Topic: swing arms

[captain rats]

Is it the F series swing arm that's slightly longer than the early k series or the K8?

After a longer swing arm that will bolt on with no mods. Advice appreciated?

[bjbuchanan]

F is longer

[78 k550]

I have a 76 swing arm and chain guard.
PM me if interested.

Paul

[754]

77/78 f or k are both longer, not a lot mind you.

[Bailgang]

The left side shock mount sticks 10mm farther out on the 77/78 F and K so shock alignment issues can be a problem when mounting the later swingarm to an earlier K or F.

[Stoli]

A CB650 swingarm is longer than all of them but does require a slight mod. I realize you stated no mods but thought it was worth mentioning. All you have  to do is englarge the holes in the frame to accommodate the larger pivot bolt. You will also need the axle and spacers from the 650.

[754]

500-4 is also longer, but I think same pivot size. Opening pivot hole is not easy to do a nice job,  but you can make spacers, and run, original size bolt.

[MiGhost]

A CB650 swingarm is longer than all of them but does require a slight mod. I realize you stated no mods but thought it was worth mentioning. All you have  to do is englarge the holes in the frame to accommodate the larger pivot bolt. You will also need the axle and spacers from the 650.

The '79 CB650 used the the smaller 14mm pivot bolt common to 76-78 550\750 and would be no mod bolt in.

[754]

Be careful opening the frame hole for bigger pivot. If not done accuratelly, you could end up with slop there, be simlar to worn swingarm bushings..

[Retro Rocket]

Be careful opening the frame hole for bigger pivot. If not done accuratelly, you could end up with slop there, be simlar to worn swingarm bushings..

+1, its far easier to modify the swingarm...

[Stoli]

+1, its far easier to modify the swingarm...

How do you modify a swing arm to accept a smaller pivot bolt? All I can think of is custom bushings and although that is probably a more elegant solution than opening the holes in the frame, I wouldn't consider making brass bushings easy. Hondaman makes custom SA bushings so you could send it to him I suppose. That would be easy.

[dusterdude]

Bushings

[Don R]

Remember the F's had disc brakes. That requires a mod.

[captain rats]

Some great advice and tips there including stuff I never thought of.

How much extra length we talking about with a k8 swing arm, if anyone knows?

[Stoli]

In a nutshell, you gain an inch with the K8 and 2" with the later ones. Here are some pics from another thread - link to that entire thread below. As you read through that thread and some others on here, you might be scratching your head as different guys point out different things that they had to do to make things work.  I think the biggest source of confusion (for me anyway) is that very few refer to the year (and/or model) of the DOHC that they were using, and there were differences just like there are differences between the different years of the SOHC.

The above pic is from this thread which has some good info -

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)

http://forums.sohc4.net/index.php?topic=34880

[Stoli]

... As you read through that thread and some others on here, you might be scratching your head as different guys point out different things that they had to do to make things work.  I think the biggest source of confusion (for me anyway) is that very few refer to the year (and/or model) of the DOHC that they were using, and there were differences just like there are differences between the different years of the SOHC.

Case in point - in the pic above, the DOHC shows a "pivot" length of 9-3/8" which you would need to grind down to fit in the CB750 SOHC frame, but an '81 CB650 has a "pivot" length about 1/16" less than a CB750 SOHC, so instead of grinding, all you need is a large washer used as a spacer.

I know you are not looking to go with anything that needs a mod, but I am just posting that here in case there is someone else that reads the thread and is thinking about a DOHC swingarm.

[captain rats]

That's awesome, thanks will be a good help. Good to see some fit a wider tyres too.

[Retro Rocket]

That's awesome, thanks will be a good help. Good to see some fit a wider tyres too.

Rats, I have a pic somewhere of a 4.5 inch rim in a stock 750 swingarm, you would be surprised just how big a tire you can squeeze into a stock arm mate... I'll dig it out and post it...
Here you go...



And here's a pic of a modified GSXR swingarm i have , monoshock removed and shortened, I also have a GS1100 {gsx here} that i'm having the pivot area removed and shortened at that end and a new pivot tube made up, anything is possible mate...
The alloy arm is on a CB750 F1 frame...

[calj737]

Retro - is that a 17" wheel on that swing arm?

[MarshallCS]

So between a 78F swingarm and a 79 650 arm, the 650 arm is longer with no other mods needed?

[Retro Rocket]

Retro - is that a 17" wheel on that swing arm?

Yes Cal, its a 4.5 inch x 17 off a 1988  gsxr750J, same size axle as the 750 too...