#6

[Grumph]

I'd be curious to see the weight of my old one. The rear subframe alone i reckon saved about 5kg

[F5 Dave]

It's looking more and more likely that it's gonna get a pricey shock from ebay. No promises have been made yet.

I have put the standardish shock that it came with back in the chassis. I've played with the rebound damping adjustment and can detect no difference between either end of the adjustment. I left the standard dog bones in place.

I made an alloy strut to replace the shock in Greg's bike. Whatever happens I'll need a different shock for that bike as the Suzuki shock is too long to work.

I also drained the oil out of one fork and after pulling the spring and the many washers and spacer found there was an emulator in it. It looks a bit different to how I remember the Racetech gold valves I have in my twin but look to work in a similar manner. The oil needs to be changed as well as it's dirty. I'll probably dismantle the forks to check them out.

I weighed the bike as well using our bathroom scales. 39.9Kg on the front and between 46.3Kg and 44.4Kg on the rear. I made a number of measurements and for some reason got different numbers on the rear. Either way the bike weight with no fuel is between 86.2Kg and 84.3Kg so it isn't as bad as it looks. It still has the big steel tank and the rear disc could easily lose more weight, if I could be bothered.

That does sound suspiciously light. Just the wheels would be much heavier than the RS yet only 14kg heavier despite tiny alĺy tank, tiny frame forks, no linkage?

[speedpro]

Double checked with a better way of getting the bike on and off the scale. 40.1kg front, 44.5kg rear. Total of 84.6kg. I have a baggage scale which I’ll do a measurement with as well

[speedpro]

Bit the bullet. Two R6 shocks are on their way from the USA. One is an 06-07 model so should go straight in and the other is an 08-16 model which hopefully will also slip in without too much agro.
I bought 4L of kerosene this arvo to use to test the flow of the new injectors which have arrived, I'm not 100% what size the injectors are in the bike at the moment so will need to test them as well. I've borrowed an injector test setup from Rob.
I'll drain the forks and use some of the kero to flush them out before filling with fresh oil. The plan is to try 5W first and go from there. I have 5-10-15-20W in stock and it's easy enough to drain and refill the forks.

[speedpro]

Thought I'd have a chat to my mate Kev about how to measure the springs and then modify them to reduce the rate. As usual it went well off track and things got complicated fast. Also as usual, Kev had stuff lying around to make the proposed jig including a solid steel frame already welded up. He also pulled a couple of struts out of the neighbour's bin which have useful long threaded portions for adjusting the jig for different length springs. On top of that there are also a couple of springs with the same 62mm ID which are possibly a bit softer than the current FZR spring fitted to the GSXR shock. The lengths seem close or slightly shorter so I'm gonna give them a go at the start anyway. Be a fluke if the springs out of the bin are good to use. They are Blitz brand. Not sure of the relevence of the numbers.

[speedpro]

Shit just happens sometimes. I read somewhere that the stock FZR spring rate is something like 8.1Kg/mm and the 600 spring is 8.3-4Kg/mm. Given the light weight of the MB/FZR I thought I might try something like 7kg/mm. One of the springs I have out of the bin has the numbers 62.200.007 on it. The .007 at the end stands for 7kg/mm.

[speedpro]

Correction. FZR spring rate is supposedly 9.2kg/mm and R6 spring rate 9.8kg/mm

[speedpro]

I had an idea of fitting a 200mm 5kg/mm spring to the FZR(?) shock in the MB/FZR. It can be done but it got harder and harder the more I looked at it. In the end it wasn't worth doing with the R6 shocks on their way. The original spring on the shock is about 275mm long.

I've had a thought about testing the springs. All I need is a platform, either a bit of wood or steel/alloy with a hole through the middle. Sit the spring on the platform with something on top to tie a bit of string to. Put a baggage scale on the end of the string and add weight until the spring is compressed a set amount as measured with a DTI. Weight/mm compressed is the value I'm looking for. So easy.

I used an old trick to compress the spring enough to get it off the shock. I turned preload to maximum and put hoseclips around 3 coils of spring, spaced out around the spring, then tightened each hoseclip in turn until the spring was compressed enough to remove the collets. I left the spring on the shock while I released the hoseclips in the reverse of doing them up. I also looped a tiedown around the spring and the vice so if it did decide to jump up it wasn't going anywhere.

[speedpro]

Spring rate testing jig made and used. Very simple and worked perfectly. I used one of the Blitz threaded collars with a bit of alloy on top. A loop of lockwire went around a 6mm bolt, down through the alloy bit, through the spring and a hole in the bit of wood, to the baggage scale, which had a 20kg bucket of concrete hanging off it.
Without the bucket of concrete I setup the dti for 5mm of compression. I then hung the bucket on the scale which resulted in the spring being compressed an amount which I read off the dti. Simple math gives the spring rate.

[speedpro]

DTI reading with a 5kg/mm spring. In a perfect world it would read 4mm less than the start of 5mm. Actual measurement change is 4.3mm.

[speedpro]

Measurement of the 7kg/mm spring and the spring off the 600 shock. The DTI has moved more or less 3mm for both springs which is correct for a 7kg/mm spring with a 20kg load

[F5 Dave]

All good garage math. I just put a scale on the press and compressed the spring. 20mm made it more accurate I seem to recall.

[TZ350]

.
Team ESE sat their springs on a set of bathroom scales. Then used the press to compress the spring. Recording the scale reading and compressed length as we went.

[F5 Dave]

Yeah better explanation of what I did.

[speedpro]

I've been checking weights, spring rates, and linkage ratio. I'm not sure what it all means yet but it is quite interesting how the linkage ratio ramps up quickly from fully extended over the first 5mm of wheel travel and then increases a small amount over the rest of the travel, see the attached image. The final ratio measured at 90mm of wheel travel was 2.46:1. The first column, turns, is the turns of a nut on a piece of 8X1.25 threaded rod used to lift the wheel. I also made a tool to bolt in to replace the shock which I attached my digital calipers to which measured the amount the shock would be compressed as the wheel was lifted. The results tie up with what I feel. The initial travel is very soft but firms up quickly. In my opinion the R6 spring is way too hard. The stock FZR spring may also be too hard. I think a spring rate needs to be chosen for the middle area of the stroke where the ratio is approx. 2.60:1. I'm sure there's more to it, but with my son on the MB100 powered bike the weight on the rear wheel is 80kg. 80X2.6=208kg on the shock spring. With an 8kg/mm spring it would compress only 26mm. With a 7kg/mm spring it would compress 29.7mm. With a 6kg/mm spring it would compress 34.66mm, and with a 5kg/mm spring it will compress 41.6mm which is getting close to mid travel. If installed with say 5mm of preload the 5kg/mm spring would be compressed as if by 25kg and the travel would be decreased by a similar amount for any particular load, theoretically. I have 5kg/mm and 7kg/mm springs which could be used. They both need to be shortened and adaptors made so I'll give them a try. Probably the 7kg spring first.