the links. They want a .003" to .004 fit (.002") per side. My links pins are on the low side and the bushes on the high side of tolerance.

I can change the bushes out, no problem and ream to size, even going with as smaller hole to make up distance.

Now, with the links made out of "unobtanium", I am wondering about making new pins for them, and press fitting in like the originals. Rick Holt send me a book of British Standards for metals, or I can have the original analyzed. I'd use the best upgrade available for the pins.

Has anyone an old worn out link they can donate to science? If it works, I'll do the balance of your links for free. I just do not want to risk my only links.

Thanks

email (option): britool51@hotmail.com

Re: fork links

Robb. I bought a set of NOS links from Russells last year for my forks. I've still got the old ones. I can send them to you for experimentation. I know Jake Robins here in UK will replace the worn out pins. But I don't know what grade of steel he uses, but I don't think it's anything too special. Ron

email (option): ronpier@talk21.com

Re: fork links

I made the link pins out of 14mm "silversteel"; to ensure a good fit, a rather complicated set-up on the lathe was used to drill out the remains of the old pins and ream to 14mm. The double length links pins were hard-soldered pair-wise, and then cut off in the middle, so the pins were absolutely parallel (am I a bit clear )
Worked well, and cheaper than NOS links (IF you can find them )
The useless bushes were replaced by bushes made from standard bearing bronze and reamed in place.

email (option): viaconsu # planet dot nl

Re: fork links

My forks were professionally restored a few years ago. But the bushes were made from sintered (oil light) Bronze and wore away after a very short mileage. I have now had bespoke bushes made by a friend with a lathe using proper bearing bronze. Ron

email (option): ronpier@talk21.com

Re: fork links

Hi Ron,

Many thanks! I'll PM you with a UK address t save mailing costs.

I can get a metal analysis for $75.00. I'd wager US steel number 4140 prehard as that gives a hard surface and a strong core like screwdrivers and hammers.

I'll check with my metalurgist buddies.

Cheers,

email (option): britool51@hotmail.com

Re: fork links

The easiest way is to cut off the pins and file them flat or mill them, simply enlarge the hole a little and machine the new pins with a light interference fit into the enlarged hole in the link (pre drilled through the centre) you can do them bolted together and simply braze them in, as for the steel, the best stuff is silver steel. As long as your hole was not excessive and was smaller than your nuts and bolts you needn't worry about them falling off the pin as they couldn't fall off anyway

email (option): davmax@ntlworld.com

Re: fork links

I wouldn't consider silver steel suitable for fork spindles. It is a flame hardening tool steel and if quenched after brazing/welding it will be very hard but also very brittle. Tempering in the home workshop is also an imprecise procedure unlikely to produce a consistent or verifiable result.. If left to cool naturally wear resistance is poor and strength moderate.
A high tensile steel such as EN16 (BS970)(US 4037) is far more suitable as it has both the required strength and wear characteristics in it's 'natural' state.
However, this is a medium carbon high tensile steel. As such, and typical of these types, its weldability is inversly proportional to the carbon content...ie the higher the carbon content the more difficult to weld without losing strength/hardness..
As a result if I was doing the job myself I would either thread the links and pins and screw them in or drill and ream the links and press in a 'shouldered' pin...probably the latter. A .0005"-.00075" interference fit on a 1/2" spindle would be ample..Ian

email (option): ian@wright52.plus.com

Re: fork links

Hi Ron,
I also bought some oilite bronze bushings off the shelf, they were a match for the ones I pulled from the forks, I had posed the question here several months ago and got several replies that they should work fine. Can you tell me if they just wore out, or did they break up in use? How long before you noticed they were failing? Is the material unsuitable for girder fork use, or do you think they were damaged during installation?
Vincent

email (option): vinver-at-ns.sympatico.ca

Re: fork links

Vincent. My fork bushes wore out after only about 1500 miles. When I removed them, some were waver thin and looked like lace doilies. I'm not an engineer, but it was explained to me by Ian and my friend John, who is also a long served precision engineer that sintered bronze is the equivalent of chip board to real wood. I think it's ideal in other operations were a self lubricating light bearing is required. But not at all suitable for the heavy loadings of girder forks.

Ron

email (option): ronpier@talk21.com

Re: fork links

Oilite is manufactured using a 'powder metallurgy' process which results in a porous granular finish. Oil is impregnated into the bush at the manufacturing stage under a vacuum.
There are various types of oilite bushings with varying properties and in principle they can be used for girder forks if the correct type are selected.
However, one key thing with oilite bushes is that they must be machined with very sharp tools. This is to avoid 'smearing' the material which will block the porous structure, seriously reducing the lubrication and thus its operating life.
Reaming, in particular, is not recommended as a cutting method.
It is highly likely that the bushes were reamed when fitted, which may explain their short lifespan...
Bearing all this in mind and the fact that ideally the fork bushes should be line reamed to a finished size, a standard bushing bronze such as PB1 would be more suitable as it is less prone to suffering problems during fitting...Ian

email (option): ian@wright52.plus.com

Re: fork links

There was an article in Classic Bike or Motorcycle years ago about doing fork links for M20s. I think it was by Radco does anyone have a copy they could scan. I used to have a copy but that was several years ago now. I dont know which issue it was in or what was on the cover I cant remember.

Re: fork links

Well there you go! I know very little of the machining or technical make up of some of these metals. All I do know is how quick this honeycomb bronze collapsed. I bought some bronze from a local firm who told me it was exactly what I should use, and John who machined it confirmed this.
I did buy some ready made bushes from Russell's. But my forks had previously been bored out to take oversize bushes. Hence the bespoke bushes. Ron

email (option): ronpier@talk21.com

Re: fork links

Terry
There was an article in Classic Bike or Motorcycle years ago about doing fork links for M20s. I think it was by Radco does anyone have a copy they could scan. I used to have a copy but that was several years ago now. I dont know which issue it was in or what was on the cover I cant remember.

That was the article that I've loosely based my input on, I remember it too, but can't find it! I'm sure that the pins on my links weren't hardened as when I did mine I simply hacksawed them off, they were definately genuine links. I note that some of the links that I got from Russells for someone on here, a couple of them appeared to be repro ones as they had that metallic paint on them that some of the Indian manufacturers and these appeared to be made in 3 pieces, ie the link and the 2 pins were brazed in seperately.

email (option): davmax@ntlworld.com

Re: fork links

The original links weren't hardened. However, they would have been made from at least EN8 I would imagine and more likely EN16. EN 24 would be 'over the top' for this application.
EN16 would give them good load bearing capabilities combined with reasonable wear resistance in its untreated state.
Silver steel is a high carbon tool steel, in fact it has the highest carbon content of the tool steels. This means it can be heat treated to a high degree of hardness for the applications for which it is intended such as the manufacture of razor blades, drills etc. etc. which have to retain a sharp cutting edge.
For reference EN numbers were introduced in the war (Emergency Numbers) and although still often quoted they have been superceded by BS (British Standard) numbers. EN16 is now BS970.
Regarding the bronze bushes PB1 bronze is suitable. This is available in bar and tube form.
It is suited to medium to high loads with good resistance to impact loadings. Corrosion resisatnce and machinability are both good.
Lubrication is important with this material though so the oil scrolls present in the original link pins should not be omitted and the bushes should be greased regularly with a light grease...Ian

email (option): ian@wright52.plus.com

Re: fork links

Ian, I spark-tested the material I used some 10 years ago, and it is NOT silver steel, but so-called axle steel, a low carbon construction-grade steel. Can't be hardened, only pack-hardened

email (option): viaconsu # planet dot nl

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