Kawasaki Front End Swap For VFR700? Need Some Input.

Hi guys, I have an 86 VFR700.

I recently picked up another persons project bike and I plan to sell most of the parts, but this front end looks like it would be a good candidate for the VFR. It's from a 90 ZX-7 H2.

The positives are:
43mm fork tubes
Adjutable preload
13 click adjustable rebound
Dual 310mm floating rotors (good thickess)
Twin 4 piston calipers
A speedo drive on the front axle
A modern 3.5x17" sized rim for a radial tire
The total stem length is 11" (same as VFR)

It looks like it might swap over with just the proper sized bearings. No doubt it would be a big improvement in every way to the stock setup.

The negatives are:
The fork length is 2 1/2" shorter than the VFR. If I eliminate the extra length above the triple tree (that the stock handle bars used) I gain 1 1/2". So they are technically 1" shorter than stock. That should be okay. I wanted super bike bars anyway.

All the parts need to be cleaned and refinished. The rim and rotors have peeling chrome so I'll need to sandblast and paint. I have a sand blaster and rattle can paint should work just fine.

The forks need new seals and fluid. That's cheap and easy.

The speedo might need some adapting or a custom cable plus it might read slightly off. For cars there are mechanical drives with changable gears to recalibrate and one of those might work.

 

The front wheel looks like this which is pretty close to the stock 3 spoke style.



Here is the donor bike:

 

It seems the steering head on the VFR frame is 7 3/4" long while the ZX7 is 7 1/2". I need to gain another 1/4" if I want to use the ZX7 stem.

After careful examination of the ZX7 triple tree there is 3/16" of extra stem length not being use on the bottom. I can use that plus push it 1/16" more and gain the 1/4" of extra stem length I need.

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To do this I'll need to press the stem down part way, remove the C-clip, then weld a small dab of metal on the bottom to function like the clip did (which is a fail safe to make sure the stem doesn't pull through) and then press it back into place plus that extra 1/4" until the extra dab of metal I added bottoms out. No machine work needed.

On to the next issue.

 

This concerns the steering geometry.

The VFR700 has Rake/Trail 27.4 degrees/108mm

The ZX7 has Rake/Trail 24.5 degrees/100mm

I mocked up the new front end and assuming no changes in ride height, the angle change alone adds 19mm of trail. Luckily the ZX7 front end is designed with less trail than the VFR. So I'll be going from 108 to 119mm of trail. I theory it will make it less twitchy, less easy to turn in, but add straight line stability. Keep in mind that I can play with ride height front and rear to alter things a little.

Here are the offset numbers.
I don't know if triple tree offset is a factor here or not.

Since a lot of guys do F2 front end swaps I looked up it's rake/trail - 25*, 94mm. On the VFR frame with 27* rake I think the F2 trail would increase slightly over stock at about 110mm-112mm. I will be adding a bit more than that at 119mm. It might require a bit more effort to turn the bars, but I'll be adding Super Bike style bars on top of the triple tree, anyway. I can go a bit wider if need be. I want my bars to be about 3" taller and 3" back. That will make it a lot more comfortable for me.

I hear that running a 110/70/17 tire can help. It reduces the rake some (which reduces trail) as well as lowers the front axle which again reduces trail. Then the narrower tire seems to help make the bike easier to flick left and right or so I'm heard. So that's definetly an option.

 

At first glance I was going to say ZX7. I'm pretty sure that is correct.

It sounds like you are well on your way to getting this fitted. Keep us up to date on your progress!

 

Does the offset even come into play in this swap?

I mean, the ZX7 front end offset was designed to have 100mm trail when mounted at 24.5*. All I'm changing is the angle.





You can see the increase in trail. This is where more offset in the triple tree would help reduce the trail bringing it back to stock. Anyway, I guess my trail will not be 124mm or so. It should be about 119mm.

Wow, I found an online rake and trail calculator and I plugged in 23.6" tire, clamp offset 29mm and rake 27.5* and it gave me exactly what I predicted, a 119mm trail.
If I change the rake to the ZX7 frames 24.5* it shows 101mm trail. The numbers are coming out right so far.

 

119mm of trail is certainly not ideal but should be ok. I prefer something in the 102-105mm range. There are drawbacks to additional fork offset too, my suggestion is to keep the ZX triples and run them that way. Your 27° rake will always be the limiting factor. Unfortunately you can't change that (easily).

 

I did get confirmation that these are 89-90 ZX7 H forks. I found some ZX7 front ends on eBay and had the sellers read me the casting numbers. The forks and tree match mine. I also opened the forks and adjusted the rebound adjustors and I now get 13 clicks instead of 8.

I need the upper tree as well as the big nut and dust cover.

I need to blast the rim and rotors. De-chroming the rim would run me $80 so I'd rather blast it with media or sand first and see how it works out.

I'd like to separate the rotors from the hub so I can refinish them properly, but I'd need new floater buttons or what ever they are called. Anyone know about those? Their name or who sells them?

 

Sorry, you cannot buy just that piece.

 

I found some at Spiegler, but they are expensive at $8 each. So 12 would run $96 plus the shipping. That's way more than I expected. I guess I'll forgo any cadmium plating and just mask it off and paint it. I don't use the brakes aggressively so I don't get them super hot. I think paint will be fine.

I'm thinking of painting the forks black and the calipers gold for a factory look. I was thinking white rims, but they are so hard to keep clean. Arg! Maybe powdercoating the rims white will make them easier to clean and not let stains form.

 

I think those just fit the Spiegler rotors. Not 100% sure though.

 

I went to order bearings today, but couldn't find the lower 28x55 I needed. Instead, I ordered a set of all balls bearings with the proper 25x47 top and a 30x55 bottom. ($24 total :biggrin

I'm thinking I can take some 1mm thick sheetmetal and make a spacer around the bottom of the steering shaft and press them both tightly into place. I've never heard of that being done before, but seems like it should work.

 

You definitely do not want to do that. I know, it's tough to hear "been there, tried that", but in this case I would suggest you get the correct bearings. If you can't do that you'll have to figure out how to modify/adapt the triples to get there. It could be that you will need custom triple clamps. Those are expensive, usually when I make them for customers it is around $500-600.

 

Why do you think it won't work?

No one makes a 28x55 bearing.

I could get a 28x52 and make a spacer to fit in the frame or I could use the 30x55 and have a ring machined from a solid piece of steel to give a tight fit on the steering shaft.

 

I would do neither. Personally, frankenstien-ing something together like that will only cause you trouble. I would figure a way to make your stock steering stem work in the ZX lower triple.

 

I don't see the problem you see. I can make the lower bearing have a tight, pressed fit on the stem just like the factory does. How could it possibly be an issue?

 

I understand totally where you are coming from. In fact, so much that I tried it once. It just flat doesn't work out as you think it will. Sorry man.

 

Jamie, can you give me some details on what happened when you tried this? Maybe in a private message if you prefer.

If I did swap the stems I run into a couple of issues. The VFR stem bottom is 30mm and it needs to fit into the 28mm hole in the lower ZX7 triple tree. I need to decide which method to use that minimizes weakening of the parts.

Solution 1. Put the VFR stem on a lathe and machine 2mm off it's outer diameter. The pic below shows what the stem would look like after turning it down to 28mm. Wall thickness goes down 1mm from 4.5mm to 3.5mm, but still should be plenty strong. I could even make a 21mm plug a few inches long and press it into the bottom of the stem to make it stronger and less likely to bend.





2. Put the tree on a mill and cut the hole open 2mm. You can see that there is already a 30mm hole machined into the bottom of the tree, but it's only 1/4" deep. I don't like the idea of weaking the aluminum.



3. Cut 1mm off each. It's a compromise. I'm not sure it's the best solution.

In doing some research, it seems the main stress on the stem is shearing which pushes the lower tree front and rear. You get big shearing forces during braking and when hitting bumps, but not enough to bend the stem. The OEM made sure to design in a lot of extra strength. Now if you run into a solid object like a car, the stem will bend, but it's usually in the unsupported center, not at the end. You also get shearing forces when coming down from a wheelie.

(Coming down from a wheelie also pushes the lower tree into the frame through the bearings. It does not put a lot of stress on the stem)

My opinion is the stem is steel which is much stronger than the aluminum tree, so I would go with solution 1. I don't think bumps, braking or wheelies is going to cause the bottom of the stem to bend. Hitting a car might do it, but you've got a lot more to fix than just a stem, so it's irrelavent.


I also run into the issue of needing to machine the top of the ZX7 tree to fit the larger diameter of the VFR stem, but as you can see, there is plenty of material there to do that.



Or I could just make a sleeve to press the 30mm bearing onto the ZX7's 28mm shaft and not do any of the above. I'm still looking around for a 28x55 bearing. Maybe I will get lucky.

Does anyone know what a new steering stem would cost to make?

 

The issue is it will get loose. Not at first, but after a while the extra joints will loosened up, creating a bunch of free play in the forks. I was warned about it but listen back then. Maybe you can make it work?

I'd still say going the triple clamp-mod route is a safer bet.

 

I was thinking about it and realized that ordinary steel probably wouldn't stand up to the pounding. I would need to make a sleeve of hardened steel. I could even tack weld the top of the sleeve to the stem.

I've even heard of someone increasing the diameter of the stem by welding. They built up the material over time to avoid warping the stem and then machined it down to the proper diameter.