CB750 1981 - My Latest Project

[WENMAN999]

hey,

So ive never completed a build thread of any of my bikes.. somehow I find it difficult to find the time to build let alone write about it. (maybe its the young family). However I have enjoyed many an hour reading and learning from other build threads that I thought if I can find time to read I can find time to post. Plus if I can pass off some of wisdom to a younger eager first time builder like someone did for me then thats awesome!
Currently 39 years old living in the UK and working in law enforcement time is limited so i do what i can when I can.

I have previously built a CB550 and have recently acquired a 1981 CB750f dohc! The idea for this one was a front end USD swap, aggressive stance, clean lines and balance and proportion to be spot on! I am also relatively new to welding and metal fabbing so I wanted to use this build as an opportunity to make as much custom parts as possible! (Dont throw hate at my welds!! Im learning) I always thinks its better to have tried and failed then to have never tried at all! Plus theres something way more rewarding having an imperfect part on a build that you did yourself rather than something perfect that someone else made!!

I didn't take any pics of the bike pre fork conversion so pics start with the CBR954 front end on!!
I will try and update this as and when I do little jobs and feel free to ask anything about what im doing or throw any advice my way!!

 

[WENMAN999]

So first things first I stripped it down.. It was purchased from a trusted friend so with 15k on the clock and a known history I was confident the engine was fine. These bikes are great for getting the engine out the frame as the frame itself dismantles. Stripped the tank back to bare metal too.. starting to think of paint colours which is exciting but a long way off!!

 

[WENMAN999]

Next job was to focus some time on the engine.. I stripped the top end of and inspected the bottom end for tolernces all seemed good. Took the excess paint off which was hours and hours of labour.. it seems no matter how much you clean scouer, or degrease, when you take a white cloth to it still feels dirty. This one had been painted black before but obviously very badly. I used wire drill attachments, 3m pads, brushes all kinds of degreaser until i washappy to apply paint.

I went for a VHT paint after endless research and came up with cast iron and black. After 2-3 coats of primer and 2-3coats of colour everything that I could fit in my conventional oven went in for a bake and i devised a cunning mobile oven (cardboard box/ foil/ heat gun) to cook the main block.

Built the engine back up using a full top end gasket kit, re lapped valves new seats etc so should be good!

 

[Jimbonaut]

Hey mate - welcome to you and welcome to your 750 from a UK expat living in Montreal. I'm working on an 82 right now as well, and love watching these bikes take shape. Hope you find the time to keep us updated, and I'll be following along with interest (and no welding criticisms that's for sure! Mine are guaranteed worse)

 

[WENMAN999]

Hey mate - welcome to you and welcome to your 750 from a UK expat living in Montreal. I'm working on an 82 right now as well, and love watching these bikes take shape. Hope you find the time to keep us updated, and I'll be following along with interest (and no welding criticisms that's for sure! Mine are guaranteed worse)

Hi mate thanks for the welcome! yh i will definitely do my best to keep this updated! it is such a good place to share all our wisdom or seek help due to lack of it! lol

feel free to chip in whenever you like!

Al

 

[WENMAN999]

Finished engine pic (pretty much)!

 

[Jimbonaut]

Amen to that, without this forum my bikes would still be a pile of parts all over my garage floor. Engine's looking sharp mate - holy crap it's a job cleaning those lumps up huh? Worth the effort though, yours looks the business. Did you keep the stock bores in the cylinders? Mine ended up getting an overbore to 823cc. I squeezed in a few simple upgrades to my engine rebuild as well (an oiling mod, new chains and dampers and a new shift star) - I'd be happy to share the deets.

 

[WENMAN999]

Amen to that, without this forum my bikes would still be a pile of parts all over my garage floor. Engine's looking sharp mate - holy crap it's a job cleaning those lumps up huh? Worth the effort though, yours looks the business. Did you keep the stock bores in the cylinders? Mine ended up getting an overbore to 823cc. I squeezed in a few simple upgrades to my engine rebuild as well (an oiling mod, new chains and dampers and a new shift star) - I'd be happy to share the deets.

As it had only covered the 15k I decided to leave it as is! More budget than anything! Would have loved to upped the performance slightly but hopefully if i can tune it correctly jetting wise and a 4-1 it will be considerbly quicker than my CB550!

 

[Jimbonaut]

15K? Damn that's low mileage. Absolutely, no need to do an awful lot to an (undamaged) engine that's only been round the block a few times. Nice find! One thing you may want to look into is a simple mod (if you have the clutch basket off) - switching out the shift detent star. I bought mine for about $60, looks like this -

and installs here -

Although I'm a loooong way off finishing my build and actually testing the thing, I'm assured the new star (thanks to different profiling) makes shifting gears a lot smoother.

 

[canyoncarver]

I dig these first gen dohc F bikes. I had an 82' I never finished, let it move on but I still like them alot.

 

[WENMAN999]

Thanks for the advice on the star Jimbonaut.. i might just do that!

 

[WENMAN999]

The next step I wanted to do was to look at the frame and the rear hoop. I have used a supplier in the past who i found on ebay (Triple Humph) to supply the hoop. He builds some really good LED integrated hoops and at a reasonable price. Once I figured out how short I wanted the rear of the frame it was a simple chop and weld! These bikes have a natural kick up to the frame which personally i feel should have a cowl on.

The intention was to put a rear box swingarm from a cb400sf and wheel/brake set up to balance the rear wheel to the front mag wheel. Ideally I would go for spokes but budget or lack of means for now I have to find an alternative. However during the process of working with the swingarm I changed my mind and really wanted to go with the stock swingarm for athsetics.

I decided to refit the stock arm and go for a wheel and complete brake set up on a CBR 600 f2 1991-1994. I picked this parts up on ebay and will post a specific thread on spacers required brake stay etc when i have it completed.

For now here are some pics of the hoop!

 

[Jimbonaut]

Thanks for the advice on the star Jimbonaut.. i might just do that!

Let me know, I can point you in the right direction

 

[WENMAN999]

So on to the rear sets!! Having built a cafe/brat Esq CB550 in the past, the one thing I wanted to do to the this one was fit some sort or rear set to it! The 1977 CB550 is notoriously difficult to find bolt on rear sets that don't cost the earth or require some sort of frame modification. Therefore I didn't bother and left it stock.. maybe because im getting old but i regretted that as the on longer rides it gets slightly uncomfortable!

So thinking of rear sets for this I had a few options.. obviously forking out in excess of £300 quid for some nice shiny bolt on Cognito Moto ones would be handsome but budget dictated otherwise. I also wanted to test my fab skills on this bike from the outset so decided to find a cheaper alternative that required a few mods here and there and some fabbing!
Having taken some inspriation from 'Jordandogtown' BOTM winner back in october with his awesome 750 I decided to go down the route of retrofitting the sets off the cbr600 f2! Its nice that a lot of parts from that era CBR are being used on the build.. in fact it may have been cheaper to find a donor bike from the start.

The sets themselves came up relatively cheap on ebay! I created a mock bracket to carry them using an old nylon chopping board.. I was quite impressed with myself with this idea as it enabled me to mount them rigidly sit on the bike and get a feel for the correct positioning. Then is was a matter of tracing the prototype onto 8mm steel, cutting them out with the angle grinder, chamferring the edges, drilling and tapping some holes and bingo bango bongo i had a pair of rear set brackets!

Then it was a matter of getting a few ally spacers made up and they were on!

All in all the total cost of these sets were no more than £60!!! In comparison to the cognito ones the look is nowhere near but the joy of thinking outside the box and developing my skills, make them look even better to me! I will get bits of them powder coated when the frame gets done!

Ideally i want to replace the rear master cylinder for a short bit of clear hose if possible.

Let me know what you think...

PS.. thanks Jordan!!!

Excuse the claret in the last pic.. didn't even realise i cut myself prior to taking the pic! def putting some blood sweat and tears into this! lol

 

[Jimbonaut]

They look great mate, really nicely made and thought through. We Bleed For This.

 

[canyoncarver]

The rear set mounts look great. Nice work. I'm guessing they are just mocked up there but did you run out of length on the swing arm bolt?

 

[irk miller]

You're not reaching the locking part of the lock nut. Any plans to lengthen the swing arm pivot bolt to accommodate the extra distance?

 

[WENMAN999]

Hey all.. I intend to recess the head of the swingarm bolt inside the cavity of the left side rear set! This will then provide an extra 10-15 mm of thread on the right!

 

[cb250nproject]

This is shaping up to be a good build I like the rearset brackets, I’m just about to embark on the same mission.


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