FRANKENHONDA II the 1982 DOHC CB 750F2 Build

[cb250nproject]

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

 

[cb250nproject]

Re: 1982 DOHC CB 750F2 Build

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.

 

[cb250nproject]

Re: 1982 DOHC CB 750F2 Build

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,

 

[cb250nproject]

Re: 1982 DOHC CB 750F2 Build

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

 

[cb250nproject]

Re: 1982 DOHC CB 750F2 Build

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 )

 

[cb250nproject]

Re: 1982 DOHC CB 750F2 Build

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

 

[cb250nproject]

Re: 1982 DOHC CB 750F2 Build

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

 

[cb250nproject]

Re: 1982 DOHC CB 750F2 Build

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

 

[cb250nproject]

Some stuff arrived in the mail, pity I'm at work

Ultima wiring loom

Woodcraft 2.5" risers

CBR 600 F2 coils

 

[Tim]

Wow! Thanks for posting up the build detail - is this where you are now or is the bike complete?

 

[cb250nproject]

Thanks Tim (my apologies for typo text on the phones starting to get a little too small to read these days), this is where i am now, working away for the next 5 weeks so once i get back home i will instal the cb 900 cam and hopefully get the valve clearances sorted, then the handle bars just to get an idea of the riding position.. then start to dream up the seat and tail end maybe look at making up some brackets to mount the rearsets.

Sent from my GT-I9305 using DO THE TON mobile app

 

[cb250nproject]

I want to install an oil cooler can anyone point me in the direction of a supplier of a kit ??

 

[spotty]

looking good, can't think of a finer thing to do to an old cop bike (who knows it may have been one of the ones used to nick me for something in days gone by...)

didn't CB1100's (and maybe some 900's) have a cooler stock? maybe search the info and see if any of the wreckers have got one somewhere.

theres plenty of a/market stuff out there for the actual coolers but getting the fittings, the wreckers might be your only option

are you using the old wheels? I might be interested in the front for my CB750K8 which already has CB900 forks but its going to be easier to use the 900 wheel and discs than try and get decent brakes and such to work with the stock wire wheel

where in (not so ) sunny Melbourne are you? i'm in Kalorama, right on top of mount Dandenong so I get one of the best trips home every night after work, straight up the tourist rd

 

[cb250nproject]

Sweet spot to live in, mad roads up there I use to ride the black spur back on my little RGV 250 good times.

This is the front wheel I removed was going to off load it for $125 with discs there should be plenty on them but i wont be able to get the calipers on them until i come home in June. Im on the west side in the bronx of sunshine west :-\

Got any photos of your build ? Im always interested in how peeps go about their builds

 

[cb250nproject]

ok so finally came home and tried to install the cb 900f cams

had a few mishaps along the way :/ two of the cam journal bolt broke off, a common occurance but none the less inconvenient.

has to drill and tap out new threads then when i reinstalled the bolts I added a little bit of antisieze and then worked out the torque setting for wet bolts (different to the dry torque settings)

I was also unable to use the sprocket from the 750 cam which I tried to do because the sprocket was chamfered on the 900 cam and I was unsure how it would effect things. but the decision was ade easy when i realised it wasnt interchangeable.

then had to reshim to get the valve clearances right still need to find some 260 and 265 shims that will be tomorrows mission hopefully and ill put on the woodcraft riser clip ons on.

 

[cb250nproject]

Went out and got studs to mount the rear disc that I had. Now just to make a spacer for the left side of the wheel.

Also got a chance to fit the 3" riser clip ons, it doesn't look as trick as low clip ons but it sure is comfortable. Tomorrow I'm hoping to get a start on the tail end see how that goes


Sent from my iPhone using DO THE TON

 

[brad black]

man, that rear disc is huge. you need to cut it down and fit a smaller caliper.

 

[spotty]

man, that rear disc is huge. you need to cut it down and fit a smaller caliper.

i'd leave the disc that size but replace with a matching one to the fronts or even just get it drilled so it looks similar, the solidness looks kind of wrong with the front drilled ones, and get rid of the black plastic thingy off the back of the caliper or put a matching 4 piston nissin on, the more brakes the better.

 

[CarbsAndCylinders]

Yeah, I think that black plastic thingy is just to keep water from getting flicked upward.

 

[cb250nproject]

I agree the disc does look odd, would it be cheaper to get it drilled? or just buy a brand new disc?

Also im trying to work out exactly what model of cb 750 had the 6 stud bolt pattern for mounting that disc, the other ones I had were all a 5 stud bolt pattern, that was off the original wheel that came off. dont want to oreder the wrong one.. again

Given how little the rear brake does i dont think I will go to the trouble of putting a nissin caliper on, I have ordered a kit and was going to strip down and refurbish the original caliper. I think the brake upgrade that came with the GSXR fork conversion will still make it like night and day.. thats wat I'm hoping anyway