Topic: 75' CB400F front end swap

[x_O]

So I recently purchased this front end from a 93 CBR600F2:


A quick background, I'm new to motorcycles but I feel I'm learning pretty quickly. My aim with this is to build it up over the summer and put it onto my 1975 CB400F.

My questions:

Shock Rebuild: Since they're used and I don't know their history I plan to do a rebuild on the shocks. Seals and all that. Maybe even some Race Tech emulators if I'm feeling fancy.. Can anyone recommend any good websites, or youtube videos for how to do this on these shocks? I can't imagine it's too hard but I'd love a guide to follow for peace of mind.

General: At my purchases current state, what are all the things I'll be required to get to make this install happen? I assume to I'll need to get the obvious new head tube bearings, brakes, rotors, cables, speedo system (Don't know much about these) lever, rim, and tire. Am I missing anything?

Wheel: I don't really care for the look of the mag wheels and want to keep to rims... I've seen people talk about using Harley rims, so I'm curious if there's a certain kind that works best for the dual disc brakes? Also, What would need to be done to the hub for it to be ready for the dual disc?

I think that should take care of my questions, any insight into the project a head is greatly appreciated.

Dereck

[Bodi]

There are a few things to look at:
Steering stem diameter - same as the stock one? Tough to fit if it isn't.
Steering stem length - this can be changed but not easily.
Triple tree offset: this distance, plus the rake angle (set by the frame) and wheel trail (varies with wheel diameter and axle offset, if any) sets the steering geometry. This is critical, bad geometry can be unpleasant to ride... or seriously dangerous to ride. My stock CB77 has to be deliberately forced to turn, my old stock RD400 was super twitchy by comparison. The 400F stock setup is very neutral, easy to turn and quite stable.

I don't know the 600F2 rake, unlikely it's the same as a 400F. The triple offset is unlikely to match either.

There are folks who have done it, and you should check with them what they did and if the bike was rideable with the swap.

[x_O]

Bodi,

Thanks for the reply. I still start looking into those things. I got this fork based off this build:
http://www.dotheton.com/forum/index.php?topic=28160.0 since it didn't sound like there was too much work involved. However, in the write up nothing was too descriptive.

[754]

You may have to build a new stem.

[calj737]

AllBalls Racing makes steering stem bearings for conversions. Put in your stock bike, choose which front end you are using, they provide the upper and lower bearings needed to accommodate the conversion.

If the stem is too long, pressing that one back and trimming it is easy enough, or, www.cognitomoto.com probably has a stem that can be swapped in to fit.

Using a front hub that is spoked, thats a tad trickier. Harley hubs can be had, laced to a modern rim, but you'll need to tinker a bit to get rotors properly spaced to fit your calipers. Or, again, cognitomoto sells hubs for these forks that are ready to lace and bolt up.

I think you'll find the stock valving of those forks is already plenty good, and emulators from Racetech probably not needed. You may choose to have the internal springs changed, as they are single rate springs and you'd want them rated for your new bike's weight plus your rider weight. Search YouTube for a video on disassembly and rebuild of the shocks, its pretty easy and straightforward.

That front end does have less offset than a stock 400, but, its also a much stiffer setup and you'll likely use a wider front tire. Those forks also have a built-in location for a steering damper that is a good idea. Biggest issue is lock-lock steering clearance against the tank with clip-ons. Plan carefully there.

You can source replacement Brembo calipers off eBay all day long to fit your front end for a pretty cheap. Rotors are widely available either aftermarket or stock. Using the stock Honda speedo will be very tricky. An electronic gauge or GPS gauge for speed will be much easier. And of course, bar controls from that front end will be a wiring trick, or do you plan on using the stock 400s?

[BomberMann650]

Damnit Cal I was about to mention the cognito moto conversion trees.

[x_O]

Thanks for the heads up on the AllBalls process.

I got in contact with the guy from the blog build and what he had to say about the process in more detail was this:
-
"I had a 400 stem pressed in to the 600 lower triple. The diameters are the same, so it's an easy swap. I measured the axle to top clamp measurement of the 400 forks, and made sure the 600s were set to the same length. They are longer, so stick up a bit above the clip-ons. You might see I have a 400 hub, into which I've fitted a couple of disk rotors with adapters I had made. The bearings to fit the 600 axle fit straight in to the 400 hub. Inner diameter is larger from memory. I had to weld some steering stops on the bottom of the steering stem to engage with the stops on the triple clamp."

Being that I'm new to motorcycles I don't fully understand everything that's being talked about. I'm starting to research it all as it comes up though.

What I do understand so far is that I need to measure the axel to to top clamp and match the height, and that some adapters need to be fabed up, (I asked if he would make me some for a price) or spend $$$ on the Cognito hubs. New wheel bearings to fit 600 axel. The AllBalls headset bearings. And that something will need to be welded to engage the stops on the lower triple tree so the clipons don't smash the tank. and lastly that I won't need the emulators but to look into some progressive front springs. Each piece going on this setup will be rebuild also.

As far as pressing the stem into the 600 lower triple, I don't follow. TBH I don't know what the stem is? Is it the bar that connects the upper and lower triple tree's together? What is offset when in this context? Would the use of the steering damper be needed on my bike if I don't plan on bringing it to the track?

To answer your last 2 questions I would rather use a digital speedo, and I'm using the old bar controls since this is going to be alarge enough project for now haha.

[calj737]

Some answers:

The stem is the vertical tube that is pressed into the lower clamp, passes thru the frame's "headstock" and is then topped off with the top clamp (fastened by screw on nuts). The reason he may have used the stock 400 stem is due to the length difference, but again, the 600 stem could be pressed out a bit, then trimmed with All Balls bearings mated to take up the outside diameter differences.

A Cognito hub makes things much easier. No fab, stock 600 axle, rotors, calipers, wheel bearings. Cognito also makes adjustable triple trees (the upper and lower clamps plus a stem) to convert your 600 forks onto a 400 frame. They're pricey, but they are complete, bolt-on products and beautifully made. Something to consider...

The offset is the distance from the center of the stem (looking down) to the line between the fork tube centers (again, looking down). This distance is the offset, and your 600 probably has a smaller offset compared to the stock 400. That was the reference made in an earlier post about effects of steering geometry. While mathematically its true, I suspect most riders don't suffer the negligible effect.

A steering damper is not required for street or track, but they are a very good investment when you modify steering geometry, especially for newer riders. But it's mostly a 50/50 opinion on their need.

Your forks have very good springs already, so you probably don't want progressive rate springs, but instead stick with single rates. Your forks also have more adjustment to them than the stock 400 forks. Again, use YouTube and search " 1993 CBR fork adjustments"

[slikwilli420]

If you are going to do trees and want to save a bit of coin I have a bunch of designs I can do in a variety of thicknesses with custom dimensions like offset and fork spread. My signature has more details or feel free to shoot me a PM.

[BomberMann650]

Hey x_O

Can we call you wink?

[754]

Is your lower tree steel, theory stock 400 stem is welded into the lower tree.
 There is maybe ways around the welding.