RoulezTandem

typo. System wear.

We have had excessive chainring and chain wear on our custom build in just a few hundred miles of mostly unpaved rail trail riding.
I would appreciate thoughts or insights into cause and how any gear may be better matched.

All these components are a couple of hundred miles old, mostly unpaved rail trails with motor assist. We pedal fulltime.
Our top pedaling speed is 15mph with this gearing. Designed for hill crawling with one person (me) power and motor assist for our 400# GVW consist.
Front to back skew of chainline from frame is no more than 3/16" of an inch, and less between any one chainring and another.

The gear:

Rohloff 500/14 speedhub, 14 tooth steel drive sprocket. Rohloff chain tensioner having two plastic wheels. I do see some metal shavings on the tensioner and we are feeling/hearing drive chain noise back there that we did not hear earlier. Not hitting frame or bolt, and not out of line side to side.

Stoker- pair Orion 42t 110/130 5-bolt aluminum chainrings (drive, timing). Mic-ing them I see 0.075” machined tooth width and the full plate width is 0.125”. I assume that calls for a 1/8” chain??

The two stoker chainwheels are spaced a full ˝” apart including freewheeling crank spider made by Sick Bike Parts, and two thick chainring spacers on each bolt.
They do not spin concentrically, but create a slightly oval orbit around the crank center, causing the chains to bob up and down visibly.
This is a result of the chainwheel male/female sexbolts, whereby the female slotted-head side closest to frame does NOT nest into a machined countersink.
There is not too much side to side runout.

Bafang middrive motor under captain. It contains the crank and bolts through the bottom bracket.
Is is not perfectly centered in the bottom bracket, nor perfectly parallel to the frame.
Further the Bafang has visible runout up and down and side to side. Lifetime mileage probably under 3K in six years on two frames.

Captain- single Orion 40t 110/130 5-bolt aluminum chainring (timing), mounted to five arm spider made by California Ebike that adapts the Bafang inside bolt holes to a five-hole not bafang four-hole chainring.
It is concentric without significant runout.

Chains- drive chain and timing chain appear to be ˝ x 1/8 Shimano Nexus CN-NX10.
We originally built with the heaviest available 1/2x3/32 KMCZ51/18 and found it ground the heck out of all the chainrings, not sure why.
I just tried the Park chain wear tool and it appears not to indicate excessive stretch.

I guess I need to get a dial indicator and measure runout at each location.


Rear wheel- Rohloff 500/14t and tensioner. Not able to get phone camera to focus.


Stoker- pair chainrings 42t. Oblate around centerpoint causing chain to rise and fall.


Stoker side view of freewheeling crank. Love it.


Captain 40t chainring mounted to inside of Califoria Ebike adapter spider which mounts to the Bafang middrive motor.
Chainring location chosen to keep driveline parallel to frame. Ground the ends of spider to enable chain clearance, it is really designed for a larger chainring.
We started with a 42t front chainring and switched to 40 to gear motor down slightly.

Alcanbrad

Just a few comments:

- From your post I was not able to tell how much wear you have actually experienced. Does a chain gauge show that the chain is nearing end of life? Is the chain skipping under power suggesting the ring teeth are wearing out?

-The Steel in the chain is much harder than the aluminum chainrings and as such, the rings will show wear very quickly. Any anodization layer is only a few microns thick and will get chewed through almost immediately. This is normal and not necessarily an indication that the ring is worn out.

-You mention that the stoker chainrings are not concentric about their crank spindle. This is not a problem for the chain to the rear wheel (as the spring loaded jockey cage will mitigate) but could be a problem for the timing chain. If the timing chain is tightening and loosening on each rotation, depending on how tight, it could be putting additional stress on the rings and especially the bottom bracket bearings. If you have spring loaded jockey wheel in the timing drivetrain this shouldn't be a concern. You can mitigate this type of issue by rotating the rings to even out any run-out extremes. (I posted such an endeavor on this forum a year or so back)

-I did not see any mention of how the chains are lubricated. The pictures look as though either there is no lube or maybe you hot wax. Also, I see a lot of dust and grit build up on the drivetrain. This is typical of the type of riding you are doing, and unfortunately, that grit leads to accelerated wear. This may be what you are seeing. I would recommend avoiding any kind of liquid lube and use only a hot wax regimen and the grit will not stick to the wax wear-as it will cling to any lube and grind away at everything. I would also suggest that you keep the drivetrain clean of any grit build up. If you hot wax, this is easily accomplished with a stiff brush and possibly compressed air. After (or before) every ride, brush any grit off the chains, rings, and cassette, then finish up with blowing any remaining grit with compressed air.

sapporoguy

That stoker’s chainring system looks complex, so maybe I don’t understand it. Unseated bolts/nuts would certainly be something to fix first, but then you might need to center the chainrings. I’ve found our timing chains (and belts) bobbing a bit on the rings after I reassemble, and the answer is under “Adjustment” in the timing-chain section of Sheldon Brown’s excellent guide on tandem mechanics, linked here.

mikemelbrooks

I use always try to use chainring bolts with a hex on both ends I find it much easier to work with than the slotted ones.

longpete

Steel e-bike chainrings and hot wax wit several chains. ( at least 2 drive chains, 2 timing chains)
We use cheaper shimano linkglide chains. (suited for 10 to 11speeds). Even Ebikes chains with 136 links are not long enough.
So we have to cut one chain in several parts to have timing chain with te right length.
With not waxed chains, the chains and cassettes lasted 2500 to 3500 km. With wax past 3500 not worn. Chainrings over 6000(2500 with oil) and good fo another 6000.
Shimano cassettes wear slower than sunrace.

RoulezTandem

Thanks all for some helpful insights. Appreciate hearing what other tandem riders have encountered and/or overcome.

I'll skip the hot wax. 40 years of hot torch waxing my wood XC skis was enough. Still smell the Gruenvald tar base.

Just ordered some steel chainrings.- Pair timing rings at stoker 42t 5 hole; one at motor/captain 40t 5hole
<Correction- 110/130bcd as in picture>

https://www.jensonusa.com/Surly-Stai...teel-Chainring
Appreciate the pointer to Sheldon Brown how-to align chainrings for concentricity, some great info there.

Leisesturm

104bcd is 4 bolt standard. And wouldn't you want the captain and stoker timing rings to have the same tooth count?

RoulezTandem

<Correction- 110/130bcd as in picture>
from above: "The two stoker chainwheels are spaced a full ˝” apart including freewheeling crank spider made by Sick Bike Parts"
stoker and captain pedal independently
thanks