How to identify an original sandcast CR750?

[denizen224]

I rescued one of my sandcasts from a breaker as basically just the motor and frame.  The frame is definitely set up as a CR.  It could be somebody's pretty well done mod of a standard CB750, but some of the little tabs and nibs are different from both my earlier CB750 sandcast (frame# about 600 units earlier) and my 10/69 diecast (frame# about 3500 units later).  Those aren't the sort of things I'd imagine somebody changing in building their own CR, and has me wondering if this could be an original factory bike.  Doubtful, but some aren't accounted for.

The frame number starts with the usual CB750-1005xxx.  Did the factory CRs use the same numbering scheme for the frame?  Or no numbers?

The engine number also looks normal, CB750E-1005xxx, where xxx is about -100 units different from the frame.  Is there anything in the engine that would easily identify it as being CR-spec that I could verify without digging *too* far into it?

My plan is to restore it as a CR since the frame is already set up that way, but it'd be extra-special if I could determine how much of it is the real deal.  

Mr. Bill

[Bowswell]

http://www.daytona70.com/Francais/Historique.htm

[chrisnoel]

I bet Vic would be a wealth of knowledge on this subject.  I'd work on establishing a long term dialog with him before picking his brain right out.  Might take years. 

[denizen224]

I bet Vic would be a wealth of knowledge on this subject.  I'd work on establishing a long term dialog with him before picking his brain right out.  Might take years. 

Heh, that.  It may be years of research and cash hoarding before I really get into this one, but I was hoping to start the research portion a little bit quicker than that... 

ISTR the CR750 engine kit had different cams.  I was hoping maybe somebody would know how they'd be marked, if my memory there was right.  I suppose I could compare the markings to the cams in my other early CB750 motors, but I'd prefer to just tear into one motor rather than two or three.

Mr. Bill

[tomcourtney]

Hi Bill I know they had 2 ring pistons and were bored to 61.5 (thanks Keith I have corrected it) to get close to 750cc for formula 750 class. Tom

[kmb69]

Hi Bill I know they had 2 ring pistons and were bored to 61.25 to get close to 750cc for formula 750 class. Tom

I think they were bored to 61.50mm to get 748.58cc. The CR Parts List published in 1974 shows 12100-300-970, Cylinder Comp. (61.5mm) and 13101-300-970, Piston A, and 13102-300-970, Piston B, and 13121-300-970, Ring, Piston Top, and 13141-300-970, Ring, Piston Oil. This is non-standard Honda nomenclature for Piston B and the rings but those numbers are consistent with any info I can find on the CR parts.

I have a new set of genuine Honda 13101-300-970, Piston A, and matching rings, part number unknown and they are 61.0mm. Kind of weird.

CR Parts List attached.

Keith

[denizen224]

Thanks for the info, Keith & Tom.  A little deeper to dig into the engine than I was hoping to do, but that's something definitive to look for to see if the engine has had the upgrade.

And thanks especially for the parts list, Keith.  No, I guess I really wasn't planning on using that retirement account for retirement... 

[sancastnorway]

As far as I know and found out, is that the CB750 racing type was the four bikes that Honda built for Daytona 200 in 1970. some people say that they have a different steel in the frame. It also have a welded bracket on the frame for the steering damper. As for the engine, it looks right that it has 61.5mm bore, as it was max. 750ccm that counts.

In 71 or 72, Honda built some CR750, where CR stands for Client Racer, and then introduced the racing kit that was sold for private racers. The CR has hinged clip-ons, and a separate bracket for the steering damper, placed where the ignition bracket is. The first series of CR-parts was numbered 970 and there was a later series and modifications that got 971. As the first series of CR31 carbs was sandcasted, the later was diecasted and got number 971. Most of the engine parts is different from a stock engine.

Do you have some photo's to share? I am soon start to build a Cr750 myself, and have collected some parts for it, but it is a long way to go...

Jan

[4pots1969]

Jan,

I have a very rare NEW OLD HOSE B SHORT CR750 Daytona Réf partlist : 45128-300-970
It is new old and original, I sell you $120,00 more the expedition, if it interests you tell me because it is necessary that I search in my stock of parties.
It seems to me that on 4 750CR of Daytona Engine Crankcases were molded Magnesium...

Gerard

[kmb69]

Gerard,

I would love to buy your 45128-300-970 brake hose for my CR replica if Jan declines.

Keith

[4pots1969]

Agree Keith, I take good note.

[sancastnorway]

Gerard.

Is this the upper or lower hose?
Did you get my PM?

Jan

[4pots1969]

Superieur Hose B Short because the dispatcher was above it seems to me on the CR750..
Yes well formed your MP, I replied.

[sancastnorway]

Can you add a photo of it?
Jan.

[4pots1969]

I attached you a picture with my mail...