81 CB750f cafe inspired

[Casual]

Hi everyone, this is my first bike build so don't expect great workmanship or expert mechanical repairs. I've worked a little on vehicles before (mainly my 88 4x4 Hilux) and have the Haynes 79-84 Cb750/900 manual to guide me, and so far I think I've gone ok. Feel free to let me know about any steps I miss or tricks I could use. Hope you enjoy the thread.

So, I bought this (my first roadbike) mid November. At the time of the sale it started easily with a bit of choke, idled a bit rough, went through the gears smoothly and didn't blow any smoke. Inspection of the bike revealed a large oil leak on the front around the head gasket, weeping fork seal, bald tyres, dead battery and starting relay/solenoid, bad bubbly fuel tank paintjob, seized front brake and turn signals didn't work (flasher unit sounds ok though). $750 later I was taking it home. Some images below.

 

[Casual]

This thread is playing catch-up for a little while (during breaks at uni anyway).

After getting it home I had a quick test ride and parked her in the shed to begin work. The first thing on the list was to clean up an area to work in. Once that was done I starting taking it apart.

As I want to cafe style the bike I thought I'll rip everything off and start from there. I also ordered a head gasket at that time and the Haynes manual. After stripping I cut off the sidecover mounts/tabs and square seat mounts/seats on the 'bridge' at the tail end (easier to fit a cafe seat over it now). At present I'm not chopping the frame off as I would like to pass a roadworthy first.
The frame and swingarm were then degreased, cleaned of rust and painted with good paint (rattle-can gloss black). I'm sure I'll be cutting other bits and/or welding bits on in the future so I'm waiting to get it powdercoated until later.

Have to think about where to mount the battery now. I am still toying witht the idea of keeping the bike as a two seater and therefore need to put the battery somewhere other than under a cafe style seat cowl, and keeping the area under the seat open. I'll measure up some batteries and see if mounting it under the swingarm is an option (I think I've seen it done before). Anyone have any thoughts?

 

[resin]

HI Casual,

I'm very interested in following your thread, because last month I bought a 82 CB750CS Nighthawk having 23,000 miles. My bike had been sitting for about 8 years, and I got it with no paperwork. So far today, I will have made a total 6 trips to either the CHP, or to the AAA to complete my vehicle registration. I will be getting a title only. I curious as to how you will address your tank, seat, and possible fairing issues. Where will you be mounting your license plate, and will you be installing turn signals on your bike. Once I'm convinced my bike has been properly registered, then I'll begin my cafe build. I'm in hopes we can compare notes and ideas during our build.

In regards to your seat, do you plan to flatten your seat making in straight, and doing away with the aft end passenger hump? If so how do you plan to to this?

Resin

 

[IndieSol]

Lots of guys put their batteries over or under the swingarm. Should be a cool bike!

 

[Casual]

Im guessing you are in the USA Resin. Locally it seems to be less trouble to get vehicles registered (so long as they are roadworthy). My bike had been sitting for a good while too although the owner said he would start it regularly, hope not too regularly as it was way over full of oil when I first saw it The only paperwork I got with it was a proof of sale (checked if it had issues with the road authorities beforehand too).

Unfortunately the bike was a bit damaged and run-down when I got it and not in roadworthy condition. I'm using the original tank and throwing away (as in selling or shelving) the sidecover (only had one), original seat (damaged), handlebars, instrument cluster (probably) and battery box. To pass roadworthy I'm mounting the number plate on the rear of the shortened rear mudguard; the mudguard ending as close to the frame as looks good. Will get LED taillights and indicators, and keep the original headlight.

I'll try to do a couple of concept sketches and post them, at present I'm hoping the seat can be modelled on the modern CB400/1100f (and others) type seats (the passenger sitting higher) and be able to cover the rear position with a rounded cafe style cowl for solo riding. I'll post a sketch when I have decent one

Battery under the swingarm sounds a good option. Thanks for the input guys.

 

[Casual]

So here is a quick concept pick. The seat looks longer than what I think it would actually be, maybe the perspective of the photo I used makes it look skinny. In any case this is the best drawing I could do. I'm lifting the rear of the tank about 50mm (2") so the fibreglass seat pan would be ~25mm (1") and seat padding same thickness over that.

Murphy's law says that now I have shown the picture, the end product will look nothing like it.

So more updates to catch up. Painted the triple clamps, cleaned the wheels up a bit and the engine removed for repairs. Please excuse the messy work table.

 

[Casual]

With the engine out and the head gasket and manual in my hands, I thought it best to tackle the oil leak. Stripped the cams from the engine (reading later I could have left the inlet....you live and learn) and carefully removed the head with the help of a hammer and piece of hardwood. Didn't look too bad inside the cylinders and the valves seemed ok (a compression test when I got the bike, showed 165-175psi from all cylinders. I was worried about carbon build-up).

I cleaned the head and cylinder surfaces very carefully with a little petrol, razor blades and scotchbrite pads (takes forever), before putting a very thin smear of gasket sealent around the central cam-chain/oil 'tunnel' on both parts and reassembling the motor.

Of course everything was going great until I found one of the cam cap bolts (a allen head replacement) was stripped. Not a huge issue as I can use a helicoil kit, but I would've been much happier if I'd have known about it when the head was off.

 

[resin]

Since your head has been removed, will you be replacing your timing chain and tensioner? You were wise to perform a compression test before removing you head! You're correct in your assumption, I'm trying to get my bike registered in Southern California. Due to the upcoming holidays, I'm getting my bike ready for her build, but not until after the first of the year. Your postings will be a big help to me. It appears you'll be making your own custom seat, but how will you be handling your fuel tank and exhaust work?

 

[Casual]

Hi Resin. Soon as I got it back home I did the copression test, I would have done it before buying the bike but didn't have the time. It didn't show any signs of low compression so I took a chance.

Not replacing the cam chains or tensioners. I had a look at the tensioners and both had little discernible wear, and I had no way to check the chains themselves. They weren't making any noise. Plus Im going with my gut in thinking the engine hasn't done much work :-\

The seat will be fibreglass over foam (I have some experience with it). The tank will be the stock one, with the sidecover mounting eyelet bit trimmed off. The rear tank mount will probably be incorporated into the seat (somehow) at the higher level. At first I'm using the stock exhaust with a slip on muffler, but really like the idea of making an underslung unit (similar to Buell) later down the track if I can manage it.

Thanks a lot for the interest, glad I can be of help (maybe, hopefully). What do you plan to do to your beast?

 

[teazer]

I like your seat ideas. May have to lower the bottom edge a little to blend in the rear of the tank though. You could also re-shape the rear lower corner of the tanks if you are feeling adventurous.

Where in OZ are you located?

 

[Casual]

Hi Teazer. Im not sure how to tackle the issue of blending the tank, to me the thinner the seat the better the cafe seats look. As the tank curves down at the rear I was thinking of mirroring that curve into the front of the seat base. Your right though, trimming the tank would be a great option (but a little (read "a lot") outside my know how currently). I may get adventurous if I can pick up another tank somewhere cheap. Higher of the list is hunting down some 35mm clip-ons.

Im in Victoria, a couple hours north of Melbourne (ie: south east corner of the country).

 

[Casual]

So, been a little while. I have helicoil'ed the stripped cam cap bolt successfully, no issues with them as usual other than making sure no cuttings drop into the engine (I used a plug of grease in the bottom of the hole to catch any cuttings, as well as coat the drill bit and tap in grease). I'll post a couple of pics when I get them off the camera.

Afterwards I had a go at trimming and shaping the rear mudguard. Below you can see the results; I would like to trim the frame back but that can wait until later. I have enough to do as it is, including smoothing, filling, sanding and painting that mini guard

 

[resin]

Trimming and the fitting your fuel tank to your existing frame isn't easily done, since your tank is a metal tank, but later I'll have and all epoxy composite tank available specially for your frame. The physical appearance will be similar in style to the old Rickman Brother's CR cafe tanks. so when that 's available I'll be sure to let you know.

Keep up the good work!!!!

Keith

 

[Casual]

Thanks for the support, and please do let me know when you have some pics of your tanks. I probably can't afford one but am still very interested in seeing mods for our model bikes

 

[teazer]

Casual up near Castelmaine or Bendigo? I used to live in Melbourne, geelong and Out in Eltham at one time or another.

Do a google search for Cb750 and CB900. The tank just needs a slight trim at the rear to take out that last dip at the rear if you want to go that way get a spare tank, split the saem at the rear corner and weld in a new piece after you wash the tank out no explosions please.

 

[Casual]

Im up in Bendigo, although the bike is at my parents place a few k's northwest of Bendigo. Its annoying because I only get a few hours a couple of times a week to sneak off and work on the bike, but I do because Dads shed has the tools

I'll have a look for a spare tank, they shouldn't be super rare as they were the same for 750f/900f/1100f's (I think). Hopefully start playing with the seat and tank mockup in the next couple of weeks ;D

I may have jumped the gun a little re the mudguard chop as for roadworthy a part of the bike must reach beyond an imaginary line that goes rearward at 45 degrees from horizontal, from the rear wheel axle. Looks like thats where my number plate will be mounted

 

[teazer]

Vic roads are pretty anal about things like that and I doubt things got easier since I left OZ. But once teh RWC is taken care of, the fender can go back in the box...

 

[Casual]

Thats what I figure

 

[resin]

There's some mentioning of opening up your tank, now if something like that is done, be sure to take the opportunity to free your tank of any rust, and consider coating the tank for future rust prevention.

Keith

 

[Casual]

Thanks for the advice, all the info I can get the better at this stage. Especially with things such as this that I have very little experience with. I appreciate everyone's input