CB750 Barn find project - First Timer

[Underdog1]

I did re-stake mine Just gave it a sharp belt with a punch.
The spokes soon go black if you don't clean them.

might as well just in case then if its that easy.

Im still yet to put oil in my forks as I've not got the front wheel back yet but will be doing it this week sometime. I've got Hagon progressive fork springs and im unsure about how much to put it.

On the website it state 160mm air gap:

https://www.hagon-shocks.co.uk/catalog/partdetail.aspx?partno=400-083-02

the instructions that came with the forks don't mention any air gap and are incredibly vague. is it a case of just filling the forks up to 160mm from the top of the tubes and thats it? presumably thats with springs in. If anyones got any experience fitting these then please pipe up!

The shop manual for the standard springs suggests 145CC of ATF oil in each fork. Would be easier if Hagon specified a volume rather than gap

[K2-K6]

Think the 160mm air gap would be more accurate a measure if you were to drain and then refill the forks as it would accommodate any residual oil left inside the assembly and not cause you to increase the volume.

It's not too critical as 145ml should be fine to make sure all the damper functions are covered and operated as expected.

You'd trim the 160mm measurement if you wanted to get the air gap adding to the spring rate (it effectively makes an air spring if the fork seals hold the pressure) as the fork reached full compression.  To be honest, it's not something most people would notice in general use.
If the fork stoke is 102mm,  you've got to allow at least that before the oil hits the top of the fork cap and stops it compressing hydraulically.
So in reality,  allowing for some space above the oil,  you've only probably between 130 to 160  to play with total.

If they are totally dry then 145ml is accurate enough.  If not certain, then with springs installed the 160mm is probably most concise.

[Underdog1]

Think the 160mm air gap would be more accurate a measure if you were to drain and then refill the forks as it would accommodate any residual oil left inside the assembly and not cause you to increase the volume.

It's not too critical as 145ml should be fine to make sure all the damper functions are covered and operated as expected.

You'd trim the 160mm measurement if you wanted to get the air gap adding to the spring rate (it effectively makes an air spring if the fork seals hold the pressure) as the fork reached full compression.  To be honest, it's not something most people would notice in general use.
If the fork stoke is 102mm,  you've got to allow at least that before the oil hits the top of the fork cap and stops it compressing hydraulically.
So in reality,  allowing for some space above the oil,  you've only probably between 130 to 160  to play with total.

If they are totally dry then 145ml is accurate enough.  If not certain, then with springs installed the 160mm is probably most concise.

Forks are bone dry so might just pour in 145ml and see where that gets me, thanks for shedding some light on this.

[Underdog1]

Done a few things this week, a friend sandblasted the inside of the tank with mediocre results so I’ve cut the two flat sections on the bottom out for better access, will see what that yields! Managed to get some huge chunks of resin out though.

Wheels are back and quickly stuck the rear on when I finished work, can’t seen to get the rear brake mechanism in place as it’s hitting the swingarm. Very close though so might just be that the bike needs to be on the ground to move the swingarm up to allow the linkage into place.

Also had a small amount of rust in the oil tank, soaked in vinegar all week which cleaned it up nicely, then neutralised with bicarbonate of soda. Unfortunately I got a bit of flash rust so may just use bottle brushes and carb cleaner and see how I get on

[Trigger]

The rear brake mechanism goes to the front of the swinging arm (between the arm and engine). It needs to be put on (through the frame mount) before you put the swinging arm on 


This goes on before the arm

[ Guests cannot view attachments ]

[Underdog1]

The rear brake mechanism goes to the front of the swinging arm (between the arm and engine). It needs to be put on (through the frame mount) before you put the swinging arm on 


This goes on before the arm

(Attachment Link)

Well that’s a pain!

[Trigger]

Also attach the brake rod to it, not easy to get the pin in and the split pin afterwards 

[Underdog1]

Also attach the brake rod to it, not easy to get the pin in and the split pin afterwards 

All sorted now. Spent ages trying to crack it with the swingarm still on but it’s impossible to get the spring into place so had to strip the rear end back down like you said. Made some good progress, both wheels on, both brakes on, bars internally wired and installed. Hopefully can crack the electrics today.

One thing I’ve noticed is there’s a reaaaally tight clearance between the swing arm grease nipple and the little bracket for the carb bowl overflow tubes at the back of the engine



Ive purposely bent the bracket to allow enough clearance there, it’s not the original grease nipple as that one snapped a while ago when it hit that bracket when installing the swing arm for the first time! Have I missed something here?

[Rob62]

Also attach the brake rod to it, not easy to get the pin in and the split pin afterwards 

I found this out the hard way.....although not impossible it is a pain in the arse.

[Underdog1]

Had some slow progress today with the wiring. Basically all I’ve managed to achieve is an oil pressure light and a gurgle from the horn. Tried the horn directly onto the battery and it’s plently load which makes me think it’s a ground issue. The frame ground is bare metal as I’d already sanded it back. I haven’t sanded the frame on the engine ground as I didn’t think it was needed. Seeing that the switches ground through the handlebars should I be removing paint for this? Only one of them (left) has that drilled locating tab.

[Trigger]

The horn needs to go to ground , the earth lead and the coils  If you have drilled the bars, be careful that they don't snap

[Underdog1]

The horn needs to go to ground , the earth lead and the coils  If you have drilled the bars, be careful that they don't snap

I think the ground for the horn is in the actual switchgear itself and grounds to the bars? Would make sense as the horn could be weak from having to ground through a layer of powder coat.

They are steel bars so should be good to go with a few little holes

[Trigger]

Nope, the ground to the horn is PN 38105 323 000  Or 38120 392 620

[Underdog1]

Nope, the ground to the horn is PN 38105 323 000  Or 38120 392 620

Yeah I’ve got that, just connects the horn to the harness by the coils, so all good there. Next step is to get some batteries in my multimeter and start poking around. Wish I’d just spend the extra few ££ and got a K6 harness rather than shoehorning an earlier one in

[Underdog1]

I think I’m going to repair the old harness and try that, conditions not too bad, couple of connectors need cleaning up and the connection to the battery +ve is a little fried.

What else can I do outside of a spray with contact cleaner to try and improve the state of all the bullet connectors?