Suspension Grafting

Grafting F2/ZX6/FZR4 Suspension Bits onto an EX5

This page relates some of my experiences grafting ZX6 and FZR swingarms onto EX500 frames, as well as the prints for captive spacers to mount an F2 rear wheel in the ZX swingarm, and some pictures of my F2 rear wheel in a ZX6 swinger, on an EX5. I hope it saves someone from some of my mistakes. As always, advice is worth what you pay for it (or less) so be prepared for new and exciting problems of your own if you try this. No guarantees or warantees (expressed or implied) are made with this information, use it at your own risk, and all that, eh?

JULY 2000 free advice: A few people have contacted me to say they were getting into racing and had heard that they should do this modification, and how much did it cost? My answer is DON'T BOTHER! Race the snot outta your current platform with the best tires you can get, then buy a bike which can wear race-tires when you've reached their traction limits (An SV650 would be my first choice). The hassles of building/assembling a bike complicate matters more than they help for the first couple years. With regard to price: complete F2/F3 front ends will cost something like $500 to $700; forks are $250, wheels are $150 each, swingarms are $75 to $200 depending on what bike it is, 520/F2 sprockets cost $45 and must be ordered from a race-shop (the local guys probably won't know how to order the funky non-stock sizes you want), don't forget axles, bars, brake systems, etc. If you want to make your own spacers and solid-mounts, and machine your own cush drive, then you will need a lathe. The cost of which varies depending on what you want to do. My little combo-unit from China cost $600, with another $600 or so invested in tooling. A welder will be necessary if you want to make frame mods and such on-the-fly ($350 with AR-CO2 bottle). I am glad I did it, but not for the quality of the bike, simply for the machining and welding fun. In many ways I would have been better off to just buy an SV, and leave my garage space alone. Hello, my name is Wade. I am an EX-parts junkie and engineer-nerd. (grin). With those caveats and warnings, on to the project.

SWINGARMS
Despite the wise suggestion of some learned folks (particularly Andre at Outrace) that I might want to use an FZR400 swingarm, I took the advice of others and went with ZX6 hardware, as it was handy at the time. Having been-there-done-that with all three swingarms, now, I'd endorse the FZR400 first, the '86 ZX6 second, and don't bother with the '89 ZX6. Of course, since I had two 88-89 ZX6 swingers, I figured I'd be a smart fella and use them, so that I'd have a spare. I didn't understand that they were so different. What a hassle. Good judgement comes from experience, which tends to come from bad judgement, right?. See below for a brief discussion of bushings vs. needle bearings in swingarms.

FZR swingarms
The 1990 FZR400 had a killer-appearing aluminum deltabox swingarm. The critical dimensions for this and the 88-89 FZR400 swingers are the same, I'm told, but one fellow from the FZR list advised me that the deltabox is heavier than the earlier models, and that many racers who have '90 FZR4's replace their swingers with 88-89 units. He also advised that the internal adjusters on the '90 tended to freeze up, which could be a hassle. I bought what was reportedly an '89 FZR 400 swingarm. Installing it in an EX frame required two things: (1) drilling the frame to accomodate the 16mm pivot bolt and (2) about 40 minutes with a hand file and die grinder to take a smidge off the inside of the frame mounting bosses. What a joy. I wish I did this in the first place. The axle-notches in this swingarm are about 3/8 of an inch closer to the pivot point than the ZX6 swingarms, so this can provide slightly faster steering. I have also been told that the contemporary FZR600 swingers are the same as the 400's, except that they offer about 1" more adjustability than the 400's, allowing a longer wheelbase, for a more stable bike.

ZX6 swingarms in general
The 86 is different from the 88-89 models. They can be distinguished by looking at the ends: the 86 has a radiused section between the top surface of end plate and the rear surface, it's kind of rounded-looking; while the 88-89 model has three flat sides on the end-section and is very angular. They are both designed to use 17mm axles and traditional external adjusters.

One amusing (sort of) thing I noticed while playing with two ZX6 swingarms in my office was that one of them made swishing sounds when I moved it around. At first I thought I must be dreaming, but no. There's water inside one of them. It doesn't leak out, and I don't see a hole, so I'm not sure how it got in there, but in there it is. Upon further inspection I noticed that the sides of this one were bowed out slightly, in contrast to the very flat sides on the non-swishing swingarm. I'm guessing it sat in a puddle, filled with water through a very small leak, and was frozen solid at some point. (This is New Hampshire, after all).

'86 ZX6 swingarms

[UPDATE 27JAN00: I wrote this section before I took an '86 swingarm off a bike myself. I was surprised to find a set of end-caps at the pivot area that were NOT present on any of the other three early ZX6 swingarms which had graced my garage. These endcaps had center holes just large enough to accomodate the axle, so the collar pins them against the inside of the frame, and the swingarm pivots *inside* them, which explains the marks on the early-model ZX swingarms in this area. The endcaps have lips which wrap around the pivot area's outer diameter, acting as a dust seal for the bearings, thus replacing the inner-diameter dust seal found on the later model (shown below). Including these endcaps in the installation would be a good idea, but will require significant additional grinding of the frame bosses (less desirable), or cutting of the swinger pivot tube area, as described below for the 89 model, which was a modest p.i.t.a. This new discovery leads me to say that this swap is only marginally better than the '89 by virtue of the collar diameter]

I don't know for sure, but rumor has it that the '87 ZX6 swingarm was the same as the '86. The '86 requires you nip off about a millimeter of material either from inside the EX frame or off the ends of the swingarm. I'd suggest filing down the frame, and leaving the swingarm the hell alone (see below for the basis for this comment). The 86 also has a 14mm pivot bolt, which allows the use of the stock EX pivot bolt, which is very convenient and nice looking. This means that you won't *have* to remove the needle bearings and replace the center collar if they are in good condition. Remember that this collar acts as the inner race for the needle bearings, so it needs to be in good condition. NOTE: all the swingarms I got from the salvage yard desperately needed new bearings and collars as a result of the corrosion and dirt they picked up while being stored uncovered outside in a swamp after removal from their original frames. This would be less of a problem if you buy a swinger from someone who is taking it off his frame just for you, as these areas would have been protected. The FZR swinger I bought privately this way was in great condition.

'88-89 ZX6 swingarms
The 88 & 89 ZX6 swingarms are identical, if the two I bought were correctly labelled. The pivot bolt is a 17mm, so you either have to make some sort of bushing or drill out the EX frame to accomodate a 17mm bolt. The 17mm EX rear axle will do this job, but it will poke out one side about a half inch (one cm for you metric-ites) and you'll have to machine the bolt-head flange down a bit to get it to fit inside the frame recess. A 43/64" bit does an ok job of providing a clearance-fit hole if you don't happen to have a 17mm drill bit.

I'd suggest that you start by cutting the pivot bolt collar so that it just barely fits in place in the frame. You want a good tight fit here. You may have to buy a new collar (for about $37). I was able to salvage one of the two I had by cutting the rusty-nasty end off in this process. I had to take about 8 or 10mm off the overall length.

Now cut the pivot area of the swingarm down equally on both sides so that you can fit it into the frame. The '88-'89 pivot area is much longer than the '86's, and so requires the removal of about 9mm of material (as opposed to the little filing job required for the 86's). The proper length for the pivot area will be about 1mm shorter than the collar, in order to fit the bearing-seals on the ends.

I'd suggest cutting the ends a bit long, and filing them down slowly to get to the right length to allow the swingarm to move freely without lash between the frame rails. Test the length by installing the collar and bearing seals, and putting the swingarm in the frame and torquing the pivot bolt down. Keep filing down the high spots on the swingarm until it just moves freely when installed.
swingarm pivot

Leaving the old needle bearings in the swingarm while you cut it to length allows you to verify that you've actually made a square cut on the end by measuring the depth of the lip from the bearing race to your new edge (The value of a decent set of verniers can not be overlooked for jobs like this). Making a square cut sounds easy, but may be quite tricky with most of the tools non-machinists have available. I used a cut-off wheel mounted on a radial-arm saw. Watch out for the sparks and fire (radial arm saws often have sawdust packed in the legs of the stand, etc...). This process will generate a bunch of little aluminum chips and bits that will pretty much ruin whatever bearing is in there, so I'd plan on buying new needle bearings.

Then pull the needle bearings out of the swingarm. The first step is to use a puller to rip out the needles and their cage (I have a slide-hammer that did the job, but required lots of elbow grease. Eventually I broke the outer lip off the outer race, which allowed the needles and their cage past). Next use a Dremel-tool or die-grinder to grind a notch out of the race, making it look like a C instead of an O. Be gentle as you approach the end, so that you don't gouge the dickens out the aluminum swingarm boss when you cut through. As soon as you get it cut through, the race pops right out. I spent about an hour figuring out how to attack this, then another two hours or so actually ripping out the four bearings.

Then clean everything up, and install new needle bearings. Smoothly press them in (I used spacers and the pivot bolt with a big wrench as a press) far enough to install the bearing seals. Grease the bearings and insert the collar, making sure the bearing seals are not bunched up, slide the whole thing into the frame, and pop a bolt in there.

INSTALLING THE F2 WHEEL
The salvage yard where I bought the swingers and stuff had a box full of unlabelled axles which had come from bikes being disassembled. I was allowed to paw around and take from it what I wanted. I took several axles to try out, and several spacers. I used some of these spacers as raw material to fabricate the captive spacers in my F2 rear wheel. They fill the wheel's 20mm centerhole, and allow the use of a 17mm axle, which is what the ZX6 swingarms are designed to hold (so I didn't have to bore out the notches to 20mm, though I've heard lots of people do just that, and have no problem). I borrowed heavily from Todd Bates' spacer design (below) but I had to modify them to suit my funky brake caliper carrier, which I fabricated out of 1/4" aluminum plate. I originally used a front EX-500 caliper, and the stock ZX6 caliper-brace, and drilled a 43/64" hole for the 17mm axle I used.

Later, I acquired a front caliper off a DR350 (?) dirt bike in the junk yard, which I cleaned up enough to make work. I had to mill off some of the friction material to fit it around the F2 rear disk, but it works. I mocked up the caliper carrier with 1/4" thick panelling, then transfered that design to aluminum plate. Currently, an ugly bar made of flat-stock acts as the caliper brace, since I couldn't make the nice aluminum ZX part line up properly.

CAPTIVE SPACERS
The following box contains information provided by Todd Bates (tbates2@juno.com), with my comments in green. Basically this provides a means of centering a 17mm axle in a 20mm hole.

WRITTEN BY TODD BATES, WERA #192(n)
I will keep this basic, for all different experience levels of responders. I am just completing my f-2/zx600 conversion and do not claim to be the source for higher moto-knowledge, so use your own judgement for this. This is what worked good for me.

"Captive spacers" mean spacers that stay with the wheel. You do not have to hold them in place with your third hand while inserting the axle. This is done by keeping the f-2 rear wheel stock, and using the smaller diameter ZX600 rear axle. Two spacers stick inside of the wheel, and the third is loctited into the hole in the rear caliper carrier. You can then just hold up the wheel and put the axle in the swingarm! You will have to cut down the top plate on the swingarm (where your wheel fits in) to fit in your tire. I did this with a disc grinder and a file. My D207 160 is about 6.75" wide, so I took the swingarm to 7.25". This could also be done with a hacksaw or a mill. This does not go into the weld so it shouldn't affect the strength of the swingarm [NOTE: Reducing the gussetting will reduce the arm's stiffness slightly, but it will only be a minor effect, since the front and rear of the swingarm are fairly well constrained. I wouldn't worry about it. -Wade]

I think the best material to make them out of is stainless steel. Most small time machine shops (myself included) do not have this on hand, so I used "stress-proof" steel, c.r.s. would also work fine. I would not recommend aluminum because the thin wall would be weak.[recall though, that this component should be trapped between a fixed axle and a fixed center tube, with no rotating contact points. It shouldn't need to be very strong...Just strong enough to prevent it from mushing out under the compression of torquing the axle nut...My point being that I think aluminum might work, but watch it carefully if you try it.-Wade] [JULY2000 NOTE: I used aluminum for my bike, and after 3 hours of race-pace over three weekends, there is no visible spacer deformation. I will use aluminum for this application on my bike from now on. -W] Good stainless will not rust, but stress proof and c.r.s. will. If everything is coated with grease at assembly this should not be a problem

If you are going to hire this out, the prints should be easily understood by any competent machinist/toolmaker. They will thank you if you take the axle in so they can be sure of the size. What we want is a "slip-fit." Our Japanese friends build awesome bikes, but their reputation for exacting tolerances is kind of over-rated [I concur with this.-W] I've seen a fair amount of variance in parts. The bearings in the wheels do not vary much at all, so this is not a problem. What we want here is a "snug slip-fit." Meaning you can slide it in my hand, but without excessive "slop." [NOTE: I'd suggest bringing the whole wheel in to the machine shop, so that they can test assemble it. -W]

BUSHINGS OR BEARINGS
The consensus on the chassis design list is that bushings are better than needle bearings for swingarms. As an engineer, I'd say that bushings' ability to swallow dirt chunks without damage would make this probably true. They should also be quieter than the needle bearings, but that's not usually an issue on racebikes, eh? Hoyt McKagen (batwings@usit.net) is one person who will fabricate such bushings for you, if you are so inclined. He charges approx $125, inner sleeves cost an extra $25, $175 for fork bushings. Never tried his stuff myself, but there it is.

If I had the swingarm swap to do over, I would not have simply over-drilled the swingarm holes. My inexperience as a machinist showed pretty clearly there, eh? Well, anyway, a better method which would produce much tighter tolerances would be to drill the frame out to a few thousands UNDER size, then ream them with the correct reamer. A cheap alternative to buying just the right reamer would be to again start with the holes a few thou undersized. Turn a 14-inch (give or take) piece of brass until it'll just slide through the holes on each side of the swingarm. Turn about an inch of one end to 3/8ths (so it fits in your hand-drill chuck) and slit the other end for about four inches. Chuck it up in that hand drill, stick it through the bearings, and coat the end of the lap with fine valve grinding compound (fill the slit, too). Fire up the drill, working the end back and forth through the far hole - the near hole will keep the lap aligned while you grind the far hole. Once it moves freely, take a very slightly tapered piece of metal and tap it into the end of the slit to open up the end of the lap a bit, add more grinding compound. Repeat as necessary. Frequently remove the lap and wipe the holes out to test the fit, until your pivot bolt JUST fits. Leave a few inches worth of over-sized shoulder near the drill-end so that when you turn the frame around, you can match the diameter of the lap-guide area with the newly-reamed out hole size while working on the second hole.

It should take less than an hour to do a swingarm. The big advantage here is that there's no planning necessary beyond having brass on hand - no need to have the right size reamer. Plus, when a reamer goes dull you have a dull reamer, but once the lap is worn too much you can turn it down for smaller holes and bearings, and at the very least you have a drift.

The same method can be used to fine-tune home-made bearings. Rumor has it that generic bearing bronze works well for the bearings: it's hard enough that it doesn't appear to have any problems with the abrasive getting embedded in it, but the softer brass lap sure does. Sintered bronze may not work as well for this type modification.

FIXING THE CUSH DRIVE
In order to get the F2-rear wheel sprocket lined up with the EX500 motor output (countershaft) sprocket, one must machine down the sprocket-mounting face on the F2 cush-drive. Before you can do that, you have to remove the studs. These are held in place with some modest threadlocker. I'd suggest torch-er-ing the studs one at a time for 3 to 5 minutes with a propane torch. As an aside, I simply love my electric-lighting torch head!

Then hold the cush stationary (I used a pry bar between the cush-drive lugs) and twist the stud *real* hard. I found that Sears "robo-grip" and vice-grips were not suited for the job, as a result of interference in their rotation by portions of the cush drive. A set of medium channel locks did the trick. I mangled the studs getting them out, but since I don't plan to reuse them, it's not an issue. I have heard that if one uses a narrow set of vice-grips they can be removed without damaging the threads. Remember, everything is *real* hot now!

Here's the stud-bare cush drive.

With some advice from Andre, I was able to mount the cush on my lathe and mill the face down the 7mm it seems is necessary to get the sprockets lined up. Very cool. I love making chips. Various sources have suggested that as little as 4mm might be necessary. YMMV, check your installation yourself, ok? The bolts required to replace the studs are M12-1.25 x 25mm.

-------------a colorful spacer bar-----------

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Last modified on 30JULY2000