Swinging arm

[bsa-bill]

Yes it was rust and corosion, my point was that even with the spindle siezed the sw/arm still swinug (via torsion on the rubbers),
Come to think about it quite a few bikes and car used rubber torsion for suspension

All the best - Bill

[rocket man]

hi you could go to the bsa super rocket site they tell you howe to remove
the silent blocks

[rocket man]

heres what they say Separating the swing arm (and removing the silent bloc)
The swing arm on an old A10 does not come apart easily. It is held together by the swinging arm fork spindle (42-4362) running through the center of the swing arm. This spindle is held in place by a securing bolt on one end and a nut on the opposite end. I used the following technique successfully for removal of this swing arm:

- remove the bolt on one end of the swing arm and loosen the nut on the other end

- run a piece of continuously 7/16" threaded rod through the holes in the plate on each side of the frame above the spindle, place nuts and washers on the inside of the plates

- torque the nuts outwards to apply a slight pressure on the two plates at each side

- Drive the nut with a hammer until the spindle breaks free

An attempt to drive the spindle out should be made before doing any jacking of the frame to minimize potential impacts to the frame (I have only had to resort to drastic measures like above in one instance). Additionally pry bars and a blow torch may possibly be used for this procedure before attempting to use a jack to force the frame apart (I have never tried the pry bar/torch technique).

Once the swing arm is separated, the inner housings (or silent blocs #42-4662) around the spindle can be removed and replaced if necessary. In my case, I had to remove the silent blocs to prepare my frame for the thermal portion of the powder coating process (to prevent the rubber part of the silent block from catching fire when the powder coating was baked to the frame). There are two silent blocs within the center of the spring arm. These silent blocs are tubular and consist of a rubber spacer sandwiched between a metal inner and outer shell. The rubber spacer and outer shell are half as long as the inner shell (which runs all the way to the center). While the silent blocs could potentially be pressed out (I did not have sufficient equipment to try this approach), I had to use a more destructive removal technique. I was able to successfully remove my silent blocks by torching out the inner rubber. The outer metal shell did not come out as easily after torching the rubber.

If difficulty is encountered with removal of the outer metal shell, a Dremel tool with a 24 inch flexible shaft and a cutter bit can be used to cut one slot along the length of each bushing.

Once the bushing is cut, a long steel rod can be used to knock each bushing out (driving from the opposite side). Note: I forgot to take this outer shell off my swing arm prior to powder coating (which complicated outer bushing removal and caused scratches to my new powder coating when I tried to get it off).

To put the new silent blocs in, a press can be used or, if you are like me and can't afford a press, than a long piece of continuously thread rod can be run through the center of the bloc and swing arm with washers and nuts at each end to draw the silent bloc into the swing arm. In my case, I found that a 3/4 inch threaded ROD (with nuts) used in combination with two 3/4 inch washers and two 1 inch washers was needed to do the job properly. The inner metal shell of the silent bloc is designed to protrude slightly and is not level with the outer metal shell. To prevent the inner shell from taking any torque, on each side place one inch washer around the inner shell (it fits perfectly), than the 3/4 inch washer, followed by the nut. This method forces all the torque on the outer shell. 

[MikeN]

Hello Richard,
  Bill has remarked that his s/arm had the bushes rusted to the spindle.
 Clearly it is not supposed to be rusted.Although it doesnt matter because it demonstrates that it does not affect the correct functioning of the joint, as he found out.
   If he decides he wants to take up moto-crossing and fit longer than standard rear shocks, then they probably would tear out the centres of his bushes.I believe that some off-roaders fit coventional bronze bushes for this reason.
  Im not saying the system relies on the spindle being a very tight fit in the bores .Im not saying its even a very good system.
   The way it works is ,If you look at the bushes you will see that the inner core is slightly longer than the outer .
  This allows the 2 inner bushes to be clamped ENDWAYS between the frame plates when you do up the centre spindle (which should be a nice slide fit).So preventing rotation.If yours rotate then the ends of those thin tubes are wearing away your frame
  You have 4 other joints on your bike that work in exactly the same way at each end of your shock absorbers. They dont revolve on their fixing bolts (I hope).
  Consider this.
 a)The centre part of the bush is made from a soft steel,the spindle is made from   (hopefully)high tensile steel.This is not a good choice for bearing materials.
b)How is one supposed to keep it lubricated, there are no grease points or instructions for maintenance in any manuals.
c)What is supposed to control sideways movement ? There are no thrust washers .If it is as you say then the s/arm would slide laterally and rub on the frame side plates.

Also as Bill states plenty of cars used rubber in torsion for suspension .Thinking about it ,My old Austin A35 used this method somewhere in the front wishbones.
  Cant think of any other  bikes though .
Speak again,Mike

[RichardL]

Mike,

Thank you for an interesting explanation, and it almost had me, but then I thought: why not continue the debate just for fun? I'm guessing you and others are still amused rather than p*ssed off.

So, Roland Pike says to the engineering team, "Boys, what we need is 90 (or so) sq. mm of surface between the frame flange and the inner sleeve of this rubber sandwich so that the frame flange will twist the entire length of rubber in the sandwich, thereby damping vibration from the swing arm."

My point being, I don't think there is enough friction between the inner sleeve and the frame flange to cause the rubber to twist, rather than the sleeve just slipping on the metal-to-metal contact. I'm thinking, grease the spindle like any other surface that requires infrequent lubrication (as in permanently sealed wheel bearings) and let the swingarm move on the spindle and, if it so happens, wear against the flange up to the force available from the resistance of the rubber. The slow and minimal-arc rotation of the swingarm is not going to heat the grease to even within the same universe as its breakdown temperature, and the grease really has nowhere to go, and if it does, it's not that big a deal. It will be just like when someone who thinks no grease is needed tries to remove the rusted-in-place spindle.

Richard L.

 

[trevinoz]

Richard, you are wrong, wrong, wrong! The rubber definitely twists, a small amount at the bush becomes a large amount at the end of the swinging arm.
I have dismantled some with the inner solidly rusted to the spindle and the outer never having moved in the swinging arm. I have actually had to cut the spindles on some.
I have had others with loose nuts on the spindle and the frame was badly worn where the spindle moved in the frame and deep grooves were worn in the side plates where the ends of the bushes were moving.
My Norton Atlas has the same set-up, I couldn't remove the spindle as it was frozen solid so I left it alone, making sure the nuts were tight.
Trev.

[RichardL]

Help me, Clarence, I want to live!  

(I'll be amused if Brits or Aussies know the reference.)
 

[Brian]

Nup, got me. The only Clarence I remember was a crossed eyed lion !!!!!!!!!!!!

[MikeN]

Richard,
  I agree with the last point you made.
   There is not much metal to metal area of contact to do the gripping and frankly, i think its an engineering abomination.

  But thats how its supposed to work and we're stuck with it!

Mike

[BSA_54A10]

Well considering that most silent blocks are in the order of 50 years old, sound like BSA got it right to me.
Also consider that even with trashed silent blocks the bike still runs and handles quite well.
Try riding a modern bike with a loose tapper roller, let alone a trashed one.
If you pretend that the swing arm is a proper triangle and use the length of the swing arm as the base and 4" ( movement in the shocks ) as the height then you can use the trig functions on your kids calculator to work out that the swing arm rotation is some thing like 8 deg.
They are a total pain to do but it some thing that only gets done once every 50 years so it can be tollerated.

Now as to powder coating there is about 100 different types.
If done properly then it is tougher, stronger and more corrosion resistant than the original paint.
OTOH if it is the "melted plastic" then it is a recepie for disaster.

The original powder coating was in fact a fully vitrious enamel that chemically bonded to the oxadized surface FeO ( mill scale ) not Fe2o3 (rust) and was impossible to remove once in place.
The newer cheaper stuff is just finely a ground thermoplacstic plus some pigment. Good fro cheap out door furnature, not good for motorcycle frames.

[coater87]

  Hello,

 While we are on this swing arm subject, I also knew I had to replace my bushings. The right hand bushing feels like its either missing, or too far into the swing arm and that side is very sloppy on the spindle.

 I went ahead and ordered a new pattern pin, and silent blocks. I have not even tried to remove the old yet, but I did do some measuring. The new pin measures .811, and the inside of the bush measures out at .803. I understand these should be a press/jam fit, but that seams like a lot of difference to make up. Does that sound about correct, or are these pattern pieces a little off? I am worried I will peel back the threads quite a bit- should I ream the bushes to say .808 or some such?

 To see if I have this correct, there is a slight bit of the inner bush that sticks out, these little bits are supposed to fit into the frame plates- the larger outer bush should be flush with the swing arm itself. Then you would spread the frame a little, seat the swing arm and try to install the pin. Now one end of the pin has a cam lobe shaped piece of metal, when this is turned just so a hole in this piece lines up with a small hole in the frame plate. Should I try to get these small holes to line up with the swing arm level to the ground- or is it just coincidence that these holes line up at all and maybe the one in the pin is for a spring to hook to or something? Kind of confusing back in this area.

 Thank you,
Lee

 

[RichardL]

Lee,

The pin in question does go into the frame plate and, though no one has mentioned it, it does give creedance to the tight-pin-twisting-rubber theory, as much as I hate it. Now, I'm not sure, but I take it from a previous post that the protrusions rub on end and not circumferentially. If the latter, it would, as you say require spreading the frame. That seems odd and perilous, considering the nearby crossmembers.

As to pin diameter, you are welcome to borrow my adjustable reamer if you need to enlarge the inside sleeve. As for my own bike, I am perfectly comfortable riding in ignorant bliss with a slip-fit spindle.

Richard L.

[RichardL]

I just made a phone call to SRM to hear their position regarding the Silent Bloc bushings. (Not that I didn't believe every one of you, faithfully, trustingly and invariably.) First question: should the spindle be a press fit or a slip fit? Answer: "Slip fit." Second question: is the swingarm supposed to rotate freely on the spindle?   Gulp!   Answer: "No." Third question: is the force on the the inside sleeve from end pressure or circumferential (I'm not near my bike to know if this is obvious)? Answer: "End pressure." Forth question: then, you shouldn't need to spread the frame, right? Answer: "Not if the bushes are meeting properly at the center, however, it can be a fiddly job."

So, I guess I must acede to the throngs. I now think that the necessary force to make this work (if, indeed, it does) comes from pushing at the outside with the force of the tightened nut while the inner sleeves meet at the center to affect enough frictional force to matter.  

I have an acoustics-based discussion on this that must wait until I have time.

Richard L.

[bsa-bill]

Not sure about the last bit as the SW/arm has a stop midway so the outer sleeve meets up with that.
Same thing really as the rubber would transfer pressure

On the subject of rubber torsion suspension was it not Greeves that used on the front suspension with leading/trailing link

All the best - Bill

[RichardL]

Bill,

Look at the long extensions of the inner sleeves toward center.

Richard L.

I hate this. Am I now making the twisting rubber arguement?