Topic: can you add a 750 swing arm to a 550 frame

[neil young]

a guy down the street is selling a 76 or 77 750 f  swing arm with the wheel and disk brake,and master cylinder.will this fit on a 71 500 k frame or a 77 550 k frame without any mods.he wants $60.00 bucks for  it

[Jerry Rxman Griffin aka MuthaF'er]

Not sure but you need to clarify whether it is a 75/76 or 77/78. Can't be a 76/77. The master cylinder is a dead give away.

[neil young]

ya just talked to him .he says it is a 75-76 750 f...;thanks...now will it fit

[cleveland]

I have a 74 CB550 that I would love to put the rear disc & MS from my 75 750F onto.  (Fingers crossed)

[Jerry Rxman Griffin aka MuthaF'er]

I have my doubts about the swap. IE I don't know. One thing I always do is cross reference part numbers for an actual match. There are many interchangeable parts between the 550F and the 750F but the K is probably another story. Trial and error perhaps? Hopefully someone has attempted this.

[neil young]

the owner say that it is the same width as a 750 k model.it is 1" longer.

[Schultz]

I think the 550 swingarm is 1" longer than the 750. I'm going by memory but would be interested to know for sure. If I'm right then the 750 swingarm is too short for your aplication. I wouldn't mind going 1" over but I wouldn't go 1" under.

In my opinion (I'm not trying to start any fights so don't flame me) the 750 swingarm is sub-par and was always the weak link of my bikes. I went out of my way to find aftermarket arms for my bikes (Dresda, RC). If it were my money, I'd keep the stock 550 swingarm and buy the wheel, disc, brakes, ect and see if you can modify it to suit your existing swingarm.

[Schultz]

I think I'm going to have to revise my previous statement. I've never owned an F model and it seems that the F model has a longer swingarm than the K models. GroovieGhoulie posted the below in the topic "Lets talk extended swingarms for a minute..."

                                            *     *     *
The F model swingarm is right about 1" longer than the K swingarm.  This was done when the factory modifed the frame for the Super Sport models.  They initally shortened the rake by one degree, which in turn shortened the trail.  They did this to make the steering quicker, more lively, more "Super Sport-ish", whatever.  In order to restore some straight-line stability to the bike, they extended the swingarm by 1" in order to lengthen the wheelbase.

Inital test rides were not too good with most testers saying the bike's handling was "diabolical", "unpredictable" "scary" or "just plain dangerous".  At the tester's advice, Honda went the other way and cranked in more rake and trail: one degree more rake than the K models (28 degrees 10 minutes, versus 27 degrees, 10 minutes), this also lengthened the trail from 3.7" on the K to 4.5" on the F, which brought it more in line with period British bikes (regarding trail).

Despite the fact that the longer swingarm was sort of a "band-aid" to restore straight-line stability in the steeper-rake/shorter trail designs, it was kept for the production F models with the longer rake and trail.

The '77 and '78 K models used the F frame (with it's longer rake and trail and longer swingarm), however, they still had the drum rear brake.  They did however, have the 630 chain, unlike the earlier 530 chain.  The wider swingarm, originally designed for the wider disc brake system, could accomodate the wider sprocket and the drum brake hardware and axle was reportedly unique to the K7 and K8 models (wider). 

The F model swingarms are a little wider to accomodate the rear disc brake and associated hardware, and supposedly it is not a drop-in mod to a K model bike using the stock rear wheel and drum brake (which also means that the F rear wheel and disc set-up is not a drop-in mod with a K swingarm either).  However, reportedly, you could swap the entire F swingarm, wheel, disc, caliper and brake system and brake system mounting hardware onto a K bike.

Hope this rambling discourse helps somewhat
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[neil young]

alright so you can swap the F on a K 750....but can you swap it on a 550 or 500 K.seems feasable..the person i purchased my 72 500 from said he had swapped out the front and rear end on his 77 550 K with 750 parts.but i dont know if it was a K model (or what year for that matter)he had a dual disk setup on the front and a disk on the rear.i would just buy it for the $60.00.but i dont have the room to store it if it dosnt work.buy the way if anybody is interested he has a titled F frame as well and 2 seats in good shape

[olds-cool]

So if I understand, it can be done as long as everything is swapped???  I've been looking for a slightly longer swingarm myself.

[Schultz]

Well, I put a Dresda swingarm for a 550 into a 750K once. It was a tight fit, I mean real tight which I assume is what Dresda had in mind. I had to use a bottle jack to open the frame up a few mm the get the arm in. Yes, a bottle jack. Anyway, it did fit and gave me 1" over stock. So, I assume the F model swingarm will fit in a 550 and give you stock wheelbase. The only "problem" that I see is how you would mount the master cylinder and actuate it. You might want to think about that before you dive in. When I've gone down this road I welded tabs onto the frame for rearsets and mounted the master cylinder on the backside of the rearset plates. Early F models had a one piece master cylinder and resevoir which is better suited to that aplication. For footpegs I used sportbike pegs I bought on eBay for next to nothing. The whole thing was hassle free once I had a plan.

[neil young]

for some reason yesterday when i searched swingarms nothing came up.but today it did.some interesting reading.i think I'm going to try it and see what happens.if the gentelman still has it for sale

[neil young]

bummmp