Rocky Mountain Powerplay crank length

Rocky Mountain Powerplay bikes come with a mix of 170mm and 165mm crank lengths. Given their relatively low bottom bracket, the 170mm cranks results in frequent pedal strikes. The 165mm cranks are better, but I still had too many pedals strikes with them. Because the one-way chainring spider on the Powerplay requires a Cinch to connect to the crankarm, the crank alternatives are limited to Race Face or North Shore Billet. There are several options to reduce the crank lengths under 165mm.

Race Face 160mm:

Race Face recently released their Turbine crankset in 160mm, which are probably sufficient for most riders. It's both the cheapest and easiest way to do to a shorter crank. The cranks are $180-200 new:

https://www.raceface.com/products/turbine-crankset

If your stock crankset is a 24mm spindle you'll also need need to buy the 30mm spider lock ring (part #1347006) from Rocky Mountain ($40-50), along with a press fit BB92 30mm bottom bracket. The Race Face Double Row Cinch 30mm is my recommendation at $85:

https://www.raceface.com/products/bb92-double-row-cinch-30mm

In addition, if your stock crankset is 24mm, you'll need the Race Face 149.5mm spindle kit:

https://www.raceface.com/products/spindle-kit-cinch-149-5mm

North Shore Billet 145mm, 155mm:

If you want to go shorter than 160mm, the easiest solution, though the most expensive, are the Powerplay cranks from North Shore Billet in 145mm and 155mm lengths for $535: 

https://northshorebillet.com/products/talon-crankset-rocky-mountain-powerplays 

They're a direct upgrade. If your stock crankset is a 24mm spindle you'll also need need to buy the 30mm spider lock ring (part #1347006) from Rocky Mountain ($40-50), along with a press fit BB92 30mm bottom bracket. The Race Face Doubel Row Cinch 30mm is my recommendation at $85: https://www.raceface.com/products/bb92-double-row-cinch-30mm

Race Face Atlas 155mm:

A less expensive, but more difficult alternative is re-drilling Race Face 175mm Atlas crank arms to a 155mm. This can be done because the Atlas cranks aren't hollow, and the back side ribs don't extend very far, leaving a lot of aluminum around the new pedal hole. New Atlas cranks can be had new for $180, but can be found used for about $100:
https://www.raceface.com/products/bb92-double-row-cinch-30mm

Like before, if your stock crankset is a 24mm spindle you'll also need need to buy the 30mm spider lock ring (part #1347006) from Rocky Mountain ($40-50), along with a press fit BB92 30mm bottom bracket. The Race Face Doubel Row Cinch 30mm is my recommendation at $85:

https://www.raceface.com/products/bb92-double-row-cinch-30mm

The Atlas cranks will also need the 151.5mm RD151DH spindle, if it doesn't already come with the crank arms:

https://www.raceface.com/products/spindle-kit-cinch-151-5mm-rf151dh

Although the cranks can be run like this, I recommend added Race Face crank boots to make it look better for the nominal cost of $12:
https://www.amazon.com/dp/B00JNAK4OU

You'll need the following tools:

• Mill or drill press
• 1/2" drill bit
• 9/16-20 tap - left and right hand
• 13/16" end mill
• Dremel or angle grinder

You need to mark and center punch the location of the new hole on the back of the crankarms, 20mm up from the existing holes.

Then they need to be drilled with a 1/2" bit. This can be done using a drill press or a mill. It is not recommended to try and do it free hand. I found it easiest to fixture the crank arm upside down, though there are multiple way to accomplish this.

After drilling the new hole, flip the crank arm over and use an end mill to flatten the area around the new pedal hole to give a flat surface for the pedal to seat against. I used a 13/16" end mill. Since this is a drilling operation and not a milling operation, a drill press should be safe to use.

The new holes now need to be tapped. A set of 9/16-20 taps on Amazon are less than $30. Make sure to use plenty of tapping oil and make sure to use the left tape on the left arm and right tap on the right arm.

Once the holes are tapped the extra crank arm length can be cut off. I prefer to use a vertical belt sander to give the end of the crank arm a nice rounded shape, similar to stock. Note, part of the original pedal hole will still remain at the end of the crank arm.

Finally, install the crank boots.

I think it's pretty evident that unless you already have some of the tools needed (and some experience using them), it's probably cheaper to go with the North Shore Billet cranks. 

Additional information can be found in this thread on EMTB Forums:
https://www.emtbforums.com/threads/shortening-your-cranks.29059/

Yamaha YDX Moro torque specs

 

Yamaha Moro YDX display

The Interface X on the PW-X3 motor equipped Yamaha Moro YDX is Bluetooth enabled and can connect to smartphone apps, GPS devices, or bike computers. However, the display itself is horrible, with just a series of LED lights to tell you the assist level and battery level (in only 25% increments). The location isn't great either right next to the stem.

Yamaha also makes the Display A which is a plug-and-play upgrade. While it doesn't have Bluetooth, it shows the speed, assist level, and battery level in 5% increments. It also combines the assist buttons with the display itself, so it's fewer wires and an altogether more compact design.

To replace it, remove the right side cable cover, and gently pull the wire out until you get to the connector. With a bit of finess the connector will come out through the cable port. At that point just disconnect the Interface X, and connect the Display A.

Rocky Mountain Powerplay / Dyname transfer chain

Transfer Chain

NOTE: This is written for the Dyname 4, but the Dyname 3 is extremely similar regarding the transfer chain.

The Dyname 4 system uses an ANSI #25 roller chain to transfer power from the motor to the through-shaft. Unfortunately, motor sprocket is machined into the motor spindle, which makes replacing/fixing it very difficult. The through-shaft sprocket is also custom, but that at least should be easier to deal with. Regardless, it's in our best interest to prevent either sprocket from wearing as much as possible.

Sprockets primarily wear due to chain elongation, which is turn happens as the chain's pin/link interface wears. As a worn chain mates with the sprocket, the extra length between links causes the chain to ride up on the tooth, and most of the power is transferred through that one tooth until the next tooth engages. This wear a divot into the face of the sprocket's tooth.

The Dyname 3/4 motor sprocket is particularly interesting because it uses o-rings on either side of the sprocket which the chain actually rides on. The chain rollers only engages the face of the sprocket tooth, so as the chain wears it doesn't have the opportunity to ride up on the tooth. The chain wears a groove into the o-rings, so the o-rings lose their effectiveness before it's readily apparent that they're worn.

NOTE: The maintenance intervals mentioned below are very aggressive because doing the maintenance is fast, cheap, and easy, while the costs of sprocket wear are very high. Therefore we always want to do the maintenance before the maintenance is actually needed and parts can begin to wear.

To keep the sprockets from wearing, we want to:

- Regularly replace the transfer chain.

- Regularly lubricate the transfer chain.

- Regularly replace the motor sprocket o-rings.

Replace the transfer chain

I don't want to wait until the transfer chain has notable wear before replacing it in order to minimize sprocket wear. Therefore I plan to replace the chain on a fixed interval. The original Tsubaki chain went 450 miles 0.25% elongation, so I think replacing it at 200 mile intervals is extremely safe. Since new chain usually comes in 10 foot sections, it should last 1,800 miles. For me that works out to approximately $10 per 200 mile replacement.

Tsubaki is a quality Japanese manufacturer, and their prices reflect that, However, they are available on the surplus market at a reasonable price. Timken also makes high quality #25 chains under the Diamond name (www.diamonddrives.com). ANSI #25 roller chain is readily available from other manufacturers and through Amazon and McMaster-Carr (and many other online sellers), though the quality and change interval on those is unknown. 

The stock Dyname 4 chain is only 26 links long (including the connecting link), so a single replacement chain should last through several replacement intervals. Be sure to use a new connecting link when replacing the chain. 

NOTE: Unfortunately, it does not appear anyone makes an o-ring or x-ring #25 chain, which would be ideal. If anyone finds one, please comment here to let me know.

Lubricate the transfer chain

Depending on what documentation you're looking at, Rocky Mountain says to use standard chain lube or Park Polylube 1000. Both of these recommendations are wrong:

- The chain is enclosed, so there's no reason to use dry lube or dirt shedding wet lube, and the lubricant can be optimized to reduce wear/elongation.

- Grease cannot get inside the rollers and plates, so it won't lubricate where the chain actually needs to be lubricated to prevent wear/elongation.

Tsubaki, the chain's manufacturer, recommends using an SAE 20 oil to lubricate the chain (pages 10-11: https://catalog.ustsubaki.com/view/303394094/10/). Since the chain will be turning at a decent RPM we also want something which is very tacky so it'll stay in place and won't fling off. In my opinion the best option is Mobil Vacuoline 1409 which is a way lubricant designed to minimize wear on very expensive machine tools (a "way" is where the moving parts of a machine tool slide on each other). It's in the same viscosity range as SAE 20, but includes a lot of tackifiers to keep the oil in place and prevent it from being flung off.

https://www.mobil.com/en/lubricants/for-businesses/industrial/lubricants/products/products/mobil-vacuoline-1409

A temptation would be using chainsaw bar oil since it's also loaded with tackifiers, but all the ones I've looked at were heavier viscosity than the Tsubaki recommendation. 

Tsubaki recommends oiling the chain every 8 hours of use. Lubing the transfer chain is easy, as you only need to remove the 4 bolts holding the left hand motor cover in place. Just brush the oil into the rollers of the chain.

Immersion hot waxing might also be a reasonable alternative, but a bushing chain like the #25 transfer chain is very hard to wax due to the tight tolerances preventing wax getting to the pin. Silca recommends their Synerg-E oil-based lubricant for this application, but its viscosity is twice the Tsubaki recommendation, so I think that's risky.

NOTE: Using oil instead of grease on the transfer chain will increase the chain noise when riding.

Replace the motor sprocket o-rings

The stock o-rings appear to be nitrile/Buna-N, size -208, and a 75A-80A durometer, which is problematic because nitrile doesn't come standard in that durometer (nitrile is available in 70A and 90A). 

My solution was using square profile 208 o-rings in a 70A durometer. Because more of the o-ring supports the chain it provides the same chain tension as the stock o-ring as measured by mm slack in the middle of the chain: 8mm for square profile 70A versus 8.5mm for the stock. This amount of slack is also well below Tsubaki's recommended maximum tension (page 15: https://catalog.ustsubaki.com/view/303394094/14/). The square profile also better supports the chain and helps reduce the chain eating into the o-rings.

Square profile -208 70A o-rings can be easily be found at any o-ring supplier or at McMaster-Carr: https://www.mcmaster.com/4061T23/

Square profile o-rings installed.

Since I'll be oiling the chain every 8 hours, I'll inspect and potentially replace the o-rings at the same time. 

Yamaha YDX-Moro rear shock upgrade

The Yamaha YDX-Moro isn't well suited for a coil rear shock. As seen below, the leverage ratio isn't very progressive, and becomes regressive in the last 17% of travel. 

Regardless, the tolerances around the Yamaha YDX-Moro rear shock are very tight. Although a RockShox coil shock will successfully bolt up, at full compression the coil will hit the frame. A Fox coil shock or Bomber CR coil shock uses a coil with an outside diameter 4mm smaller than the RockShox, which might technically work but with coil bulging it might still hit.

The best option is sending the stock shock out for custom valving. I personally use Avalanche Downhill Racing: http://www.avalanchedownhillracing.com/Rock%20Shox/Rockshox%20Super%20Deluxe%20RC3%20SSD_HSB%20Mods.htm

Yamaha YDX-Moro geometry

The Yamaha YDX-Moro has a listed actual seat tube angle of 70.3*. However, the seat tube connects well ahead of the bottom bracket, so the effective seat tube angle is significantly steeper. Unfortunately, they do not list the effective seat post angle. 

The effective seat post angle of the YDX-Moro and YDX-Moro Pro is approximately 74.5*. 

The effective seat post angle of the of the YDX-Moro 05 and YDX-Moro 07 is approximately 75.5*. The angle is steeper for the 05 and 07 because they use the newer PW-X3 motor whose bottom bracket spindle sits 5mm further back.