Topic: CB750 Box Swingarm, why?

[JBCB500]

Genuine question:  I have in my possession a boxed swingarm for a CB750 - but why should I use this instead of the factory tubular (alligator head) type?

And does anyone recognize the make, etc. from the pics attached?

[BomberMann650]

Box tubing is stiffer than round tubing.

Hopefully someone knows whats up with the extra supports.

[Duke McDukiedook]

Not always. It depends on the thickness, yield stress and moment of inertia of the materials in question.
Tubular sections can be stronger in moment resistance than box sections.

[kmb69]

Not sure who made it but that is a drag bike swingarm with provision for wheelie bars.

First dibs if you decide to sell it and go with the standard swingarm.

[BomberMann650]

Not always. It depends on the thickness, yield stress and moment of inertia of the materials in question.
Tubular sections can be stronger in moment resistance than box sections.

True.  To make a cylinder with the same bend/buckle resistance as a box is no small feat however!  Sure, a thick heavy cylinder could outlive a box of lesser weight and vice versa.

Its fun to explore motorcycle history as you can see where designers were trying to solve problems.  Some got more creative than others.  Tho there is a marked shift in standards where frame material went from cylinder to boxed.

Current manufacturing has further opened the list of possibilities.  As hydroformed parts can contain very complex geometry that favors some pretty light material use!

[HondaMan]

Actually...that resembles an old part from one of the custom shops in the 1970s that made hard-tail conversion swingarms for these bikes. Do those "triangled" upper supports tie to the shock mounts on the frame? The lower multi-hole gizmos were not on the parts of old, but otherwise it looks real similar?

[kmb69]

Actually...that resembles an old part from one of the custom shops in the 1970s that made hard-tail conversion swingarms for these bikes. Do those "triangled" upper supports tie to the shock mounts on the frame? The lower multi-hole gizmos were not on the parts of old, but otherwise it looks real similar?

Not just any old custom hard tail. It's a drag bike clubfoot arm with wheelie bar provision. Check out the left side in the top view. The "lower multi-hole gizmos" are for adjusting the wheelie bar height. The wheelie bar pivots in the holes just below the frame shock mounts.

And, I want it if he decides to sell it.

[754]

Yes a clubfoot, looks like the one I got from Nalley...

[HondaMan]

Actually...that resembles an old part from one of the custom shops in the 1970s that made hard-tail conversion swingarms for these bikes. Do those "triangled" upper supports tie to the shock mounts on the frame? The lower multi-hole gizmos were not on the parts of old, but otherwise it looks real similar?

Not just any old custom hard tail. It's a drag bike clubfoot arm with wheelie bar provision. Check out the left side in the top view. The "lower multi-hole gizmos" are for adjusting the wheelie bar height. The wheelie bar pivots in the holes just below the frame shock mounts.

And, I want it if he decides to sell it.

A genuine hotrod part!

[JBCB500]

Thanks gents as always for the input.  I actually bought a trailer load of parts locally last week and I'm sorting out what to build, what to sell, and what to scrap.

This and several other items are on ebay right now - sorry kmb, I saw this response a bit late.  If you are still interested, this swing arm and a set of drag bars are on ebay.

Also selling a Windjammer SS if anyone is interested.

Cheers,

JB

[kmb69]

Are they already sold?
Are you jb9273?

[calj737]

This and several other items are on ebay right now - sorry kmb, I saw this response a bit late.  If you are still interested, this swing arm and a set of drag bars are on ebay.

Man, he posted his reply 35 minutes after your initial post  Easy enough to pull that item and sell it to KMB in the interest of "community"...

[JBCB500]

jb.1981 and I think everything on there is still available

There'll likely be plenty of swingarms, calipers, and clocks going on over the course of the next few weeks.  Maybe a 750 oil tank or two, and when I figure out which motor I want to rebuild, some engine parts (jugs, cylinder heads, valve covers)

[JBCB500]

This and several other items are on ebay right now - sorry kmb, I saw this response a bit late.  If you are still interested, this swing arm and a set of drag bars are on ebay.

Man, he posted his reply 35 minutes after your initial post  Easy enough to pull that item and sell it to KMB in the interest of "community"...

Not sure what you mean Cal.  All these responses were a couple of days ago?  Anyway, KMB, I have PM'ed you.

[ekpent]

swingarm  http://www.ebay.com/itm/Drag-Racing-Motorcycle-Swing-Arm-/182552315631?hash=item2a80f746ef:g:PfMAAOSwrhBZBRZH

[754]

JB, got any wide rear wheels for 750, let me know.. Thanks
 Or 750 oil tank without dimples..

[kmb69]

I'm guessing that swingarm is worth $200-250.
What ya'll think? Low? High?

[Stev-o]

swingarm  http://www.ebay.com/itm/Drag-Racing-Motorcycle-Swing-Arm-/182552315631?hash=item2a80f746ef:g:PfMAAOSwrhBZBRZH

No longer available on ebay

[JBCB500]

Did the community thing and sold to kmb

[kmb69]

Did the community thing and sold to kmb

Yes, he did. Even delivered it from across town. Thank you JB.
Keep meeting forum members from this area.
Probably several more close by and just don't know it.

[JBCB500]

Cheers KMB!

It was nice meeting you and I hope that part works out for you. It was good talking to you and thanks for showing me around your collection.

First time meeting another member face to face, which was fun.

JB

[JBCB500]

JB, got any wide rear wheels for 750, let me know.. Thanks
 Or 750 oil tank without dimples..

754, not sure what you mean by wide?  I've got what look to be standard spoked wheels and 2 sets of comstars. Please let me know.

I have at least 3 oil tanks - I need to get them off the bikes but two of them look good from what I can see.  The other has a hole in it.

I'll try and pull them off this weekend and see what they look like.