Author Topic: The 1970 Daytona CR750s. (Read 269918 times)

HondaMan · « **Reply #650 on:** February 09, 2011, 07:35:15 PM »

Hey, all you CR gurus:
Someone has approached me about building them a CR replica or something like it. I can't say I hate the idea (in fact, can't say I even dislike the idea...), would like to start with a conversation to collect pointers about the base: a frame. Anyone here have a good source of detailed info about one? I'd prefer to make one from a stock frame (to come close), because of the titling issues here in Colorado. More trail and a longer wheel stance would be tops on this list.

I remember the discussions about the narrower head (about which I have some small experience to share) back in the day: it was considered to be a HP enhancement as well as a fairing-fitter, according to supposed "inside info" in the 1970-72 era. Increasing the heat in the head for more top-end power was also a midget-car racer's first move when using the Four in their cars (12k+ RPM service). I do know (also from experience) that heating up the outer edges of the head with a fairing makes for far more even cylinder wear over the long haul, compared to unfaired engines in similar service. That's probably a clue...

What is the practicality of taking a stocker's head and fitting the smaller exhaust seats, in your experience(s)? The deeper, narrower combustion chamber can be accomplished by moving the bores to 811cc size, then fitting the head to that bore in an oval shape, reducing the swirl-inducing shrouding in the process, IMO. Does this seem reasonable to those of you who get to gaze into the real heads?

lordmoonpie · « **Reply #651 on:** February 11, 2011, 04:48:21 AM »

Hey HM!

There are about 25 small changes to the stock frame to give you a good CR replica. I have some RSC technical drawings of the same and will scan and send them to you if you like? Might take me a few days but these are the real deal...

napoleonb · « **Reply #652 on:** February 11, 2011, 09:15:37 AM »

LMP, would you be so kind as to share these files on the board?

Ricky_Racer · « **Reply #653 on:** February 11, 2011, 10:13:57 AM »

Thanks, Napoleon! RR

napoleonb · « **Reply #654 on:** February 11, 2011, 10:48:49 AM »

I'll show mine if you show yours...
In regard to the frame I should have a pic of the placement for shifter hole somewhere.

I'm sure there are more then one Honda (or RSC for that matter) parts- and modificationlists

lordmoonpie · « **Reply #655 on:** February 12, 2011, 12:49:31 AM »

Quote from: napoleonb on February 11, 2011, 09:15:37 AM

LMP, would you be so kind as to share these files on the board?

Sure will guys. Give me a short time to scan them though. We have a new scanner and it's a bit temperamental so scanning is slow at present. Shoudl be able to get them into a format that will load. Faiing that I could load to a dark corner of my own website and link to them. We'll see what works when I get the file sizes.

MRieck · « **Reply #656 on:** February 12, 2011, 06:19:14 AM »

Quote from: HondaMan on February 09, 2011, 07:35:15 PM

Hey, all you CR gurus:
Someone has approached me about building them a CR replica or something like it. I can't say I hate the idea (in fact, can't say I even dislike the idea...), would like to start with a conversation to collect pointers about the base: a frame. Anyone here have a good source of detailed info about one? I'd prefer to make one from a stock frame (to come close), because of the titling issues here in Colorado. More trail and a longer wheel stance would be tops on this list.

I remember the discussions about the narrower head (about which I have some small experience to share) back in the day: it was considered to be a HP enhancement as well as a fairing-fitter, according to supposed "inside info" in the 1970-72 era. Increasing the heat in the head for more top-end power was also a midget-car racer's first move when using the Four in their cars (12k+ RPM service). I do know (also from experience) that heating up the outer edges of the head with a fairing makes for far more even cylinder wear over the long haul, compared to unfaired engines in similar service. That's probably a clue...

What is the practicality of taking a stocker's head and fitting the smaller exhaust seats, in your experience(s)? The deeper, narrower combustion chamber can be accomplished by moving the bores to 811cc size, then fitting the head to that bore in an oval shape, reducing the swirl-inducing shrouding in the process, IMO. Does this seem reasonable to those of you who get to gaze into the real heads?

Replacing the seat isn't that big a deal Mark. I replaced all the intake seats on the head I'm using for my 1000cc engine. You cannot fit any valve smaller than a 28mm on the stock seat....I checked this out. I imagine you would have to tig up the throat area below the seat to eliminate the overhang of the smaller ID seat. You could blend the smaller seat into the throat but I assume you are looking to reduce the overall throat ID to keep exhaust gas speed high. If that is the case I'd build up the exhaust port floors and raise the roof. Tapered primary pipes (like modern pipes i.e. TiForce, Akrapovic etc) would work well on these engines too IMO. You can just about anything you want to do the chamber once the bore is opened up. The Kibblewhite 5mm kit would work well with the 34mm intake and 27mm exhaust. If your client is interested in this combo let me know and I will take care of you.

Ricky_Racer · « **Reply #657 on:** February 12, 2011, 10:47:53 AM »

Quote from: lordmoonpie on February 12, 2011, 12:49:31 AM

Quote from: napoleonb on February 11, 2011, 09:15:37 AM
LMP, would you be so kind as to share these files on the board?
Sure will guys. Give me a short time to scan them though. We have a new scanner and it's a bit temperamental so scanning is slow at present. Shoudl be able to get them into a format that will load. Faiing that I could load to a dark corner of my own website and link to them. We'll see what works when I get the file sizes.

Thanks, LMP. Many of us may have not interest in creating a complete CR750 clone, but some of the techniques developed by the early Honda engineers may have some value for other higher-performance builds of the classic SOHC. We appreciate your efforts. RR

Sam Green Racing · « **Reply #658 on:** February 13, 2011, 02:56:54 AM »

Stand by guys, there are 21 pages of data (a lot of it just part numbers) coming through from member Ken736 when we can get them the right size to post, Bob Wessner will be posting them in here.

or what ?

Sam.

lordmoonpie · « **Reply #659 on:** February 13, 2011, 03:22:22 AM »

After spending 4 hours pi55ing about with HP drivers my scanner now seems to work. The following files are single pages copied many times over of notes taken by Kent Rockwell in 1970 at the Honda USA Training Centre. Because they have been copied many times the quality is poor on a couple but if you print them out A4 size they can be deciphered OK. In addition I found a copy of a fax from Honda RSC in the early 70's. Again because it's on fax paper it has faded over time and I can't scan this in so will type in the changes that Honda RSC said needed to be done to a standard frame to get to a CR750 frame. These need a bit of interpretation as they don't come with pictures but this list is straight from the horse's mouth so to speak - about as good as you will get a list of changes right from within the Honda race shop so coupled with the scanned training pictures it should give you a good stab at the overall jigsaw....here goes!

lordmoonpie · « **Reply #660 on:** February 13, 2011, 03:23:14 AM »

Last three pics...

lordmoonpie · « **Reply #661 on:** February 13, 2011, 03:33:30 AM »

Finally the list of RSC frame modifications...word for word. As you will see there is not much in the way of dimensions etc for these things but it may help.

1. Remove extraneous tank/seat/sidepanel brackets
2. Remove sidestand and centrestand lugs
3. Remove battery/tooltray holding plate and replace with single tube
4. Remove brake pedal mount tube and refill chassis tube
5. Remove pillion footrest/silencer mount tubing and replace with race kit replica mounts in 2mm sheet steel fabrications with steel footpegs (see diagram above)
6. Fit fairing bracket holding tube
7. Increase thickness of steering stop plate
8. Fit cross bracket fabrication with seat mount pegs and fuel tank strap holder
9. Fit four 6mm threaded bosses and two brackets for central oil tank mounts
10. Finish weld around rear shock absorber mounts
11. Fit hydraulic damper mounting tube
12. Fit four 5mm threaded bosses for HT Coil mounting
13. Fit weld on fairing brackets (For dzus fasteners) to front frame downtubes (if required)
14. Fit left hand horn bracket to match existing one - together both brackets will take various types of oil cooler - this modification not required for genuine kit cooler
15. For alloy Daytona seat cut off rear frame ends and blank off. Move existing ear mudguard mounting bridge forward by 5cm using round peg fittings for front of seat instead of flat tabs
16. Shotblast chassis for stress relief and finish in gloss black coating of choice
17. Fit swingarm with bronze bushings, centre spacer, spindle and chrome nuts.

napoleonb · « **Reply #662 on:** February 13, 2011, 04:20:14 AM »

I see there's no need for me to post the modification for right shifting as you've already posted it.
Great info! many thanks

kos · « **Reply #663 on:** February 13, 2011, 08:00:02 AM »

Quote from: lordmoonpie on February 13, 2011, 03:22:22 AM

After spending 4 hours pi55ing about with HP drivers my scanner now seems to work. The following files are single pages copied many times over of notes taken by Kent Rockwell in 1970 at the Honda USA Training Centre. Because they have been copied many times the quality is poor on a couple but if you print them out A4 size they can be deciphered OK. In addition I found a copy of a fax from Honda RSC in the early 70's. Again because it's on fax paper it has faded over time and I can't scan this in so will type in the changes that Honda RSC said needed to be done to a standard frame to get to a CR750 frame. These need a bit of interpretation as they don't come with pictures but this list is straight from the horse's mouth so to speak - about as good as you will get a list of changes right from within the Honda race shop so coupled with the scanned training pictures it should give you a good stab at the overall jigsaw....here goes!

Just to clarify, these pictures or scans are of original factory drawings that RSC in Japan created for dealers to use when constructing CR750 Kit bikes and not from notes by Rocky (Kent Rockwell)

Mark McGrew
M3 Racing

kos · « **Reply #664 on:** February 13, 2011, 08:06:19 AM »

Quote from: lordmoonpie on February 13, 2011, 03:23:14 AM

Last three pics...

These drawings were done by myself and taken from the spare factory RC750 that was used at Daytona 1973 when Honda had Sumiya, Steve McLaughlin, Roger Reiman competing there.

Mark McGrew
M3 Racing

kos · « **Reply #665 on:** February 13, 2011, 08:08:27 AM »

I will post the notes and drawings by Kent Rockwell of the RC750 Daytona bike in a few days once business slows down her at M3.

Mark McGrew
M3 Racing

kos · « **Reply #666 on:** February 13, 2011, 08:38:59 AM »

Here are the notes/drawings by my friend Kent Rockwell that he did while at the Gardena, Ca Training center at American Honda... circa 1970 of the Factory team Daytona bike. Not Dick Mann's actual bike, as that bike was sent to Japan for inspection by Honda engineers and totally disassembled and never put back together. However the body work was taken off of Mann machine prior to the bike leaving for Japan and placed on Tommy Robb bike for use as display bike at dealer shows and other promotions. (information gained from Bob Jameson, crew chief on 1970 Daytona effort who contacted the Team manager and engineers from Daytona effort)

Mark McGrew
M3 Racing

kos · « **Reply #667 on:** February 13, 2011, 08:46:18 AM »

2nd page Kent Rockwell notes/drawings

JohnN · « **Reply #668 on:** February 13, 2011, 09:25:02 AM »

How is the front of the kit seat secured?

HondaMan · « **Reply #669 on:** February 13, 2011, 11:32:36 AM »

Quote from: lordmoonpie on February 13, 2011, 03:33:30 AM

Finally the list of RSC frame modifications...word for word. As you will see there is not much in the way of dimensions etc for these things but it may help.

1. Remove extraneous tank/seat/sidepanel brackets
2. Remove sidestand and centrestand lugs
3. Remove battery/tooltray holding plate and replace with single tube
4. Remove brake pedal mount tube and refill chassis tube
5. Remove pillion footrest/silencer mount tubing and replace with race kit replica mounts in 2mm sheet steel fabrications with steel footpegs (see diagram above)
6. Fit fairing bracket holding tube
7. Increase thickness of steering stop plate
8. Fit cross bracket fabrication with seat mount pegs and fuel tank strap holder
9. Fit four 6mm threaded bosses and two brackets for central oil tank mounts
10. Finish weld around rear shock absorber mounts
11. Fit hydraulic damper mounting tube
12. Fit four 5mm threaded bosses for HT Coil mounting
13. Fit weld on fairing brackets (For dzus fasteners) to front frame downtubes (if required)
14. Fit left hand horn bracket to match existing one - together both brackets will take various types of oil cooler - this modification not required for genuine kit cooler
15. For alloy Daytona seat cut off rear frame ends and blank off. Move existing ear mudguard mounting bridge forward by 5cm using round peg fittings for front of seat instead of flat tabs
16. Shotblast chassis for stress relief and finish in gloss black coating of choice
17. Fit swingarm with bronze bushings, centre spacer, spindle and chrome nuts.

A million thanks, LMP!

A great start, considering the parts I have on hand already. I find it interesting that the "kit" included the swingarm mods that I have done to these bikes for 40 years, now. I didn't know that part about them, but it sure makes a lot of sense.

M3: looking forward to seeing those additional notes. After Mann's pit crash and the overnight urgent rebuild that they did, and it being the only successful one in the debut, I'll be interested in seeing any additional changes. Rocky made some marvelous parts in the years past: I wish they we still around today. I used a lot of their pieces in bikes I've built.

kos · « **Reply #670 on:** February 13, 2011, 02:51:36 PM »

I don't know what you are talking about when referring to a "pit crash" by Mann, as he had none. What they did have is upon inspection of the oil after someone had told him it sounded like the clutch was slipping on the high banking was... a worn cam chain tensioner rubber wheel. So the crew headed by, Bob Jameson, tore down the entire engine, to clean out all the small rubber parts that had infiltrated the oils system and cleaned the entire engine and replaced all worn parts with new OEM cam chain tensioner and tensioner rubber wheels, as this is what the works bikes used. Stock cam chain tensioner parts!!!

KOS

M3

lordmoonpie · « **Reply #671 on:** February 14, 2011, 04:27:49 AM »

Quote from: kos on February 13, 2011, 08:00:02 AM

Just to clarify, these pictures or scans are of original factory drawings that RSC in Japan created for dealers to use when constructing CR750 Kit bikes and not from notes by Rocky (Kent Rockwell)

Mark McGrew
M3 Racing
[/quote]
I'm sure you're right Mark - I wasn't there so can only go on what I was told when sent the documents. I have more that are individual hand drawn items so will look at your files posted and see if they are in part similar. Maybe there was some "Rocky" in my pile of papers :-)

lordmoonpie · « **Reply #672 on:** February 14, 2011, 04:32:43 AM »

Quote from: JohnN on February 13, 2011, 09:25:02 AM

How is the front of the kit seat secured?

I'm not sure about the "kit" securing - my seat is secured as per the RSC drawings. It basically has two holes underneath and the frame has two 90 degree rear facing tabs welded to it. The holes in the seat push down on the tab and you slide the seat forward to grip it. The rear of the seat then bolts to the frame to hold it all together. My seat is off at present while I fill the seat hump with things I don't wan tto be seen so I can take a photo of the tabs if you like?

These are the flat tabs referred to in step 15 above. It implies if you have the daytona alloy seat you use pegs instead of the tabs I have....

H2Eric · « **Reply #673 on:** February 14, 2011, 09:43:34 AM »

Hi Simon

While your at it, could you please post a pic of the underside of the seat. I have an Air-tech seat that I wish to use on my project, but it hasn't got any holes in it as you describe.

Thanks
Eric

lordmoonpie · « **Reply #674 on:** February 14, 2011, 11:20:13 AM »

Sure thing Eric - you have to cut your own holes but it'll be the same principle on the airtech seat...

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Author Topic: The 1970 Daytona CR750s. (Read 269918 times)