Hybrid project

[Gerrit]

I will be using a 4TW TZ250 fairing, which has two separate intakes for the two airboxes. The RH cylinder gets its air from an intake in the upper fairing's RH leading edge, the intake for the LH cylinder is next to the front number plate area on the LH side. I will be using the LH intake with a 4TW LH air duct:



The stub has an OD of about 50 mm which is a bit marginal for two 35 mm PWKs so it will be replaced with a length of 55 mm OD or 60 mm OD carbon fibre tubing. The duct may require some further alteration but this will be determined when the chassis is assembled and the upper fairing half fitted.

[Gerrit]

Minor update: I received a length of 40 mm OD titanium bar which will be used to make a steering stem nut. I'm waiting for the delivery of a 28mm OD x 300 mm piece, this will be used for a steering stem. Total calculated weight saving will be about 230 g.

[Gerrit]

As Jarno has started to weigh all components of his project, I've decided to do a bit of my own weighing. The main frame (KR-1 based) weighs 8.71 kg, the cut off rear subframe 2.4 kg. This gives a total of 11.11 kg, which is practically the same as Jarno's bare KR-1S frame. This should answer the question whether there is any difference in frame weights: none. Admittedly I've added some brackets and removed others, but this should have no effect on the outcome.

[KR-1R]

longshots..


https://titanclassics.com/?s=stem+nut&post_type=product

see what others they do. might save



have you got a dimensional drawing of the swingarm tube - might inspire some manufacture

[Gerrit]

I've found a titanium steering stem nut for the vj22 Suzuki RGV, but not for the KR-1(S). In general there are very few KR-specific goodies available, unlike for TZR and RGV, so making one-offs is the only alternative. Some of the stuff Beet made would be nice, but unfortunately No Longer Available.
If you are interested I can send you a drawing of the swingarm sleeve.

[Gerrit]

I obtained a brand-new 35-tooth 1st gear for the output shaft from Mark Jordan (thanks, Mark!) which alters the ratio from 2.533 (38/15) to 2.333 (35/15) and closes the gap between 1st and 2nd gear.



The gear was made by Ellis Moore but unfortunately he seems to be out of business,his website disappeared a few years ago.

[Gerrit]

Front brake calipers will be Nissins rather thanTokicos. I will be using vj22 RGV fork legs and the Nissins are a bolt-on replacement. Furthermore they are better than the Tokicos according to the knowledgeable folk at the RGV forum.
I got a pair of used calipers for about 30 pounds each:



They will require a full service plus repainting, so I first pumped out the pistons as faras they would go:



Both calipers stripped:



All the seals will be replaced with new ones. The pistons are still serviceable, but will be replaced with titanium pistons. Titanium doesn't rust, is lighter than steel and has a poor heat conductivity. I looked at Yamaha TZ250 pistons which are aluminium and offer even more weight reduction, but although still available they cost over 100 pounds each- EEK! A set of four titanium pistons is 80 pounds so the choice was easy. The steel Allen bolts will also be replaced with titanium items. Estimated weight saving is about 0.3 kg forthe two calipers, which is of course unsprung weight.

[Gerrit]

Five of the eight cylinder base studs could be removed, but the remaining three wouldn't budge despite my best efforts:



To aid in removal I obtained lengths of 4 mm ID/8 mm OD, 6 mm ID/8 mm OD and 8 mm ID/12 mm OD steel hydraulic tube, which I used to make drill guides for a 4 mm drill:



These will be used to drill through the studs lengthwise:



As a 4 mm drill was a sloppy fit I obtained a 4.1 mm drill. Now to drill through all three studs. The second stage will be to use 6 mm ID/8 mm OD tube with 8mm ID/12 mm OD tube to make drill guides for a 6mm (nominal) drill. This, if all goes well, will leave a thin-walled stud which can be removed without damaging the threads in the crankcases.

[JanBros]

I will be using vj22 RGV fork legs

reconsider these.
they are very old-school , don't work very well (they certainly ain't an upgrade to KR forks) and heavy. any modern fork is superior.

I've got a ZX6 2004 fork in mine. the suspension works sooooooo much better, they weigh less and the radial calipers are superior. They are so good you could use the 280mm discs (I uses 300) and still have superior brakes and again save weight !

[Gerrit]

Jan, my RGV legs have White Power internals so they should be better than standard legs. Furthermore, I want to use as few four-stroke parts as possible.
Weightwise, have you weighed both the RGV and ZX6 legs? The only real advantage the ZX legs have is adjustable compression and rebound damping and while it isn't possible to add compression damping adjustment to the RGV fork legs, adding adjustable rebound damping may be a different matter. This is being looked into. And how often do we fiddle with the damping and preload settings once oil viscosity and quantity plus spring preload have been set to our satisfaction anyway?
Re the brakes, Luders uses 280 mm discs on his final race bike project with old-school axial calipers and I haven't heard him complain that his bike is underbraked. 4DP and 4TW TZ250s use 300 mm discs by the way, plus axial Nissins. I haven't checked what 5KE TZs use, and haven't definitely decided on the front disc size yet.

[Coose]

TZs use cast iron discs as standard too, where my '94 had the best brakes I have every had the pleasure to use. So much feel, and they'd chuck you over the bars if you were cack-handed...

[JanBros]

the thickness of the steel inner tubes has come down a lot since RGV/ZXR days, so there is a significant loss in weight.

the brakes : I never complained either about stock KR brakes, and they still do what they are supposed to do.
but when you have ridden modern radial brakes, you understand the difference, and it is huge. You can brake as hard with one finger with the radials, leaving more on the handlebar to feel what the front is doing. the harder you have to squeeze (with "old brakes"), the less you feel. and because your feeling is much better, you can brake harder and closer to the limit.

at the time, I didn't complain either about the standard brakes on my Z650 (single disc !), simply becase I didn't know any better. Now I know they were not brakes, only "slowing down devices". I wouldn't dare to go out these days on a Z650 and do with it what I used to do

I never go back to "old" brakes again.

[Gerrit]

Another advantage of the RGV fork legs is that they are the same length from axle centreline to top of the fork leg as the KR-1S fork leg, i.e. 722 mm. ZX legs may be longer, which would add weight and thus reduce any weight advantage, if any, over the RGV legs.
Reduced wall thickness of the stanchion tube will reduce weight, but also stiffness, assuming the same OD. Anyway, without actually weighing the individual parts we won't be able to compare directly.

[JanBros]

ZX6 2004 is 725mm long from center to top.
just put them on a scale :
one comple leg with noting mounted on it weighs 3.6kg
as a comparison, a ZXR400H leg weighs 4.8kg

stiffness ? if it's good enough for a much faster bike, it's the least of my worries.

you are doing every effort to save a few 100 grams here and there, but you would discard a potential gain of 2.4kg just from the fork legs with the benefit of much better suspension and brakes because it's not from a 2-stroke ?

each his own choice off course

[Coose]

Wow, that's actually quite a difference. It'd be interesting to know how much of the 1.2kg saving per leg is unsprung weight.

I'm not going to dissassemble them to find out

but I'd say most of it. modern legs are so much easier to straighten after they've bend.