CB750 cafe racer build

**jonbuoy** · 23rd January 2007, 20:35

A run down and picture diary here for anyone whos interested in doing one of these. I bought the donor bike cheap off trade me - a 77'F, it has some issues:

Low Compression
Cam chain rattle
Rear master cylinder stuffed
Fork seals leaking (pitted forks)
Leaking head gasket
Clutch

Other than that it's pretty tidy. I don't want this to just be a show pony so I've taken some good advice and decided to start with the motor. Compression test showed most of the loss was due to the head not the bore/pistons. Exhaust valves are beyond lapping so will have to be refaced along with the seats. I will try to keep the picture diary going and maybe a few words every now and then.

Parts have been sent away here is a rundown of the engine work:

Heads cleaned, valves and seats re-faced, skim.
Barrels cleaned, bore hone

The following will be replaced:
Clutch plates
Piston Rings
Cam chain tensioner
Cam chain
Filter
Gaskets

Doing all the work except machining costs I reckon its going to cost a grand to get the motor running good (carb refurbs will be extra...)

The body work will be:

Clip ons
Rear sets
Fibre glass tank and seat
Paint job
Sort front forks
Sort rear master cylinder

All up I'm hoping to do it for around 5K, for a custom bike this isn't too bad. I was thinking of doing it on the cheap to start with but I reckon I will hold onto this beast till I die. Not everyones cup of tea but I like em'

This is what I hope to get it looking something like:

**jonbuoy** · 23rd January 2007, 20:38

Some pics of the bike now.

**Eurodave** · 23rd January 2007, 20:42

I can probably help with the figlass tank & seat......have a look at my public profile/attachments etc & then PM me if interested.......

**98tls** · 24th January 2007, 05:46

Nice..........looking forward to updates...........

**merv** · 24th January 2007, 07:30

Its a '77 you say and by the look of those forks and wheels its been fitted with those off a later CB750 or CB900 already.

**jonbuoy** · 24th January 2007, 07:47

Its a Canadian import and a bit bizarre as it also has a K3 73' motor but an F frame stamped 77'. I'm not so worried as the later motors sound like they had issues with the valve guides, also the barrels aren't matt black which looks better IMO. I can live with the Comstar wheels.

Cheers

**Eurodave** · 24th January 2007, 09:30

That front wheel & maybe the back wheel but cant see it clearly,aint no comstar! looks like an american aftermarket Lester alloy [they had a similar spoke pattern to the later Yamahas like the SR500 XS650 XS1100 etc]

**Bonez** · 24th January 2007, 17:38

Originally Posted by Eurodave

That front wheel & maybe the back wheel but cant see it clearly,aint no comstar! looks like an american aftermarket Lester alloy [they had a similar spoke pattern to the later Yamahas like the SR500 XS650 XS1100 etc]

Agreed. A previous owner has obviously done a bit of custom work. Front looks like an 18" instead of the standard 19"er too. Should look sweet when tidied up.

**jonbuoy** · 25th January 2007, 08:30

Interestin, I didn't realise the wheels were aftermarket. Someone has cared for this bike in the past. I got lucky I think. Got blocks and head back yesterday. Will put pics up tonight.

Cheers

**Coyote** · 25th January 2007, 08:35

Awesome. I'll be watching the progress

**jonbuoy** · 25th January 2007, 19:13

Heres head and barrels looking pretty tidy now. Just making up my mind on if I change the rings or not, its had a hone and the old rings look fine and in spec. New ones are over 300 bucks..

**jonbuoy** · 25th January 2007, 19:27

I'm also a bit confused about the order the rings on my piston have been put. I've asked on the SOHC forums but no-one has come up with an answer - two people have come up with two ways of putting these on. There are three rings in total - two compression rings, and an oil control ring. One of the compression rings looks like it has a cutaway for oil control and is a bit thinner than the other solid ring. Attached is a poor sketch (I exagerated the notch). It looks like this engine has been worked on in the past so I don't know if its been put together right. My pistons have been put together with the ring with the notch on first, then the solid compression ring, then the oil control ring. If I measure the side float of the rings like this - the top ring is too loose and the middle one looks tight. If swap them over and put the solid one at the top and the notched one in the middle they are both in tolerance. Hard to explain hence the drawing. It seems odd to have the notched ring at the top. All mine are all like this. Anyone know?

Solved - Rings were in the wrong order from previous rebuild.

**jonbuoy** · 11th February 2007, 20:51

Bottom end pretty much finished:

Casting - degreased (paintbrush, toothbrush, ear buds..) etch primed and sprayed engine enamel, had the odd lump fly out of the rattle can - bloody annoying. I used supercheap auto stuff - I should have used the VHT stuff, good enough for the time being.

Alloy 400/800/1200 then autosol, not mirror finish but way better than before. Should have gone a bit harder with the 400.

Leaving the top end until bike nearly ready to run, engine enamel stays surprisingly soft until engine has some heat to it and I'll be getting mucky paw prints all over it when I put the head back together.

**jonbuoy** · 11th February 2007, 20:55

Aftermarket exhaust was pretty quiet so I've cut out one of the baffles and shortened the pipe. Painted with black high temp paint as chrome was looking sad.

**jonbuoy** · 11th February 2007, 21:01

Found some cheap GB500 clip ons - same fork diameter. Had to shorten the headlight ears so they could fit under yolk, left the old bars on to show how much its lowered by. Will have cut and smooth out the old handlebar mounts un less I can find a top Yolk that will fit - pretty unlikely.