Suspension
After contacting a few people on the internet that race the YZ125K, i managed to get the info i needed. Matt Wiley at Race Tech had the details of previous YZ125K customers and sent them to me for reference. The Race Tech dealer in Australia is Shock Treatment. Terry Hayes at Shock Treatment contacted me after getting an email from Matt Wiley. Terry said that when i am ready, just get the suspension to him and they will do the job.
Below is the hot suspension setup for the K based on Race Tech's experience.
1983 YAMAHA YZ125K SHOCK RIDER 175lbs & WANTS PLUSH RIDE
VINTAGE SHOCK REBUILD
SMGV 4616S
SK GOLD VALVE 4631 SHOP
KIT
SPSC B5747
SPRING SIZING COLLAR- 23
EACH
SRSP 672750
RT SHK SPR 66.9x64x267 5.0kg
KIT
SYSH 4614
SEAL HEAD 46x14x19 no t/o YAM
EACH
SSBO 144439
B/O BUMP 14x44x39L SHOWA
EACH
US1 PT
US-1 LIGHT (pt) REBUILD
PINT
LS12
83 YZ125 FORKS
FRSP 305543
RT FRK SPR 30x500mm .43kg
PAIR set @ 5mm Preload
FEGV 3801 Gold Valves
EMU VALVE SPRING 40 lb BLUE @ 3 turns
4 Bleeds Valve Plate
15wt Fork Oil @ 130mm Oil Level
I also had a quote sent through for a rebuild of both ends with all the parts i need. The quote below does not have the correct rate springs. They are all the same price. The springs are chosen based on your requirements. This is just a quote. It is in US dollars and is based on 2014 prices. This is a full rebuild and custom suspension setup for both ends complete. It is an updated system with gold valves, emulators and everything.
Below is the hot suspension setup for the K based on Race Tech's experience.
1983 YAMAHA YZ125K SHOCK RIDER 175lbs & WANTS PLUSH RIDE
VINTAGE SHOCK REBUILD
SMGV 4616S
SK GOLD VALVE 4631 SHOP
KIT
SPSC B5747
SPRING SIZING COLLAR- 23
EACH
SRSP 672750
RT SHK SPR 66.9x64x267 5.0kg
KIT
SYSH 4614
SEAL HEAD 46x14x19 no t/o YAM
EACH
SSBO 144439
B/O BUMP 14x44x39L SHOWA
EACH
US1 PT
US-1 LIGHT (pt) REBUILD
PINT
LS12
83 YZ125 FORKS
FRSP 305543
RT FRK SPR 30x500mm .43kg
PAIR set @ 5mm Preload
FEGV 3801 Gold Valves
EMU VALVE SPRING 40 lb BLUE @ 3 turns
4 Bleeds Valve Plate
15wt Fork Oil @ 130mm Oil Level
I also had a quote sent through for a rebuild of both ends with all the parts i need. The quote below does not have the correct rate springs. They are all the same price. The springs are chosen based on your requirements. This is just a quote. It is in US dollars and is based on 2014 prices. This is a full rebuild and custom suspension setup for both ends complete. It is an updated system with gold valves, emulators and everything.
The suspension has been a real pain. The original shock was in poor condition and the Race Tech representative said the body was unserviceable. This is because the shock body is aluminum and has not been hard anodized. With poor maintenance over the years, the shock body wears. I sent two more good used body's to Shock Treatment and they found one good one that just has some polishing marks in it. They sent it to the anodizers but because of the design, they would not attempt to hard anodize it. Shock Treatment are in the process of rebuilding it now to the above specs. In the future, i have the opportunity to get a new shock body made by YSS suspension in Australia.
On another note, the swingarm and linkage bearings were all stripped out, everything was cleaned up and replaced with allballsracing kits. The kits are great and fitted perfectly and contained everything including bushings, seals, bearings and special covers, caps, etc.
Finally received the suspension and set about getting it on the bike. Race Tech rear springs only come in blue. I removed the spring, rubbed it back and painted it gloss yellow. While the spring was off, i fitted new top and bottom bearings and seals.
On another note, the swingarm and linkage bearings were all stripped out, everything was cleaned up and replaced with allballsracing kits. The kits are great and fitted perfectly and contained everything including bushings, seals, bearings and special covers, caps, etc.
Finally received the suspension and set about getting it on the bike. Race Tech rear springs only come in blue. I removed the spring, rubbed it back and painted it gloss yellow. While the spring was off, i fitted new top and bottom bearings and seals.
After fitting the suspension, the initial feel from the rear was perfect. I have about 10mm of preload on the shock spring with compression and rebound adjusters set to Yamaha specs which is about 8 clicks out from stiffest for both. This gives about 30mm of static sag and an overall great feel.
The front was a different story. Initial feel was stiff with no static sag and the bike wasn't balanced. I pulled the forks apart again and found the problem area's. The emulators have a bleed plate which controls initial stiffness. They come drilled with 2 holes each. Race Tech recommends having four holes in the plate. They are 2.5mm diameter. I drilled 2 more in each plate and refitted them making sure i had 3 turns of emulator spring preload.
The next problem was that i had too much fork spring preload. I had nearly 15mm. Race Tech recommends 5mm but you can go down to 0mm. I opted for 2.5mm. This makes a big difference to initial sag and softness.
I made sure my oil height was set at 130mm again and assembled the forks and fitted them to the bike.
What a difference! Bike was balanced front to rear and i had 25mm of static sag both ends. Fork stroke was smooth and plush but with a stiffness that you know you will need for the big stuff.
The front was a different story. Initial feel was stiff with no static sag and the bike wasn't balanced. I pulled the forks apart again and found the problem area's. The emulators have a bleed plate which controls initial stiffness. They come drilled with 2 holes each. Race Tech recommends having four holes in the plate. They are 2.5mm diameter. I drilled 2 more in each plate and refitted them making sure i had 3 turns of emulator spring preload.
The next problem was that i had too much fork spring preload. I had nearly 15mm. Race Tech recommends 5mm but you can go down to 0mm. I opted for 2.5mm. This makes a big difference to initial sag and softness.
I made sure my oil height was set at 130mm again and assembled the forks and fitted them to the bike.
What a difference! Bike was balanced front to rear and i had 25mm of static sag both ends. Fork stroke was smooth and plush but with a stiffness that you know you will need for the big stuff.