Broken 856 rear swing arm

[dglane]

Hello to everyone who reads this and thank you for you attention and thoughts.
Currently own a 856, recently discovered the rear swing arm pivot connection clamp (at the frame) has cracked. I am not certain if I can get away with welding or if someone has a replacement swing arm laying around. Any advice would be great.
Sincerely
Dglane

[shovelon]

The pivot clamp has been successfully welded in the past.

The proceedure I use is to bevel the crack sufficiently, clean, weld with 5356 alloy filler, and immediatly quench in cold water if possible to initiate age hardening.

From there, let it sit for a week or longer for the stresses to settle, or stick it in your kitchen oven for 4 to 5 hours at 450 degrees F. to stress relieve and artificially age harden somewhat.

If you use the oven you can reassemble and ride immediately.This is the same proceedure that the manufacturer used.

Good luck!

[dglane]

Thank you

[kiwi]

i would be murdered if anything like that went into our oven!

[Colin]

i would be murdered if anything like that went into our oven!

Given my wife's cooking style, we might accidentally serve it up as the Sunday Roast! <GRIN>

[willem]

Only 450F?
We just leave 'em out on the asphalt for the afternoon in Texas!

Sheesh it's hot today!

[shovelon]

Only 450F?
We just leave 'em out on the asphalt for the afternoon in Texas!

Sheesh it's hot today!

Time to do the "Cook an egg on the sidewalk" experiment.:-)

[willem]

My ten year old daughter (the biker!) actually did that last week. Not great results.

In July she'll have omelettes al fresco!

Question for Terry and Simon: If I do a proper bearing conversion on my 856 swingarms, will there be less flex than the factory pivots? My single speed has really shown me how much side-to-side flex there is in the pivot. I put the factory pivots back in and it's still pretty bendy.
(And please don't tell me 200# is too much weight!)

Will

[shovelon]

My ten year old daughter (the biker!) actually did that last week. Not great results.

In July she'll have omelettes al fresco!

Question for Terry and Simon: If I do a proper bearing conversion on my 856 swingarms, will there be less flex than the factory pivots? My single speed has really shown me how much side-to-side flex there is in the pivot. I put the factory pivots back in and it's still pretty bendy.
(And please don't tell me 200# is too much weight!)

Will

I don't notice any more or less flex, but the verticle freedom could be cancelling out the feeling of flex.

What I mean is that the the wobbleing of the swingarm side to side is now prevented by earlier shock compression. I have 2 bearing conversions, and and an Evo with factory sealed bearings and I notice the same pattern with all. My other bikes with bushings feel very sluggish vertically in comparison.

Make any sense?
Terry

[willem]

Thanks Terry. I think that you're on to something there.

Here's my plan...
Since I've got external BB's on both 856's they present a really wide and well placed pivot point.

What if I just replaced the swingarm with a BB mounted pair of arms? I could still use the strut for suspension, but make a much stronger set of chainstays.

This would provide two other benefits:
1. No more chain growth when the susp. compresses.
2. Variable susp. ratios by moving the strut fore & aft like Simon did on his faux bar...

If I draw up prints, is this something you could fab out of stock box section aluminum using an old swingarm for the dropouts?

Will

[shovelon]

I could do the welding for sure. I am not sure how the "no chain growth" plays into it, but I am intrigued.

So would not a new frame mount be required to house the BB?

[willem]

If your pivot point is centered on the BB, there's no change in chain length when the suspension travels.
(My 856 chain length goes up 2.5" from rest to when I bottom out the suspension!)

The idea is to simply clamp bearings on the external part of the X BB. It sticks out over 1/5" from the 68mm BB shell and is 1-3/4" in diameter.

So... if I have 1-3/4" internal diameter bearings that clamp on the outside of the X BB shell, on both sides, then I can use that for a swingarm pivot.

This would be great in some ways, and not so great in others. For instance, it would really stiffen up the rear end with such widely spaced swingarm pivots. On the other hand, pedal pressure would compress the suspension somewhat.

Gotta try this someday...

Will

[willem]

Take a close look at the Haro Werx suspension for an idea of how to pivot on the BB...

[shovelon]

Ok, now I understand. As far as suspension bob, a good platform shock will do the trick.

Several bikes like Jamis have been abandoning the Horst link in favor of just using stable platform to overcome the bob.

Horst link or High forward pivot(proflex), and stable platform is the best combination in my mind. Infinately variable.

[Simon]

One point to add
by moving the pivot point you are removing
one of the main things Bob engineered into his
designs and that is his dig in system, something that is
quite fundementle to a Proflex and why they are such noted climbers,Bob pretty much hit the sweet spot in his design.
Just something to consider before embarking on such a redesign.
Will if you do do it I will still be very interested in the
engineering redesign.

Simon.