R6 swingarm on FZR

It’s done! After over a year our frame is rolling on it’s own wheels again. I finished the new suspension strut in the rear and rolled out the garage. For all of you, who are interested in such a swingarm swap/conversion i summarized the whole thing again. Beware, i assume NO warranty for your modifications! I just want to point out what is possible and how it could be done.

Comparison of the two swingarms

FZR 600 (already the pentagonal arm, Deltabox) and the R6 swingarm of the last year of manufacture with model code RJ15. It’s hard to believe, but the aluminium swingarm is not heavier, but due to the tremendous size of course much more torsionally stiff. The R6 swingarm is slightly wider, precisely wide enaugh, that it does NOT fit into the frame.

Bearing shells turned out of steel

The recesses in the middle are purely to save weight, here are the drawings: You MUST NOT forget the M32 fine pitch thread inside! The tangential cut was milled out by hand. They prove to be very useful later, when the swingarm will be assembled/disassembled. Here are the drawings and dimensions of the bearing bushes. (Sorry for quite bad drawing)

You need to work very precisely, to get the new bushings really centered. I installed the old axle and built together a small tool for scribing (on all four sides). The dimensions of course depend on the diameter of the new bushings, you can see this in the assembly drawing below.

Before milling out the old seating, the center has to be measured, since any reference point is gone then. Therefore i stretched a wire from the top down (rasp a small wetch into the frame, where the wire fits in on it’s own), exactly the same distance to the bearing bushing on each side. Afterwards measure the assembly dimensions of the new bushings.

Then, with the angle grinder (and after that by hand) mill out the old seating to the dimensions of your mark.

Caution is advised when inserting the swingarm, so that it is centered in the frame.
I spent a day measuring the FZR 600 frame and YZF R6 swingarm to determine the mounting dimensions, and to ensure the correct tire alignment in the front and rear. Now here we are going to use our artificial midplane (the steel wire in the middle) by measuring the distance to the sockets.

The sockets have the following distance:

  •      Right socket (clutch side): 127.5 mm from the center.
  •      Left socket (chain exit): 124.5 mm from the center.

ATTENTION! The drawing view is from front to rear. So you look from the steering head to the rear tire. In addition, you can also see the diameter of the sockets which are needed for the cutouts. After fitting the sockets only tack-weld them. Before welding screw/fix the swingarm with all distances. This way, the welding distortion can be minimized.

R6 2008 Body part weights

Out of some interest I put some body parts on the scale. These were fairly thin but proper fiberglass racing body parts for a R6 RJ15.

The body part weights in detail:

Base part: 982 gram
Top part: 1.430 grams
Seat, rear fender, rear lower panel: 874 grams
Tank cover: 618 grams
Total: 3,9 kg + Windshield: 263 grams

Alltogether about 4.1 kg.

Removing the kickstand

I have a problem carrying around things on the bike which i actually don’t need. This include simple things such as light, mirrors, turn signals and fuses. Furthermore we have all the generator/starter parts: alternator, starter, the thick cables, controlers and relays which are required for the alternator.

And last but not least, there’s the kickstand – after all i want to DRIVE, not park. The kickstand itself can be removed fairly quickly. On the frame trussing there is a heavy cast part which is heavy in the first place, but also takes a lot of place. These castings are often oversized on alloy frames. If a 120kg guy is leaning on his bike, several hundret kilograms of load can develop which have to be distributed over a large area.

So i cut the casting with a 60° miter on the buzz saw, then i put the frame together and tacked a squarish profiled pipe (2.5mm wall thickness) to it. Afterwards i assembled the whole frame distortion-free, fully welded it, sanded and primed it. Alltogether we saved about 470g of weight.

Some time ago, i weighed the whole frame on a rather inaccurate bathroom scale (1954 model) and it showed me about 18kg. The rear frame with it’s 5kg was already removed at the time. The FZR frame is in terms of weight reduction certainly one of the greatest problems.

In comparison, alloy bridge-head frames (CBR 600 RR) weigh about 9kg.
The deltabox-frames of previous years (YZF R1 RN01) weigh at least 11kg and the Ducati/KTM tubular steel frames are likely to level out at about 7kg. Of course the engine always acts as a supporting element here and enormously large frame structures are used to bear the load. Hopefully i can scale a few frames in the future to give some good comparisons here.

Pinion lid minimized

In real life, nobody needs the pinion lid. Nevertheless this cover acts as shifting support and without it, the thin shaft would stick out of the body quite far. Furthermore the shaft would have to stand great force. The cover also carries the mechanical release unit for the clutch. So we decided to minimize it only. Additionally we found a vibration damper below the pinion lid which we also removed.

FZR Cover with the damper under it:

Pinion lid (incl. release unit and vibration damper): 733g
Vibration damper: 121g
New weight: 493g
So in the end we saved almost 300g.

Maybe i can bring myself to construct a whole new release unit and a brace to reach 400g or less.

Inner Wheel spacer -172g unsprung mass

Inside the wheels between the bearings the inner wheel spacers are located. On older bikes (YZF 750), these spacers are made of steel. In newer models (R6 RJ15) they are alreay made of Aluminium, but theres still room for imrovement.

So we made a whole new spacer for the rear wheel and improved the one for the front wheel.

Weight Savings:

Yamaha YZF R6 RJ15 Inner Wheel spacer Original (Aluminium): 67g // new 40g  (- 27g)
Yamaha YZF 750  Inner Wheel spacer Original (steel): 233g // new 88g  (-145g)
Overall savings unsprung mass: 172g

If you convert these savings into titanium screws (break body / caliper), then this is quite a considerable amount.