Honda CB750 Sandcast
General Category => General Discussion => Topic started by: Nap Bollemeijer on December 10, 2017, 04:52:59 pm
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I hope I'm allowed to post this thread here, if not or when it should be replaced please let me know.
My intention is to build a CR750 / CB750R replica like the one Dick Mann rode and with which he won Daytona in 1970.
There are a few different type of "Kits" you could buy back in the day to build a CB750R like the Novice kit, Sports kit and RSC kit.
Depending on the kind of funds available and your personal power needs.
My goal is to build the bike in the background with as many as the original parts as I can find and afford.
(http://www.ozebook.com/cr750_files/crkort2.jpg)
I started with a beat down K7 as my base, removed all the unnecessary brackets and chopped the frame.
After that I've made the footrest brackets from mild steel and welded these to the frame.
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Most items are different from the normal production bikes.
The front forks from the production racers have 4-bolt magnesium lowers, the first kit bikes had these as well.
Although these changed quite quickly to regular K0 type forks which were adapted.
For the 4-bolt lowers the nut and axle were also different as you can expect.
I did ran into one of the original early type front axle nuts:
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The front wheel had the same disc as the regular CB750 but are turned down to 4mm in order to save weight and a dual setup.
For the right hand brake there is a kit bracket, which is just a mirrored left hand bracket.
I'm a teacher in mechanical engineering so when I couldn't buy one I decided to make my own.
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A few years later the possibility arose to buy a NOS one so I did off course.
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The front hub on the production racers were smooth in the middle, made from magnesium and had a different look.
For the right hand side brake disc to be placed outwards 2mm there was thicker right side.
As I can't buy the correct style hub I turned a standard type hub down in the middle and placed a spacer between the hub and disc.
The production front wheel has an 18" DID aluminum rim, there were different kit versions it started with 44701-300-970 but was later replaced by 44701-300-971, there is even mention of using 42701-300-970 (rear rim as a front rim)
I'm not sure which number corresponds with which size and if they are front or rear wheel but these were the first DID choices: Aluminium rim 1.85B - 19 (front) and Aluminum rim 2.15B - 18 (rear)
Some kits had the same rim diameter and size in front and rear while others obviously varied and had different numbers front and rear, I chose to use the 18" front and rear wheel size with the slimmer front wheel.
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The top bridge for the CR750 was smooth and had to be fabricated as well.
I took a regular K7/F1/F2 style top bridge, cut the excess lugs off and welded a piece of aluminium in the gap.
Then filed and sanded everything until I was satisfied with the result, the homologation shows the RSC style top bridge which I tried to mimic.
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The bore of the CR was enlarged to 69,5mm to get 749cc.
Originally that was the only difference in cylinder blocks, these had different types of cam chain tensioners.
(The parts depicted aren't mine unfortunately)
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However there was an updated cylinder block and different type of cam chain tensioner.
I got the chanche to buy a NOS cylinder block, cylinder gasket, top piston ring, cam guide and 2 used pistons (A and B).
Perhaps I will be able to buy the remaining items in the future to put this together, if not I will fabricate the missing components for this setup:
(The first pictures of the complete setup aren't mine, the rest is)
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The frame has a few modifications, one of them is the right hand gear shift.
As most riders outside of Japan were used to English machines the racers were fitted with the possibility of a cross linkage and extended brake cable.
Initially I made my own parts by lack of the real thing, but I was able to buy the correct engine hanger bracket and bearings.
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All these parts are rare as hen's teeth and I've been collecting them for 9 years, but the hunt is far from over.
I hope you guys enjoy the pictures and if there's a request for more detailed information or a side by side comparison with other standard parts just let me know.
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Im enjoying it for sure! Keep it up!
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On the CR750 they use a clutch lever bracket different from the production models (which houses electricity and switches).
I was able to buy a good reproduction bracket from the UK but when compared to other race brackets like the CR110 there was something missing/not right.
With the help of a friend we made several castings to correct the problem, along with a bunch of other parts as well.
Besides it always nice to have some spares...
As you can see I make 3D drawings of almost every (special) part which goes on my bike.
Part of this is so I can show my student real life items and processes, but also so that I can reproduce these in the future if necessary.
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The kill-switch and light on the standard CB's are located in the clutch lever bracket .
Because the CR doesn't need lights but only a kill-switch and uses a total loss ignition system without battery a separate kill switch is used.
Unfortunately I just missed out on the chance to buy a NOS one, but I do have the pics and perhaps I can reproduce these later on.
For now a standard item which is rewired should suffice.
The production CR750's had a clip-on which could only be taken off by removing the top bridge, even though most Honda production racers had already used hinged clip-ons.
I guess they chose for this because of the weight reduction they could achieve by making it a solid piece, there was also a lightning hole in the single piece clip-on.
In the kit versions the hinged clip-ons were made available, as well as a separate plastic cap to plug the open end.
(Those parts depicted aren't mine)
I made a solid version for my CR as I wanted to replicate the Daytona bike.
This is my trail version, I still have some tweaking to do.
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Because the CR has a full fairing and is developing more power an oil cooler was added.
The production racers had most probably 2 bosses welded to the frame on which the oil cooler was mounted.
For the kit versions the same oil cooler and hoses were used but with a special bracket which mounts the oil cooler to the horn mounting point under the steering stem.
I still have to make or buy the correct style oil cooler but bought a NOS kit bracket.
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The CR750 had a special front brake master cylinder, which I think has a slightly tilted reservoir as well as an adapted piston diameter.
Because the clip-ons tilt the master cylinder there is more risk of sucking in air whilst cornering, but this is an assumption as I've never had one in my hands.
Running from the master brake cylinder is a special brake hose, which is shorter.
I had the chance to buy 2 of them still NOS, just for fun and comparison as I don't intend to use them for safety's sake.
The brake hose comes to a brake splitter (joint, 3 way) and continuous with another special kit brake hose to the standard steel tube connecting them to the calipers.
Factory production CR's had the brake splitter mounted directly to a single screw under the steering stem.
Kit bikes used the standard steering stem and were supplied with a different style bracket.
Funny thing is that because later kit versions made use of standard parts which changed over time the joints changed as well.
At first I thought I was scammed because the joint I bought looked like an F2 type, but a careful look at the package showed it was never opened and genuine.
So I decided to keep and open it, after all it makes sense because racing parts always end up in standard bikes if proven effective.
(the pictures of the first 2 types of joints aren't mine as is the brake master cylinder pics. The NOS parts are in my possession)
If there is an interest in the numbers corresponding to the story and parts depicted I can add the numbers in the previous posts.
Here are the part numbers used in the CR's front brakes besides the standard part which are re-used, those with a star I've got NOS:
*45115-300-030 Holder, Caliper (standard item, but an additional one is required and comes with the joint right holder)
*45116-300-030 Pin, Holder (standard item, but an additional one is required and comes with the joint right holder)
45117-341-700 Bolt, Adjusting (standard item, but an additional one is required)
45119-300-020 Spring, Adjust (standard item, but an additional one is required)
45120-300-970 Disk, Front Brake
45125-300-970 Hose B, Front Brake
*45127-300-970 Joint, 3 Way
*45128-300-970 Hose A, Front Brake
45130-300-970 Clip
45146-300-000 Packing, Hose (standard item, but an additional one is required)
45200-300-970 Caliper Assy., Right
*45204-300-970 Joint, Right Holder
45228-300-970 Pipe, Right Front
45245-300-970 Clip, Right Brake Hose
45500-300-970 Cylinder Assy
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Nap,
Your attention to detail is amazing. I'm also enjoying your build! Keep it up.
Arnold
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Great stuff!
If we donīt comment, we are just speechless.
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The standard generator is far too heavy in terms of weight and delivers more output then necessary which in term hinders performance (magnets and coils create rotational friction).
From another perspective the front profile makes for more wind resistance so another sleeker generator makes sense so does placing it more inside the frame like the RC166 for example.
Honda chose to put a lighter and sleeker generator with less output.
I could buy an original generator in fair shape, don't know if it does work if not I have to rewind the coils but the magnets are still strong.
A few years back I bought an cover which was an unmachined reproduction form a notable CR750 guru. Funny thing is the generator didn't fit when I dry fitted everything.
I don't know if the revised 971 item has different mounting holes or the generator cover I have isn't originally for the CR750 generator.
I also acquired 2 spark plug terminals which are just basically hollow.
The cam point has an advanced spark, I have to look if I can obtain one or CNC mill one with the correct characteristics in the future.
11631-300-970 Cover Dynamo (in my possession unmachined)
30200-300-970 Cam, Point
30505-300-970 Sub Cord, Coil
30700-300-970 Terminal Assy. A
*30710-300-970 Terminal Assy. B
31100-300-970 A.C. Generator Assy. (not sure if I own this one or the 971 item)
31100-286-971 Generator Assy.
32100-300-970 Harness, Wire
35300-300-971 Switch Assy.
98069-60711 Spark Plug *D1OES*
98069-62410 Spark Plug *D12E*
(the spring in the 3D model is in its free form, so in this pic it is protruding through the disc were in real life it is compressed)
(the last pic isn't mine but shows how the cover looks mounted, notice the different mounting point of the frame tube which all production racers had)
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Fascinating - keep the information coming please!
Chris R.
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Great Learning!
:)
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hello
you can go on this website
the guy maybe can help you
he's owner of an original CR750 from Daytona 70.
http://www.motojlmreplica.com/Francais/ventes.htm (http://www.motojlmreplica.com/Francais/ventes.htm)
see you
benji
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Fascinating Nap and incredible attention to detail ..please see my post in wanted section.
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Thank you all for the kind words, I do know of Daniel Mercier he has some great items indeed.
For the fuel supply there have been some changes as well, most distinctively the massive tank of course.
There were two versions of this tank in 22 or 28 liter capacity as can be seen by the part numbers below.
Both had a "bulge" below which was slightly offset to the left in order to keep clear from the oil cooler line going from the engine to the cooler.
The petrolcock / Fueltap had an enlarged diameter and twin output in order to supply sufficient fuel to the gas gurgling smoothbore carbs.
I own a replica petrol cock and an original Fuel tank band, these same parts were also used on other factory race bikes like the RC166.
The tank I've got was made for me in Germany but I have to make some adjustments to it in order to really fit the bill.
The photo's of the tank are those of a real one not mine, the fuel band and petrol cock are.
Note the smaller and wider tank in the last 2 photo's
*16950-300-970 Cock Assy., Fuel
*16997-300-970 O RING, 125x35 (I assume the punctuation marks were forgotten it should be 12.5x3.5)
*17500-300-970 Tank Comp., Fuel (Aluminium fuel tank with a capacity of 28 liters for the sports kit and RSC kit)
17502-300-970 Clip, Fuel Tube
*17503-300-970 Band, Fuel Tank
17504-300-970 Sponge, Tank
17505-300-970 Pad, Fuel Tank
17600-300-970 Tank Comp., Fuel (Aluminium fuel tank with a capacity of 22 liters for the RSC kit)
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I posted about the kill switch on the previous page, well I just happened to find one in a general assortment bin of a befriended Honda dealer!
He didn't have a clue as to how he got it or what it was so even after I told him whilst jumping up and down it was still at a bargain price for me.
It needs some TLC and rewiring but that's better then having none at all... ;)
*35300-300-971 Switch Assy.
The picture is off the CR style switch besides the regular 35150-300-730 (HL and OFF).
There seems to be a 35150-300-620 made for France, perhaps it looks the same as the CR item but I have no way of telling.
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Pretty sure you will have this already Nap. But just in case it's here in my Dropbox (I got it from another site)
https://www.dropbox.com/s/w128vp6hqpxgpyr/HondaCR750partslist.pdf?dl=0 (https://www.dropbox.com/s/w128vp6hqpxgpyr/HondaCR750partslist.pdf?dl=0)
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Thanks, I did have this one as well as some other versions. One just couldn't do without these lists.
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The rear wheel hub is truly a thing of beauty and an enormous one to look at.
As a teacher my funds are somewhat limited which explains why I havent bought a replica of it yet (exceeding 4000,- USD).
But when the bike is finished i could always replace the standard rear wheel when funds are sufficient.
However the smaller parts i can afford and for my collection and just the heck of it I bought some.
The rear brake cables are supplied in 2 different lengths, so you can change the side on which to shift.
41231-300-970 Retainer, Bearing
42000-300-970 Wheel Assy., Rear
42100-300-970 Brake Assy., Rear
42200-300-970 Hub Assy., Rear Brake
42311-300-970 Collar
* 42313-300-970 Collar, Side
42601-300-970 Hub Comp., Rear
42606-300-970 Spoke A, Rear
42607-300-970 Spoke B, Rear
* 42620-300-970 Collar, Distance
42701-300-970 Rim, Rear Wheel
43100-300-970 Panel Assy., Rear
43102-300-970 Washer, Brake Pin
43120-300-970 Shoe, Rear Brake
43141-300-970 Cam, Rear Brake
43151-300-970 Spring, Brake
43200-300-970 Panel Assy., Rear Brake
43411-300-970 Arm A, Rear Brake
43421-300-970 Arm B, Rear Brake
43451-300-970 Rod, Rear Brake
43452-300-970 Nut, Brake Rod Lock
* 43460-300-970 Cable, Rear Brake
* 43470-300-971 Cable Comp., Rear Brake
43472-300-970 Spring, Brake Arm Return
43473-300-970 Pin, Rear Brake
* 90128-300-970 Bolt, Sprocket
* 90665-300-970 Circlip, External, 115mm
The complete hub isn't mine, the parts are.
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The steering damper is the next subject of the journey.
Honda used a steering damper for the Daytona bikes which was directly fixed to the frame and steering stem.
In both cases the fixing points were integral of the above mentioned parts, for the kit bikes this wasn't an option.
So for the kit bikes brackets were made available to attach the steering damper to the frame and front fork.
The steering damper itself was a special part but was closely related to the CR93 (CYB72/CYB77 and CL72/CL77).
With some minute differences off course mostly using the same components but a slightly different exterior.
For my bike a bought several CR93/CL72 dampers in different conditions and started to taking the worst apart.
Checking the internals and replacing the fluid (which is a real pain in the @ss to do) to make them better again.
I am still contemplating on welding/reworking the exterior but as these CR93/CL72 dampers are getting rare as well I don't dare screwing one up.
53700-300-970 Damper, Steering
53710-300-970 Bracket A
53720-300-970 Bracket B
53131-268-810 Rubber, Steering Damper
The complete bikes with dampers aren't mine, the mounting eye for the frame side is cylindrical for the CR750.
All the dismantled pics are mine, here you can see the mounting eye being ball shaped.
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I would also like to say a big thanks to ashimotok0 for making it possible to buy some original 970 parts from him!
Its this type of helping each other out within a very specific nice in the CB750 variants and documenting which I like so much in this hobby.
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Hi Nap!
If you are going to visit Bikers Classic at Spa 28/6-1/7 it would be interesting to meet you there. Since I have a pure CR750 and also find your work with your CR-replica interesting it might be interesting to have a talk about R:s. I will be at Spa from 28/6-1/7. You can call my cellphone +46709519040 and let me know if we can have a medting.
Bo from Sweden