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Author Topic: FRANKENHONDA II the 1982 DOHC CB 750F2 Build  (Read 5896 times)

Online cb250nproject

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FRANKENHONDA II the 1982 DOHC CB 750F2 Build
« on: Apr 16, 2017, 01:57:48 »
Hey All,

For a long time I have gained insight and answers by reading through the various articles here so I thought I would post a build thread here.

About 9 months ago I purchased a 1982 DOHC CB 750 F2, pretty sure it was an ex police bike as it had the charger wired in the paniers and the fact that the ex motorcycle cop that sold it to me told me it was pretty much confirmed my suspicions.

It was pretty tidy and for $3400 I couldnt pass it up, other than having a flat battery mechanically it was fine started it up and rode it home not a problem

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I already had a fair idea of some of the modifications I wanted to do in this build, one was the GSXR 750 front end upgrade, upgrade the exhaust, rear shocks, wheels, cam, carbs, rear hoop installation and the rest I found out as i went.

First of all i removed all of the fairing to see what lay beneath



« Last Edit: Apr 16, 2017, 05:44:18 by cb250nproject »

Online cb250nproject

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Re: 1982 DOHC CB 750F2 Build
« Reply #1 on: Apr 16, 2017, 02:22:10 »
So after removing all of the fairing, airbox and fuel tank I noted the original rear shock were starting to show signs of rust as you would expect from a bike 30+ years but overall everything was looking pretty good.

The wiring loom that resembled an anaconda was something that i would look at slimming down at a later date/ the wiring never was pretty on these old Hondas

So I got onto Ebay and started hunting for a donor front end, it took a little while to find a set but i ended up getting a 2008 GSXR 750 front end that had the top and bottom tripple and axle for about $980

Next on the list was rims after looking around I decided to go with the Cognito Moto conversion hub, I picked up a rear spoked hub from and earlier model 750 that still had rear disc. both front and rear hubs were 42 spokes

The next challenge was to find rims to suit, I wanted to try and get a slightly fatter rear tyre on the back without blowing the budget out going crazy with the rims. For the front i ended up getting a 17" x 2.5 Morad brand new by the time i got it freighted here it was about $270, luckily i scored a second hand BMW rim that was 17" x 3.5 not as wide as i was hoping but for $42 i couldnt say no.


Online cb250nproject

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Re: 1982 DOHC CB 750F2 Build
« Reply #2 on: Apr 16, 2017, 02:45:26 »
So i sent the front hub of to get anodised as I found a place that could do it pretty cheap at home, while i was doing that I sent the rims away to get hydro blasted and powdercoated gold.

Originally I had planned for the bike to be all black except for the rims being gold with gold decals on the tank, but as it ended up turning out that wasnt the way it was going to be.

It took me a while to find the exact gold that I wanted I came across a company Prismatic Powders who offered a few different variants of gold I ordered colour swatches but after a few weeks didnt think they were going to arrive so I bit the bullet and ordered a a powder called prismatic gold unfortunately just after I received the powder the swatches arrived and I quickly realized that wasnt the colour I wanted, so I went with another colour Goldtastic which ended up turning out spot on

but i ended up going with a powder from prismatic powders called goldtastic, 

Online cb250nproject

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Re: 1982 DOHC CB 750F2 Build
« Reply #3 on: Apr 16, 2017, 04:03:03 »
Before starting the build i had done a bit of research and knew that the triple stem would need to be changed there seemed to be two options get a Cognito Moto one or look at fabrication one up, luckily for me the old man has a lathe and is always up for a challenge so we made some measurements and guesstimations

The bearings and races also need to be changed I found a conversion table online   

http://www.allballsracing.com/index.php/forkconversion

After looking here I went into a bearing shop and simply ordered the bearings i needed for less than half the price it was going to cost me to order them. The bottom races are fairly similar but the top race is thinner than the original Ive attached a photo so you can see for comparison

First I grinded off the stops from the bottom triple, then we pressed the original stem out from memory there was some sort of retaining pin and I think we heated it up a little, she was fairly stubborn but eventually came out in the press.

Next we measured the CB 750 stem against the GSXR stem to work out the difference then went to work on the lathe, i wont lie there were a few attempts before we got it right, you can see the original stem up top with the two failed attempts and the final in the lower triple

To press it in we put the stem in the freezer and i think we warmed up the lower triple before pressing it back in

Online cb250nproject

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Re: 1982 DOHC CB 750F2 Build
« Reply #4 on: Apr 16, 2017, 04:27:51 »
After the stem had been pressed in it was time to give it a test run.

Unfortuntely we miscalculated by about 4 mm so the thread of the stem was a few threads shy for the nut to go on properly, luckily the old man had anticipated it and left a lttle extra shoulder on the bottom of the stem so we pressed it out again and put it back on the lathe repeated the process and she came up sweet.

Im still to install new stops on the bottom of the triple.

When building this bike there was one underpining principle functionality over form, while having an asthetically pleasing ride was what I am hoping for safe comfortable rideability was what I was going for. so as much as low clip ons would look cool i ended up ordering some woodcraft 2.5" risers ( yet to arrive in the post )



 

 

Online cb250nproject

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Re: 1982 DOHC CB 750F2 Build
« Reply #5 on: Apr 16, 2017, 04:42:25 »
When I ordered the Cognito Moto conversion hub i opted to get all the spacers and bearings which we had to press in after I had the Hub anodised, just a FYI and something I learned by fu$king up unless it CNC billet aluminum anodising wont come out so good so when i went to get the rear hub anodised it ended up coming out a greyish colour (booo) it ended up getting sprayed out of a can.

For the rear hub i simply took the old bearings into the bearing shop and reordered the same.

After the front hub bearings had been pressed in i did a little mock up as we had the GSXR front end in the garage, and as advertised it fit like a glove

Online cb250nproject

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Re: 1982 DOHC CB 750F2 Build
« Reply #6 on: Apr 16, 2017, 05:01:03 »
Now that the Hubs were in order and the front end conversion was completed it was time to get the Hubs laced up, it actually took a little bit of searching to find someone to do it, finally i came across Bruce at Fastline Spokes

I had ordered some new front brake discs that arrived so i fitted them up then took the rims and Hubs to Bruce to be laced up and trued

While the hubs were away getting laced I figured it was time to look at installing the tail hoop. I had one in the garage that I had purchased for a previous build that i ended up not using.

First we worked out where the cuts were to go using the measure, measure and then measure again before cutting rule, after the cuts were made we used some smaller steel tube inserted into the frame as a lug. We then cut the hoop down to the required sized and welded it in place.

after looking at it ive realised that the hoop needs to be bent down about an inch this will be a little bit of an operation :/ and one yet to be done

the rims came back so i thought I'd just mock it up with the wheels just because there was nothing else i could do at the time

Online cb250nproject

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Re: 1982 DOHC CB 750F2 Build
« Reply #7 on: Apr 16, 2017, 05:40:53 »
I ordered myself a Delvic 4 into 1 exhaust, then headed down to Pablos and got some tread onto the wheels ended up getting a 110 / 70 front and 150 / 60 Pirelli Diablo Rossi II.

at the same time I ended up finding some Hagons rear shocks on ebay for $150 so i snaped them up and mocked it all up to see how the bike would look.

i removed the wiring loom and original foot pegs, I ended up getting an Ultima wiring loom but that will be one of the last things to get installed

she sits pretty low :/ we will have to see how she goes i think i can get a few more mm out of pushing thr forks all the way through the triples

900 cams to come

 

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Re: FRANKENHONDA II the 1982 DOHC CB 750F2 Build
« Reply #8 on: Apr 21, 2017, 21:38:50 »
Some stuff arrived in the mail, pity I'm at work

Ultima wiring loom

Woodcraft 2.5" risers

CBR 600 F2 coils

Offline Tim

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Re: FRANKENHONDA II the 1982 DOHC CB 750F2 Build
« Reply #9 on: Apr 21, 2017, 22:33:37 »
Wow!  Thanks for posting up the build detail - is this where you are now or is the bike complete?
"Quality . . . you know what it is, yet you don't know what it is. But that's self-contradictory. But some things are better than others, that is, they have more quality. But when you try to say what the quality is, apart from the things that have it, it all goes poof! There's nothing to talk about. But if you can't say what Quality is, how do you know what it is, or how do you know that it even exists? If no one knows what it is, then for all practical purposes it doesn't exist at all. But for all practical purposes it really does exist."