Vintage Mongoose Posters

 

26.8mm dropper seatposts

26.8mm seat posts weren't ever an overly popular size, and not are obsolete, which makes finding a dropper post for them extremely problematic. I found three options: 

1. Gravity Dropper - The Gravity Dropper was one of the first dropper posts and is the only out-of-the-box solution for a 26.8mm dropper. There are some issues though. First, Gravity Dropper has seemingly gone out of business, so you'll be stuck trying to find a used one in a rare size. Second, the maximum travel for a 26.8mm version is 100mm. Third, because of the actuators location, they have a very high stack height. Finally, they have a large protective boot (their design requires it), but they are very robust seat posts and will last a very long time with maintenance.

The venerable OG dropper post.

2. Modified 27.2 dropper - I took a 27.2mm dropper post with under-the-seat lever actuation and turned the body down to 26.8mm with my lathe, which meant reducing the wall thickness by 0.2mm. The only reason I'm comfortable running this post is because it's inserted all the way into the frame, and the post's collar is resting on top of the seat post clamp. This means the entirety of the turned down body is containing within the seat tube of the frame, making the loss of strength a non-issue. 

The post has 125mm of travel, which is the height I needed for this specific bike.

Turning the seatpost body down from 27.2 to 26.8 on the lathe.

Reassembled.

Installed on the up position. Note the dropper collar is sitting on the seatpost clamp 

Installed in the down position.

3. Modified DT Swiss D232 dropper - The DT Swiss D232 dropper only has 60mm of travel, but is notable because the entire dropper mechanism is contained with the top part of the seat post, making it possible to cut the top off right where the stanchion starts, and transplant it to a seat post diameter and length of your choosing. This is the only dropper option for my bike with an interrupted seat tube that's only 160mm long. 

Because the activation mechanism is house in the top of the seat post, with a little bit of work you can have the cable enter the seat post pretty much anywhere below the stanchion.

In my case I cut the stanchion off the D232 (make sure to cut it below where the wiper sits in the down position), then I machined a new 26.8mm seat post body, and pressed the stanchion onto the new seat post with a helping of Loctite retaining compound. From there, it was simply a matter of routing the cable and reassembling it.

Notes:

• Because of the design, there must be a minimum of 200mm of seat post exposed. If you modify the D232 mast to accept a OneUp seat clamp, that can be dropped to 190mm of seat post exposed.
• The activation spoke (yes, it's literally a spoke) can be removed and the dropper cable run directly through the activation piston. This just requires a way to terminate the cable house at the bottom of the post, which can easily be accomplished via either 3D printing or modifying the existing bottom cap.
• The spring guide is glued into the top of the slider tube. If you remove it, you'll need to use VHB tape to reattach it after a thorough cleaning.

D232 disassembled.

Turning the new 26.8 seatpost body on the lathe.

The D232 stanchion press fit on the new 26.8 body. It's a 0.02mm interference fit.

Installed on the bike and in the up position. I decided to make things harder for myself and routed the dropper cable through the frame's seat post clamp.

Installed on the bike and in the down position.

Wireless dropper stack heights

Model	Stack Height	Stack Delta	Travel	Max Insertion	Notes
Fox Neo	47	0	175	255	293mm with bottom cap
Magura Vyron V3	54	7	175	270
TranzX EDP01	55	8	170	260
Seekrun	57	10	175	282
KS LEV Circuit	58	11	175	264
RS Reverb AXS A1	65	18	170	245	268mm with vent valve
RS Reverb AXS B1	62.5	15.5	175	250

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.

Single speeds and half links

Single speeds often use 8 or 9 speed chains because of the significantly higher quality and the lower weight. However, it can be challenging when a half link needs to be added to achieve the property chain length. Every 3/32 half link I tried, and I think I've tried them all, is slightly too wide to be used in a multispeed 3/32 chain.

To do it right you want two of these:

KMC Z610HX master link
https://kmcchain.us/products/z610hx-c-l

And one of these:

Gusset half link
https://www.universalcycles.com/shopping/product_details.php?id=22297

The KMC master links in the link above is nickel plated and very nicely made, unlike most BMX style master links. They're slightly wider than a normal 8/9 speed connector link, so they play nicely with the half link, and the slight added width isn't a problem with the narrower multispeed chains since the difference is so small. They'll also digest any half link out there while still working nicely with a multispeed chain. 

The Gusset half link is another quality product. The entire thing is nickel plated, unlike most half links. They also sell it already joined to a set of inner plates, the reason being they can peen the ends of the pin for extra strength. Also, unlike other half links, the Gusset uses the superior bushingless design.

You want to use the two KMC master links to join the Gusset half link into your chain. Make sure the flat side of the Gusset half link faces away from the teeth. 

You can still use a connector link, but it cannot connect to the half link as the connector link simply isn't wide enough. When I run a connector link and half link together, I'll usually install the half link on the opposite side of the chain.

Vacuum bleeding a shock

WARNING: ALWAYS WEAR EYE PROTECTION. I’ve had suspension fluid sprayed in my eyes and it sucks. It can happen even if you do everything right.

Degas the Suspension Fluid 

Suspension fluid has a lot of dissolved air in it, and before bleeding this air must be removed for two reasons:

• Dissolved air makes the oil more compressible.
• It allows the oil to absorb any small air bubbles left after bleeding.

Fill the vacuum bleeder reservoir no more than halfway with suspension fluid. Close the compressed air valve, open the vacuum valve, start the vacuum pump and run it to -30 in of Hg, then close the vacuum valve and turn off the vacuum pump. The the fluid sit in vacuum for 15-30 minutes. The vacuum can then be relieved by slowly opening the compressed air valve.

Bleed the Damper

NOTE: These bleed instructions are for bleeding a reservoir shock with a bleed port and an IFP. Although the basics of the bleed procedure are the same, the details for other damper architectures are different, so be sure to familiarize yourself with those before bleeding. 

Preparation

• Service/rebuild the damper and assemble it without suspension fluid.
• Connect the appropriate bleed adapter to the bleed port on the shock, and position it so it’s the highest point of the damper.
• Install the IFP and the reservoir cap retaining clip. It is very important the IFP be retained inside the shock during the bleed process.
• Fill the vacuum bleeder reservoir no more than halfway with the desired suspension fluid.
• Set your compressed air regulator to 45 PSI.
• Connect the compressed air source to the vacuum bleeder.

Bleed

1. Close the compressed air valve, start the vacuum pump, and slowly open the vacuum valve. Once there’s a good vacuum, close the vacuum valve and turn off the vacuum. Be sure to close the vacuum valve before turning off the pump.

NOTE: What look like bubbles under vacuum are actually pockets of vacuum and will collapse during the pressure phase of the bleed.

2. Verify the vacuum valve is closed, and slowly open the compressed air valve. Oil should start flowing from the reservoir into the damper. Once the pressure is stable, cycle the damper several times by hand. It can also help to tap the damper to dislodge any bubbles.

4. Repeat steps 1-2 several more times (I usually do 5 cycles) to help insure all the air is evacuated from the shock. Any small bubbles which remain will be absorbed by the degassed suspension fluid.

5. Close the compressed air valve, and use the pressure relief valve to release the pressure.

6.  Disconnect the air compressor, open the compressed air valve, and set the IFP depth. The excess oil will be pushed back to the vacuum bleeder reservoir.

7. Disconnect the vacuum bleeder from the bleed adapter, then remove the bleed adapter and close the shock's bleed port.

8. Install the reservoir cap and pressurize the reservoir to spec.

Building a vacuum bleeder

A suspension vacuum bleeder uses alternating vacuum and pressure to bleed a damper. It's much easier than hand bleeding, does a better job, and is a less mess.

Bill of Material

A bleed adapter specific to the damper will be required to connect the vacuum bleeder to the damper. ANSO (https://anso-suspension.com) makes good bleed adapters at a reasonable price, and the list below reflects using ANSO adapters. If different bleed adapters are used, the "3/8" FNPT V-Style coupler" would need to changed to work with those adapters.

• 1/4" NPT 50 PSI pressure relief valve - $9 -  https://a.co/d/7lOzOpp
• 3/8" OD 1/4" ID polyurethane (PU) tubing - $9 - https://a.co/d/7cUTqff
• 1/2" NPT to 1/4" barb 90* fittings - $10 - https://a.co/d/fgpZFRI
• 3/8" spring hose clamp - $6 - https://a.co/d/gdm5f48
• 3/8" FNPT V-Style coupler - $9 - https://a.co/d/8DQBxJ5
• 1/4" NPT pressure gauge - $13 - https://a.co/d/f1TbRqJ
• 1/4HP 3.5 CFM vacuum pump - $55 - https://a.co/d/2L3zF0F
• Hydronix HF2-10CLWH12 filter housing - $23 - https://a.co/d/dYMTLSv
• 3/8" NPT 3/8" tubing push to connect fittings - $9 - https://a.co/d/auJHnwp
• 1/2" NPT mini ball valves - $13 - https://a.co/d/72oPZEk
• 1/4" FNPT air hose quick connect adapter - $4 - https://a.co/d/aGIQmXG
• 1/4'' NPT 1/4" barb fittings - $5 - https://a.co/d/cOngmrj

TOTAL - $165

Assembly

NOTE: Whenever installing a fitting the threads should be wrapped with at least three layers of Teflon tape. Be sure to orient the wrap so that tightening it doesn’t try to un-wrap it. 

Vacuum Pump

• Fill the vacuum pump’s sump with suspension fluid, roughly the same viscosity as you’ll be using.
• Remove the inlet fitting and replace it with a 1/4” NPT barbed fitting.

V-Style Coupling

• Install a 3/8” NPT push-to-connect fitting.

Quick Connect Coupling

• Install a 1/4” NPT barbed fitting.

1/2” Ball Valves

• Install the 1/2” NPT barb 90* fittings so they point away from the valve handle.

3/8” Push-to-Connect Fitting

• In one of the fitting, drill out the bottom of the fitting so a tube can extend all the way through the fitting.
• Meticulously clean any metal swarf out of the fitting.

Filter Housing

• Drill a 19/32” hole in the top of the lid and and thread in the drilled out 3/8” push-to-connect fitting. Teflon tape is not needed on the thread. The fitting will tap itself into the plastic of the lid. Keep threading it in until the bottom is just proud of the inside of the lid.
• Drill a 15/32” hole in the top of the lid, then thread in the pressure gauge. Teflon tape is not needed on the thread. The gauge will tap itself into the plastic of the lid. Keep threading it in until the bottom is just proud of the inside of the lid.
• Drill a 15/32” hole in the side of the lid and thread in the 1/4” NPT pressure relief valve.  Teflon tape is not needed on the thread. The valve will tap itself into the plastic of the lid. Keep threading it in until the bottom is just proud of the inside of the lid.
• Clean out any plastic shavings from the lid.
• Install the two two ball valves into the two threaded holes in the lid. The valve handle should face upward, and the barb fitting should face downward.

Putting it all Together

• Insert the polyurethane (PU) tubing through the push-to-connect fitting in the lid and feed it down until it sits about 1/4"-1/2” above the bottom of the reservoir. Install a zip-tie or clip to prevent the push-to-connect release collet from being depressed.
• Cut the PU tube to length. It needs to be long enough to go from the vacuum bleeder to the damper with some slack in the tube. However, the tube should be kept as short as practical to aid in bleeding.
• Connect the V-style coupling to the end of the PU tube. Install a zip-tie or clip to prevent the push-to-connect release collet from being depressed.
• Cut a length of PU tube to connect the reservoir to the vacuum pump. Put two spring clamps on the tube, warm up the two ends with a hair dryer or heat gun, connect them to the barb on the vacuum pump the barb on one of the ball valves on the reservoir; this is now the vacuum valve. Put the spring clamps in place.
• Cut a length of PU tube to connect the reservoir to the air compressor. Put two spring clamps on the tube, warm up the two ends with a hair dryer or heat gun, connect them to the barb on the quick connect coupling and the barb on the other ball valve; this is now the compressed air valve. Put the spring clamps in place.

Testing

• Test the reservoir to make sure it holds vacuum. Close the compressed air valve, open the vacuum valve, and run the vacuum pump until the pressure gauge registers 30 in. of Hg vacuum, then close the vacuum valve and turn off the pump (air can bleed through the vacuum pump when it’s not running so close the vacuum valve before turning off the pump). The reservoir should easily hold the vacuum for several minutes, if not hours. If it doesn’t, there’s a leak which needs to be found.
• Test the reservoir to make sure it holds pressure. Pressurize the reservoir to 45-50 PSI and close the compressed air valve. Set the air compressor’s regulator to 45-50 PSI, DO NOT pressurize the reservoir with higher pressure air and try to stop it at 45-50 PSI using the pressure gauge. Again observe the pressure gauge for any changes in pressure. If the pressure drops over the next several minutes, there’s a leak which needs to be found.

If the system passed both the vacuum and pressure tests, install it in its final position or install it in its stand/frame.

Andreani Thread

Many vacuum bleed adapters use "Andreani thread" named after the Andreani vacuum bleed machine. It's actually an 1/8" BSPP (British Standard Pipe Parallel) thread. 

Adapters from BSPP to NPT are available:

https://www.amazon.com/dp/B0CLHK1CP2

https://www.amazon.com/dp/B01LQU8FV8

NOTE: There is a British Standard Pipe Parallel (BSPP) and also a British Standard Pipe Taper (BSPT). Make sure you purchase the Parallel.

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.