Author Topic: CR750 replica build  (Read 19895 times)

Offline CR21

  • SOHC Member
  • Posts: 162
    • View Profile
Re: CR750 replica build
« Reply #150 on: July 30, 2019, 10:15:58 PM »
Thanks for the replies guys!

Rob - it certainly did amazing sound  :) Yes they do look a little home-cast!

Phil - your rep is a lovely bike and you have done it remarkably quickly, its great that we have all met through these builds and have managed to help one another. Thanks Phil with a bit of luck it will turn out alright!

Cheers,
CR21

Offline CR21

  • SOHC Member
  • Posts: 162
    • View Profile
Re: CR750 replica build
« Reply #151 on: October 07, 2019, 10:18:55 PM »
Hi all,

I am gathering parts at the moment for a push on the rolling chassis.

I have a week off soon and the plan is to focus on the rolling chassis to progress that along so that I can properly start the dry build.

Hopefully I can kick some life back into this thread!

Oil catch tank:

A little progress on the oil catch tank, this is located underneath the seat of the works CR750.

This is the type of tank I will be replicating:



Thanks to Eric for the info!

Modelled up in CAD a while ago:




I ran a 3D print off in a draft resin (quick and cheap! around 2 hrs build time) to check fitment and clearances before fabricating in Aluminium. As the part is going to be made from thin aluminium I thickened the walls for the 3D print and split it into to pieces, for ease of printing:





I have seen a few different types of tanks, so will do a little more research before starting!

Cheers,
CR21
« Last Edit: October 07, 2019, 10:21:04 PM by CR21 »

Offline CR21

  • SOHC Member
  • Posts: 162
    • View Profile
Re: CR750 replica build
« Reply #152 on: October 13, 2019, 10:33:54 PM »
The oil catch tank or 'Sniffer box' as some people call it, is quite the point of controversy across forums!

The one that I drew up and 3D printed was a copy of a copy. This was created over in France by a chap who has built a few replicas, however it does not seem to be as accurate as I originally thought. Another CR guru (thanks if you are reading!) has steered me towards a more correct design, based on some old images and notes from the factory bikes.

It looks a little different now!

Ref image 1



Ref image 2



Apparently two versions of this tank were available.

The side breather/exhaust was apparently what was at Daytona and on the works bikes. I imagine this was to do with the short seat.





And the rear breather on the kit bikes:




As I am creating a CR works style bike replicating the Daytona winning bike, I will be going for the side exit catch tank variant. I will probably make up a 'buck' to create the radii on the edges, and roll a piece in the centre to match, then spring bend the inlet/outlets. The original notes show some baffles as well so it would be good to build these in.
 

It is so difficult with these bikes to be 'accurate' as the bikes that were at Daytona were all slightly different, the 'kit' bikes had a variety superseded parts across the years and of course there are a few replicas out there.

Another can of worms is the oil tank brackets  ::)

Cheers,
CR21

Offline Napoleonb

  • Newbie
  • Posts: 5
    • View Profile
Re: CR750 replica build
« Reply #153 on: October 15, 2019, 11:36:58 AM »
Can't wait to see this part getting shape!

Offline CR21

  • SOHC Member
  • Posts: 162
    • View Profile
Re: CR750 replica build
« Reply #154 on: October 15, 2019, 03:35:50 PM »
Can't wait to see this part getting shape!

Thanks Nap!

Cheers,
CR21

Offline CR21

  • SOHC Member
  • Posts: 162
    • View Profile
Re: CR750 replica build
« Reply #155 on: October 18, 2019, 11:35:47 AM »
Quick 3D print of the breather box:





This will allow me to mock it up on the bike to check clearances with the seat etc

Cheers,
CR21

Offline CR21

  • SOHC Member
  • Posts: 162
    • View Profile
Re: CR750 replica build
« Reply #156 on: October 20, 2019, 09:19:08 PM »
In my view, there are a handful of important parts that really 'make' the CR replica true to the original bike:

- Fuel tank
- Exhaust system
- Fairing shape, style, fitment and screen

- And finally the rear hub:
The CR750 was produced as a works machine for Honda to demonstrate the advanced performance that the new model was about to bring to the market. The main campaign for doing so was at the Daytona in 1970, where Dick Mann ended up finishing first, other team members (and breakdowns) aside it was an impressive feat. A very iconic part of the Daytona winning bike, and the subsequent CR kit bikes was the twin leading shoe rear brake

This rear hub was cast in magnesium, but that did not make it light!

A company in Italy used to make a replica of the CR rear hubs, which looked very smart in the images I have seen online but were very expensive and are lo longer available. A CR 'guru' in the UK also made a batch around 10 years ago.
I was going to make a replica of the rear hub by scaling photographs and begging for measurements however this has never really excited me as it was replicating a replica and would only ever be a tribute rather than a detailed replica part.

Cut a long story short, after some serious looking I found an original part:





Another bit of this jigsaw started.

Also purchased the ignition for the bike so I can start to think about coil and CDI unit lugs:



Although this was expensive, it is nicely made and is rated pretty well.

Cheers,
CR21
« Last Edit: October 20, 2019, 11:15:09 PM by CR21 »

Offline CR21

  • SOHC Member
  • Posts: 162
    • View Profile
Re: CR750 replica build
« Reply #157 on: October 21, 2019, 10:49:16 PM »
A little bit of progress today!

It took me a long time to re-set into CR mode after working on other projects for the last couple of years.

Got a few things done:

Started to re 'hang' the oil-tank:

Fiddly one to get right this and waiting for the correct style bottom brackets:



Fitted the right hand gear-change bushing, so that a right hand gear change assembly could be fitted if required:

Fitted up:





Welded in:



This bush accommodates the plain swivel bearing #5




Front hub

The original CR bikes had a magnesium front hub. This was a simple part with no ribbing

Ribs removed on the lathe

Going



Going



Gone!



As the offset is not quite central I will make up a 2mm spacer to sit behind the right side disc at some point.

Next frame jobs on the list:

- Front seat mountings
- Rear seat hoop and frame cross brace
- Steering damper mount
- Mirror image oil cooler mounts

Other jobs:

- Oil tank filler neck
- Skim the discs (or have them ground) down in thickness. As far as I am aware they were either 4.8 or 6mm thick
- Oil catch tank

Cheers!
CR21

Offline Trigger

  • SOHC Jedi
  • Posts: 6959
  • Engines built on reputation, not advertising.
    • View Profile
Re: CR750 replica build
« Reply #158 on: October 21, 2019, 10:52:44 PM »
Why did you take the cooling fins off the hub ? They are there is cool the hub  :o

Offline CR21

  • SOHC Member
  • Posts: 162
    • View Profile
Re: CR750 replica build
« Reply #159 on: October 21, 2019, 10:58:51 PM »
Why did you take the cooling fins off the hub ? They are there is cool the hub  :o

Hi Trigger,

The CR's did not have this detail on the hub - this is why the ridges were removed.

Thanks,
CR21
« Last Edit: October 21, 2019, 11:01:37 PM by CR21 »

Offline Trigger

  • SOHC Jedi
  • Posts: 6959
  • Engines built on reputation, not advertising.
    • View Profile
Re: CR750 replica build
« Reply #160 on: October 21, 2019, 11:13:11 PM »
I think the CR would of had a different hub and a different heat displacement system ?
When I have been fitting new liners to the rear hub, I have had quite a few customers ask, if I could also remove the fins as it is in the lathe and I always refuse because I have known a few people do this and had over heating problems. More so with a front drum but, a few with a disc.

Offline CR21

  • SOHC Member
  • Posts: 162
    • View Profile
Re: CR750 replica build
« Reply #161 on: October 22, 2019, 07:36:04 AM »
I think the CR would of had a different hub and a different heat displacement system ?
When I have been fitting new liners to the rear hub, I have had quite a few customers ask, if I could also remove the fins as it is in the lathe and I always refuse because I have known a few people do this and had over heating problems. More so with a front drum but, a few with a disc.

Hi Trigger,

Yes you are correct it was a different part, and was cast in Magnesium but my bike is a replica. I don't think It will be problematic due to the size of the disk, and surface area change, but I will certainly keep an eye on it,

Cheers,
CR21

Offline Trigger

  • SOHC Jedi
  • Posts: 6959
  • Engines built on reputation, not advertising.
    • View Profile
Re: CR750 replica build
« Reply #162 on: October 22, 2019, 08:00:15 AM »
You will need to get info on heat displacement in alloy of that grade, it is totally different than magnesium. You will always see more fins on a rear drum as, it needs to cool the shoes and bearings. The front hub fins will just cool be bearings, no fins means a overheating problem to the bearings.

Heat always transfers to the smaller area with alloy. Think about removing all the engine fins on a air cooled engine, it will overheat  ;)
I studied this years ago but, can remember all the tech on it and I had a look around last night for the study and data paperwork but, it must of been binned when I moved.

Offline CR21

  • SOHC Member
  • Posts: 162
    • View Profile
Re: CR750 replica build
« Reply #163 on: October 22, 2019, 08:16:26 AM »
You will need to get info on heat displacement in alloy of that grade, it is totally different than magnesium. You will always see more fins on a rear drum as, it needs to cool the shoes and bearings. The front hub fins will just cool be bearings, no fins means a overheating problem to the bearings.

Heat always transfers to the smaller area with alloy. Think about removing all the engine fins on a air cooled engine, it will overheat  ;)
I studied this years ago but, can remember all the tech on it and I had a look around last night for the study and data paperwork but, it must of been binned when I moved.

Hi Trigger,

I understand this, as I also studied it and will do some calcs at some point as I have the part drawn up. Before doing the calcs my gut is that as this bike will never be 'raced' and that I have not removed much material/area I will still have a good factor of safety,

Cheers,
RD17

Offline CR21

  • SOHC Member
  • Posts: 162
    • View Profile
Re: CR750 replica build
« Reply #164 on: October 22, 2019, 10:58:57 PM »
A little more progress from today:

Rear hub stripped and inspected:






Filler neck bezel offered up:



And welded on:



This replaced the Monza part.



I have linished this down so the weld is flush, but I forgot to get an image!


Seat

Rear hoop tweaked to fit, holes drilled in the fibreglass (always hate that bit!)



Front seat mounts jigged up:



Seat fitting well now, and the bike is starting to resemble a CR!



Cheers
CR21
« Last Edit: October 22, 2019, 11:01:24 PM by CR21 »

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal