Topic: Extended Swingarm

[WestCo]

anybody here have any experience or ideas on extending your swingarm? ive seen a couple that look like theyre cut right behind the bolt tube but before the rear drum stabilizer attachment(leaving your rear braking system unmolested) and a steel plate of your desired stretch welded in between. i was thinking about trying this with a spare swingarm i have but a couple questions arose.... 1) what guage steel plate to use? 2) is it going to be strong enough to hold up with the weight and road vibration? and 3)whats the best way to be sure it stays straight and true?  ive seen the finished product just curious if anybody has any experience with the process of doing one this way? or another way?
this would be for a 750, if it makes a difference.
Adam

[ekim98]

Are you thinking of doing this for looks or are you planning on doing some drag racing. I would assume it's for looks since a stock 750 doesn't really need it, although it would probably give a smoother ride. Seems like a lot of work just for a look, at least to me, by time you make the changes for the brake,chain,shocks and possibly the rear fender.

[754]

Machine a replacement tube same as stock pivot. Move it ahead desired amount, cut two tubes to fill in the space. Assemble to weld using original pivot to square up & comfim parralell.
 Box in if desiored.. , quick method, there are other ways (but not as easy to do w/o fixture.

You can drill 2 pcs of flatbar clamped tpgether to put against sides of pivots with a bolt running thru the pivots, will keep them dead parralell

If you are running struts you do not need bushings.

[WestCo]

yeah ekim98 this would be more for looks..the bike is a project that i started that arrived in boxes so the work doesnt really bother me, im always trying to learn something new especially with metal fab.

Machine a replacement tube same as stock pivot. Move it ahead desired amount, cut two tubes to fill in the space. Assemble to weld using original pivot to square up & comfim parralell.
 Box in if desiored.. , quick method, there are other ways (but not as easy to do w/o fixture.

You can drill 2 pcs of flatbar clamped tpgether to put against sides of pivots with a bolt running thru the pivots, will keep them dead parralell

If you are running struts you do not need bushings.

thanks for the tip that definitely sounds do-able...might have to see what i can work out this weekend or next, got a broken timing chain and gears to replace in my truck first...arrrggg
~Adam

[ekim98]

I only asked because I made an extended swing arm for a friends 165 honda dirt bike .he raced. 2" longer than stock, only 6 ounces heavier than a $600 after market alloy arm and about 2 lbs lighter than stock. It was a lot of work but he liked how it preformed and the price was cheap (free). Did I say he work for the local Honda dealer and my bike always ran real good!!! I got real great dealer service.

[UnCrash]

You could run a 77 or 78 750F swingarm, they're a little longer...

[void909]

did you get that bike in a box off ebay?

[WestCo]

did you get that bike in a box off ebay?

yeah a couple months ago

[bill440cars]

       How about some pictures of this bike? Before you said that you were going to do the work on the swing arm, I was going to recommend the Great Lumbee, he's offered extended swingarms before.Sounds like you are getting the info you need though, so we'd sure like to see the end result of that little endeavor. 


                                   Take care, Bill  

[rustrocket92]

If i want to use my 78f swing arm in my k3 frame do have to do any modifications to the k3 frame ?

[Alan F.]

you may have to do a few mods as the shock mounts on the K8 swingarm will be wider than the shock mounts on your frame, also I understand that the passenger peg mount will be either very close or in contact with that swingarm.

I also understand the early DOHC cb750's swingarms will bolt right up, and are a good couple inches longer, check the chopper boards for info on these.

[RRRToolSolutions]

This is how I did mine - I simlply took my cut swingarm down to my local steel supply and had them match-up thickness and diameter. Those guys looked at it for 5 seconds and told me exactly what size and type I needed for the 3" tube extensions and the brace.

Regards,
Gordon

[rustrocket92]

I stuck my 1978 f swingarm in there this weekend just to see what would happen. It seems to fit fine at the shock mounts. But it does make contact at the rear peg mounts of the k3 frame.

[Geeto67]

you could just get a 1979-1982 cb750F swingarm. Very early ones fit the frame with no clearance issues, later ones (mid 1979- onward) need to be trimmed at the pivot to fit but still no real issues. Outside of the pivot trimming it is a bolt on deal.

[ratSOHC]

Here's three swingarms for comparison

top to bottom, left to right... '74, '77, and DOHC.





(ignore the obvious screwup with the 10&15/32"... it's 10&7/16" but I can't be bothered to go back and modify the pic)

To swap the DOHC swingarm into my '74 frame I;

trimmed the swingarm with an angle grinder and a plastic ziptie as a guide. ALL the meat comes off the "lopsided" side of the swingarm.
Deburred the cut end
installed new bronze bushings
Installed. Greased.
Used the early hub, late model cush drive and spacers, late model axle. Perfectly aligned sprockets.

it was easy.

[Really?]

Sweet!  Gotta love the pics!

[katmol]

What do you mean by the "lopsided" side of the swingarm? The side with the brake brace?

Here's three swingarms for comparison

top to bottom, left to right... '74, '77, and DOHC.





(ignore the obvious screwup with the 10&15/32"... it's 10&7/16" but I can't be bothered to go back and modify the pic)

To swap the DOHC swingarm into my '74 frame I;

trimmed the swingarm with an angle grinder and a plastic ziptie as a guide. ALL the meat comes off the "lopsided" side of the swingarm.
Deburred the cut end
installed new bronze bushings
Installed. Greased.
Used the early hub, late model cush drive and spacers, late model axle. Perfectly aligned sprockets.

it was easy.

[Hooligan]

Used the early hub, late model cush drive and spacers, late model axle.

What is a late model "cush drive"?

THX!

[Geeto67]

Used the early hub, late model cush drive and spacers, late model axle.

What is a late model "cush drive"?

THX!

A cush drive refers to the rubbers inside the wheel that the sprocket drive slides into, a late model one means he probably used one from a DOHC as well as the sprocked drive and the spacers to fill out the wheel. 1979-1980 cb750F rear rims are near identical to 1977-1978 rims which means you can use your SOHC wheel with the DOHC parts in getting the rear end sorted.

[kmoll70]

so what is the appropriate year range to get for the swingarm?

[ratSOHC]

Sorry.

The swingarm is from an 80 or 81 DOHC.
Forgive my error, I should have said sprocket drive.

I, when switching engines in the '74 frame from a seriously beat up '72K, to the '76F, had to use the wheel spacers from a '77, plus the sprocket drive from the '77 to get the drive sprockets to line up.

[Industrial Cafe]

i know i'm late coming in on this topic but, i just got a 1980s dohc swingarm and the pivot bolt seems to be 16mm, whereas my pivot bolt is 13.8...

are the pivot tubes the same size and i just need to use my '71 bronze bushings or what?
 

[Don R]

I did one using the method you described. I pushed 1 1/4" angle down the legs of the swingarm, welded inside and to the front section then boxed with 1/8" plate. I have not ridden it yet. The method using the new tube sounds better.

[Industrial Cafe]

looks like i'm going to have to drill out the mount holes on my frame... 
the 80 dohc swingarm i have has needle bearings. and the original off the bike has bushings.

[bronco7794]

I'm looking at a '78 cb750A swing arm... do you think it is the same arm as a "K"