YZ250 update Yamaha should have done years ago

Yz229
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Yz229 12/6/2018 10:14am
12/6/2018 10:14am
Would like to do comparison of my 315 Tom Morgan stroker vs ESR 325
Yz229
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Yz229 12/6/2018 3:49pm
12/6/2018 3:49pm
For sure not bolt on. But really need to modify the crankcase (too little volume) to get good power out of big bore. Tom noted about 48hp with esr and 58hp on Dyno with TMR 315, smoother and better partial throttle torque. And being plated is nice. That's why I'd like to ride them back to back.

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Zesiger 112
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Zesiger 112 12/6/2018 4:16pm
12/6/2018 4:16pm Edited Date/Time 12/6/2018 4:18pm
yamaha Is so far behind on the updates. Luckily the bike is solid from the start.
The cool thing is you can pick one up cheap, put work into it and not have to worry about something better being sold at the dealer the next year.
Also you can build something that an average joe can't go buy.
I like your oem style shroud graphics!
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psg119 12/6/2018 4:26pm
12/6/2018 4:26pm
Zesiger 112 wrote:
yamaha Is so far behind on the updates. Luckily the bike is solid from the start. The cool thing is you can pick one up cheap...
yamaha Is so far behind on the updates. Luckily the bike is solid from the start.
The cool thing is you can pick one up cheap, put work into it and not have to worry about something better being sold at the dealer the next year.
Also you can build something that an average joe can't go buy.
I like your oem style shroud graphics!
I have no clue but you can't help but think they are going to be making changes soon with how much everyone complains that they haven't done so... and with updates to all nearly all of their mx bikes this year except the 125 and 250. One can hope anyways.
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Joko 12/6/2018 5:45pm
12/6/2018 5:45pm Edited Date/Time 12/6/2018 5:48pm
Yz229 wrote:
Would like to do comparison of my 315 Tom Morgan stroker vs ESR 325
How much $ was the 315 kit? What gearing are you using? Do you know the torque output? Thanks...
Yz229
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Yz229 12/6/2018 6:47pm
12/6/2018 6:47pm Edited Date/Time 12/6/2018 6:49pm
Yz229 wrote:
Would like to do comparison of my 315 Tom Morgan stroker vs ESR 325
Joko wrote:
How much $ was the 315 kit? What gearing are you using? Do you know the torque output? Thanks...
Usually about 2.5k-2.8k, but little less then 2k since I've had Tom build a couple motors and mine was already at the right bore.

It includes engine build, blueprint of stroker, machining and mod case for stroker, decomp valve in head, porting, head mod for 100 octane, stroking and balancing crank (with FWW), and carb/reed valve flow bench porting. And of course, all new parts.

15/50 gearing for MX.
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Joko 12/6/2018 9:50pm
12/6/2018 9:50pm
That’s impressive, it pulls a tooth more on the countershaft. How’s the power spread? Top end? How’s it compare to a 450?
Underground 12/6/2018 11:07pm
12/6/2018 11:07pm
mark911 wrote:
I don't want to hijack the original OP's thread so I'll answer this one time with my rationale. If anybody want's additional information they can contact...
I don't want to hijack the original OP's thread so I'll answer this one time with my rationale. If anybody want's additional information they can contact me via email.

In my case, having owned several KTMs/WP equipped bike in the past I've managed to collect quite a collection of spare parts and some very unique items. It was therefore logical that I try and extend that collection of parts to my latest project, the YZ125.

Forks/Clamps/Front wheel/Front Brakes
I had a set of Factory only WP 52mm forks identical to those used on the 2005 KTM Factory GP bikes of Tyla Rattray and Ben Townley and National bikes of Grant Langston and Mike Brown. Owning 3 different sets of 52s from different eras I can say that these are truly unique. They were originally designed for the much lighter KTM 125 two strokes of that time and therefore have stiffness characteristics consistent with such. The cartridge/rod are almost identical to my newer 52s (and all cone valve forks) except they used a conventional shimstack midvalve combined with a tiny little basevalve. Coatings were different as well. I upgraded the cartridge's and basevalve to modern specs but retained the shimstack midvalve. The biggest external (visible) difference is the use of what I believe to be Boron Nitride Electroless Nickle plating on the lower tubes producing a matte gray finish.

Using the KTM front wheel with these forks was a logical no brainer as it was a simple "bolt-on". The Triples were another story and needed stem/bearing mods along with custom stops to use. I picked my clamps with 20mm offset. In addition, the Works forks used a different caliper mount which allowed the riders to pick from several different Brembo calipers based on personal preference. The mount I have is made for a Brembo caliper that looks similar to the current production bikes but utilizes oversized pistons and requires the upgraded Brembo master cylinder assembly.

Rear Shock/Linkage/Swingarm/Wheel
My original goal was to adapt the Yamaha to use my spare WP Trax Shocks. Not that the Trax system is superior (I've disabled mine), but I've got quite a bit of tuning data on my Trax Shocks and wanted to continue to develop them. I initially thought that by using the KTM rocker and link it would be possible. Close but not quite. The linkages were remarkably similar dimensionally, however, the Yamaha swingarm was gusseted farther forward and interfered with the WP shock. My only option was to try and adapt the KTM swingarm which required machining on both the arm and frame, different bushings/bearings, and a few custom spacers. The final kinematics of the rear linkage ended up to be a hybrid curve almost directly between the stock KTM and Yamaha, which look to be pretty similar to start with. It however, adds about 1 inch to overall wheelbase. My past YZs seemed to need a bit more front wheel weight bias so this was an unexpected benefit in my book. In addition, the rear wheel (KTM of course) required custom spacers to properly align it to the bikes centerline which produced a chainline that was a few mm too far outboard relative to the Yamaha countershaft sprocket. Luckily, there's enough spline engagement and threads to space the CS sprocket outboard by the proper amount.

One of my requirements before attempting any of this was to be able to return the bike to stock. With the exception of a few non-stock shims between the frame and stock swingarm it's all reversible!
Nice write up. Obviously training and work experience influenced a lot.
Interested though on why you went the YZ125 and all the engineering route over going the SX?
Yz229
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Yz229 12/7/2018 1:51pm
12/7/2018 1:51pm Edited Date/Time 12/7/2018 1:53pm
Joko wrote:
That’s impressive, it pulls a tooth more on the countershaft. How’s the power spread? Top end? How’s it compare to a 450?
Engine isn't completely done yet, but he did a YZ295 for me before so just the top end on 91 octane. It easily pulled 15/50. Much broader power then stock YZ250. 295 was a little less then most modern 450's but felt pretty good in comparison to my buddies 08 CRF450. Little less grunt but much more fun to ride!

To give an idea on dyno figures on his dyno.

44HP stock
49HP YZ295 w/ Vforce, FMF fatty, long silencer (bottom end volume too small for bigger top end)
58HP YZ315 stroker C12 50/50

I asked for slightly less bottom for topend/overrev so maybe close to 60HP with race gas head and porting. I run 11oz FWW, DEP pipe and R304 shorty (prob will end up going long). Riding modified 2015+ S1000RR's I seem to like soft bottoms with more top end.

Tom is working on a YZ345 now. He's been working on it for a bit but won't sell it till mid next year just for dyno testing, track testing and make sure no bugs.
mark911
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mark911 12/8/2018 6:32am
12/8/2018 6:32am
mark911 wrote:
I don't want to hijack the original OP's thread so I'll answer this one time with my rationale. If anybody want's additional information they can contact...
I don't want to hijack the original OP's thread so I'll answer this one time with my rationale. If anybody want's additional information they can contact me via email.

In my case, having owned several KTMs/WP equipped bike in the past I've managed to collect quite a collection of spare parts and some very unique items. It was therefore logical that I try and extend that collection of parts to my latest project, the YZ125.

Forks/Clamps/Front wheel/Front Brakes
I had a set of Factory only WP 52mm forks identical to those used on the 2005 KTM Factory GP bikes of Tyla Rattray and Ben Townley and National bikes of Grant Langston and Mike Brown. Owning 3 different sets of 52s from different eras I can say that these are truly unique. They were originally designed for the much lighter KTM 125 two strokes of that time and therefore have stiffness characteristics consistent with such. The cartridge/rod are almost identical to my newer 52s (and all cone valve forks) except they used a conventional shimstack midvalve combined with a tiny little basevalve. Coatings were different as well. I upgraded the cartridge's and basevalve to modern specs but retained the shimstack midvalve. The biggest external (visible) difference is the use of what I believe to be Boron Nitride Electroless Nickle plating on the lower tubes producing a matte gray finish.

Using the KTM front wheel with these forks was a logical no brainer as it was a simple "bolt-on". The Triples were another story and needed stem/bearing mods along with custom stops to use. I picked my clamps with 20mm offset. In addition, the Works forks used a different caliper mount which allowed the riders to pick from several different Brembo calipers based on personal preference. The mount I have is made for a Brembo caliper that looks similar to the current production bikes but utilizes oversized pistons and requires the upgraded Brembo master cylinder assembly.

Rear Shock/Linkage/Swingarm/Wheel
My original goal was to adapt the Yamaha to use my spare WP Trax Shocks. Not that the Trax system is superior (I've disabled mine), but I've got quite a bit of tuning data on my Trax Shocks and wanted to continue to develop them. I initially thought that by using the KTM rocker and link it would be possible. Close but not quite. The linkages were remarkably similar dimensionally, however, the Yamaha swingarm was gusseted farther forward and interfered with the WP shock. My only option was to try and adapt the KTM swingarm which required machining on both the arm and frame, different bushings/bearings, and a few custom spacers. The final kinematics of the rear linkage ended up to be a hybrid curve almost directly between the stock KTM and Yamaha, which look to be pretty similar to start with. It however, adds about 1 inch to overall wheelbase. My past YZs seemed to need a bit more front wheel weight bias so this was an unexpected benefit in my book. In addition, the rear wheel (KTM of course) required custom spacers to properly align it to the bikes centerline which produced a chainline that was a few mm too far outboard relative to the Yamaha countershaft sprocket. Luckily, there's enough spline engagement and threads to space the CS sprocket outboard by the proper amount.

One of my requirements before attempting any of this was to be able to return the bike to stock. With the exception of a few non-stock shims between the frame and stock swingarm it's all reversible!
Underground wrote:
Nice write up. Obviously training and work experience influenced a lot. Interested though on why you went the YZ125 and all the engineering route over going...
Nice write up. Obviously training and work experience influenced a lot.
Interested though on why you went the YZ125 and all the engineering route over going the SX?
That's the real key and it's called a 167cc kit! The 150SX didn't benefit too much from the 125 over bore, some say it even lost some performance (at least for MX). The YZ 125 really responds well to the slight stroke increase (compared to just a 144 kit) making for a very formidable package. I've owned other 167s and the other brands simply don't run as strong.
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