Topic: CR750 Project - Where to start?

[RickB]

Hi guys,

Let me start off by saying I hope this is in the correct section. It pertains to the CR750, but it's not about racing per se. So if this should be in the Project Shop area, I apologize and mods please move it.

Secondly, I have been doing as much reading as I can, but have no real-world experience with a CR750 so please keep that in mind when you're chewing me out for not knowing the difference between Works and RC bikes. Is that even the right terminology?

Ok so I recently finished a 'way-in-over-my-head' rebuild of a 1975 CB400F down in Australia. I then moved to the USA. So far, my 400F hasn't come with me. However I've got the itch to work on a bike and have been wanting to upgrade to a CB750.

I can't fathom tackling a restoration job, it's just too vanilla for me. However I don't want to chop up a survivor to build another cafe racer. So my thinking is, find a cheap/donor CB750 and make it a 'streetable' CR750 tribute. I don't race, but would like a strong performance bike. The Daytona CR750's thread was a great inspiration, if a little confusing for a noob like me.

You could argue a streeted CR750 is just another version of a cafe racer, and you may be right. Yet it's respectful to the marque and something I think I would really enjoy looking at. Plus if I start with a rescue bike, then I won't hate myself for destroying a survivor. At least that's how I'm justifying it to myself.

So now that that's out of the way, here's what I think will be required to make said streetable CR750 tribute. Please correct me if I'm wrong.

• The big question is which CB750 to start from. From what I can tell, a 1972 CB750 K2 is the base model that the Dick Mann Daytona CR's where built from. Do I need a K2? Or will any K series CB750 suit?
  

• Then I need to do a bunch of frame modifications which are well documented here. Removing brackets, shortening backend under seat, some fairing mounts, shortening rear shock mounts, rear set brackets.
  

• I think the Daytona bikes had a shortened wheel base by reducing the headstem angle and rear swing arm, but I'm not sure I really need to go that far. I don't know how to weld, but I'm sure I can find a builder here in LA that could do this relatively simple stuff for me. I'd actually like to learn for myself too.
  

• I'll need braided oil lines, clip ons, gauges and custom mount, custom oil tank and oil breather tank, fuel tank, seat. Tank and seat should all be alloy I think. I should be able to do this for under $1000. I could do tank and seat in fibreglass, but I'd rather do that right. I've heard horror stories about fibreglass tanks.
  

• Carbs will be Keihin CR33's. Not cheap at $800 odd, but maybe I'm able to find some used. But again, if I can get a beater bike cheap, I can justify it. I can put the correct velocity stacks on with mesh covers or go with pods if they prove troublesome. My mechanic back home runs open stacks on his Laverda Jota replica and he says they're easier to keep tuned than his pods.
  

• Wheels. If it's a beater, I'll need new rims as that's cheaper than rechroming. Doing a two disc front end isn't difficult. Finding a 240mm CR spec rear drum is impossible. So maybe I just live with the stock rear drum and fit the CR correct sized rear sprocket (assuming the CR rear sprocket was different).
  

• As for the motor. There's a guy here in California who's selling his '77 CB750 project. It has a freshly rebuilt 836cc engine. If it's still for sale when I have the money, I'll hit him up and make an offer for the motor alone. Otherwise I'm ready to tackle an engine rebuild on my own I think. It'll be intimidating but I'm actually excited to learn how.
  

• If that happens, I'll be relying on APE quite a bit. APE sell rebuild kits for 836cc or even 1000cc! It's not cheap, but if I'm rebuilding everything entirely anyway, I can find a beater for nothing in the US if I'm prepared to wait. Regardless of the decision there, I'll have to rebore cylinders, new valves, lap valves, new springs, new cam shaft, new chains, new hardware and whatever else needs repairing/replacing.Electrics will need hiding under the seat. Again I leant how to do a lot of this myself already on the 400.
  

• It would be good to wait until the end to get a full fairing but I wonder if I can still weld the fairing mounts in the right spot. This website has some good photos for what needs to go where (although apparently is terrible to order from). An alloy fairing would be great, but maybe a little too pricey for me. Finding a fibreglass one that will fit over my stator cover might be tricky. I don't intend running a total-loss system.
  

• So really the big question is finding a suitable bike to start from. In the short term, it'd be great to have a bike to ride around on. Seeing as the weather is nice and I'm missing my 400. However I think if a beater 1972 CB750 came up, it'll be cheaper to get one that is busted but all there (no broken fins, no twisted frame etc). So really, like my how 400 started out but with a serial number and almost free!
  

So in short, do I need to start with a 1972 CB750 K2 frame and engine to make a tribute CR750?

If you've read this far, thanks for sticking with me.

Rick.

[lordmoonpie]

Welcome Rick - plenty of info on this HiPo forum and if you go back through the pages you will see about all the answers you could ever want. Personally I built my CR using a K3. Apart from some early K0 parts like forks etc, the K model series up to K6 are ver very similar and lots of parts are interchangeable and if you go K2 onwards you shouldn't have a problem finding replacements. Havng said that the work you do will depend on how deep your pockets are. Once my frame mods had been done it was very different to a stock frame and as for engine, I have basically got only the externally visible cases left from the donor motor, everything else is new internally. You can do as much or as little as you want...

So, it just depends on how far you want to go. One thing's for sure, this is the place to be, the place for help and the place frequented by people who not only have the knowledge and experience but also real connections with Daytona. Enjoy your time here

[RickB]

Lordmoonpie,

Thanks so much for the encouraging words. I've said before and I'll say it again, SOHC4.net is the most valuable resource to a SOHC enthusiasts bar none. I'd have a SOHC4.net membership before I have a manual!

Your advice on which K frame to start with is exactly what I was looking for. The only reference I have for which frame is Andy Downes's thread on frame mods which I linked to above. I assumed because the Daytona bikes were built in '69 and that the earlier frames would be a better starting point. Maybe not then.

I have to make up in my mind how far I take the CR spec. Like am I going to the nth degree or just a close approximation. Seeing as I don't intend to race it, I'm already way outside the 'replica' zone. So maybe starting with the cheapest K2-K6 I can find ain't all that bad.

I hear you on the deep pockets. My CB400F was meant to be a clean it and ride it affair. It ended up taking two years and thousands of dollars. I intend to use the lessons learned from that adventure and make things easier on myself this time around.

The hunt for a CB750 begins. A K2-K6 with everything there, not broken (busted fins, twisted frame etc) but worse for wear I think. I'll have to start tooling up and finding a place to build this thing.
 
Thanks again for the welcome,

Rick.

[madmtnmotors]

Welcome to this side of the pond! Looking forward to following your new build thread. There are many more SOHC's just waiting to be resurrected here in the states, seek and ye shall find.

[lordmoonpie]

There was a thread recently Rick that got loads of Honda technical pictures added to - I added a bunch of frame pictures there myself and he list of modifications that I had from an HRC fax. If you can't find it I can email the pictures to you if you pm me your email address.

[MRieck]

Welcome Rick - plenty of info on this HiPo forum and if you go back through the pages you will see about all the answers you could ever want. Personally I built my CR using a K3. Apart from some early K0 parts like forks etc, the K model series up to K6 are ver very similar and lots of parts are interchangeable and if you go K2 onwards you shouldn't have a problem finding replacements. Havng said that the work you do will depend on how deep your pockets are. Once my frame mods had been done it was very different to a stock frame and as for engine, I have basically got only the externally visible cases left from the donor motor, everything else is new internally. You can do as much or as little as you want...

So, it just depends on how far you want to go. One thing's for sure, this is the place to be, the place for help and the place frequented by people who not only have the knowledge and experience but also real connections with Daytona. Enjoy your time here

How is your CR running Simon???

[kos]

Welcome to the CR building club. Any details or questions you are free to ask me, as I would love to help. Having built 8 of these bikes and assisted 5-6 others buy supplying parts and advice, I have a fairing good knowledge of these machines.

one of the first things you need to decide is if you are replicating a "Kit" machine that is noted as a "CR750" or a works factory machine like Dick Mann used to win Daytona in 1970. They are coded as RC750. Big difference is the rear seat... as the kit bikes had different profile at rear of seat and attached to frame at rear fender mounts, vs RC750 which had smaller rear hump and special frame bracket to mount to. Also, kit machine had "bolt on" brackets to mount steering dampener to frame under fuel tank and RC750 had a stub of steel, to locate rear of steering dampener to.

Once you have done that, you will be off to spending money!

more at www.m3racing.com

KOS

[lordmoonpie]

How is your CR running Simon???
Ah yes - that thing!
Well I got sidetracked into restoring my old XV750 yamaha and building the CBR250RR race engine for my RC163 replica so the CR is sat waiting for its timing to be done on the new ignition you kindly supplied Mike. It's all a big rush as we're planning some building work in 8 weeks time which will mean I have to send my bikes on holiday for about 4 months so I want to get them able to be wheeled out rather than carried out in boxes.

I must get the CR timed up - think I found a problem with the running under the Boyer setup, I'm pretty convinced now I had a dodgy earth connection so am hoping the Dyna with proper earth connection will more than do the trick.

The good news is I have some carb vacuum take offs now for synching (thanks again Mike ) and the little bits like throttle/tank clearance are sorted and a nice "works" modification to the exhaust to bash it in a little so the chain clears the pipe on the over-run. I've also cut the screen down so it looks more racer ish and a bit less like a mismatched part. All I need to do is run it up so am back to waiting to amass brownie points to get the Mrs to help.....or finish building my electric solo starter contraption.

It's all progress....and it's all slow 

[RickB]

Guys,

Long time between drinks as it were but I didn't want to jump the gun until money had been spent.

After much deliberation and research (and a lot of help from a few of you here) I decided to reach out to the experts and do this the right way.

Whilst I loved re-building my CB400F from the bolts up, I realized with the amount of fabrication and obscure knowledge needed to build a CR750 replica approaching some sort of authenticity, I would need to lean heavily on the experts. I figured so much so that in the end, I might as well have one of them do all the 'heavy lifting' for me.

So after a lot of reading here on the SOHC forum, I got in contact with Mark at M3 Racing and asked if he'd be interested in building me a streetable CR750/Dick Mann replica of sorts. He has been terrifically patient and understanding with me while I sorted my finances out and changed my mind about things.

The overall goal of the project is to make an authentic enough CR750 replica that is ridable on the street. So a headlight, indicators and side stand. Outside of those parameters, I am erring on the side of authenticity wherever I can. I understand that is where the value is in these bikes. Sure, I could end up with a very expensive cafe racer that resembles a CR bike, but I'm sure I'll love it regardless.

We're a few weeks into the process and we've settled on his M3 Racing team 766cc piston. I want a CR750, not a CR836. However the real reason is because my best mates got a BMW 75/7 and I want there to be an even playing field when I beat him! I was also worried that if I were to ever get good enough to attend a track day or whatever, I would like to stay in correct class.

I would like to have the faring be removable. As I'll be riding this bike around as much as possible, I don't always think a full fairing will be practical. So with Mark's help we have agreed on a faring mount that will be removable at the front tube but still leave the gauges and headlight on the bike. Mark even said he recalled seeing a fairing mount exactly the same as this when he purchased some of the left over Honda RC750 factory parts year ago. This sums up what I would like this bike to be. A street version of a CR750 (which I guess you could argue is the CB750!).

As I want this to be authentic, I believe I need to add the large rear hub. That would be the easy part really, because as the devil is in the details on these bikes as you're all aware I'm sure. I see what H2Eric is doing with his CR750 build and I drool. I would love to reach that level of detail. Front and rear hubs, engine fins, magneto cover, front 4-bolt lowers etc.

Cost is a factor, but I also know I spent way too much on my CB400F and figure with M3 Racing handling this, my money will be well spent.

I'll keep you all updated with progress and try to get some progress photos up soon.

Thanks again to everyone that has helped.

Rick.

[Old Scrambler]

We seem to build at about the same pace......patiently

Your in good hands with Mark........you always meet the