Yam RD "Blue Dream"- Ride,Maintain,Tune

[TranceMachineVienna]

Ryan
If the the plastic shims are increasing your spring pre-load then the forks will be stiffer. Suggest you first remove the shims and see how much improvement you get. Do you know the thickness of the shims? 5 or 10mm does makes a difference.

I thought so,but back then I had no idea :-)

To be honest I think It was more like 2-3cm :-)!!!

Ill dig out my docu pics.

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[XS750AU]

20 to 30 mm is a big adjustment if they were standard springs. They are not shims they spacers!!!!!!
Have a look at the pre-load adjustment on your XS750. The max adjustment is about 15 mm!!

[TranceMachineVienna]

20 to 30 mm is a big adjustment if they were standard springs. They are not shims they spacers!!!!!!
Have a look at the pre-load adjustment on your XS750. The max adjustment is about 15 mm!!

Found these pics on my documentation...look how big these spacers are!I have to check if the workshop that reassembled put them back in...

That will explain the massive stiffness on the front :-)

[XS750AU]

The good news is that you have progressive springs. You need to check the slack length of springs to the factory spec. If the springs are to spec then the spacers (look more like 40mm) are just taking away the soft rate and putting straight onto a preloaded heavy rate.
You might want to be very careful when you pull the caps off, they will fly with so much preload. 

[crazypj]

Couple of things no one seems to be aware of?
1. Yamaha used progressively wound springs stock.
 Progressive manufacturer springs look and feel exactly the same as stock springs in my experience (yes, I bought Progressive springs and wondered why I bothered)
2. The Rickman brothers did a lot of testing with different swing arm bearings. As pointed out, needle roller have a high rotational speed. As swing arm doesn't fully rotate, they found bronze bearings actually worked better as they are supporting pivot point over a greater area, giving better handling.
 If your bike doesn't have a grease nipple, check best position before removal then drill and tap swing arm for one

[CrabsAndCylinders]

"2. The Rickman brothers did a lot of testing with different swing arm bearings. As pointed out, needle roller have a high rotational speed. As swing arm doesn't fully rotate, they found bronze bearings actually worked better as they are supporting pivot point over a greater area, giving better handling."

This is a very interesting point, especially in light of the facts that rollers are more expensive and the better handling bikes tend to come equipped with them, maybe it is a marketing thing.   

[der_nanno]

To comment on the above:

1) Progressive springs (if dialed in correctly for your weight, i.e. right amount and viscosity of the oil are important as well) are totally worth it. With those spacers I am inclined to say, your forks aren't moving much at all any more? I've put in a 10mm spacer in my SR500-sidecar-forks to compensate and they always were too stiff, so with the spacers you run...
2) Totally agree with the bronze bushings. Did the same about ten years ago on my XT500 and they are the dog's danglies.
3) Have you checked the number on your Konis? I seem to recall that they weren't originally meant for a RD?

[jpmobius]

My 2 cents:  Those look like stock springs.  Roller elements in the swing arm pivot are silly from an engineering perspective (unless tapered and so with adjustable lash).  Absolutely zero lash both axially and radially in this pivot is important and noticeable!!!!  (and easily had with plain bearings, shims, and a dedicated technician.)  Koni shocks were the cat's meow back in the day (I still have them on one of my drivers) but likely they are a bit long in the tooth now without a rebuild.  Considering springs and preload:  Sit on your bike.  Have someone hold it up vertical so you don't fall over and bounce it up and down a bit to see where the ride height is.  If it tends to stick and not move easily, figure out why before you blame the springs or damping.  Take off any fork brace or fender, and loosen the axle pinch bolts and axle nut and try again for example.  This is commonly assembled incorrectly causing the suspension to bind.  The suspension should be maybe 25% to 35% compressed from topped out.  This should hold forth regardless of how you like to ride, or how stiff you like the suspension.  ON OLD BIKES, MOST PEOPLE LIKE STIFFER SUSPENSION ONLY BECAUSE THE DAMPING SUCKS!  If you get good damping, your bike will likely be safer and be able to be ridden faster with a "softer" suspension.  Compliance in your suspension is at least as important as the spring rate and damping situation, so get everything to work well mechanically first.  A lot depends on the springiness in the frame (or lack thereof), so it is complicated!   In the main, you can't do anything about it so all the more reason to not overwhelm the chassis with overly stiff springs, damping or mechanical binding!

[crazypj]

Mr. Carlos, it's a shame I don't have my little piston-port MZ* anymore. I would have loved to give you a ride on that one, instantly killing your complains.

On a serious note, you may simply want to reconsider your riding mode - one of the things I had to work very, very hard on on the racetrack: On a two-stroke you have to step the gears down until you hit the power-band. Dare to hazard a guess, why I ride a big, tuned V-twin as my daily? 

*It was tuned for high-rpm, following the MZRC-tuning guide

I  liked the MZ250's, based on 1965 ISDT motor.
 Around 1978 I was working at Honda/Yamaha/MZ dealers.
At the Pau-San Sebasian-Pau rally/race the shop owner had class wins multiple times on MZ250  (Haydn Reese, I think around 1979~83?) I think one year he took a SILK 600 though (engine based on Scott water cooled two-stroke from 1930's)
 After 500 mile 'service' (including new main bearings and seals  and sometimes big end/con-rod replacement ) they were actually pretty quick (100mph on a stock bike) plus didn't handle too bad all things considered.  It was great fun pissing off the 'RD crowd' during road tests (although the MZ customers were often upset that exhaust had turned 'pretty colours' from the heat  )