Topic: CR750 project New Zealand

[750deepsouth]

Hello all, I've had a CR750 project going for probably 15 years or so, of and on, and finally 'completed' it over the last two years. I'm a long time Honda CB750 fan and had the chance to purchase a pretty ropey old K1 about 20 years ago, and thought that will make a nice project. The idea of having a stock CB750 and a CR replica took hold and I starting looking for parts, and searching forums such as this to gain knowledge. Thank you Sam, for your early help 

Firstly I'll list all the places I source parts from:

Mead Speed
Air-Tech Streamlining
Swarbrick Racing
Simon Tappin
Graeme Crosby
EconoHonda
roadandrace.com.au
Slingshot Cycles
Bunbury City Motorcycles
F1 Engineering
David Silver Spares
Classic Cycle City
Andy Cepok Motorradteile
OEM Cycles
Vitalcycleparts
Chris Schumann
Andy Smith @ http://www.good-bits.co.uk

There are some lesser-known companies there, but I wanted as many genuine original CB750 parts as possible (or NOS replacements) and it's fairly hard to find some genuine parts.   
The first item was the Airtech bodywork items and this is what it looked like way back then.
Fitting the Swarbrick exhausts meant inverting the bike. The only time I ever want to see it like that.

[750deepsouth]

So: about 3 years ago I had the time, the parts, and the money  so I'm going to skip a few steps in construction. Suffice to say, that this gif animation tells the story of the early stages. I thought a bit before fitting the motor into a newly powder-coated frame. We all know this is a difficult job, and impossible for one person to do it without scraping the frame. The solution? the pictures tell the story. The cords holding the frame go to pulleys on the roof beams then over to that container with 18 litres of water. This nicely balances the frame, which can be then brought down very slowly over the motor, on it's side. Perfect.

[750deepsouth]

I rebuilt the motor from the ground up, but I haven't gone for power. It was pretty worn and had to start with a new crank and I did the following work:
Bored to fit 0.5mm o'size pistons, this takes motor to 750cc, new pistons and rings. I wanted to keep the motor the same cc as the original CR750 Hondas.
Tsubaki high performance cam chain, complete new cam chain tensioner. New valve guides, new exhaust valves, new stem seals, single coil tapered valve springs with new keepers. 125-05 Megacycle cam. Mod cylinder head - stage 2 porting. Cut seats - throat out ports to increase port area.
From Chris Schumann
new .002" oversize O.D. valve guides for the Honda CB750 SOHC. They will work in all models '69-'78. These are oversize to restore the press fit in loose guide bores. They are a good upgrade for some early types that don't accept stem seals on the exhaust guides. These guides are designed so they can be installed deeper in the head (if desired) for greater stem seal to retainer clearance when using high lift cams. CB750 VALVE SPRINGS RACE SPRING KIT. This is a set of high performance valve springs for the SOHC CB750 Honda '69-'78. These are a brand new product that were not available on the retail market. They are a single coil tapered design offering better characteristics than conventional straight dual spring setups. Single coil conical spring designs are being adopted in all fields of automotive motorsports and now have arrived in vintage motorcycle racing. This design offers reduced valve train weight and far greater resistance to spring harmonics. Don't let the single spring design fool you. Spring pressures are significantly greater than stock yet not quite as aggressive open pressures as some aftermarket kits, helping prolong cam lobes and rocker arms. This kit includes hardened shims as the stock cupped units are eliminated. The step in stock retainers must be turned down to fit in the tops of these springs, thus further reducing valve train weight. The spring specs are as follows: Upper O.D. 1.120", Lower O.D. 1.250", 1.710" free length, wire diameter .177", pressure closed 75 lbs. at 1.450", 185 lbs. at 1.100", 205 lbs. at 1.050", coil bind at 0.955". 

It requires deep pockets to really bump the HP up big, and I was concentrating, with this project, on a bike that looks good and sounds good. Yes, I'm shallow  But it's a strong base to build on, should I have any wish to go further down that track.

[750deepsouth]

I spent quite a bit of time on the twin disc conversion and getting the front end ok. I used old CB750 guard stays along with a bespoke bracket to hold the front guard. It was a job for patience and small fingers when fitting the RH caliper mount and brake caliper together. Quite a bit of work to get the spacers on the RH side ok as well.  I'm pretty happy with the outcome. This was a time consuming part of the build.

[750deepsouth]

Oil cooler, rev counter and oil pressure. I was lucky to get a hold of a rev counter from roadandrace.com.au and starting at 4k rather than 0. The oil pressure gauge? a standard Smiths oil gauge, fits a Mini, and quite cheap. Sadly there are folk out there selling what appear to be similar gauges ('CR750 Oil Gauge') for 4,6,8 times the price. Be careful out there! The oil gauge line goes to the rear top of the crankcase, when the CB750 oil light switch fits. Several people told me to draw oil all the way up to the gauge. No, not necessary. Oil pressure in the motor will compress the air in the gauge to exactly the same pressure in the cases.
Front brake lines. I used the standard fitting on the lower triple tree mount as a three-way splitter by removing the (unnecessary) brake light switch and inverting it. This frees up another point to screw in the other lower brake line while keeping them the same length. So the two line nicely mirror each other. Initially I had some trouble getting a 'soft' feel out of the brakes, despite careful bleeding. Several people suggested I use steel braided lines in case the old style lines were bulging, but the lines were specially made and very solid.  I had rebuilt the master cylinder on the bike, thought I might have made some error is getting it right, so I tried a new one. This was also soft (!!) but a bit of use has seen the brake action firm up quite a bit. So I conclude I may have had a little bit of air trapped, perhaps in the splitter, and it's taken time to float up the line back into the master cylinder.

[750deepsouth]

I had the bike set up to run total loss on Dyna S pointless ignition with standard coils. I've had no issues with using standard coils. Then I found Andy Smith's website and couldn't wait to get his alternator conversion kit. Very good stuff, I also bought the CR carbs. I just love the CR style alternator cover, I had the HONDA name engraved on it. Sandblasted both that cover and the cut-down gearbox cover. It looks really good. All this then the bike on the dyno to get the fuel/air right. Oh, and here's a picture of the bikes first start-up too. This was a bit before fitting the CR carbs and small alternator.
Andy's alternator kit still requires a battery to provide enough initial current voltage to load up the coils. It does not produce enough current to do this when using pit rollers to spin the back wheel, but once revs are 3-4k it produces enough to run the bike and keep the battery charged. I have the small battery sitting in a small frame in the starter motor cavity. Held down, of course, by an original CB750 battery strap. Pingel fuel tap with very small filters to keep the fuel clean.

[750deepsouth]

I started with bling, and had to continue with a good paint job.

[andy750]

Wow love the attention to detail! Amazing build. What oil cooler did you use and where did you get it?
Many thanks
Andy

[750deepsouth]

A project like this is hard to  finish. Depending how closely you want to replicate something, you are going to spend a huge amount of time, and a possibly a lot of money. Be careful out there in Internet Land because there are a lot of people who want to separate your from your hard earned cash in return for incorrect and/or over-priced stuff.
If I was to do more, it would be the rear end - replica footpeg mounts, footpegs, and rear brake. This may happen over time. I haven't 'raced' this bike but in 2017 and 2018 it did some laps at the Teretonga Circuit during our annual Burt Munro Challenge here in Invercargill, Southland, New Zealand. In three weeks time (the 2019 Burt Munro Challenge) I'm taking it out again for a few laps. Meantime, I've had a lot of fun building this, it's my first, and if I were to start afresh I'd do a number of things differently. I've learnt that if you strike a problem, go away and think it over. There is a solution every time that doesn't involve a hammer  - I never did use a hammer actually, but the thought was there. There is an engineering solution to every problem!
Finally, I have a few clips on youtube - nothing too exciting. Visit here https://www.youtube.com/channel/UCRgr-lGtrbsCrMlEHTso54g

[750deepsouth]

Wow love the attention to detail! Amazing build. What oil cooler did you use and where did you get it?
Many thanks
Andy

Hi Andy
Thank you very much for your comment! Oil cooler from Mead Speed
http://www.meadspeed.com/products/honda/cr750/oil-cooler

[turboguzzi]

very nice work, and yes, meditating over problems usually yields a clean solution. thing is that after you've implemented, you often realize there was an even smarter way!

What's the next project then?

[750deepsouth]

very nice work, and yes, meditating over problems usually yields a clean solution. thing is that after you've implemented, you often realize there was an even smarter way!
What's the next project then?

Often the need for a smarter way would have been prevented by doing something slightly different several steps earlier!
The NEXT project?! I haven't fully completed this one!

[PeWe]

The bike look really good!
Possible to ride it on the street? Registration might need dB killer in the pipes
That bike would be a nice café racer, show it for people as a piece of mechanical art celebrating the old times tech.

Small details can be replaced or added afterwards when bike is completed and proved to be running. This can be the fun for years, the project will never end.

[750deepsouth]

The bike look really good!
Possible to ride it on the street? Registration might need dB killer in the pipes
That bike would be a nice café racer, show it for people as a piece of mechanical art celebrating the old times tech.

Small details can be replaced or added afterwards when bike is completed and proved to be running. This can be the fun for years, the project will never end.

At the moment it's not a street bike, but you are right, it wouldn't take much to make it street legal. Reducing the sound would be vital, this is one loud machine with open megas. But I don't intend to go down that path. Riding on a race track doesn't worry me too much, I'm too old to go silly there, but I'd never be happy taking it out amongst the cars and trucks!

[Sam Green Racing]

Wow Andy, what a great thread and thanks for the mention in your opening lines and I'd like to help you once more by reminding members of the High Performance and Racing Forum to get on over to the BOTM forum and give this great bike your vote.

http://forums.sohc4.net/index.php/topic,175714.0.html

Sam.

[bwaller]

Great looking bike.

[napoleonb]

Nice bike!

[scottly]

I have the small battery sitting in a small frame in the starter motor cavity.

The starter motor cavity is not the best place for a battery; it's like an oven. The heat will kill a battery in a short time.

[SOHC4 Cafe Racer Fan]

Thanks for putting together the thread, Andy. It's a beautiful bike.

[750deepsouth]

I have the small battery sitting in a small frame in the starter motor cavity.

The starter motor cavity is not the best place for a battery; it's like an oven. The heat will kill a battery in a short time.

My mechanic and I discussed this. It is exposed to the airflow around the motor. It is not sitting in contact with the sides or bottom of the cavity, I have it in a small frame within the cavity, this small frame held in place bolted in place at the starter motor bolt points. This small frame is lined inside and outside including the bottom of that frame, with cork sheet about 1.5mm thick. Cork is an excellent thermal insulator, so the battery is fully insulated from contact with the top crankcase. So far I've had no battery issues but I'll let the forum know if that happens.

[Santiago]

So: about 3 years ago I had the time, the parts, and the money  so I'm going to skip a few steps in construction. Suffice to say, that this gif animation tells the story of the early stages. I thought a bit before fitting the motor into a newly powder-coated frame. We all know this is a difficult job, and impossible for one person to do it without scraping the frame. The solution? the pictures tell the story. The cords holding the frame go to pulleys on the roof beams then over to that container with 18 litres of water. This nicely balances the frame, which can be then brought down very slowly over the motor, on it's side. Perfect.

I'll bring my frame and engine down to Invercargill and borrow this system Andy ;-) Cheers, Brooksy

[Santiago]

PS, did you get back out on the track after we spoke at Teretonga?

[750deepsouth]

Hi Mark
No, we just couldn't sort that wee miss and I didn't like running it when it's not 100%. We are looking at the issue next week, spent this afternoon getting the fairing off and the bike loaded on my trailer.
You are welcome to use my pulleys 
A few pics: one from a year ago (when we fitted the generator and CR carbs) three weeks ago at Teretonga and today. The fourth pic is the battery sitting in the starter motor bay. You can see there is space for air to circulate around it. I made a tray for it to sit in, from an original CB750 battery tray, of course You can just see a bit of the cork lining the inside of the tray, which is bolted to the starter motor mounting points.
Andy

[turboguzzi]

interesting battery solution, but take into account that hot surfaces emit also infrared radiation and that could cook the battery nicely.... would say ok if you are doing just a few demonstration laps, but not for longer stints... still amazing build

[peter400four]

G'Day there Mr Deepsouth,
Just tried to send you a PM, but it disappeared so I'll go public.
Your mention of the Tsubaki cam chain in the engine build got my interest because, just across the ditch, I've had no joy locating one for the CB500 motor in my John Blanchard Flying Dragon homage. (The motor in the bike is standard at the moment, but a second, high-compression, larger-valved, hot-cam motor is underway. Dynoman said they only supplied them with full engine kits and the distributor in Oz didn't reply to me email. May I ask, where did you source yours?