Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Phil on February 27, 2008, 09:21:26 PM
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Hi - I am putting together a CR 750 Replica and would welcome advice, photos etc of the genuine article. I have two engines - a K7 and a K6. I believe a K7 is an unpainted F2 and will have bigger valves and combustion chamber (?). Similarly it has a closer ratio gearbox. I intend to use a special 836cc Dynoman piston kit, race cam (Megacycle or Dynoman), s/steel valves with titanium retainers, stronger springs and Keihin CR 31mm carbs. I want to use standard rods. I need someone to port the head and fix the new valves and guides - anyone know anybody? The K6 engine will be tuned to rev higher and will use a Nova c/r gearbox and Carillo rods, etc. Any help/advice most welcome!! Phil (philipclark2@mac.com).
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Hey there Phil,
First the K7 is not a unpainted F2, I personally think the K7 is the better of the two. The advantage of the F2 is that it produces more power, but at a cost. The head of a F2 is crap, due to the sharper cam and the bigger valve the valveguides wear out very rapid, hence 'smoke' and oil consumption. Have build a Japauto Endurance replica with a K6 engine and am in the process of building a 850cc Turbo based on a F1 engine. Look out if you're using a sharp cam and heavy springs, the construction of the 'camtowers' cannot take to much stress. There are lying a lot of blown engines around.
Cheers, Rob
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Hi and thanks for the response. I have obtained parts books for F2 and K7 (thanks to this great site!) and you are correct: the valves on the K7 are the same as K6 and different to F2. I also note that there are slight differences in the gearbox. The K7 and the F2 are identical, according to part numbers, but different to the K6. Is this the 'closer ratio gearbox'? I want to run a standard gearbox on this engine so this is a bonus - or am I missing something?
Phil
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Hi Phil, check out my bike in this thread. http://forums.sohc4.net/index.php?topic=25400.0
Also check this thread in same forum. http://forums.sohc4.net/index.php?topic=27902.0
PM if you need any further help.
Sam. ;)
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Wow! That is a lovely bike! The thread is interesting. The original CRs are very rare birds indeed. The only one I have seen in the flesh is in the old Honda museum at Suzuka. Sadly they would not let you take pictures (they do now). Is that the standard rear hub on your bike or one of those expensive magnesium jobs? What are the footrests - Disco Volante? Did you beef-up the cam holders? I have 101 questions ...
cheers,
Phil
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101 questions is good.
Catch Sam at the Woodbridge Sprint in May (10th I think).
I'm supposed to be riding in the Thundersprint Cavalcade that weekend (on the Rickman) so will miss him again....
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Wow! That is a lovely bike! The thread is interesting. The original CRs are very rare birds indeed. The only one I have seen in the flesh is in the old Honda museum at Suzuka. Sadly they would not let you take pictures (they do now). Is that the standard rear hub on your bike or one of those expensive magnesium jobs? What are the footrests - Disco Volante? Did you beef-up the cam holders? I have 101 questions ...
cheers,
Phil
The rear hub is stock Phil but has been converted to twin leading shoe.
The footrest are home made to CR spec.
The cam cover has welded on bosses that line up with the cam holders bolts. Bolts are threaded through the bosses untill they touch the cam holder bolts, then they are locked into position with lock nuts.
See it in the flesh at a track near you on the 10th May. ::) ::) ::)
Three down, 98 to go. ;D ;D ;D ;D ;D
Sam. ;)
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101 questions is good.
Catch Sam at the Woodbridge Sprint in May (10th I think).
I'm supposed to be riding in the Thundersprint Cavalcade that weekend (on the Rickman) so will miss him again....
Is the Thundersprint not on the 11th Steve. We will be there if all goes to plan on the Saturday.
If we can get it on time, the bike will have a fully covered front end in the shape of a Georg Brown/Nero dustbin.
Sam. ;)
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Yes Sam, but the "scrutineering" for the cavalcade starts at 0700 on Sunday. We'll be in a hotel...
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Thanks again Sam. I will be there if at all possible. Q96 - do you use 31mm or 29mm Keihin CRs? I am told to use 29s as my first engine will use standard con rods and therefore won't be able to rev high enough to enable the 31s to work. This is a "parade" engine - I am planning a Wiseco 836cc kit, Dynoman/ Megacycle cam, stronger valve springs and some mild headwork and the CRs. I am tempted to try a standard'ish F2 head? I have plans for engine 2 which I want to keep 750 with a light crank, Carrillos, Nova box etc. Q95 ...
Cheers
Phil
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Woodbridge Sprint? Thundersprint? Northwich? Am I missing something? Where will you be on May 10/11th Sam?
Phil
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Thanks again Sam. I will be there if at all possible. Q96 - do you use 31mm or 29mm Keihin CRs? I am told to use 29s as my first engine will use standard con rods and therefore won't be able to rev high enough to enable the 31s to work. This is a "parade" engine - I am planning a Wiseco 836cc kit, Dynoman/ Megacycle cam, stronger valve springs and some mild headwork and the CRs. I am tempted to try a standard'ish F2 head? I have plans for engine 2 which I want to keep 750 with a light crank, Carrillos, Nova box etc. Q95 ...
Cheers
Phil
Phil, the 31s work great with stock rods. If you go with Wiseco 836 forged pistons, the Megacycle 125-65 camshaft, and a good port job with decent valves, the motor will make more power than the factory CRs without putting undue stress on the rods as the rev limit will remain stock at 8,500rpm. what you will have is a motor with enough torque to make you think twice about cracking it wide open in the lower gears. ;D ;D ;D ;D ;D ;D
Sam. ;)
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Woodbridge Sprint? Thundersprint? Northwich? Am I missing something? Where will you be on May 10/11th Sam?
Phil
The Sprint meeting at Woodbridge is on the 10th and 11th May. We will run on the Saturday and if we have no problems and the bike achieves what we expect from it, we will leave it at that and head home for the Thundersprint at Northwich on the Sunday. If we have any problems we will stay at Woodbridge untill we get the job done.
Sam. ;)
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Q92 and Q93 (don't want to overload Sam!) - I am hoping to race/ parade this replica in CRMC events and the rules are strict and confusing! I need to get alloy rims put on the standard hubs. Anyone know A) the max rim size that is allowed (and that the swinging arm can accommodate); B) the best tyre size/ make? I am also using the standard stainless discs because I can't find steel replacements (anyone know a supplier?). The s/s discs weigh a ton and say on them that the minimum thickness is a wopping 6mm! My s/s NSR discs say maximum thickness is 3.5mm. Does anyone have experience of machining discs? Does anyone know where I can get the discs drilled? Thanks!
Phil
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Can't help with either there Phil, we stuck with stock rim size (WM2/WM3) and stock brake discs.
Sam. ;)
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...................... The s/s discs weigh a ton and say on them that the minimum thickness is a wopping 6mm! My s/s NSR discs say maximum thickness is 3.5mm. Does anyone have experience of machining discs? Does anyone know where I can get the discs drilled? Thanks!
Phil
Hey Phil, I have machined down a few disks, as long as they are not drilled it's ok. If they're drilled you tend to get a vibration in the disk because of the holes and then the surface isn't smooth. Drilling isn't that hard to do, as long as you use sharp drills. Must have a template somewhere in my archive, if you want I will look for it.
Cheers,Rob
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Forgot the picture:
(http://i238.photobucket.com/albums/ff74/voxonda/Japauto8.jpg)
Cheers
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I have done a few disc aswell. i skimmed the rear disc on my F1, i think it is 4.5mm now, and most of my mates cars have had a skim at some stage or other 8)
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I want to reduce the (huge!) weight of these discs. Given your helpful advice, should I (a) skim them to 4.5mm or b) drill them? Thanks to all. Phil
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Hi Phil - if you want to change discs, talk to Len at CAT Engineering, Crwothorne, Berkshire. He can take your stock discs (by post), take them apart, refurbish the centres and rivet on a nice new cast iron rotor, drilled as well which will put you over the bars compared to the standard steel discs. OK cast iron does rust up after getting wet but as long as you scotchbrite the discs when dry they'll last just fine. I had both of mine done by Len on the 750 and also the disc on the 450 racer. I can stop the 450 on a sixpence! They're 290mm diameter but 4mm thick and the stopping power is awesome.
For your rim sizes for the CRMC, suggest you contact their Honda expert, John Davidson and he will be able to help or Gordon Russell the eligibility officer via crmcelig@aol.com. I'm running a WM3 front, WM5 rear btw!
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Hi my lord,
Do you have a picture of your 750 disk setup?
Cheers, rob
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talk to Len at CAT Engineering, Crwothorne, Berkshire.
That's 3 miles from me (and I've never heard of them!
Where are you Moonpie?
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Steve - I'm up in Cheshire not that far from Sam. CAT Engineering are very big in the supply of parts for CB350 K4 and CB450 Bomber racing (twins) but have started branching out into CB750s as well. What Len Cooper doesn't know about the CB350/450 race engines isn't worth knowing. You can check it out at their site - http://www.ajhw.co.uk/cateng/racing.html
They're fantastic all round engineers too so any job that you need doing is OK by them and that's where they came in for me to do the 750 discs. Normally they don't go as big as 290mm but did this for me no problem.
Vox - sorry I don't have a picture of the setup on my bike yet, as you'll see from sohc4.net I'm still trying to get too the bottom of the darn fork bracket for the mudguard! I could post some pics of the lovely job done by CAT on these discs though if it's of interest?
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Vox - sorry I don't have a picture of the setup on my bike yet, as you'll see from sohc4.net I'm still trying to get too the bottom of the darn fork bracket for the mudguard! I could post some pics of the lovely job done by CAT on these discs though if it's of interest?
No worries, would like to see pic's of the discs.
Cheers.
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Thank everyone - I will certainly speak to CAT about some iron discs! Phil
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Well I have a nice photo to post but for some reason I don't have the additional option to be able to load the file up?! Any ideas folks?
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We should have a FAQ for this:
Posting Pictures
When you post, there is a link called "Additional Options..." to the bottom left of the text box. Click on this.
Now you can attach a file (usually a JPEG for a picture, but any standard file format can be added to your post) by clicking on the "Browse..." button and selecting the file from your PC.
To add more files, click on "(more attachments)"
Files must be <128kb to upload so please cut those pictures down using a graphics or photo programme.
A maximum of 4 images allowed per upload.
Hosted Image files
If you host you pictures (on photobucket for example), you can insert them into the text field of your post which makes narratives much easier to read. Use the "Insert Hyperlink" button (the one with the globe) and post away!
If you have cut and pasted the URL and it shows only an empty post, try this:
* Right click the picture that you want to display
* Select "Copy Image Location"
* Paste into the post between the IMG tags
Resizing Images for Upload (Windows XP)
Here's a question that is asked a lot! Go to Microsoft Downloads and search for "Resize Picture" - It'll be in the "Power Toys" section. I can't post a direct URL as it moves around. Download the application and anytime you right-click a picture file (or files) it will allow you too resize them. Easy.
Uploading an Avatar
You need to be in your "Profile"
In the "Modify Profile" box on the left, click on "Forum Profile Information". Specify a URL location for your avatar picture or upload it from your PC by using the "I will upload my own picture" radio button. Anything you type in the "Personal Text" box will appear under your avatar. Avatar pictures must be no larger than 150 x 150 pixels.
While you are there, fill in the rest of your bio - especially your location.
Also fill in your signature - this will appear at the bottom of every post. Current bikes, past bikes and a link to your gallery are all good. Big pictures are not so good...
Adding www links to your posts
Anything you type that begins with "www." or "http/:" will automatically be converted into a link.
You can also cut and paste links from the address bar of you browser.
To be really cute, you can use HTML text to post a link with a much more descriptive label (as opposed to an eBay address which stretches across the page and means nothing)
Type this: [ 8)=http://www.ebay.com]THIS[/ 8)] where 8) = "url"
Which comes out like THIS (http://www.ebay.com): Cool eh?
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Steve - yeah I checked the FAQ and tbh this forum works by and large the same as the US one where I can attach pictures no problem. When I open the additional options here though I get 1)Notify me of replies, 2) return to this topic and 3) don't use smileys checkboxes but no 4) Attachment....
Is there something wrong with my profile setup?!
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You should see this:
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Yep - that's exactly what I get - blank space LOL! :D
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No luck with the pic's yet?????
Cheers,Rob
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No - still no attachment option available to me. I'll start a new thread on sohc4.net and post them there...
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Hi,
if you need detailed (repro) pics of CR750 parts, you could go to:
http://www.daytona70.com/Francais/ventes.htm
nippon