Topic: DOHC CB750 swingarm in a K1

[Industrial Cafe]

I really like it, it handles really well and it launches better than the short swingarm.
I think it has something to do with weight distribution, I sit -pretty much- right over the shocks. and my front end used to come up enough to get light under hard acceleration.

not anymore.

[MCRider]

thanks,  hopefully, someone can get the general idea from this thread.

   I hear ya, it just might get to be a "Common Conversion" that folks just get in on and DO! THAT would  be something.

What's the advantage of this arm over stock? It is tubular and longer, anything else?

Edit: I just read the last post from IC. Things attributed to length. I see.

[brycegp]

I should have cut a 1/4 inch off each end of the inner race.
but it works.

I am doing the same thing on my K2 now.   And I have some additional questions on this swap, if you don't mind me asking.

1.  What do you mean by "1/4" off each end of the inner race"....?  Is this the metal tube that goes in the pivot tube??
2.  Once you trimmed the length off the swingarm pivot point and removed the old bearings, did the new bearings just pushed right back in??  Or would you now recommend going with bronze bushings instead of needle bearings?
3.  Did you use the late model sprocket or the K1 sprocket?
4.  What length chain did you go with after the swap?  Does the longer DOHC chain now work?

Here are the parts I am using.
1. '80 swingarm and pivot bolt. (all length trimmed .5" and pivot mount hole on the frame bored to fit 16mm pivot bolt)
2. K2 hub
3. K2 brake drum
4. K2 Sprocket
5. '80 axel, cush drive and spacers.

Thanks for reading...

[Industrial Cafe]

I should have cut a 1/4 inch off each end of the inner race.
but it works.

I am doing the same thing on my K2 now.   And I have some additional questions on this swap, if you don't mind me asking.

1.  What do you mean by "1/4" off each end of the inner race"....?  Is this the metal tube that goes in the pivot tube??

yes, the one thats shiny on both ends and machined in the middle

2.  Once you trimmed the length off the swingarm pivot point and removed the old bearings, did the new bearings just pushed right back in??

yeah, the inside of the swingarm is machined in quite a ways

 Or would you now recommend going with bronze bushings instead of needle bearings?

I went with needle bearings cause they were readily available and they were a direct replacement (so it was just like stock)

3.  Did you use the late model sprocket or the K1 sprocket?

I used my original K1 sprocket. the chain is easier to find in different lengths and colors

4.  What length chain did you go with after the swap?

120 link, and cut out 6 links

Does the longer DOHC chain now work?

the DOHC chain is a 630. you'd have to change your drive sprocket as well as leave off your front sprocket cover for clearance

Here are the parts I am using.
1. '80 swingarm and pivot bolt. (all length trimmed .5" and pivot mount hole on the frame bored to fit 16mm pivot bolt)
2. K2 hub
3. K2 brake drum
4. K2 Sprocket
5. '80 axel, cush drive and spacers.

Thanks for reading...

be real REAL picky on your spacer lengths, you gotta line that chain up PERFECT. you might need to do some mods to the spacers.
you shouldn't have to stretch the swingarm apart or squeeze it together either.
do not hesitate to ask more questions.

[brycegp]

thanks for all the help...I've got the arm mounted up and the sprocket seems to be lining up perfect.  but I don't have a chain yet so I'll have to wait to see for sure.

As far as the spacers go...I used the sprocket side spacer from the early model on the brake side.  And I used the sprocket side spacer from the late model on the sprocket side.  That made it mount up at the right over all width between the axel mounts.

Question:  Did you have to modify the brake lever rigging?  Now its seems to be hitting the new swing arm in a couple spots.  Maybe in reinstalled the rigging wrong...

[Industrial Cafe]

Question:  Did you have to modify the brake lever rigging?  Now its seems to be hitting the new swing arm in a couple spots.  Maybe in reinstalled the rigging wrong...

yeah, it's supposed to hit I think... it did on my original swing arm, stops the pedal from just hanging there and bouncing around.

 I repositioned the foot pedal on the splines cause the pivot tube on the swingarm is larger and pushed the lever down about 1 spline tooth.

[Industrial Cafe]

thanks for all the help...I've got the arm mounted up and the sprocket seems to be lining up perfect.  but I don't have a chain yet so I'll have to wait to see for sure.

you'll know when you go to ride it around and it starts leaving grease marks on one side of the rear sprocket

[brycegp]

Now I am noticing that the wheel is offset about .5" to the brake side of the bike.  But the sprocket lines up!  And the wheel is lining up in the center of the swingarm.

I think its because I used the late model cush drive (which is about .25" wider).  But now I am thinking there is no reason I couldn't just use the original cush drive.  Then the wheel will be back to original.

like you said...just find the right spacers to position the original wheel correctly within the new swingarm.  (I thought I'd already done that.) Can you tell me how many inches of spacers you've used on each side?

thanks, man!

[Industrial Cafe]

heh, mine is offset about .25in or so to the brake side as well, I think it's because I used the inner spacer from the k1 on the k8 carrier. the reason I say this is because the carrier sits inside the hub a bit.

[KRONUS0100]

no pictures yet.  using 1981 cb900f swingarm into a 1976 cb750f.......stock 1978 cb750 rear wheel/brake....fits centered in swingarm just like it should.  have trimmed the right side of the pivot 10mm......waiting on new bearings.  having sleeve made for the stock pivot bolt so i dont have to bore the holes in the frame.

[Industrial Cafe]

good idea.

[Free Booter]

1997 HONDA CB250 NIGHTHAWK SWINGARM?//