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Monkey Wrench
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105 Posts
Discussion Starter · #1 ·
I have a '68 CL350 that I'm wrenching on. Most of the riding is in NYC with some highway. My largest concerns are narrowness, lightness, and (in terms of the front end) potholes. I'm taking the bike down to the frame, so I figure I might as well put some nice bits on when I put it back together. To that end, it seems like a lot of improvement can be had by swapping a modern front-end on.

The front runners seem to be front-ends from the EX250/300 and the CBR250R. I considered going with a real sportbike front, but my thought was that it would be significantly heavier than the 250 fronts with no appreciable improvement in braking, stability, or comfort. This bike won't see the track, and a good single disc should stop the bike excellently at ~500 pounds (bike and rider). At 37mm, the 250/300 forks are already beefier than the 33mm forks of the CB350, believe it or not. I think it would also be weird to have a front tire (120/70) that was wider than the rear tire (110/90 is about all that will fit the swingarm).

The CBR250R and EX300 are quite new. I'm having trouble finding good specs for these bikes. I need to know steering stem dimensions as well as axle dimensions, as I hope to maintain a spoked wheel to match the rear wheel. Fork length and weight would also be tremendous to know...

I'm also having trouble figuring out if the forks on these new bikes are any better than those on the Ninja 250, or if I should just go with the old faithful. I plan to swap out the internals with Race Tech cartridge emulators either way. I might even upgrade the brakes for the new front-end, so the aftermarket is a consideration. That said, 45-year-old drums up front are pretty crappy to begin with, so...

Can anyone point me to some specs for these modern front-ends? I'm also open to other suggestions for a CL350. I'm open to changing the rear wheel or going to alloys, but I'd like the front wheel to match rear wheel at least somewhat.
 

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UnicycleMode
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7,569 Posts
My brother is building one of the first fightered CBR250R's gutted to the bone and turned into something all together different. I'll see what kind of specs he can get from his forks and report back. I'm pretty sure he can get you everything you need spec wise. They are nothing special, trust me there. And the brake disk is on the right side, so you are rather limited in wheel choices unless you run a universal speedo setup as the cable drive would be totally gone to fit the hub and disk the way you would need it to go if you built a rather part by part setup for the front end of a CBR with a spoked wheel, something he considered and is still exploring for his bike.
 

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re-tarded
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1,283 Posts
I'm pretty sure both are basic damper rod forks. If you're set on 37s another choice would be 94+ Ninja 500s, all the forks are the same basic tech. Once you put Cartridge Emulators in them any will be reasonable.
 

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Monkey Wrench
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105 Posts
Discussion Starter · #4 ·
And the brake disk is on the right side, so you are rather limited in wheel choices unless you run a universal speedo setup as the cable drive would be totally gone to fit the hub and disk the way you would need it to go
This is an interesting consideration that I hadn't considered. I plan to get rid of the speedometer entirely, so this wouldn't be an immediate concern, but I'm pretty sure it's illegal to run without one. If it became a hassle, I would want to be able to get something on there. I recall some SV650 putting magnets on their wheels and forks, so maybe it can be gotten around. I would have thought most bikes had the disc on the right side, old and new.

I'm not opposed to thicker forks, but I want to be wary of walking down the road to overkill. I'd love to have a set of USD forks on there, but not at the cost of 20 pounds and maintaining an unnecessary caliper. I suppose I could always just leave one disc/caliper off, but...it just seems strange. My guess is that the benefits I would see with a set of big-money Ohlins vs a set of Ninjette cartridge-emulated forks would be minimal on a bike that is only seeing potholes and limited lean angles...CB frames are not known for their rigidity. If there's real riding benefit to a serious front-end on a light, noodly CB, I'd consider it.

I'd be fine going with the stock wheel for the front-end as well, but it means I'd need to figure how to get an alloy wheel on the CB350 swingarm, which will probably be difficult with the drum that's on the stock spoked wheel. Welding and fabricating would be something I'd have to pay someone to do, which makes a wheel and/or swingarm swap tricky.
 

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UnicycleMode
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7,569 Posts
I fit a KZ550 16x3 to the rear of my CB360T some time back. There is options out there they just are not too pretty at all.






The biggest advantage to any modern front end on one of those old CB's is the braking performance increase. I ended up with a VF500F caliper on the front of my 360 in an attempt to get at least a little more out of it and if I had it to do over again I would happily use a CBR600F2 rotor on the 360 hub with a Nissin caliper off a 900RR, was pretty close to that before I got rid of the bike, so I am dead sure it works.

With a fresh set of seals and bearings on my stock 360 forks I couldn't tell a difference between them and a more modern setup from the 80's Honda's. ;)



The 350 models had a pretty standard size stem and bearing, meaning you can fit a pretty wide range of Honda front ends on the bike. The options are pretty vast.
 

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Monkey Wrench
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105 Posts
Discussion Starter · #6 ·
If a front-end swap on a CB is well-tread territory such that I can get excellent brakes with a spoked rim, I may just try and see what is easiest...Maybe I can get away with a bolt-on CB360 front and a serious caliper, rotor, lines, and master cylinder.
 

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Is my bike ok?
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I am not 100% sure on the following, but of you could supply measurements off your existing front end we could verify.

Your stem should the same as a 1969-78 CB750. Which is the same as the 1979 and up DOHC CB's. The dohc CB had pleanty of option for factory dual disc setup using a cable driven speedo. So that may be a true bolt on option for you to get improved braking, retain your cable speedo drive (with matching Honda ratios) and keep it looking pretty stockish. Swapping a sohc wire wheel onto a dohc front end is very simple. You could make the needed spacers with simple tools. Hacksaw, grinder....

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Monkey Wrench
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105 Posts
Discussion Starter · #8 ·
The problem with the disc setups of the era is that they're even worse than the drums. They're often considered a downgrade. A dual-disc setup would probably stop better, but it would be heavy. My goal is to get modern brakes on the front, with any pair of decent forks that will work well with cartridge emulators, all attached to a spoke wheel of some kind. I really just need the hub, as I can get rims and spokes laced up to anything that will work with the forks and brakes.

Maybe get a disc setup from the era, but try and get modern bits onto it...I'm hoping to walk well-tread paths in this area, but it's hard to find start-to-finish writeups or specs, 'cause most of the time guys just slapped on whatever they had in the garage, and fabbed up the little bits they needed until it fit.
 

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Is my bike ok?
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Very true about that era of brakes. I have a 76 CB750 with dual stock discs and a modern MC. Braking is awesome, but that pair of rotor does weigh over ten pounds!

One thing I recently discovered, that you may find helpful, is that several modern Ducati rotors share the same mounting bolt pattern as the CB750. Same bolt size and everything. You would have to sort out a new caliper mount, but that'd give you a modern rotor on a CB hub. Click on the link in my sign and look at the last page. I just got finished doing this to a bike.
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Is my bike ok?
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Yep,that's it.

Forks and calipers are -02 GSXR750
Discs are Ducati Monster (and a few other models)
The hub is 69-78 CB750 (and maybe other CB models)
The adapter is to space the disc out the proper amount.

I know you might have to hire out machine work to get something like this done,but I was just throwing out any options I knew of. Then you can decide what would be best for you.

A dual disc conversion (using stock parts) and early CB's is easy,cheap and actually pretty effective. My CB750 weighs in at 480 lbs and I'm 225 lbs. I have had my current brake setup loft the rear tire once during a panic stop situation. You really can't get much more braking power than that :D. And my current seating position has me much further back on the bike than stock. By about 4'' or so.

You can also use EBC rotors made for the early CB's. They are pricey, and I have no personal experience with them,but they have a modern look and use modern materials on the friction area. Supposedly they provide a much better friction coefficient than the hard,stainless rotors the CB were known for.
 

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Is my bike ok?
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Something else to consider when doing a front end swap (and something I overlooked on my own build) is the offset of the trees. The early CB's used a major amount of offset in relation to the steering stem and the fork legs. Modern bikes tend to use much less offset in the trees. When the stock rake on the steering neck stays and you reduce the amount of offset in the trees it produces a good deal of extra trail into the front of the bike. Supposed to make for slower,lazier steering. Of course,some also says it creates extra stability at speed,so who knows.

Like I said,I overlooked this on my own build but figured I'd mention it to you. Learn from my mistakes :D. I'm just gonna let it ride on my bike and see how it does. Will address as needed,but right now I'm using the "fingers crossed engineering " approach. lol
 

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Is my bike ok?
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The problem with the disc setups of the era is that they're even worse than the drums. They're often considered a downgrade.
Only if you are comparing that era's disc's with twin leading shoe drum's. Twin leading shoe drums fookin rock,but they are heavy as shit (rotating weight) and require a fair amount of fiddling with to keep them stopping just right. But yes, when they are right they are great brakes.
 

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Monkey Wrench
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105 Posts
Discussion Starter · #14 ·
This is all great info. It seems like the trickiest bit to all of this is getting a spoked wheel on there. If I compromised that requirement, it's just a question of buying a front end and maybe some new steering head bearings.

Some of the rake/trail issues can be resolved by choking up on the forks, but I might have an inch or two to play with...I really wish all these specs were centralized and searchable. I have charts for fork diameter and steering head bearings, but neither include the length of anything...

I wonder if the front of an RS125 would fit the bill...41mm USD, single 320mm brakes...300 pound bike stock.
 

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Monkey Wrench
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105 Posts
Discussion Starter · #16 ·
I feel like I can't ask for specs until I have a better idea of what I'm going for...The 250 fronts I was investigating don't have handlebar mounts, and I don't think I want clip ons. I'm now considering the front from an old Ducati Monster, but they, it would seem, are their own crapshoot:

http://www.ducatitech.com/2v/monster_faq.html

I mostly just want the lightest front-end I can find that can have great internals, great breaks, a set of handlebars, and are more than stiff enough for a CB350. Bonus points for a fabless wap, USD forks, and easy conversion to a spoked wheel...
 

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Is my bike ok?
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The only fabless, usd, spoke wheel setups that come to mind are supermotos and dirt bikes. Both of which are gonna have super long legs compared to your bike.

There's probably usds on some cruisers running spokes, but I really don't know.

BTW, a long ass set of usds off a dirtbike would make for a sweet front end on a chopper. Always wanted to do that!

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Monkey Wrench
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Discussion Starter · #19 ·
A set of dirt bike forks would be perfect, but I'm not looking for a cruiser, and I don't think I want to cut down forks.

They don't really need to be inverted, I just think it looks cooler. I'll probably wind up with the front end of a small, modern sportbike that'll give me a place to mount handlebars.
 

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Is my bike ok?
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Old GS500's come to mind. They had bars on them and were not a bulky front end. Inverted is cool, but there's definitely nothing wrong with conventional.

You could always toss in a set of emulators. But they cost as much as a fork swap would. Hired machined work included, probably.

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