Topic: A CB750 race bike build...

[Santiago]

Made a few more bits for the clip ons, might get them finished tomorrow. Need to make a jig to hold the bars against the clamps at the right angle. I fish mouthed the bars for a 5 degree angle. The pins for the hinge are stainless, I'll peen the end a bit to keep them in place. Also need to make a wee jig to position the clamp fitting to weld that on, then turn up a couple of stainless bolts for it.

[johno]

yeh nice work bro   

[Santiago]

Thought the handlebars were done, minus painting, however I'll need to cut a slit in the tubes about 2cm down from the fork clamp and bend them slightly to the rear, then reweld the tube, so that the brake master cylinder protrusion that the hose bolts to will clear the clip-on hinge. I kind of knew this, but wanted to see if it would clear without cutting the tube ( one less step to do 🤣). Alas, it will neeed to be done. I chucked the clutch lever on to see what it looks like, its made from a GL1000 perch and lever with a bit of spring wire bent to touch the adjuster. The plan is to weld up the mirror and also the switch wire hole in the perch, file it to shape, then paint it black. Next year after I come back from work 😖.

[Santiago]

It's been a while for me, but despite what it looks like, I am making small steps of progress with the bike (working on other bikes as well). Still at the 'mocking up' stage really, hence the dummy engine in the frame (the actual engine is built, I only want to lift it into the frame once, once the frame is done). I've basically finished the handlebars, brake lines, 3 way splitter (it is now painted), steering lock. Got to sort out cutting the frame rails under the seat, adding the oil tank mounts etc. And tidy the workshop

[Dresda500]

Great thread! Curious what guys are doing for proper race forks on these and being as period correct as possible? If I remember correct the early CB sliders dont have bushings and didnt get them until the late DOHC version. Are people mahcining for insert bearings like the late versions? Tubes...the originals I think were used for spares for the Howitzer cannons as they weigh a ton...are you guys using a thinner wall high tensile fork tube? I guess if installing cartridge kits, the originals might be a tad small on the ID anyway, necesitating new tubes.
What's your plan for this one?

[Santiago]

Hi, my fork lowers are standard CB750 K0-K1 type, these have bushes on the staunchions and are crap 😁. The only thing that retains the sliders to the staunchions is a circlip at the top of the slider...pretty terrible in my view. This is unlike the later forks where the damper tube cannot go through the bottom of the staunchion and is bolted throught the slider by the m8 bolt throiugh the bottom of the slider under the fork cap. These later forks are much easier to modify with gold valves. Anyway, I'm going to run this 'as is' initially, but am working on making a set of 'replica' four bolt forks (the axle cap to be retained by 4 nuts on each cap  a la the CYB 750 Racing Type forks. How I am doing this is by cutting the 4 bolt caps off a set of XL350 fork sliders, and then cutting the corresponding piece off a set of CB750 K1 sliders, machining both to suit (ie: one is rebated, one is spigoted) and welding them up. Then I will send the modified sliders to Maxton in the UK for a set of their GP20 cartridges to be inserted into tubes with bushes provided by them. I have these GP20 cartridge forks on my CB350 race bike and they are superb.

[Dresda500]

Excellent! Great minds think alike... I'm building a new set of forks for my Dresda as well and using the XL350 lowers, some Marzocchi tubes I had laying around and some trees I just stretched tonight from 180 to 200mm centers as I run dual AP Lockheed calipers with spokes so need the width. I'm usign the aluminum stem from an 80s XR350 as well.  I'm getting Maxton to make me cartridges as well. Should be a proper fork I think.

[Santiago]

That triple clamp looks like a Betor off an Ossa, I have a set like that with a stem for a Honda CB350 twin frame, 180 centres, was too narrow (by a gnats you know what) for a AP Racing caliper on a set of 500/4 lowers and Maxton tubes / internals, even though I machined the inside of the slider for disc and caliper clearance, spaced the disc off the hub and spoked the wheel o the LH spokes were as long as posible and on as much of an angle as possible and stil keep the rim in the centre of the forks. Had to go with std 500/4 honda clamps at 182mm, the 2mm made the difference. The Maxton forks work amazingly, I have the GP20 cartridges, rebound in one side and compression in the other.

[Dresda500]

You are correct, Ossa trees. I cut and welded them to get the 200mm width and shortened up the offset to a 50mm. Would ahve been a lot less work to buy a set of CBX trees, but these look better.. I corrected above , the alloy stem is XR350 form like '84, the XL had a normal steel stem. This alloy stem has standard 26mm ID bearings so easy interchange. I have a CB500 hub, so a bit wide. I should have built the wheel on a narrower spoke flange hub. Some of the Yamahas have very narrow spokes so lots more room for twin pot calipers, but also most are 36 spoke

[Santiago]

So, I managed to get a bit of shed time for the CB750, been working in Papua New Guinea so haven't  been able to work on the 750 for a while, and actually I've been doing some post racing improvements to the CB450. Anyway, a while ago I started making an oil cooler out of a VF750 cooler, I cut the hose connections off and today made some bits and pieces for a sort of copy of the Honda race cooler. I used the LPG torch to anneal some 6061-T651 22mm tube, it has a 10mm hole and a thick wall. Once it cooled I put it in the bender with a 7/8" former and gave it a couple of bends. Then after cutting it where I thought was correct I made some fittings out of 6061 on the lathe, I reckon it came up pretty well and will be good enough. I need to take it to a mate to get welded up, my tig won't do aluminium, but you can see what it looks like more or less.

[MRieck]

Nice work. Love the early Gixxer too.

[Santiago]

😱 It's an RG500, 4 cylinder 2 stroke. It eats Gixxers for lunch😁

[Rocketman]

Enjoying your build. Thanks for sharing.

[Santiago]

I posted ths on the FB page but not here for some reason: I decided I didn't like the glass tank I made from a mould that is floating around here in 'the system' in New Zealand, not sure where it came from. It's the long skinny tank, as opposed to the short fat tank. I bought a short fat tank in aluminium from Germany I think it came from, not sure where it was made, but it's pretty good, probably not as good as Asa Moyce tanks, or Peter Keyte, but they are unobtanium now. So I'm going to use the short fat tank, but it means I need to cut and move the cross piece that supports the seat and tank strap. More work😫. I'm going to remove the Monza cap and fit one from a CR93, closest thing I have to the actual cap on the Daytona bikes. Also I'm going to remake the tap fitting to take a 3/8 NPT Pingel. I've decided my tribute bike doesn't need an exact copy of the twin outlet tap Honda used, mainly because I have no idea how to make one or where to buy one🤣

[MRieck]

😱 It's an RG500, 4 cylinder 2 stroke. It eats Gixxers for lunch😁

I should have blown up the pic and noticed that.....at 65 looking at pics without my glasses causes problems. I certainly know what an RG is even though they were never imported into the USA.

[Santiago]

No problem, looking at pics without my glasses cause me problems as well and I’m only 55😂

[Daggless888]

Hi Santiago. Great build. Can’t wait to see this one finished. If you haven’t purchased the pingel fuel valve send me a pm. I have a 3/8 npt race valve ( on/ off only) brand new that I need to off load. I’m in chch.
Cheers
Dave.

[Santiago]

Daggless888 I sent you a PM.

[Santiago]

Soooo….I managed to get the oil cooler tigged up and painted. Other than that no progress, I’ve been building a new CB350 race engine and have started a Ducati 907ie ‘Paso’ tidy up. But the ‘homage’ to Dick Mann’s 1970 CB750 Racing Type continues. 😂

[RAFster122s]

Nice work on the cooler, very trick!