The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Frame => Topic started by: rwbeard on 26.06. 2016 12:02
-
Good morning,
Having acquired an almost completed RGS replica machine 3 years or so ago, I have worked my way through the bike getting it to near perfect running order. The machine had been put together by previous owner starting in 2007, and has virtually all new parts including a £5k+ SRM engine rebuild!
I have never been happy with the front forks, they felt stiff, and there was always a roughness to their action. Also there was significant vibration on braking, even though the brake drum was perfectly set up and had been checked for distortion and found to be OK.
So decided to strip down forks (having invested in the right tools some time ago), and was very easy indeed. Fork seals were hardened, and leaking. But it soon became evident why the fork action was rough when I removed the bushes for inspection. The lower bush that slides within the bottom fork leg is worn, and the inside of the fork legs are not smooth. I have included photos. There was also slight play on the right hand bush to its stanchion, and I suspect that this may be the main constructing factor to the vibration through the forks when braking. Bearing in mind what I found, I suspect that the original fork components were not particularly well matched.
Considering the bike has probably only done 150 miles since being rebuilt and recommissioning, I am surprised at the wear, and I know the bushes and stanchions were new as I have the original receipts.
Whilst it would be a simple matter just to fit new bushes, I am worried about the potential damage to the inner surface of the fork legs on the longevity of the bushes. Can the insides of the fork legs be gently honed to a smooth finish? Or would it be best to buy a new set of fork legs? If the latter, does anyone know the best source to purchase from as well as the respective part numbers.
Much appreciate your help
Thanks
Bob
-
hi, its easy to resolve your problem but you may not want to copy my old shop method.
i fit the new bottom bush on the stantion , done up tight, then attatch to a bottom yoke put in a bench vice. i add loads of grinding paste to the bottom bush and slider and twist on the slider[ if its not tight bush is wrong] . continue back and forward along the bush until it doesnt bind.adding a little oil also helps.
removing all the old grinding paste is a challenge which is why i m loathe to post this method. but i use it.
-
Hi rwbeard,
Those legs look bad, secondhand replacements are needed as new legs are very rare and expensive if you find them
Usually if theres only slight damage they can be lightly honed
but any metal removed adds to play in the assembly
Edboy
if grinding paste is used it will embed in the bronze bush and continue its grinding once the fork is assembled *eek* *eek* *eek*
John
-
The sliders typically get 'belled out' where the lower bush slides. Nasty, - new bushes won't help if this is the case. Should be possible for a machine shop to replace the tube section shouldn't it? Anyone ever done this? (Mind you it would probably cost a leg ;) ).
-
No you don't put a sleeve in there.
You get the leg line bored and then make up some custom bushes the same as you do with any worn out bush.
-
Ruddy'ell who said put a sleeve in there!!!
If you're referring to my post I said "replace the tube section", not sleeve it. There's precious little wall thickness for line boring down there as it is, you'd be weakening a very critical structural component, I certainly wouldn't trust it on our roads around here! Surely easier and MUCH better to machine off the top and bottom lugs and fit new tubing to them?
-
an amazing amount of work suggested for an easy repair. with grinding paste you are only honing the fork bore to the bush. all old grinding paste does has to be removed but i cant agree with greybeard [sorry greybeard ] about it remaining in the bush after it has been properly cleaned. however my suggested method is shop and not really for a beginner which is why i was loathe to post it. but the choice rests with the owner.
-
an amazing amount of work suggested for an easy repair. with grinding paste you are only honing the fork bore to the bush. all old grinding paste does has to be removed but i cant agree with greybeard [sorry greybeard ] about it remaining in the bush
I've been guilty of this (if guilt is there to be found) - the logical safeguard is to use a sacrificial bush
-
you tube BSA FORK BUSHES a guy rebuilding a65 worn forks interesting he also takes on work
-
.. I cant agree with greybeard [sorry greybeard ] about it remaining in the bush...
Not me guv!
Mind you, I agree that bronze bushing is very likely to hold particles in its porous structure.
-
sorry greybeard, no it wasn t you who originally suggested old grinding paste remained in the bush but now i see your firmly in the leave camp. what is this country coming to.
-
...greybeard...
...i see your firmly in the leave camp...
Only with regard to grinding paste on bronze bushes.
-
Really, how bad would it be if some microscopic particles of grinding paste remain embedded in the fork bushes after a thorough scrubbing? The forks are not reciprocating at thousands of times per minute, like a piston, wherein warnings of cleanup with sandpaper may be appropriate. The gobs of paste used in the first place to actually get the job done will be gone. The microscopic particles will not be leaving the forks to contaminate other surfaces, like rod journals. Others will have more experienced opinions, but it sounds like much ado about nothing to me.
Richard L.
-
G'day Richard.
You'd be surprised how many times the slider moves up and down just riding around the block. You'd also be surprised at how much grit will be inbeded in the bush even after a good scrubbing. I myself would not do it.
I'd give the sliders a quick hit with a cylinder hone then machine new bushes to suit.
cheers
-
Hi All,
A new bush should be a good fit in the leg,
adding grinding paste as suggested will lap away the bronze and some of the leg as well,
this will lead to a loose(r) fit
It may be of use when theres a ding in the leg, but will wear an equal amount from the opposite
side ofthe leg !!!! *problem*
I would not use the bush again, as the embedded particles will continue to lap away at the fork leg *eek*
Theres a tool called a "David Brown" reamer which with the correct blades could be used to ream a worn leg circular (provided you could remove the taper plug at the bottom)
A "Sunnen" hone would do the same job, but are a megabuck item
Then special oversize bushes would need to be made to suit
Over the years I have made two different tools to overcome light scores and also to remove a ding in an otherwise good leg
The first is a hone of sorts, a steel plug thats a good sliding fit in the leg has two slots milled lengthways
for about half its length, these are sized to accept square section hone stones
cross drilled holes in the plug slots take some springs to push the stones outwards
the length of the hone stones extends past the end of the tool to work on the fork leg walls around the taper plug at the bottom.
The opposit end of the plug is drilled and tapped to accept a piece of 1/2 round steel, so the hone can be spun with an electric drill
The second tool was made from an old stanchion and bushes,
I cut away a piece of the bottom bush and leg and silver soldered in a piece of tool steel
this was then ground back and a cutting edge formed until it was a sliding fit in the undamaged part of the leg, the stanchion was rotated slowly in the lathe and the leg was fed inwards until the tool steel cut away at the high spot
It took several attempts to get the cut just right and the new leg and bush to slide nicely *work* *work* *work*
I have heard of "modern" stanchions and proper dampers being fitted into period forks
Has anyone more information on such a mod????
John
-
Well, I just got wrapped in the idea of the embedded partcles. Thinking of the whole job, of course you wouldn't reuse that bush. Love the tool with the spring-loaded stones.
Richard L.
-
I'm still interested in the idea of replacing the tube section with new tubing. I have several sets of unusable sliders that have the 'belling out' issue, where the tubing wears and expands over the area where the bush travels. Honing maybe okay for fixing minor scoring but not heavier wear. Velocette forks can be made like new, because the top and bottom lugs can be removed, and the tubing replaced with new stock, the lugs are soft-soldered on which makes it easier. I was wondering if anyone has tried this with BSA forks.
-
I dont think a Sunnen hone would get rid of his marks, they look too rough.
You would have to be a man of steel to hold that fork leg steady without it wobbling so bad the hone actually makes it worse. When I was a kid my best friends dad was a mechanic and had a beautiful Sunnen set-up, with all the hones, the rod sizer, even oil feed. I wrecked a fair number of lawn mower cylinders learning to use it, and it does not take long for your shoulders to start to burn *ex* If the part is badly scored (like that) or even slightly out of round, the hone of course wants to follow what is already there. So you have to nut-up and hold it straight so the hone can true it. With a fork leg you would not have enough leverage to clean that I dont believe, and the walls being as thin as they are it might be tin foil by the time you did.
BTW, when John retired nobody wanted the business. Everything sat unused for years until the building was sold. They junked the Sunnen, a nice Monarch 10EE lathe, and the rest of the tools he left for the "next owner". *sad2*
One thing I would try if you can find a small amount is Belzona. It looks like Hocus Pocus but the stuff is amazing and we still have huge pumps and large DC motors that do not fail using that stuff. Down side is the amount they want to sell you, I am not sure but I think the smallest amount they sell is something like 300 of those funny pounds things you guys buy stuff with.
Lee
-
I'm still interested in the idea of replacing the tube section with new tubing.
Jools, I'm sure someone like one of the ravers did that a while ago- maybe do a search?
John
I have heard of "modern" stanchions and proper dampers being fitted into period forks
Has anyone more information on such a mod????
...
After Trev said "no sleeves" my first thought was why can't it be possible to male a full- length top bush and use later stanchions and dampers; then I got to your comment. *wink2*
-
In case anyone is interested, the Belzona stuff you would need is 1311. This stuff is used in industrial settings, and it lasts.
Lee
-
G'day Mr Beard,
I read your comment "The inside of the fork is not smooth" and would like to know more about the problem you have. The sliders are usually internally dimpled from clamping them in a vice or just worn out. If worn I would recommend replacement with second hand items. My own sliders were damaged by clamping them in a vice, so I made up a mild steel mandrel (similar to a bush) and welded it to a thick rod. This tool was clamped in the vice and the slider was pushed on till it stopped, then very light taps with a hammer around the damaged area repaired the damage.
Cheers Tomcat
-
Eeeek! I can feel the pain!
-
G'day Mr Beard,
I read your comment "The inside of the fork is not smooth" and would like to know more about the problem you have. The sliders are usually internally dimpled from clamping them in a vice or just worn out. If worn I would recommend replacement with second hand items. My own sliders were damaged by clamping them in a vice, so I made up a mild steel mandrel (similar to a bush) and welded it to a thick rod. This tool was clamped in the vice and the slider was pushed on till it stopped, then very light taps with a hammer around the damaged area repaired the damage.
Cheers done the same with an old bush two washers and a length of threaded bar
-
Thanks to everyone who responded with ideas. I really do appreciate the thought and the time taken to consider solutions to my problem.
The lower fork leg bushes are badly scored, so grinding out any high spots or rough spots with paste might be worth a go, as I will need new bushes anyway.
SRM Engineering suggested having a look at the honing route, and they said that hey we're going to manufacture new RGS fork legs, but that would be the last resort.
I will keep you posted as to how I get on, now that I have been inspired to try a few of the forum member's ideas.
Best wishes to all
Bob
-
my legs were in a similar condition to these and I used a wooden dowel wrapped in wet/dry paper and spent hours working it manually up/down/around as best I could to simulate a "honing" action, then thoroughly washed them out and had new bushes made to fit. The bike is still far from road ready but the sliding action on the legs is good with no feeling of loose/slackness......
-
The fork sliders on both my outfit and rusty are replica's made with hydraulic pipe. (non standard bushes)
We did the sidecars first as I wanted a leading axle and a fork brace mod. Whereas Rusty we kept stock. We used old rusted sliders as donors for the bottoms and tops.
I can't take any credit, my engineer knocked them up
I understood that new ones were now being made though *dunno*
Pictured are copies and have A65 damper internals
-
Trust a Kiwi do do it properly. (And what's that TLS brake?) *wink2*
-
Quote
I'm still interested in the idea of replacing the tube section with new tubing.
Jools, I'm sure someone like one of the ravers did that a while ago- maybe do a search?
I had an idea it was you RR- that should've said 'racers' not 'ravers' *eek*..
[quote(And what's that TLS brake?) *wink2*][/quote]
I believe that's from a '68 A65/50 as discussed a while ago
-
So when did they produce a brakeplate like that, without the air-scoop etc?
-
yeah ok, I was just looking at the lever action, I'l have to let RR clue you in...I can only suggest it's a'68 setup adapted to a SLS back plate *dunno*
-
RR,
When these were made up, I trust the bottom was welded, did your guy braze the top on?
I just blasted both of mine, one is fine and the other is a little bellied at the top. I might have to do this to one, if its easy enough might as well do both....
Lee
-
Dutch had it, I'd posted pics on my thread "Rusty" and I think there are some good slider pics on my road rocket racing sidecar thread too, before I painted them.
I wanted a TLS that didnt look too non standard and have a few spare brake plates so my trustee engineer converted the SLS plate. The hub is later 68/70 flanged type.
I'll confirm with my engineer how he assembled it. I recall the tricky bit is the mudguard mounts as its easy to distort the tube and we had a slight tight spot to relieve with a flapper wheel.
Sadly all these sliders are well worn and fresh ones make sense.