Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - CR21

Pages: [1] 2 3 ... 8
1
Project Board / Re: CR750 replica build
« on: March 10, 2020, 03:59:22 PM »
Hi all,

Small and slow steps on this projects due to other projects consuming heaps of my time!

Anyway a tiny update! The fork bottoms are back from the foundry. How just to figure out the machining techniques and cartridge details  ;)

An original image for reference:



And the cast blanks!








H2 Eric did a wonderful job of his forks, I have asked him for a little more info.

Cheers,
CR21

2
Site Feedback / FAQ / How to... / Re: PM's not saving
« on: January 10, 2020, 03:37:28 PM »
I am in the same position here - hardly any sent messaged in my sent folder. Recent ones where I have replied to a message I cannot find...

Some help would be appreciated  :)

Thanks,
CR21

3
Project Board / Re: CR750 replica build
« on: November 15, 2019, 02:54:00 PM »
Hi Laverda, it was pretty simple to be honest but I can't call the result a success yet! I think once I have developed the pattern, along with some very consistent welding it will be more successful. Learnt a lot from the trial parts.

Phil - I remember you mentioning this - thanks for reminding me! So many details on these bikes. 

Hi Ash, I think I know who you are talking about. pm sent for further discussion.

Rear Hub

A little more progress on the replica rear TLS hub.

The CAD assembly is coming along, still a lot of detail to add!





Cheers,
RD17

4
Project Board / Re: Lets build a SOHC for less than a grand
« on: November 08, 2019, 10:29:59 AM »
Price please as I am on a tight budget  ;)

Hi Trigger, pm sent.

Thanks,
CR21

5
Project Board / Re: Lets build a SOHC for less than a grand
« on: November 08, 2019, 10:16:30 AM »
Hi Trigger,

I believe I have a spare one of these...





Cheers,
CR21

6
Project Board / Re: CR750 replica build
« on: October 25, 2019, 11:43:39 PM »
A little progress from today:

Oiltank

Oiltank brackets tacked on, ready to check chain-clearance etc:



Exhausts

The CR75O exhausts are a 'big' part of the appearance of the machine, and something that I would like to get looking tidy.

I believe on the original bikes each exhaust pipe was made of two pressings, which were then welded or seam rolled together. This left the appearance of a seam running at the top and bottom of the pipe. The headers were formed separately and were welded or clamped to the pipes.

Although the shape profile could be achieved with rolling or even sand bending rolled cones, the appearance of a seam is hard to achieve



The obvious next step was to give it a go...


So a good chunk of time was spent today trying out hydroforming! Something that I have watched many videos on and read about but never tried.

Quick trip out to pick up various fittings to allow the cheapo pressure washer to be hooked up to the sheetmetal assembly, tapped hole in the blanking plug for bleeding air out of the system:



The hardest part of the CR exhaust shape is the curve, so the first flat pattern was knocked up to test the curve profile section. Complete guesswork for the angle and diameter (scaled off of photographs) at this stage and purely for experimentation:




Seamed together and valve welded in:





Hooked up, with a little safety cage!

Pumped up around 400psi



Happy for a first attempt, but very wavy edges and some buckling  :-\

The pattern next to the product:




Round two!

Stainless sheet, smoothed pattern shape, special attention on matching the two halves and having smoother curves:







The latest attempt above the first attempt and pattern:



What I have learnt about hydroforming today is that the pattern, weld penetration and consistency are key to repeatability.


And that it is with a bit more experimentation I could possibly achieve what I am after...


I think I am going to purchase off the shelf header pipes, however I may experiment with another process I have been wanting to play with for a while which is sand-bending...

Cheers,
CR21

7
Project Board / Re: CR750 replica build
« on: October 25, 2019, 10:40:53 PM »
Thats exactly what I did Scott

Hi Phil,

Hope it turned out ok? I think a few people have done it, how accurate it is to an original I don't know but I think it will be in-keeping once it is all painted up.

Cheers,
CR21

8
Project Board / Re: CR750 replica build
« on: October 24, 2019, 11:31:31 PM »
Thanks Phil. Your build is far from a compromise. It is a cracker of a bike.

A few more frame jobs completed today!

A couple of options for mounting the oil cooler on the CR750, a bracket was available for the kit bikes which provided the offset holes for the cooler. I have not seen the frame area on a factory bike, however my suspicion is that they may have mirrored the horn bracket to accommodate the cooler...



Folded up a mirror image bracket:



Welded on some flanged nuts:



Trimmed back and jigged up:



Welded on and ready for final fettling:



Still a fair few things on the frame to-do list!

- Rear hoop and cross brace to accept catch tank
- Steering damper mount
- Lower oil-tank mounts
- Lower fairing mounting plates
- Brake stops, and welding of the cable bushes
- Remove chain guard mountings from the swinging arm
- Many other small details!

Cheers,
CR21

9
Project Board / Re: CR750 replica build
« on: October 24, 2019, 09:01:31 PM »
Cheers Nap!

10
Project Board / Re: CR750 replica build
« 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

11
Project Board / Re: CR750 replica build
« 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

12
Project Board / Re: Lets build a SOHC for less than a grand
« on: October 22, 2019, 07:43:33 AM »
Nice project and tough target, keen to see this one progress  :)

13
Project Board / Re: CR750 replica build
« 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

14
Project Board / Re: CR750 replica build
« 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

15
Project Board / Re: CR750 replica build
« 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

Pages: [1] 2 3 ... 8
SimplePortal 2.3.5 © 2008-2012, SimplePortal