Frame/swing arm combination

[Peterwh]

I'm putting a 74 swing arm onto a 78 frame.  I thought they were interchangeable.  I've had both powder coated and bought new shock absorbers from vintagecb750.  I loose assembled everything to see how it looked and it seems like the swing arm is about an inch too narrow at the point where the mounting lugs are for the shock absorbers.  I have not tried putting a wheel in yet but it seems as if the shock absorbers will taper in at the bottom.  Any ideas/suggestions anyone?

[cityslicker]

give us pics?

[Peterwh]

I will take a pic over the weekend but the swing arm lug dimension is 9.5 inches from the centre of the plate to the centre of the plate.  The frame dimension from the centre of the shock mount on one side to the centre of the mount on the other side, with the shocks pushed on as far as possible, is 10.75 inches

[Peterwh]

In the absence of a pic, here's a sketch of what I'm talking about

[TOOLS1]

The 77-78 frames are wider then the earlier frames.
TOOLS

[Piute]

  Hey Pete,
 was looking to change my swingarm "77"F2 but finding that mine is about just as long as a 1980 and was advised that not to change cause is one of the longer and better one's made. .02 cents info I recieved.

[TOOLS1]

It is longer, but not as long. When I had the 11 inch shocks on the Toolmatic the tire rubbed against the plastic inner fender on hard bumps. This was even with the chain adjusters at their limit. The DOHC swing are cures both the height problem, and the clearance problem.
TOOLS  

[Peterwh]

Do you think I will be ok with the 74 swing arm in the 78 frame or do you think I should look for a 78 swing arm?  The 74 swing arm is the right width at the bushing end of things.

[voxonda]

Hello ,

The '78 swing is not interchangable with the earlier type. It is longer, which is a big plus it will make the bike more stable, and not prone to "wobble". But because it is re-designed for wider tires and a much heavier 630 chain it is condiderable wider at the rear axle. So the mounting point for the shocks are wider too. But........................you can alter the top mounting point for the shocks to accept the swing.
I did it by turning some special bolts and collars. Bike is still running, after some 6 years, with no issues as far as I know.

Rob

[Peterwh]

Voxonda, thanks for the comment but I'm doing it the other way round to you I think.  I'm trying to put a narrow swing arm (74) in a wider frame (78).  I'm only doing it that way because that's what I have to hand.  I think I'm going to look for a 78 swing arm.  Its just frustrating because I just got the 74 swing arm powder coated,

[Lucky 1]

Bad combination. I would not do that.

The 1978 swing arm was longer than all the earlier models.

I would get another 1978 swing arm or a 1980 swing arm but the 1974 was at least 3 inches shorter than the 1974!!!  I know that the 1978 swing arm was about 1.5 inches longer than the 1976 models.
The very early ones were even shorter. Maybe someone will jump in and tell us about the change dates.

Like I said I think it is a poor choice.

[TOOLS1]

I just happen to know where there are two 77-78 swing arms laying around.
TOOLS

[Peterwh]

How much?

[TOOLS1]

How about $35.00 shipped?
TOOLS

[voxonda]

Sorry 'bout that. Must have misread it. Do not put that shorter swing in a '78. Asking for trouble.

Good luck.

[Peterwh]

Tools, $35 seems very reasonable.  How shall we proceed?

[TOOLS1]

If, you would. Just gift it to me through paypal. My account is my e-mail. [e-mail]. I will get one boxed up.
TOOLS

[Peterwh]

Tools, thanks.  I sent the money by Paypal.  You should have it soon.  Also sent an email with my address for shipping.

[TOOLS1]

Got It. Will be in the mail Monday.
TOOLS

[voxonda]

You can always go this way:

Building it for a customer of mine, added some 1" length for better stability. Swing is more rigid than oem swings.