Topic: CR750 / Dick Mann replica - replica front forks from GL1000 forks ?

[CR750]

Hi everybody,

EDIT: I just noticed it's become quite a story, but hey it's my first post after 2 years  

Let me first introduce myself. I am Sander from the Netherlands, and the past few years I have been lurking on this forum ( and others ) absorbing as much information as I could on the Sohc's and especially the CR750. Besides the fact that I like to search and read before I ask the obvious, the main reasons for taking a few years 'hiding in the dark' were that I started up a few businesses and moved about four times in the past two years . At first I felt bad about taking this long, seeing the dust on the donor bikes and parts in my shed, while others finish their projects. Usually when I start something I don't stop until I properly finish it, but now I think it was actually a blessing in disguise. For one, by now I am aware of (most of the) differences between the Cr750 Kit and the 'original' raced by Dick Mann at Daytona, but when I started I had no idea, I just saw a beautiful bike at Spa Franchorchamps  .

Besides information I have also collected some parts and some donor bikes over the years, and I think now's the time to jump start my build process with my first topic on the Sohc.
And I am sure there will follow plenty more topics and questions, as I would like to learn as much as I can from all the knowledgeable people over here, especially about the CR bikes.


My goal:
-to build an accurate as possible replica within reason ( read: budget - time - effort ). I do want to ride/race it, so I am not after a 100.000 dollar bike, but I want it to look like that  

Decision to make:
-Yeah, I know... I need too choose if it will be a replica of the Kit or the Dick man bike.

Which leads to:

Noted:
The Dick Mann bike has very special forks on it; some specs I have read/noticed:
-Titanium inner forks ?
- magnesium bottom forks ?
-4 bolts per fork to hold the front axle.
-different diameters of the inner forks form top to bottom ( starting at the bottom fork 36 mm, in the lower triple tree 38 mm, upper triple again 36 mm ?

I anybody disagrees with above or has addendum's please let me know.

Questions:
I assume the original is an unobtainable, especially made by Honda for the race bikes in 1970, or are there any suitable forks out there ?
Of course one could rebuild anything from scratch, but because I do not have unlimited budgets and I would like to finish it somewhere this decade I was wondering if:
-an esthetically pleasing replica could be made with GL1000 forks, by means of turning the 37mm forks down and then cutting of the brackets for the brakes etc on the lower legs, and then weld correct looking custom made brackets in the right place, 'dremel' the bottom part of the lower legs, and use a lathe for the upper part, to resemble the real thing? Or am I just plain dumb for proposing this ?

Has anybody ever welded on lower fork legs ?
I can work my magic with a TIG, but I worry about contamination because of the fork oil (after you drained them that is), and if the required heat would cause the legs to warp beyond use. Also since these are brake caliper brackets; the final strength ? My normal alu welds are stronger then the material, but I would like to make sure when you race it, and not only show it ?!

Sander

[napoleonb]

I have recently bought a Front Axle Sleeve, which is supposed to be a kit item, from David Silverspares.
Tomorow I can put it next to a normal Front Axle Sleeve/Nut and compare them.

I am also wondering about the dimensions for the kit fork and am trying te reproduce one from billet aluminium.
The only thing which I am not able of doing is drilling and honing/lapping the inner part of the front leg.
Depending on the costs I will make a small serie of lower legs.

[turboguzzi]

remember seeing fork legs welded up to a four bolt setup for a CR replica somewhere in the net. maybe some googling will come up with the pics.

Whether you want to trust such a job with the forces of road racing is something else.... would crack test /  X-ray them after the work is done.


TG

[CPHjimm]

remember seeing fork legs welded up to a four bolt setup for a CR replica somewhere in the net. maybe some googling will come up with the pics.

Whether you want to trust such a job with the forces of road racing is something else.... would crack test /  X-ray them after the work is done.


TG

As my old welding guro told me : Do the drop test, if it breakes, it breakes.... if not, you are good to go!    nahh, a penetrant test, x-rat or other NDT would work... but if you thinking of a reproduction, why not get it casted??

[turboguzzi]

casting would be the "easy" bit, boring it not so much....

[kos]

The Dick mann bike along with it's Team bikes (5) had magnesium lowers and Ti fork tubes that changed sizes as the forks passed through the fork triple trees. You have a  very good eye. Which bike was at Spa? Who was the owner?

KOS

Mark@m3racing.com

[Doctor_D]

The Dick mann bike along with it's Team bikes (5) had magnesium lowers and Ti fork tubes that changed sizes as the forks passed through the fork triple trees. You have a  very good eye. Which bike was at Spa? Who was the owner?

KOS

Mark@m3racing.com

Titanium stanchions?  Really?  Given Ti's somewhat elastic nature, and the history of nitrogen embrittlement in early uses, it's not what I might have chosen as a stanchion of that diameter (unless weight was the primary consideration). I would expect a bit too much lateral deflection from Ti for it to give me confidence tossing a big bike from side to side in consecutive corners.

Off topic, but I was telling Mike Rieck that I think there'd be a market for 2024-T3 stanchions that are finished with a PTFE embedded, hard anodized coating.  Lighter and stiffer than steel, stress-corrosion resistant, and less stiction than the hard-chrome plating. Toss in some Gold Valves and Ti springs (which is a great application for Ti), top with some alloy triple-trees with a larger clamping area and a press-fit 2024 steer-tube, and... errr... well, that'd leave you with a set of light, but outrageously spendy vintage roadrace forks. Maybe after I win the lottery. 

[napoleonb]

Beste Sander,

Ik lees nu pas dat je uit Nederland komt, zelf woon ik in Hoogeveen.
And now back into English so the rest of you can follow the post.
I have asked for dimensions of the lower legs on this forum a while ago but ik seems that nobody has a set of them at home.
A company near me, in wich an aquintance of mine works, is producing Harley forks and lower legs from billet aluminum and steel so I know I can let them made.

With the dimensions taken from the front axle sleeve I should be able to work out almost every dimension.
The thing which is bugging my though is that the front axle itself is mentioned in the parstlist posted by me in the CR750 thread.
Could anybody tell me whereto that was done?

[napoleonb]

I would not withhold these pictures for you lot.
This is a standard front axle with the normal and CR sleeve, the position is their respective overlap over the axle.
Measurements are quite of, especially the inner part and of course the lower fork leg length wich is 40 instead of 30mm.
I suppose the CR front axle beiing a bit shorter in the middle part and longer in the end, but it is no more than an educated guess.
(perhaps somebody can take a picture of both the axles?

[CR750]

Hey Guys,

thanks for jumping in everybody; even though it seems a lot of my questions only arouse counter questions   so here we go:

@ Napoleon;
I am by no means an expert, but isn't the kit fork a standard item which is modified internally ( see attachements I added ) ? Right now I am referring in my questions to the Dick Mann bike, but if I choose to go after a replica of the kit your forks might indeed be of interest ! Thanks for the pics of the axle ! (Dutch: Ik 'kende' je al van MF en je topic daar; anders eens een keertje bellen, lijkt me leuk !? Ik kan ook goed 3d cad tekenen, misschien kunnen we samen aan de voorpoten werken ?)

@ TG;
very interested in those if you can find them pics again. i have seen GL forks with adapter plates but not welded up like 'my plan'. The owner might be able to share his experiences !

@ Kos;
Not to say I don't have keen eyes   but the bike I saw at Spa (3 years ago) was actually a very bad replica of a the kit version, but it already looked smart enough to start me thinking " wouldn't it be nice if..."   I  found the info years later somewhere on the web ( will look if I can trace my steps ) i think maybe in the Joep Kortekaas write up? Can you confirm the diameters I posted are correct and do you maybe have better pics then the ones I posted of the forks ? I only have these and they are quite low-res so it's hard to make out the details....

@ everybody:

X-ray seems a smart thing, yes, but first I do worry about the contamination of the oil....Well, I know people weld on old carters and such, which of course do not bear the structural forces as much, but are definitively more contaminated because of the heat... mmm.... Maybe just try it out on an old scrap fork and see if welding works out like intended...
Casting is an option that crossed my mind, but not something I can really do myself (there are limits to my workshop  ) and outsourcing is not really worthwhile with all the molds etc needed, unless I do a series and sell the others afterward.

Well keep them thoughts and tips coming !

Ps. If anybody has other / better /higher res pics of the Dick Mann bike it would help a lot, because it's hard to see the details on the low res I have got..
 

[napoleonb]

Quite an interesting article, I have not seen it pass yet, could you scan the entire text for me?
As far as I can see it has to be a late Kit fork IMO, because on the picture there is no sign of the 4 bolts.
Concerning the internals if the parts are not specifficaly mentioned on the partslist which I posted in the CR750 thread I do not think the dimensions or materials used are different then regular parst. That being said the Dick Mann and other factory bikes shall differ from the kit items and are not traceble I am afraid.

On vacation my phone took a advanced swimming course in the sea and did not survive alas.
My email is: nh.bollemeijer@alfa-college.nl you can reach me there for an appointment (which I like to make to talk and exchaince info about the bike's)

[voxonda]

Like mentioned earlier there were no two kit-bikes the same, and even the kit varied in time. Finding oem kit parts is almost impossible I'm afraid.
Following your build also on the dutch forum.

Cheers, Rob

[CR750]

Hey guys,

I would like to stay on track within this thread, to keep things clear and understandable because I see this can/will get confusing very quickly:
For everybody: there are in this case two different things in this world:

1) the original Dick Mann Cr750 bike as ridden @ Daytona 500 in 1970.
2) the cr750 kit (which was almost a complete bike ) which was later marketed by Honda to model your own Cb750 into a cr750 replica.

See the attached file with the original bike in the back and the kit parts in front.

This thread is specificallly about the Dick Mann Cr750 forks ( and the possibility to make make a replica of those out (for instance) Gl1000 forks.

@ Nap
Don't get me wrong, I really like all info on the kit items Nap ( + I still need to make up my mind which one I will try to replicate), but I think it would be better to start another thread on the kit legs otherwise we both don't get the answers we need, if you know what I mean. The pictures and the text on the kit in my previous post are screen shots of cycle mag from 1970, and the original is way to big to post, we'll do that by e-mail or when we meet. I'll send you an e-mail today !

@ Voxanda
Dutch: Hey Rob, leuk dat je er ook bij bent !

[CR750]

BUMP (to get back on track)

@ TG;
very interested in those if you can find them pics again. i have seen GL forks with adapter plates but not welded up like 'my plan'. The owner might be able to share his experiences !

@ Kos;
Not to say I don't have keen eyes, but the bike I saw at Spa (3 years ago) was actually a very bad replica of a the kit version, but it already looked smart enough to start me thinking " wouldn't it be nice if..." I  found the info years later somewhere on the web ( will look if I can trace my steps ) i think maybe in the Joep Kortekaas write up? Can you confirm the diameters I posted are correct and do you maybe have better pics then the ones I posted of the forks ? I only have these and they are quite low-res so it's hard to make out the details....

@ everybody:

X-ray seems a smart thing, yes, but first I do worry about the contamination of the oil....Well, I know people weld on old carters and such, which of course do not bear the structural forces as much, but are definitively more contaminated because of the heat... mmm.... Maybe just try it out on an old scrap fork and see if welding works out like intended...
Casting is an option that crossed my mind, but not something I can really do myself (there are limits to my workshop ) and outsourcing is not really worthwhile with all the molds etc needed, unless I do a series and sell the others afterward.

Well keep them thoughts and tips coming on the subject at hand !

Ps. If anybody has other / better /higher res pics of the original Dick Mann bike or the forks in specific, it would help a lot, because it's hard to see the details on the low res I have got..

[napoleonb]

@CR750, no problem with staying on the subject and thanks for the mail.

Here are some pictures of the Dick Mann front fork.
The first picture is of Dick Mann on his bike and the rest I borrowd from the Daytona70 site.
Which solves IMO the problem of the front fork as being one of the original 5 factory CR's as I have never seen the kit forks with the text written in them.
On the Dick Mann front fork the groove appears to be different then on the regular kit items, as is the part which is "square".

[napoleonb]

Another thing to notice in the previous pictures is that the rear mounting points of the Dick Mann front fork are a little different then the Kit or road legal bikes. Wich are in a rectangular piece as opposed to a much lighter and cut "hart" shaped piece on the Dick Mann front fork.

The most upper part of the legs also seem to be quite a bit different.....  Are there any comparisons with another fork? 

[kos]

Those forks in these last photos are NOT factory works forks like on Dick Manns bike but replicas that someone made.   Dicks and the other forks on works bikes were not machined in the lower 4 bolt area but cast in magnesium.

KOS

[kos]

Here is photo of real works factory forks that were cast, not machined like other photos show.

KOS

[CR750]

@ Nap
Thanks for your input ! Daniel M. is 'the french guy' Kos speaks so full of admiration of  , and i think he did a very nice replica (maybe with a lot of original parts) and certainly an eye for detail.
I find it hard to believe it is the original as well. I have studied pictures of his bike and the original a lot, and I (by no means and expert) already find discrepancies.
For instance for me a dead give away and obvious mistake I see made by many replica builders is that the faring on the original Mann bike was 'cut' at the black stripe ( for more cornering leg space   ) - or painted that way to begin with (see pic). Most replica's want their paint job to be perfect (can't blame them) but then fall into this trap and make the striping equal all around (see pic). For a replica this is ok, but when you claim it's the original it's not smart.... Ps. the letters on the fork a merely a pice of vintage dymo tape which shows the weight the forks are tuned to (see pic).

So as a conclusion, don't lean too much on that bike when deciding what's original and not, I only refer to the real, which is a pain becasue I can only find small often very low res pictures of it   .

@ Kos
Thank you for the picture !
I agree the you the 'Daytona site' is not the original bike, I think the team that set out to check (with a.o. Bob Hansen) also came to this conclusion ( the website makes it a bit unclear what the result was) ?
That picture you show looks like a picture taken from a magazine, with some white papers around it to frame it and to cover the text around it ?
Is it a mag from back in the day, or do you have that magazine, and care to share the rest with me Pm/or here ?

In regards to your remark on the milling, could it be that our french friend, actually did the same thing as I am planning ? And his bike actually also has modified GL1000 forks ?

I was doing some further research and found this pic of a set forks that are pretty close....Can you or anyone else identify the fork I attached ? I think it is an really early gl 1000 ? which come pretty darn close to the original already with the mounting point ? (as far as looks)

WILD SPECULATION
Could it be that in the first place honda engineers took a 'shortcut' with a design of for a fork they already had (with moulds etc for it) and then made a cast of it with lighter materials and then use those on the cr750 bikes used at Daytona in 1970 ?

Sander

[kos]

Yes, you are correct about the picture I sent in yesterday and posted on the forum. It is from a Cycle World magazine June 1986 and was a story about Dick Mann called "A Mann's Point of View" written by Dick Man...himself!

i will post to you, but it has only one picture of the Honda CR750 in it. Please give me your address to mail to.


KOS

[napoleonb]

@Sander, the pic of the front fork came from an ebay auction a couple of months ago.
The fork was supposed to be a kit item and was fully restored as was the rest of the bike.

[City Boy]

Hi napoleonb.In reference to your question re kit forks;they are one inch longer than stock and are chrome plated over there entire length,stock k0 were only plated up to the headlight holders.The internals are the same parts as k0 fork parts with the possible exception of the springs as I have never compared them with stockers..I have a set on my unit.I did own a set of the works forks for a time but have since sold them as they were not usable with stock frame due to much shorter overall length.I did however remove the ti. fork caps and they now happily reside on my kit forks.   Rock On

[754]

 The Mann bike looks like the discs are thinned, is that correct?

 Around 72 ish in a bike mag, I found an ad for Magnesium,  4 bolt clamp..lowerlegs with dual disc mounts for Honda sohc.

 But I think they were for CB500, and I think the name was Checkered Flag Racing. Also I think there was an article converting to dual disc,back around that time which used a kit that came with a lower leg with correct mounts..

 Mainly bringing this up because, it appears there was either 2 places made 4 bolt lower legs,in America.Either that or the place I mentioned, made the Mann legs..

[srook]

This is a pic of one of the works bike from Daytona, 1970.  I don't know if this is the Mann bike or not.



Another pic of a works bike at Daytona, 1970.  Notice how much different it is than Mann's bike in spec (stock forks & oil tank).



The problem you are going to run into is that not all of the works Hondas were the same.  Most of the attention is focused on the Mann bike but there were 3 other bikes that can claim to be authentic Daytona CR750s and they are not identical.  I know you are trying to replicate the Mann bike but what is the benefit of having alumium and steel replicas of magnesium and titanium one off race parts.  Like the French bike, your forks may look close but underneath they are still GL1000 forks.  My advice would be to replicate the kit bike because the end product will be much closer to what it is supposed to be.

Mann in traffic and not in the lead!  It's a good thing all those other guys broke down.

#9 Gary Nixon Triumph Trident, #25 Cal Rayborn Iron XR750, #50 Mike Hailwood BSA Rocket 3, #2 Dick Mann CR750, #75 Kel Carruthers Yamaha 350cc


#9 Gary Nixon, #50 Mike Hailwood, #61 Ron Grant Suzuki 500cc, #2 Dick Mann, #75 Kel Carruthers


Out of these 2 pictures, #2 was the only bike to actually finish the race. 
Scott

[City Boy]

Hi 754.Yes,the discs are thinned.The outside of the disc is thinned until the lipped section is gone.Discs are now 3.6 mm thick.   Rock On