[mrmauiwowi]

Hello everyone i've recently picked up an 82 cb750 with 2008 R1 forks and swingarm (full font end and rear end to be exact) and I'm going to make it work. I've already chopped the "subframe" section off and have done some mock-up as well as ordering a 75' gas tank off eBay. I know it is going to be hell and that just about every part of it will have to be customized but i expect and look forward to this. I have every intention of building the bike as close as i can to the R1 rake, trail, wheelbase and general weight distribution. Now to the purpose of this particular thread... I've found similar parts of this project being done in other threads but typically with other donor parts that are easier to use and on different models. I thought that it would be useful to have all of it in one thread and seeing as how this particular build will take more work that other swaps, it should be generally all-encompassing (and hopefully pretty cool). If you are going to tell be the CB750 is crap then don't waste your time because I'm doing this build because i got a hell of a deal on a bike with a running motor and the R1 parts together and it just makes sense, all other advise or constructive criticism is greatly appreciated. Yes i have the fabrication/welding skill necessary but I'm not a motorcycle guru but I've done a few hot rod builds as well as building some stoker motors etc so I'm somewhat mechanically versed. Ill get some picks of it mocked up when the tank arrives and ill go from there. Looking forward to learning from some of the experienced minds on here so feel free to throw out all opinions. Also ill do my best to separate the required customizations that might not be necessary on more budget/bolt-on swaps for any of you guys that might be looking for info on that. Thanks guys. Oh and if anyone needs an 82' cb750 fuel tank (I'm not crazy about them but it in good shape with only a bad paint job) then drop me a line or i might use it in a cool garage decoration later lol.

 

[roccitycafe]

its going to be hard to keep the r1 wheelbase with the r1 swingarm. you need a very short swingarm to get back into the 54" range. the offset will need to be increased as well to bring the trail back into something reasonable, and unless you're going to set the swingarm angle at about 25 degrees, you're not getting the r1 rake... best bet is to find a shorter swingarm or have yours modified so its shorter, then have some triple clamps machined to make the offset greater, try to get your trail at 4" or less, the wheelbase is still going to be long, but it will handle not too terrible

 

[mrmauiwowi]

its going to be hard to keep the r1 wheelbase with the r1 swingarm. you need a very short swingarm to get back into the 54" range. the offset will need to be increased as well to bring the trail back into something reasonable, and unless you're going to set the swingarm angle at about 25 degrees, you're not getting the r1 rake... best bet is to find a shorter swingarm or have yours modified so its shorter, then have some triple clamps machined to make the offset greater, try to get your trail at 4" or less, the wheelbase is still going to be long, but it will handle not too terrible

I've considered these things. Im going build my own swingarm based off a jig ill create using the r1 and the rake is actually 24 degrees which i plan to modify the steering tube to correct. The 2008 r1 wheelbase is 55.7" and i think its achievable (at least to the extent where the bike will perform to my liking). The only part I'm going to have to really f&*% with is the weight distribution...i doubt i can get it to the weight or even close to the weight of the aluminum and plastic r1 but if i can get it distributed similarly ill be pretty happy. I've considered building a Ti frame but I'm not sure I'm ready to take it there...its not like it won't already cost me a good bit to do all this but i like to build things i can be proud of. The triple clamps and other cnc work is about all i intend to outsource. I'm handy with the tig and I'm wondering if the considerably large gussets i see on some of these bikes are necessary? Only concern is any stress from the high speed damping with the R1 forks. My concerns are generally in line with yours but i haven't entered into this with any naivety when it comes to how much work it will be. Thanks for the advise

 

[mrmauiwowi]

I originally wanted to modify the R1 swingarm but with the necessary spacing for the mono and given the dimensions of the existing swingarm theres really no way that i could trim it in one spot and modify it to get the shortness i need (would have to chop it behind the mono mount and ahead of it due to the minimal wheel room) so it seems easier to build a new one... honestly I'm toying with the idea of a single-sided swingarm but I'm not sure i want to open that can of worms either

 

[roccitycafe]

the high speed damping on r1 forks is going to be considerably gentler on the frame than the stock forks, which essentially had infinite high speed damping, honestly for the work you've got cut out, just build a new frame

 

[hillsy]

A single sided swingarm off a VFR400 is about the right width / dimensions for your CB.

 

[mrmauiwowi]

A single sided swingarm off a VFR400 is about the right width / dimensions for your CB.

I will definitely look into that, thanks.

 

[mrmauiwowi]

hahaha. So i was roaming the forum and decided i had better do my due diligence and when i read the "new members read here" and the part about not buying a bike with vague paperwork thats mostly torn apart i couldnt help but notice that he was basically telling the story of my recent purchase. I did see the motor running but the swingarm and front end as well as the clutch cables etc were removed so as far as the drivetrain I cant be certain. It wouldnt matter anyhow seeing as i paid just over $400 for the R1 front and rear with the frame and power plant (i know many of you will bash my 750 for NOT being a power plant). Heres hoping its in decent shape for a rebuild or tune up...

 

[Witworth]

Post some good images of your recent purchase.

We are here to help.

Danger, is my business."

 

[mrmauiwowi]

Post some good images of your recent purchase.

We are here to help.

Danger, is my business."

I'm expecting the new tank in a day or two and ill get a picture of it mocked up. I had it all half @$$ together but my stupid self forgot to check the wheel base and see just how much i have to shorten the new swingarm to get my desired 58-56" (thats being hopeful but fingers crossed) I'm hoping to see it when i get home from work...

 

[mrmauiwowi]

Okay i got the new fuel tank today and decided to slap it all together for a mock up of sorts. The wheelbase is approx 62.5" as it sits and I'm shooting for under 57" so I may end up building a swingarm. As you can see in the photo of the swingarm, there is not real easy way to shave 4" off of it (i say this because i plan to modify the steering tube to get as close as possible to the 24º rake of the R1 and that should get me a bit of the shortened wheelbase I'm after). The tank obviously will have to have the valley modified a bit to sit on the 82' frame. Okay guys, tear it to pieces because i know somebody wants to

 

[hillsy]

Lose the R1 swingarm - it's too long.

Actually, ditch the whole rear - the wheel and chain line are going to be too wide.

 

[knappyfeet]

I can see that this is an ambitious project. It looks really neat mocked up like that.... Lot of potential however........how's the shock going to mount up? If its going to mount up like in the photo then it's not going to be safe. By removing the rear part of the frame you already removed any lateral structural support designed into its structural integrity. Then by adding the rear shock as it appears......no matter to a degree whatever bracing you do you are stressing items that was never engineered to do so. This is a cradle frame. The R1s frame is parameter and designed totally different.

I hope you considered all structural stress items and their importance and role in handling and function. You have a nice beginning. Good luck

 

[Witworth]

This collection of parts is going to end up nowhere .

You are building a 'cafe chopper' that will end up being neither a cafe racer, or a good chopper. This is what happens when guys without the knowledge, skills or intellect gaze at ridiculous junk customs on the web or bad TV.

You have weakened the frame by at least 30% by cutting off the subframe. Throw it in the dumpster.

You are investing a hell of a lot of emotion, hope and dreams around a collection of old and basically incompatible parts. You really have no idea if the motor is any good, as well.

Put it in milk crates and list it today on CL.

If you want to build a functional motorcycle, come back for advice in a month or so.

Danger, is my business."

 

[hillsy]

I see Witworth has come up with his usual answer of "It can't be done".

Great advice

 

[Witworth]

I see Witworth has come up with his usual answer of "It can't be done".


Great advice

Well book a flight and go and build it for him JJ, that would be a good laugh. The eager and the inept. That should be a movie title.

Danger, is my business."

 

[hillsy]

Well book a flight and go and build it for him JJ, that would be a good laugh. The eager and the inept. That should be a movie title.

No need for me then - you could star in, produce and direct the film yourself. I'm sure you've produced a few films in your time like you've supposedly done everything else in the known universe.

 

[Witworth]

Funny you should mention it, I turned down starting a movie career many years ago, honestly.

I hung out with a leading actress, a number #1 rock singer / guitarist and a award winning film director years ago. You? Cheetah the wombat, maybe?

Danger, is my business."

 

[roccitycafe]

totally forgot about the chain line, I ran into that issue with my cb750, you can machine down the sprocket carrier to bring the chain closer to the tire, and use a cyclexchange offset front sprocket, I wound up machining the carrier and didn't need the offset sprocket, but you may want to contemplate both.

 

[hillsy]

Funny you should mention it, I turned down starting a movie career many years ago, honestly.

I hung out with a leading actress, a number #1 rock singer / guitarist and a award winning film director years ago. You? Cheetah the wombat, maybe.

Honestly? You know what that word means, right?