Author Topic: CR750 replica build  (Read 32997 times)

Offline CR21

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Re: CR750 replica build
« Reply #15 on: October 12, 2016, 09:36:37 AM »
WOW i have to say the petrol and oil tank are a work of art
What do other people use for the strap
pete

Hi Pete, they are the maker is a true craftsman! Other people have used the Yamaha strap in the past, or the reproduction one,

Cheers
CR21

Offline MarkCR750

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Re: CR750 replica build
« Reply #16 on: October 12, 2016, 12:56:05 PM »
Here is the twin disc guide that I used, I found it a very easy job, people on various threads in the states seem to struggle, not at all sure why, maybe we're cleverer than our Yankee friends? 😄, make sure that you use a master cylinder that is designed for a twin disc setup, i used one from a 97 fire blade , works well but maybe wouldn't suit your bike as I think your going for a more original look, GL1000 master cylinder may be better for you, yes the mead speed seat looks nothing like the original, I used it because I needed somewhere to hide the battery, the original CR had a tiny tail cowl.
http://www.dotheton.com/forum/index.php?topic=1525.0

Hi Mark!

Thanks for the link, I have already linked from a thread from this forum (may be your build thread) its very useful. That may be the case  ;D

Cheers for the heads-up on the master cylinder, I was planning on using a GL1000 one.

Tricky one the seat as I am after one with a cover/seat swab as trimming can soon get very expensive! I have a Meadspeed unit that I picked up but I am not sure if I am going to use it.

What ignition did you use Mark? I was thinking of using the DYNA total loss system.

Cheers!
CR21
I used the piranha system that was on the donor bike, god knows how old it is but it works, but I've kept the alternator etc because mine is for road use, I assume that you are removing your alternator to be closer to the original?
Suzuki GT250A (Nostalgia)
1977 K7 CR750 (lookalike, what of I’m not sure)
Ducati 900SS (Soul & Speed)
Ducati M900 Monster (Handling & character)
Thruxton 1200 (suits me)
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Offline CR21

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Re: CR750 replica build
« Reply #17 on: October 12, 2016, 01:14:43 PM »
Here is the twin disc guide that I used, I found it a very easy job, people on various threads in the states seem to struggle, not at all sure why, maybe we're cleverer than our Yankee friends? 😄, make sure that you use a master cylinder that is designed for a twin disc setup, i used one from a 97 fire blade , works well but maybe wouldn't suit your bike as I think your going for a more original look, GL1000 master cylinder may be better for you, yes the mead speed seat looks nothing like the original, I used it because I needed somewhere to hide the battery, the original CR had a tiny tail cowl.
http://www.dotheton.com/forum/index.php?topic=1525.0

Hi Mark!

Thanks for the link, I have already linked from a thread from this forum (may be your build thread) its very useful. That may be the case  ;D

Cheers for the heads-up on the master cylinder, I was planning on using a GL1000 one.

Tricky one the seat as I am after one with a cover/seat swab as trimming can soon get very expensive! I have a Meadspeed unit that I picked up but I am not sure if I am going to use it.

What ignition did you use Mark? I was thinking of using the DYNA total loss system.

Cheers!
CR21
I used the piranha system that was on the donor bike, god knows how old it is but it works, but I've kept the alternator etc because mine is for road use, I assume that you are removing your alternator to be closer to the original?

Hi Mark,

I see, I have seen the piranha systems on Yamahas but I have never used them. I run a PVL style total loss on my TA125. Yes the alternator will go I just need to decide what ignition set-up to use. Really it will depend on reviews and price - I need to do some research :)

Cheers,
CR21

Offline CR21

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Re: CR750 replica build
« Reply #18 on: November 16, 2016, 09:10:57 PM »
This thread has been very quiet for a while... But I have been doing a huge amount of research, and have become somewhat CR obsessed!

Picking back up on the tank strap:

I have managed to source the correct rubber part to fit in between the steel bands, and have ordered some stainless steel rod to allow me to make my own replica tank strap.

Frame modifications

This research is what I have been whittling away at ready for a Christmas frame altering session. This is the list so far:

- De-lug all road mounts.

- Fit machined and fabricated rear sets. I have produced a CAD model and drawings for the rear sets, which like the image below have a 12mm thick boss, which houses the footpeg and mounts for the brake pedal and exhaust. This part is welded in-between two folded sections to create a triangular bracket. These 'inserts' will either be waterjet cut or I will machine them. Luckily I have managed to get hold of a sketch with measurements from a kit bike to be able to accurately place the rearsets onto the frame.





On these rearsets I am going to mount a set of replica aluminium pegs with the all important cured rubber over moulded grip. These are replicas cast from the original parts, with a bronze bushing pressed into them. They will be held into place by a custom 'replica bolt' which I will turn up.


Replica footpeg clamping bolt CAD:



Onto these rear sets mount the rear exhaust hangers, the brake pedal again a cast item with a rubber over moulded grip. The footpeg mounts through a bush, and depending on the gear set-up is on the left or the right side. The rear brake is cable operated with a large and very complex cable, a cable stop will be placed onto both rearsets to allow for both left and right gear changes.

Replica Brake cable 'stop':





The left gearchange is simple, as it uses a conventional style pedal in reverse from the output shaft. However the 'special' gear change option was to have a changeover shaft for British racers, this comprises of a linkage assembly, bearing holders and another frame modification to house an olive bush. This is a modification that I would like to fit at a later date so this is another frame modification.



The fuel tank mountings are fairly simple, it mounts at the front with the original HONDA rubber mounts, and at the rear it is held in with the replica strap. The frame is modified with an added 'Arc' which braces the frame for the tank strap, and provides a mounting point for the front of the seat. Again I have managed to acquire a drawing for this part  ;)

The rear of the frame is cut off, and the seat support loop is lowered. I may also add a rear frame loop as well if I feel that the seat requires supporting.

Other frame mods include an additional steering damper (a simple flanged plate that fits ontop of the lower yoke around the left fork tube and is secured by sharing the pinch fork pinch bolt) the other end of the damper fits to the frame rail underneath the tank with a clamp, a detail that is still to be resolved.

Fairing

The fairing is mounted in three places, at the headstock with the conventional 'pinched tube' onto a bracket, either side of the engine mounts to support the rear of the fairing, and on the frame rails by the headers to support the lower front part of the fairing (I believe this was a modification rather than being original however I don't want the fairing flapping.

I have managed to get a set of accurate rear fairing brackets that bolt onto the rear engine mounting plates, which again are really nicely made parts and are supposedly very accurate, similar to the ones below but detailed in a different way:

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The front 'main' fairing bracket that I have purchased is a 'tribute' part that is relatively close to the original, however I may make my own/try to source a more original one further down the line.

The fairing has been a real head-scratcher, as many replica fairings just do not look right in my eyes, this could be down to decal placement, or even the fitting of the fairing itself, I am really unsure. This led to contacting many people that have built replicas including some self-confessed classic racing Honda 'Anoraks' in order to trace down a good replica fairing.

I eventually traced down a fairing from a supplier in London and the story says that he purchased the moulds from a guy who made the mould from a 'Genuine CR Daytona fairing' so it should be pretty spot on. I am happy with the shape, and it seems to be the best that I can find. Listening to various recommendations from different people who have built accurate replicas seems to be the way forward with this build, there is a wealth of knowledge of these bikes that simply did not exist during the TA125 build and it is a real help.

After looking at many available seats on the market I was not really happy with any of them, the Meadspeed unit seems to be reasonable quality but the shape is wrong. The only seat that I did like was the Airtech seat but with shipping and a swab base it becomes a ludicrous amount! Luckily I have managed to track down a guy who has a seat mould, supposedly taken again from an original Honda racing part. The aim is to borrow the mould and create a seat for my bike potentially from Carbon  :) which would be great!

Wheels

The front wheel aside from having the double disk conversion is pretty straight forward. The hub will be turned down to remove the central cast ribs to resemble the original magnesium CR part.

The rear hub is a point of discussion of these CR bikes. Originally the CR had a twin leading shoe, cable operated brake cast in magnesium, a real work of art and a focal point of the bike. Sadly these hubs were only ever made in very small batches, and any replicas are also made in small runs and are massively expensive from £3500 upwards  :o For me this is a step too far financially, and I will be finding an alternative way of achieving a similar look. There is a company in America who are making a replica back plate to fit the standard K series CB750 hub, however this is still in development and again is not cheap. I think I will try to work out a way of mounting a cable boss to the existing brakeplate unless a replica part becomes financially viable.

Exhausts

I think that a good chunk of the CR appeal comes from the exhausts, not only the sound but the look of the original 'Swept' pipes. After researching this topic it appears that there is only one supplier who makes these exhausts properly, hydroformed with a welded seam, complete megas with a reverse cone and smoothly bent header pipes they really are a work of art! Made by Simon Tappin, these will be going on my bike!





Clip on handlebars

The original CR clip on handlebars were hinged around the yoke and clamped into place by a pinch bolt, this was for ease of disassembly without the need to remove the top yoke. As far as I know nobody makes a replica clip on, and as I want clip ons as close to the original I am going to have to make them myself! "Why" You may say when standard clip ons that will do the same job are less than £100? Well it's the details that will hopefully make this bike, and it is a good challenge for me to get stuck into!

The original CR clip ons were a two-piece clamp, cast in Titanium and then had a tube attached to the casting to form the handlebar. I doubt I wil be using titanium, however I will aim to make the parts as light as possible either in a racing steel or aluminium. In order for the master cylinder to clear the clamp on the right unit the clip on needs to be angled and kinked to prevent a clash. I have drawn the parts up using a CAD program to be able to create the design, look at tolerances and of course check the clearance angles with the master cylinder.



RHS CLIP:



LHS CLIP:



All in all the preparation seems to be going well for the frame modifications at Christmas  :) Full steam ahead!

I have referred to people without naming them in this post quite a lot, and this is because most of them are not part of forums or even online at all.  I have been overwhelmed with the help and enthusiasm from suppliers and people who are in the Honda scene, thanks to you guys if you are reading this!

Cheers,
CR21
« Last Edit: September 13, 2017, 12:04:58 PM by CR21 »

Offline CR21

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Re: CR750 replica build
« Reply #19 on: November 16, 2016, 09:14:36 PM »
To progress with the CR750 rearsets, I worked from a number of images and sketches that I have been collecting over the last two years. It appears that there may have been two types of CR750 rear sets available with the kit originally supplied by Honda. Both types were folding, one sprung and one un-sprung. I have decided to go with the un-sprung set for simplicity, and I am not entirely sure if the sprung units I have seen are replica parts or original parts. I can also get a nice replica set of footpegs from an American supplier. As mentioned in my post above, the rear-set ‘boss’ is a relatively simple form, that will be machined from steel, cut from one direction, then spot faced, drilled and tapped for the bolt.

I had toyed with the idea of making the entire rear-set machined, as the profile is very simple and there is machining to be done on the part anyway, however to be faithful to the original bike I will fabricate the hanger from two sheet metal halves. These halves are just simple folded profiles that are butt welded to form a central seam, and then the boss is welded into position around the perimeter.








In order to save on fabrication time, I have modelled up the rearsets in a CAD package. These are very simple parts to model but this allows me to consider bush tolerances for the peg, and also the ‘flat pattern’ for the sheet metal work.  When modelling these parts in CAD I start off with a flat sheet, mark out bend lines and generate the bends, very much like the manual process at a bench with marking blue and a fly press, but in the digital form.



This digital CAD model can then be ‘flattened’ to give me a profile to work with with bend lines in the correct places, which will untimely save time and head scratching when fabricating and will allow me to fabricate the parts as I intended and have planned. Of course these parts should then fit nicely around the boss for welding into place.  Overkill yes on such a simple part – but it is good to try these things out, and with the angles involved to interface with the frame, it should prevent errors.



I will follow the same process for the frame brackets, which will also allow me to build up an inventory of drawings and models for reference.

Cheers, 
CR21
« Last Edit: September 13, 2017, 12:05:31 PM by CR21 »

Offline onethumb

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Re: CR750 replica build
« Reply #20 on: November 17, 2016, 10:06:21 AM »
That is embarrassingly good. It puts most shed builds (mine included) completely in the shade.

CR21 you've got skills.





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Offline Nurse Julie

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Re: CR750 replica build
« Reply #21 on: November 17, 2016, 10:51:23 AM »
WOW !!! That's very impressive. Whatever happened to the days of scribbles on the back of a fag packet  :) :) :)
LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
https://www.ebay.co.uk/sch/julies9731/m.html?item=165142672569&rt=nc&_trksid=p2047675.m3561.l2562

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
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Offline onethumb

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Re: CR750 replica build
« Reply #22 on: November 17, 2016, 11:04:54 AM »
Nurse Julie I still do.  Hence the mess up with my frame. 


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Offline Nurse Julie

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Re: CR750 replica build
« Reply #23 on: November 17, 2016, 11:41:42 AM »
Nurse Julie I still do.  Hence the mess up with my frame. 


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LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
https://www.ebay.co.uk/sch/julies9731/m.html?item=165142672569&rt=nc&_trksid=p2047675.m3561.l2562

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
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Offline MCTID

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Re: CR750 replica build
« Reply #24 on: November 17, 2016, 12:33:47 PM »
Scott (CR21) is a Designer in real life. He's a smart Lad - and I'm looking forward to seeing his finished CR750.
Now: 2008 CB1300S, CB750K4, 1970 Bonneville. Various other 1960's 650 Triumph T120's/ TR6's/ TR6C's (all in bits...many, many bits unfortunately). Previous: 2007 CB600FA, 1976 CB500 Four. BMW F800ST. GS750E. ZZR1100. CB1300 (2). ZXR1200S. VFR800. CB750 Nighthawk. CX500. XS500 Yam. Suzuki GT500. BSA A10. Various Lambrettas. Zundapp Bella (honest).

Offline Chris400F

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Re: CR750 replica build
« Reply #25 on: November 17, 2016, 01:04:34 PM »
Scott (CR21) is a Designer in real life.
So he has a head start then! But if you have the knowledge, enthusiasm and facilities then you may as well make the most of them.
Even so the amount of research he has done and the attention to detail is very impressive.

Offline CR21

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Re: CR750 replica build
« Reply #26 on: November 17, 2016, 10:33:04 PM »
Hi guys,

Thanks for the replies. There are some extremely high-quality builds on this forum, and a lot of fantastic support. If this build can come out anywhere near some of the builds I have seen on this forum I will be chuffed  ;D

Cheers!
CR21

Offline CR21

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Re: CR750 replica build
« Reply #27 on: December 01, 2016, 07:07:07 AM »
Just a quick update:

I have made some progress on the other frame modifications, drawings are all completed for the rear sets ready for Christmas manufacture and replica pegs have been ordered.

The oil tank mounting on these bikes are a little fiddly, this is what I make of it so far:

The oil tank is 'suspended' into the frame, it is hung from the top from two L-shaped brackets and rests on rubber seats on the bottom supported by more L-shaped brackets either side like the reference image below:





Top mounting brackets (to be modified for a more triangular profile).Waiting for grommets to arrive to complete the profile:



Bottom brackets:







With the help of a member from the CB750 forum who has built a fantastic replica, I have managed to obtain measurements from his CR750 catch tank. Another piece of the jigsaw! Modelled up in CAD for future reference. This will be fabricated in Aluminium.









That is all for now,

Cheers
CR21

« Last Edit: September 13, 2017, 12:05:52 PM by CR21 »

Offline CR21

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Re: CR750 replica build
« Reply #28 on: January 04, 2017, 07:21:00 AM »
Hi all,

The CR donor was removed from the shed:



After a long game of 'engine wrestle' the engine was removed from the frame and the rest of the parts stripped off!

What a lump!!





Now for a day of de-lugging and working out these chassis mods. Rearset fork bosses all machined up ready to accept the sheet-metal work:





More to come over the next few days,

Cheers!
CR21
« Last Edit: September 13, 2017, 12:06:23 PM by CR21 »

Offline CR21

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Re: CR750 replica build
« Reply #29 on: January 04, 2017, 07:21:25 AM »
Made some progress today:

****  :o CB750K PURISTS LOOK AWAY NOW  :o *****

5 hours of de-lugging later and the frame is sorted  ;) Took a while as I did not want to damage the frame...





The most difficult of all was definitely the side-stand bosses, and I had two of them  :'( :D





The frame looks much cleaner de-lugged, I must say I think that the build quality of these frames is pretty poor! Compared to the Yamaha frames that I have worked on its really rather poor  :-\



I faced off a bit of tube to keep the frame from pulling in when removing and adding bracing in this area. Tank placed onto the frame for the first time it was good to see! (the seat is just being used for a mock-up I will not be using this for the final build). 




On with the rear-set sheet metal work, pattern worked from, folded, cut back, jigged and welded. Then the final fit on the boss to be welded in place tomorrow morning and fitted.











Cheers!
CR21
« Last Edit: September 13, 2017, 12:16:21 PM by CR21 »

 

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