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

Repair to 1971 A65 OIF fork sliders

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gavin eisler28/10/2016 13:05:10
23 forum posts

Hi Gents, my old BSA has pretty worn forks, the top zones of the fore and aft section of the alloy sliders are worn , I would like to machine out a section back to clean , about 2" deep , then fit some sort of bush, and bore to final size once fitted, A wee challenge for the new lathe. Tips for maintaining concentricity needed as well.


Any recommendations for bush material, thinking brass, bronze , plastic/delrin, the ally has been chewed and torn in the past once the chrome stanchions get pitted, nasty.



Edited By gavin eisler on 28/10/2016 13:06:26

Hopper28/10/2016 13:30:04
4395 forum posts
92 photos

What make and size of lathe do you have? Different techniques might apply depending on size. Are these the 1970-72 type alloy fork legs?

I would use bronze bushings. They are running on hard chrome so that should be a good match. Bronze will wear better than brass. Delrin or other plastic may deform too much under the fore-aft loading on fork legs. I wouldnt use that.

If you are only boring 2" deep, the boring job is nothing special. On a Myford size/type lathe you might look at mounting the fork leg on V blocks on the cross slide and setting up axial alignment using a large centre in the chuck and small centre in the tail stock that fits into the screw hole in the bottom of the forkleg. Final radial alignment could be clocked with a dial gauge mounted on a bar in the chuck, with the plunger running off the unworn fork seal area of the fork leg. Then you bore the fork leg out with a boring head held in the chuck/headstock.

On a bigger lathe, you might hold the bottom of the fork leg in the four jaw chuck, or on a mandrel made to fit into the damper rod bolt hole in the bottom of the leg etc. The other end could be supported on the fixed steady, bearing on the machined outer area where the fork boot fits. (A turned steel ring fitted there might protect the ally from being worn by the brass steady fingers) Then you just bore the recess with a normal boring bar held in the cross slide. On a good size lathe of course the whole leg could be held in the four jaw, lightly so as not to distort it, but as the casting may not be parallel over its length, getting axial alignment could be tricky.

You might look at turning the bushing to finished size then either Loctite it in position or heat the fork leg to 120C or so and drop the frozen bushing in, with interference fit tailored to suit each application. In the latter case, if the bushing shrinks a thou or so on installation, a brake cylinder hone might be all that is needed to relieve it. You want to have maybe a thou clearance there to allow oil to work up between the slider and fork tube in operation.

gavin eisler28/10/2016 14:37:02
23 forum posts

The new to me lathe is an 1950 ML7, with change wheel sets and a clutch, light wear only , I like the Vee block idea, the 70 legs were steel slider, my 71 OIF type has the first of the Alloy slider with the rib down the side and an 8" Conical hub TLS brake.

need to get centres large and small, the lathe didnt have any in the tooling that came with, I have 3 V blocks and a traveling steady, ( not much use here).

So boring bar in the chuck , hadnt thought of that,

Its worth me spending a few quid on tools for this , new sliders are very spendy and I have a few old sets to practice with.

Any particular grade of Bronze , the tooling that came with the lathe is HSS, if that makes any difference to material selection.



Nick Hughes28/10/2016 15:52:30
217 forum posts
131 photos

The bushes fitted to the BSA's with steel lower fork stancheons are "Oilite" rather than a plain bronze.

Modern forks are fitted with a "DU" style split bush :- **LINK**


Mike Lightfoot28/10/2016 18:14:59
76 forum posts
24 photos

Having half a dozen old brit bikes i understand your probs and whilst not totally original i have had some forks chromed back upto size if you have a local hard chrome place its really economical, if however you just want to have a go carry on.

Or i could have read your post properly fork sliders sorry!

Edited By Mike Lightfoot on 28/10/2016 18:18:03

Nick_G28/10/2016 18:45:54
1808 forum posts
744 photos


I would say either phosphor bronze or aluminium bronze.


Chris Evans 628/10/2016 19:07:51
1627 forum posts

I would normally favour the bronze option but..... I have recently re-bushed some Triumph forks for someone and used glass filled PTFE. Not the most stable of things to turn but silky smooth operation when done. At the same time I had to shorten a new pair of fork stanchions to match the originals and make glass filled PTFE bushes for the lower as well. I also fitted the same material to the swing arm bush position and made a new swing arm pivot shaft from hard chrome plated hydraulic cylinder shafting. The bike rides and handles well.

Lathejack28/10/2016 21:47:05
277 forum posts
334 photos

Those 1971 onward fork legs measure just over 13 inches long with the wheel spindle cap and four studs removed from the bottom of the leg. If your Myford is 19 inches between centres then there may be just enough room to grip the square lower end of the leg in a four jaw chuck and, as already suggested, use a fixed steady on the other end bearing on the machined surface under the rubber dust cap or gaitor with a steel sleeve to protect it, and a boring bar in the toolpost.

The circular machined top of the legs is around 57mm diameter, I am not sure what the capacity of a Myford fixed steady or the cheaper copies is. The legs have a wall thickness of just over 5mm, so there is just enough meat for a thin walled bush. As well as the other materials mentioned for the bushes, even aluminium alloy will be fine as that is what the legs are anyway, with the hard chrome stanchions running directly in them.

During the 1980's as well as Japanese bikes I also used a Triumph Trident and three OIF Bonnevilles as all year round everyday transport. These Triumphs had the same type of front forks as your BSA. I found that on a well maintained bike that was kept clean but regularly used the chrome on the stanchions didn't seem to pit but would still wear through to the steel underneath.

Japanese forks of the same type appeared to have tougher chrome and I never had any that wore the chrome, but they did suffer more from the odd spot of pitting, maybe because they were harder than the original BSA/Triumph items. Some of the newly made hard chromed stanchions, as well as re chromed ones, may hopefully be better than the originals.

I have seen a few sets of 71 on BSA/Triumph forks on offer at my local Autojumble over the last 18 months, and they have all had badly worn chrome. One set did have a fairly good pair of unworn stanchions, and these were the more expensive chrome moly type. But some fool had ruined them by using a pair of Stiltsons on them leaving teeth marks all the way round on the working area just above the alloy leg. Honestly! Some people.

Edited By Lathejack on 28/10/2016 21:48:33

Edited By Lathejack on 28/10/2016 21:51:11

gavin eisler28/10/2016 22:24:01
23 forum posts

Ive had this bike for years, and i am now on my 4th set of stanchions, the chrome always wears off the top front thrust zone RHS , the forks twist under heavy braking, the worse it gets the worse it gets, I would love to have fresh up to tolerance sliders. For the last 30 years its had rubber nellows covers , they help alot but the sliders are worn, no getting away from it.

Thanks for the great info so far, if I want to post pics, do i use a host like photo bucket then paste a URL here?

gavin eisler28/10/2016 22:28:25
23 forum posts

Ive had this bike for years, and i am now on my 4th set of stanchions, the chrome always wears off the top front thrust zone RHS , the forks twist under heavy braking, the worse it gets the worse it gets, I would love to have fresh up to tolerance sliders. For the last 30 years its had rubber nellows covers , they help alot but the sliders are worn, no getting away from it.

Thanks for the great info so far, if I want to post pics, do i use a host like photo bucket then paste a URL here?

Lets see.


gavin eisler28/10/2016 22:29:15
23 forum posts

Try again,

 photo IMG_1813_zpsnawxew6t.jpg

Edited By gavin eisler on 28/10/2016 22:29:36

Hopper28/10/2016 23:48:57
4395 forum posts
92 photos

Nice looking old bike. That's not a Morgo big bore cylinder barrel is it?

You might try getting your fork tubes properly hard-chromed and reground. I think some of the aftermarket tubes use chrome that is not as hard.

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.

Then you have the perfect excuse to buy yourself one of those nice 50mm boring heads to bore both the fixture and the job itself. Once you have the fixture set up and the technique perfected you might have a nice little sideline reconditioning Tri/BSA fork legs. Must be truckloads of them out there in need of tightening up.

Clive Foster28/10/2016 23:54:54
2151 forum posts
73 photos

Once you've fixed the forks you really don't wan't to have to do the job again so whilst you are at maybe its worth taking extra time to attend to the fundamental problem. Fork twist. The stanchions are, for all practical purposes, unconnected at the top and move fairly independently in the twist axis. Every movement of the forks alters the relative clearances at the top which induces rapid wear. The lack of conncetion between the sliders doesn't help braking efficiency either. Nor does that puny front wheel spindle.

I had a T150 Trident with the same forks. The uber rare Meridan built version with 5 speed gearbox and larger exhaust ports. Yup all 3. When like brown'n sticky off a polished chrome shovel but the braking was, um, embarrassingly inadequate. I grabbed a double sided 4 leading shoe front wheel off a racing 750 Yamaha 2 stroke and fabricated a proper fork brace from two old style Bonneville mudguard top hoops to have somewhere to hitch the twin brake torque arms to. One in front of the forks and one behind. It also got a proper length steel mudguard with a bottom loop stay which may have added a bit of stiffness. Front brake was much, much better. A "pull out without looking" muppet proved it now capable of locking the front wheel at 3 figure (ish) speeds on a dry road so I never did bother with re-lining the shoes of the 4 leader and fitting it to the bike.

I got it with around 10,000 miles on the clock and put around 50,000 miles on it before selling it on to a workmate who put a similar mileage on before retiring it from the daily commute. So far as I know all on the same set of forks. I never changed them and he would probably have said if they had worn out. Like me not the type to tolerate worn parts or stuff that doesn't work properly.

Which I think proves a point.


Lathejack28/10/2016 23:58:16
277 forum posts
334 photos

Nice bike Gavin, have you found an aluminium alloy cylinder barrel for it? Or is it just the iron one painted silver?

The fork twist isn't helped by those front mudguards with spindly rubber mounted wire stays. As well as possibly a stiffer mudguard I'm sure you must have considered fitting a fork brace, I have seen them fitted to those forks in the past.

While at the Autojumble last month I picked up this front wheel, with the infamous Triumph/BSA conical TLS front brake. You mention your heavy braking, so maybe they are not too bad after all, with a bit of tweaking.


gavin eisler29/10/2016 01:34:29
23 forum posts

I totally agree about the front mudguard as an inadequate fixture, the bracing Clive mentions has been on my mind, its tricky because the later forks with discs were further apart , i made a steel brace for it years ago but it was ugly. I am planning a carbon fibre U brace for the top using the existing mounts and some rear braces using the later end caps which have strut mounts, then a decent mudguard , the stock item is poor, for sure.

I have recently fitted good linings to the brake Saftek grade B , very effective compared with all that have gone before.

A good brace and decent legs becomes more necessary.

The barrels are alloy with Nickasil lining, no steel. I got the bike with 750 Devimead barrels, these mimik the shape but are 6Kg lighter and very wear resistant. Made by John Hill, like me he went to Forfar Academy, and had the same physics teacher . good man, the bike also has a 5 speed box. again from John. unlike me john has the contacts know how and verve to create lovely stuff for these bikes, I am just a very happy user ..Stock cam , 30 mm concs on rubber stubs, big valves, dynamically balanced crank. End fed devi conversion, iron pump.Stock primary apart from the clutch endplate, ally with needle roller thrust bearing.

Hopper29/10/2016 01:38:32
4395 forum posts
92 photos

Lathejack, you can buy longer actuating arms for those chronical front brakes, which give them more bite. Still a step backwards from the lovely full width 2LS front brake of 1968-70 era though, I reckon.

gavin eisler29/10/2016 01:39:00
23 forum posts

My experience with the brake , used a lot in anger the drum expands and causes fade, that was with 3 x crappy shoes, I have now fitted extended brake op arms, but the big change was the Linings, if you send Saftek ( good to speak to on the phone ) your old shoes , £34 , best money I ever spent on the brake. Grade A is for Regular B sporty C race. B works for me.

gavin eisler29/10/2016 01:57:03
23 forum posts

If this is too much of an advert please pull, but this stuff is usually unobtanium.

John Hill frae Forfar makes batches of barrels and 5 speed clusters. for BSA A65s only. The barrel fitted is one of his. If anyone is interested. Theres also a 5 speed variant by someone else using a barrel cam set up, like buses, no 5 speed boxes , now two to choose from. The alloy barrels are shorter than stock and use B44 size pistons with a lower crown to pin dimension, same as the old Devimead conversion.Shorter A50 pushrods as well. ive got 2,000 miles on the barrels, so far with very low oil consumption and no piston scuffing using straight 40W oil. the 5 speeds have just gone in , still settling down but very good so far. The5 speed conversion puts an extra bearing behind the clutch where the seal plate used to be for more mainshaft support. my old iron 750 Devi barrels were past the last rebore, the new ally ones have brought it back to life, now using air filters. lesson learned.

Edited By gavin eisler on 29/10/2016 01:58:14

Hopper29/10/2016 02:22:53
4395 forum posts
92 photos

Interesting stuff indeed. Not your run-of-the-mill A65, to be sure. Should motor along pretty nicely.

Lathejack29/10/2016 02:53:55
277 forum posts
334 photos


Yes I have seen the longer actuating arms, but the 8 inch TLS brake is intended for my 1971 250 victor so I don't want to end up with it over braked. A carefully fettled standard conical TLS should be better than the 6 inch SLS conical brake currently fitted, but the Saftek brake linings that Gavin mentions might work wonders for the 6 inch brake as well. The longer arms could be a final solution if all else fails.

I agree that the earlier pre 71 Triumph/BSA TLS brake is excellent, I have one on my other 1969 BSA and it is fabulous. Over the years I have seen many discussions in mags and on the web about problems and improvements with the conical front brakes, but not a lot said about the earlier TLS brake because it works so well as it is.



The Nikasil coated alloy cylinders on your BSA are interesting. I remember buying and fitting a set of Gilardoni Nikasil coated alloy cylinders on my 750 Bonneville. They came with close fitting Mahle Pistons matched to the bores, they made the engine run a little quieter and cooler. I wonder if they are still available.

Here a few more items from the Autojumble. A set of genuine original brake shoes for the conical 8 inch brake, plus two sets of unused linings complete with a pack of Ferodo rivets. If all these fail to work well then I will look into the brake linings you mentioned.


Let us know how you get on with the fork legs.

Edited By Lathejack on 29/10/2016 02:57:43

Edited By Lathejack on 29/10/2016 03:08:48

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