Alloy BSA M/C fork slider wear? bush material.

[gavin eislerParticipant @gavineisler66495]

re reading,, found this , thanks Hopper.

"Was thinking too that on a Myford you could make a mounting fixture to go on the cross slide that was like an angle plate with a hole bored in it at centre height the right size to fit the machined area where the rubber dust gaiter fits on and a slot and pinch bolt to clamp the fork leg right there. Then a secondary mounting from the base of the angle plate on to the front mudguard mounting boss on the fork leg. You could make the angle plate out of half-inch thick alloy for easy machining, either flat plate or a piece of 4" heavy angle."

sounds pretty do able , I know a man with some alloy plate , maybe a 2MT blank to make a boring head.

[duncan webster 1Participant @duncanwebster1]

Went to a lecture once by a guy from Manchester univ about motorcycle handling. Cant remember his name. He reckoned that a substantial fork brace was one of the bets things you could do for teles, stops the front wheel twisting about the longitudinal axis.He further reconed that leading link were even better, but that might be a step too far on a classic(ish) bike

[Clive FosterParticipant @clivefoster55965]

Probably Dr Geoffrey E Roe.

He had a thing about certain values of fork stiffness being essential for proper handling and advocated leading link forks as the best way of getting this required stiffness. He actually manged to patent leading link forks in 1977 **LINK** which, even in the US patent system was pretty good going. Interesting patent as it contains various statements as to required stiffness with no justification along with some rather wild generalisations about flutter and weave. Claimed elsewhere that leading links had never been done really well before he got involved, with Gus Khune racing I think, which is flat out nonsense. Way back I did a few handwaving calculations on his stiffness figures and concluded they weren't that great or that hard to attain. Big flaw in his reasoning was to neglect the inherent lateral damping in the system. Velocette singels handle really well but, objectively frame and fork stiffness is more in liquorice than steel tube Really helps that the flywheels are narrower than the tyre contact patches so fundamentally you have three gyroscopes flying line ahead.

Yup fork braces do work but its rather more complex than simply adding stiffness. The change in how the intertial and dynamic loads are fed back into the frame is important. Especially in relation to the damping of the frame structure. Basically in a motorcyles the various forces all chase each other around the thing until they get lost.

If you want stiff try a funny front end Yamaha GTS. The overall geometry is easily felt to be flawed due to the mismatch between front and rear tyre sizes but the beast way stiffer than any conventional machine with steering head. Huge benefits in stability but the handling is different. Effective tho' once you twig how to ride it.

Clive

[gavin eislerParticipant @gavineisler66495]

i once had an Ariel Arrow, i loved that bikes handling, leading links work for me. not doing it to the beesa, to much palaver.

I had to cut about 75mm off the stock 25lb/inch springs ( to fit the new dampers in, they take up space where the spring used to bottom out) , they are now about 28 lb/ inch and too stiff, i have MZ 250 springs which when cut to length will give 22 lb/inch and about 1 inch off the stroke to lower the front end. i want more of the tube engaged more of the time.

They are coming apart for this.

Thinking about a Carbon fiber brace, either a simple U bracket bolted to the old mudguard mounts or two holes in a cross bar across the slider tops , one maybe with an eccentric bush to fine tune.

Some bikes like Manx Nortons seem to manage on very insubstantial fork bracing, hmmm

[HopperParticipant @hopper]

Posted by gavin eisler on 03/11/2016 19:53:48:

Some bikes like Manx Nortons seem to manage on very insubstantial fork bracing, hmmm

Manx was a very light bike, running a very narrow front tire. And the Roadholder forks were a pretty substantial lump of metal, which came standard with "proper" cartridge-style damping (they copied it off BMW!). The Metal Profiles forks of 71-2 Tri/BSA were built down to a price methinks, much like the Lucas electrics and Amal carbs of the time. They were pretty basic and minimalist.

[gavin eislerParticipant @gavineisler66495]

The forks have been modified, the springs now sit against a shim stack for hi speed damping with a low speed bleed controlled by a needle valve, adjustable from the top nut, hence the spring rate issue, the cut by 76mm old springs are now too stiff, harsh but fair, so to speak..

The old damper had a crude but effective two way valve, OK for low speed damping , rubbish at high speed, pretty good for the time, and worked OK for me in the past.

As is with it being too stiff i am not getting the full picture,. cutting new springs soon to lower and soften.

[Chris Evans 6Participant @chrisevans6]

Hopper, your mention of Metal Profiles forks being down to a price. I have just refurbished a set from a 1952 ? DOT

OK a trials bike needed to be lightweight but these where very thin walled, no damping oil just grease. Maybe ahead of there time being of an "Upside Down" style. Stanchions plated and ground and new bushes they are good to go, just a few other bits to complete on the bike before I can try them.

[Gordon WParticipant @gordonw]

In my limited experience of M/C forks one of the major elements in fork stiffness is the wheel spindle. The stiffness of the spindle and the clamping method can have a big influence. Hard to do much about on a standard bike tho'. For road use handling is just what suits the rider. I liked my Velo' and also twin down tube BSA, eg Goldy. I was not fond of the much vaunted Norton featherbed.

[gavin eislerParticipant @gavineisler66495]

The BSA triumph OIF sliders have a fairly unusual wheel spindle mount, unlike almost every other bike the spindle is retained in the hub bearings,the spindle is clamped to the fork slider on each side by 4 x 5/16 studs/nuts which bear against alloy saddles, the inner pair of studs have narrower centres and locate in a machined groove in the spindle on each side. It seems robust to me , many owners have cracked the alloy saddles by over torquing the mounting nuts, the book torque figure is wrong, I use a shorty 1/2" Af ringer and have not broken any yet.

I have a Norbsa featherbed A65 , it handles , no doubt, but I prefer the OIF, its very comfortable. The Road holder damping got a going over, fitted extended top bushes and moved some holes around, , very good result.My understanding of Nortons roadholders is that they blindly copied the Matchless AMC teledraulic and failed to grasp some of the finer points of how the dampers worked.

[LathejackParticipant @lathejack]

I know it's been about two and a half years since Gavin started this thread, and since his last post on this site I think, but I have recently been doing the very job that Gavin was asking about.

The Alluminium Alloy fork legs on my 1971 BSA B50 Victor 500 were also worn around the top of the internal bore, this caused a sloppy rattly fit of the fork stanchion when in the fully extended position. So I set them up in my Chinese 13×30 lathe using the fixed steady on the machined surface at the top of the leg.

 

……………I made a fixture to securely hold the legs via the studs at the bottom, the fixture locates in the counter bored hole at the bottom of the leg and centralises the internal bore when gripped in a three jaw chuck or collet, or rather it should do. But the holes in the bottom of the legs, which is counter bored both sides and used for securing the damper rods, were not central to the internal bore of the legs so the four jaw independent chuck had to be used to get the bore running true at the bottom of the leg..

 

…………….A new stanchion was used inside the leg to get the leg running true internaly at the bottom..

 

…………….Finaly got the top of the legs bored out and the 50mm long bronze bush Loctited in place. The bush is then bored in situ to a very close sliding fit with the new stanchions, the bush wall thickness is just 0.75mm when finished.

 

 

……………..The new pattern stanchions have a superb finely ground chrome finish, far superior to the relatively rough turned finish of the genuine original stanchions. They are now a smooth rattle free sliding fit in the legs without any slop.

 

 

……………..This is the bike they are for, it is still undergoing restoration at the moment.

Edited By Lathejack on 17/04/2019 21:11:27

Edited By Lathejack on 17/04/2019 21:14:05

[HopperParticipant @hopper]

Posted by Lathejack on 17/04/2019 21:09:52:

…

…………….A new stanchion was used inside the leg to get the leg running true internaly at the bottom.….

Now that's damn clever. Well done indeed. Had me wondering there for a minute how you wuold ever true up the "deep" end of the hole. Brilliant!

Nice pile of single bangers you have there too.

[Author]

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