Topic: Rate the insanity!

[ridevana]

Hello all,

I have a 78 CB750 SOHC supersport and I am planning to make major mods on the bike (atleast major for me  ). SO here is a schematic of my plan and let me know if this insanity is going to kill me or will it be bad ass if done right that is..so please let me know what you think and also if there is anything I should be careful about making this mods.

The plan is

Chassis/Engine- 1978 CB 750 SOHC supersport
Front - 05-06 GSXR 1000 front forks, triples, clip ons, wheels and tires, brakes.
Rear - 2002 Ducati 916 single sided swing arm and brakes (thats the plan for now)

[Muckinfuss]

Keep it under 200mph and I would think you'd be fine.    The fab for the mono and swing arm might try your patience a little.  If it was me, I'd give consideration to silver or hard bronze brazing of your bracketry.  It's what I do to these old frames and tanks when fabbing.  Straight up welding with or without gas could make a brittle situation that would bite you down the road due to the higher heat in the process.  Others may have good reasons to weld instead of braze.

[Stev-o]

I rate it a 5 out of 10, all has been done.  Nice drawing, BTW.

[KiefRichards]

Save yourself the time, money and frustration. Buy the bike you really want, already "built"

My 2 cents

[Don R]

I'm a big fan of tig welding, I believe the heat affected zone can be quite small with a high quality weld. There is also silicon bronze tig for even lower temps. I do some drag car chassis work so I'm biased toward what we're  required to do.

[calj737]

I'm a big fan of tig welding, I believe the heat affected zone can be quite small with a high quality weld. There is also silicon bronze tig for even lower temps.

+1 ^^^

[Retro Rocket]

I have done a lot of research on these types of mods and read somewhere that the Ducati arm offsets the wheel a bit to one side when used on other bikes, putting a single side arm is a lot of work and finding one thats not far too long is the problem. The shortest one i found was the Ducati 996 SPS, it worked out about an inch longer than the stock swingarm which is a good length on our bikes {CB750}. A lot of this depends on what your expectations are of what the bike should handle like afterwards..?  A lot of these types of mods are done purely for looks and detract from the bikes handling, especially if done with no knowledge of motorcycle geometry and the way it works....  The stock arm is 450mm from the center of the pivot bolt to the center of the adjusters, the 996SPS arm is 475mm, {1 inch longer}...here's a link with some measurements...   It is NOT and easy mod at all, really needs to be done by someone that knows how to modify everything, including the frame to suit..

http://www.customfighters.com/forums/showthread.php?t=65092

[AbbyRider]

Save yourself the time, money and frustration. Buy the bike you really want, already "built"

My 2 cents

What fun is that?

[calj737]

Save yourself the time, money and frustration. Buy the bike you really want, already "built"

My 2 cents

What fun is that?

Amen!!!!

[ridevana]

Thanks guys,

I was expecting a mixed comment 

Great suggestions Munkinfuss and retro rocket. Thanks! I will try to look into all that details you have given. Well I am a Vehicle dynamics guy and thats what I do for a living, but motorcycles are sort of a different beast. I should admit I am not super experienced, but I am referring to as many literature as I can.

I havent fixed the rear end yet, Just had this swing arm lying around with a friend of mine and thought would use it.


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[ridevana]

So what the take on converting the existing swing arm to a mono shock setup? I am not very sure about the bending stress that the arm will have due to lack of support at the axle end.

Any thoughts? comments?

Hey Retro Rocket, Thats a cool link you have there.

[calj737]

I can not think of any successful way of modifying the existing arm into a single sided and have it still support the wheel. It's just not strong enough.

The ducati will work, you'll need to do some machining on the pivot section, and obviously mod the hoop to connect the shock. Biggest challenge may be aligning the sprockets front and rear.

[754]

Where are you at? Got a hawk ssswingarm, that at least fits into the frame..may be easier one to use..

[Retro Rocket]

I can not think of any successful way of modifying the existing arm into a single sided and have it still support the wheel. It's just not strong enough.

The ducati will work, you'll need to do some machining on the pivot section, and obviously mod the hoop to connect the shock. Biggest challenge may be aligning the sprockets front and rear.

Hi Cal, if the Ducati arm is indeed offset like i read somewhere, then major frame mods are needed to offset the offset....   Did I just say that....   If you know what i mean...

[calj737]

Admittedly, I'm not overly familiar with the geometry of the 916. But I'd struggle to understand if the arm were so far offset at the axle that the hub itself didn't reposition the wheel back into the centerline of the frame. Ultimately, doesn't the 916 frame carry the motor down its centerline and the front sprocket is outboard, requiring the swing arm to be offset? But that occurs beyond the subframe, right?

Wish I had some pictures and a frame table.... 

I'm sure it can work, but rear wheel selection/hub and sprockets will be the trick I'd think. Or am I missing something significant? Not that machining all that isn't significant, but you know what I mean-

[754]

It depends..if the Honda is 4.5 inches off centerline, and the Ducati is 6 then no go.. The honda you can manage very outward, maybe an inch and you hit the frame. Can our would haveto dogleg the motor/swingarm mount outward.. Doable,  but adds a lot of work, and you probably need a frame jig. Keep in many nd the hands has clearance issuesat a 140 tire while the Ducati probably. Came with at least a 190..

[Retro Rocket]

I think the pivot point on the Honda is centered, both sides of the frame are at equal distances from the bikes centerline, on the Ducati, if i read it correctly, one side of the frame is further from the bikes centerline than the other side. To make it fit would require major work either way..   Franks onto it...

[Wobbly]

Save yourself the time, money and frustration. Buy the bike you really want, already "built"

My 2 cents

I totally agree. it will be a lot cheaper too. Ah, the fun factor? Well, why not put a lawn mower engine into a Porsche chassis instead? That way, you have your fun, a CB 750 Four is saved, and it is just as senseless.

[ridevana]

Hello CalJ,

I do understand its not possible to make the existing swing arm into a single sided arm, my point was to weld a joint at the center to put a mono shock and keep the rest of the swing arm intact but I was worried about the over hang close to the rear axle with no support.

Hello 754,

I am in Columbus Ohio, do you have images of the hawk swing arm?

I still havent measured the offsets yet, my primary aim is to make the rear end a mono shock to have the clean look and to some extent improve handling. I have access to the 916 rear end, so was thinking of using it, but I do see the problems after you guys mention it.

Any suggestions on other rear mono shocks that would be minimal mod on my existing frame? or just plug and play would be awesome 



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[754]

Show us a pic of the Ducati  arm, the tubular ones look cool.
Here is the Hawk one.

[mac3687]

Woah woah woah!!! Where's the engine!?!?!?!

[ridevana]

Okay, So I was tinkering around with the Ducati swing arm and its gonna be one hell of a work to get it working. The offset is not going to be easy to fix and I will have to shave off some bit to slide it in etc. So I have ditched the Ducati swing arm plan. Any suggestions on a plug and play mono shock swing arm for the 78SS? I am Not focused on having a single sided so that is not a constraint.

Thanks


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[calj737]

Better than a mono, check out MotoGP's new CalFab arms. Probably easiest to locate thru their FB page.

[KiefRichards]

Better than a mono, check out MotoGP's new CalFab arms. Probably easiest to locate thru their FB page.

HAHAHAH, we're slowing getting closer to reality here.  Like I said earlier; if you've got no fabrication skills, just buy what you want and save your dignity/sanity.

[ridevana]

Better than a mono, check out MotoGP's new CalFab arms. Probably easiest to locate thru their FB page.

Hmmmm, Thanks Calj, I will keep this in my mind. If I were to go with the double shock, I might as well go with the stock arm I have. I am not sooper focused on reducing every gram so the CalFab arm just might not be my thing if I am going the double shock route. But thanks though. Will keep you posted on what I decide. Please do check out the blog I made with the detailed images  the link is given below.


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