Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: r1_pete on June 21, 2012, 05:35:42 PM
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I know all the advice is dont, bolts not available, riveted etc........
But,
Has anyone actually done it and had success? I want an 18" front wheel, better tyre choice (OK Cheaper), and I have a really neat mudguard which fits a 100 90 18 perfectly.
I have an 18" front from a CM400, but that only has one disk, I'm thinking of getting a scrap 19" F2 / DOHC comstar and fitting its centre into the 18" wheel, I figure I will only need to remove 2 pairs of spokes, but to balance things I should use the same rim end fittings on all spokes, so would use dome nuts and screws all round, loctited of course.
I can't see a problem bolting it all back together with tight fitting metric fine pitches, optimum torque figures etc.
Has anyone had any success / what are the pitfalls I'm probably missing?
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Please just forget this insane idea :( Any insurance company would run a mile in the event of a claim, even if you did tell them about it. :'() If you could do it successfully (seriously BIG if), you would alter the steering geometry and handling of your bike quite a bit, and the lack of professional wheel builders offering this kind of mod says it all. Honda fitted a 19 inch wheel after incredible amounts of research and development, and this is what they found to be the best size. Also you will reduce your ground clearance as well (I've scraped alternator casings during high speed two up cornering on standard wheels, less ground clearance means even easier grounding, to be avoided at all costs!) I have to ask, WHY? :o
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Hagons used to offer a repair service for comstars, give them a ring and ask their wheel department for advice but I think you will find they only straightened the alloy rims and left the steel parts in place for safety.
Rob
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Another issue is electrolytic corrosion, where dissimilar metals contact each other (thinking steel nuts and bolts) the alloy turns into white powder at a rapid rate, as anyone on here with an old Landrover can testify :-[
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Pete
I removed the spokes and rim from a Comstar hub so I could bolt a Citroen 2CV wheel into my sidecar tug CB550.
Once out I wouldn't have even attempted putting it back together again it was such a mess, and I do this kinda stuff lots (built chops, old Triumphs, trikes, sprinters and other assorted crap ;))
The route I'd take is trying to fit a second disc to the CM400 wheel, aren't most Honda wheels drilled right through so a disc can be fitted to both sides? even if they ain't I'd do it, the CM400 has a cover over the non-disc side, I wouldn't take that off coz it'd mean removing the pegged nuts but the centre of it could be machined out and the hub drilled and tapped, and the disc spaced out with spacer disc.
As for not fitting a different size wheel? hmm I'd be in trouble if you can't, I do it to get different steering geometry, as well as changing yoke offsets, forks, rake, trail. Using different section tyres can have as much difference. E.g. I have a 16" and 17" rear wheel for one of my bikes, the 16" has a chunkier tyre, I measured the difference in height .....6mm, so a ride height difference of 3mm or put another way ....tread depth. ::)
If you have some scrap/unwanted comstars have a play, if the end result is crap you've lost nowt but gain knowledge.
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I didn't say you COULDN'T change wheel size, just that it would reduce ground clearance and change the way it steers ;D
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I'm assuming you've seen the Wheel Refurb post by RWG, but in case you haven't, I'll just repeat . . .
. . . get hold of a copy of issue 14 (Dec 2011) of Practical Sportsbikes. There's an article in there on a bloke who's worked out a way of taking them apart and rebuilding them on small capacity 125's, but . . .
. . . like the others have said, this really isn't something you want to try to do it yourself. It's a seriously specialised job - at the very least you'll probably have to make up some triangular-oval spacers and make rivets out of aluminium rod. The guy who was interviewed about the job for the article only does them for himself and says he wouldn't want to attempt to rebuild wheels from bikes bigger than 125's because of the risk of something going badly wrong.
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There aren't enough 'spokes' on a comstar for me to even think about this kind of thing, any failure would have to be catastrophic ........
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Going back a lot of years there was a firm that made disc like rotors that bolted on in place of the comstar spokes with holes for normal spokes so you could lace up a standard type rim, BUT they did not sell well and, from memory, also failed at times so were not really recommended
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OK Cheers all, that seems pretty conclusive, anyone want to buy a CM400 front wheel.... :D :D :D
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The route I'd take is trying to fit a second disc to the CM400 wheel, aren't most Honda wheels drilled right through so a disc can be fitted to both sides? even if they ain't I'd do it, the CM400 has a cover over the non-disc side, I wouldn't take that off coz it'd mean removing the pegged nuts but the centre of it could be machined out and the hub drilled and tapped, and the disc spaced out with spacer disc.
guess not then ::)
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Hi Tomb, No the cast in lugs for the disc fitting are only half width on the cm400 wheel.
Cheers.
Pete.
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bugger!! :o
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As already discussed, it's a noted specialised area as the localised demands are so high that if you do get it wrong it's probably going to be a very quickly occurring failure. I for one wouldn't want to be sitting on it when it did.
On a positive note though the CM400 wheel is from which model? as far as I can remember the bike I know as the "Superdream" had twin discs fitted to the 400 model and not the 250 which could have been 18" rim size, so may be a scource for you.
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19 on the superdream front wheel, the cover on the other side to the disk unbolts to allow twin disks on the 250's I've had my grubby mitts on (the wheels are still awaiting being remade into a horse drawn convayance in my garden)
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Hi
Thought i just had to reply to this as you can see from my photos Ive taken the rear hub out of a comstar to convert my rear drum to a disc . I cans see what everyone is on about the bolts that have small dowels onto the threads of the bolts to lock them in place.
when i removed the bolts the threads on the nuts were totally knackered because of the pins in the bolts,ive managed to save 3 of the bolts with pins intact which i will reuse with new nuts (tighten the nuts up then hammer the pins back in the bolts ) I have another wheel with these bolts so should get another 2 out to finish the rear disc project.
Please give me your view to the use of an other hub in a different wheel and whether you think its safe ? ive moved the wheel spokes a minimal amount so not to stress the metal,not touched the rivets at all so they should be ok..
Thanks Amos
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I certainly would not attempt to use those spokes again, the angle they have been bent to will almost certainly have caused stress to the metal, that you would not see without specialised X-Ray equipment. The spokes were never designed to be bent like that, the spokes are pressed out at manufacture and bolted and riveted together with extreme care, bending them as you have is a fatigue fracture waiting to happen :o It would be madness to trust the spokes for integrity now, would it not have been easier (and infinitely safer) to have hunted out a disc braked wheel? (750F2 or even the later DOHC 750?) I'm sure anyone seeing those photos with the slightest knowledge of metal stresses/loadings will tell you the same, it's now just a pile of scrap :'( But ultimately, it's your bike, and your life, if you don't value those things, it's your decision
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What he^ said.
The bolts and nuts are drilled and pinned, "hammer the pins back in" without drilling???!! :o
If you really want to use the bolts again, angle grind the side of the nut off so the pin can fall out, then wind off whats left of the nut, and use new nuts, and redrill another hole.
I'm sure anyone seeing those photos with the slightest knowledge of metal stresses/loadings will tell you the same, it's now just a pile of scrap :'(
Yup!
Tom (Toolmaker 18 years, Mech Tech 13 years)
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+1 on the 'scrap them'
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Thanks for your input
Luckely the wheel in the photo is a spare one that I had with a rear disc on it I was going to just put the wheel in but the spokes where very rusty and I couldn't polish them up as you can see from one of my photos the bike and wheels are very shiny and I didn't want to spoil it .
I haven't stripped the rear wheel yet off mine or touched the spokes.
I'll be looking out for another rear comstar with rear disc in good condition ( anyone got one for sale ?? ) so I don't have to mess with the spokes.
Thanks for the comments
Amos
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Just to add a bit to that already posted; The bit where the spokes have been bent is at the point I perceive to be the most stressed, so ANY compromise at this point is likely to raise the risk of failure signficantly.
The materials used including the bolts/nuts/rivets etc will have been specified with the full knowledge of the designing engineer, to substitute off the sheld items without that background information I would place as a high risk choice and one that you may not find out the shortfall of until it stops working.
Believe me, i would certainly re-use anything that I can and not be an advocate of just "new is better" but I consider the risks here just too great to take on without a very good knowledge of what you are doing.
If you get just one joint failure, the design of these wheels to me would seem to have a high chance of the rest following shortly after. They are a very strong reliable design in their original form but rebuilding without an appropriate level of skill is not something I'd like to ride around on.
Just imagine that failure happening while you were on a busy motorway and I think you'd consider it differently, the risk is not worth it.
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Just think you could do the repair to these wheels, and all goes well,and they seem perfect, you sell the bike at a later date and some poor unsuspecting person could have a nasty accident ,and possibly loose their life
These wheels usually only fetch about £20 second hand, so its well worth replacing with a good second hand one, rather than going to all that effort
Pete
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Point Well made and understood will be looking out for a good secondhand F2 rear wheel comstar,the one i had was very rusty anyway and not usable so stripping it didnt cost me that much.
Would a cb900 early comstar fit does anyone know ?
Thanks again for all your advice im still going to look into a rear disc conversion but without stripping a wheel to do it
Amos
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Mickharrow has a set of Comstars for sale in the for sale section give him a shout & see what he has ;), cheers Mick.
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i got a pair OF F2 wheels front and rear with discs and tyres but im in wales probably to far away for you
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Thanks for the reply
Watching a rear wheel on eBay looks like the one I stripped ,says its off a CB 900 I presume it will fit ? Anyone have any ideas ?
Amos
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Bluemouse1006, I am building a special from a '79 F2 and will not be using the wheels. I will take a couple of photo's for you today and will post tonight. I live in Scotland and have a mate who is a long distance lorry driver so perhaps I could organise a drop off close to you. What else do you need to convert to disc as I have the lot. WHY, am looking for a couple of engine parts.
Archmill
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Thanks
Im bidding on a rear wheel on eBay for 15 quid at the mo but thanks for the offer might take u up on the offer later what engine bits do u need ? I'm selling one on eBay at the moment with 25 watchers !! So should seek finishes on Sunday , I have a casing and some small bits and bobs from another if your desperate ? Let me know
What's the condition of the comstar s ?
Thanks again
Amos
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Amos, photo's as promised:- (http://)
I have given you a photo of each side, plus the worst parts of each side.
I am looking for a good alternator caseing ( want to polish it ) and 3 valves.
Let me know mate, the wheel ain't going anywhere soon. ;)
Archmill
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Archmill
Hi recieved the wheel from ebay and its the wrong one !!! its only got 5 studs for the disc and mine has 6 !! Ive decided to paint the spokes now and polish the rims
Ive looked for another but there is a few about but quite rough is yours still about ? how much including postage ? (i was charged £15 for posting the last one from portsmouth to Hull HU129PJ )
I would appreciate it if you could help
cheers
Amos :)
PS sorry i dont have any engine parts left
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Amos, have sent a text to my mate the long distance driver to see if he or any of his mates deliver to Hull. What else do you need apart from the wheel, I.E. brake disc / brake caliper and bracket / spacers / spindle ?
Archie
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It might be easyer to find a disk to match the new wheel you have?
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Archie
Thanks for that,could do with a disc that matched the rear wheel aswell if you have it ?
I have a rear disc but not sure of the un warpness of it if you know what I mean and its quite scored.
If your mate cant deliver i can sent payment for postage etc via cheque or paypal if needed just let me know.
Cheers
Amos
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Got all the bits now !! Thanks to Archie thanks again am looking at getting the wheels chrome powder coated when I make sure it all works
Anyone heard of any horror stories or any one had it done ?
Thanks
Amos