Vintage Style Moto-Velo

My current build is nearing completion. All components are mounted and the drive train is mostly debugged. It's nicely rideable as an ultralight motorcycle, no pedaling needed in most situations. It pulls away from stop easily in 1st , and top speed in 4th is around 32 mph, plenty for local traffic. Lack of neutral is annoying at stop lights.

The motor is a 2009 Skyhawk2 "80cc", box-stock except for mounts and carb. Reliability is more important than performance at this stage of development. Once it's stable, I'll probably add a big-fin head and better exhaust.

The most serious remaining problem is a violent chain oscillation and surging in 5th gear, which I think results from that specific set of sprocket ratios. There's no trace of this issue in the lower cogs, and I've locked out 5th and higher for now, to prevent damage.

I'm also having to deal with the usual chain stretch/adjustment with the SBP shifter kit. I just-received a 1G8 chain for the jackshaft, which should help. I also need to add some reinforcement pieces to the SBP frame, because the metal they used is mild steel and shows some bending distortion at the mounts.

Comments welcome..

 

[FurryOnTheInside]

Yeah, my thinking as well. Been distracted by another (pics coming) but will get back to this one soon.
I picked up a Cycle-Ops exercise stand to use as a dyno for testing. I'll make a video of the drive line to see what's happening.

I'm thinking maybe it's the screw fit freewheel cluster. High gears are simply further from the supporting bearings.
I would (will) use an 8 speed cassette on a freehub (with a 10 speed Shimano XT "clutch" derailleur (Shadow + (plus)) and an old (not Shimano compatible) 8 speed SRAM ESP grip shifter and a nine speed KMC X9e e-bike chain).

 

[magicsound]

The most serious remaining problem is a violent chain oscillation and surging in 5th gear, which I think results from that specific set of sprocket ratios. There's no trace of this issue in the lower cogs, and I've locked out 5th and higher for now, to prevent damage.

Now that my Cruzer project is out of the way, I am back on this problem. I did a test today and made a video of the drive line to capture the problem. Here's a .gif at 1/10 speed to show the violent oscillation. The full test video is at https://goo.gl/mNqGcJ

I'm shocked that the frame and rear axle both flex so much from the oscillation. I eliminated chain rubbing as a possible cause by installing the guide plate you can see. What next ??

 

[gary55]

A internal shifter hub or a Nuvinci hub. I'm sure the flop is not as bad when the tire has some resistance, but like Magic said when the gear gets smaller the spring tension gets weaker. I don't know if high end derailleurs have greater tension, but you can see the flop is happening due to the derailleurs inability to maintain tension.

 

[FurryOnTheInside]

It looks like the chain could be catching on the adjacent cluster sprocket.
Or perhaps the occasional misfire is allowing the cluster to get ahead of the chain. If there is no resistance from the trainer/stand.
Or perhaps the slap from the slack in the middle chain (and first chain) is feeding through to the final chain.

 

[magicsound]

The problem only starts in 5th cog. I think it needs a better quality derailleur. The Shimano Altus that's on there shifts OK but has a lot of wear on the idler teeth. I see lots of similar current models from Shimano, like Acera and Alevio - any recommendations? I don't mind spending more if it solves the problem.

 

[FurryOnTheInside]

The problem only starts in 5th cog. I think it needs a better quality derailleur. The Shimano Altus that's on there shifts OK but has a lot of wear on the idler teeth. I see lots of similar current models from Shimano, like Acera and Alevio - any recommendations? I don't mind spending more if it solves the problem.

This could be a chain line problem. Which rear cluster sprocket is the front output sprocket lined up with?

Any 1x drivetrain will have to deal with more cross chaining and requires greater capacity (of slack take up) than a 2x or 3x drivetrain with the same rear sprockets.

How many sprockets are on the rear cluster? What exact model of chain do you have?
Running a 9 speed chain on an 8 speed freewheel cluster or cassette can help when trying to avoid the chain catching on the adjacent sprocket.

With such a great used parts market there's little point in upgrading to anything less than an old shadow SLX or XT 9 speed IMHO (or like I suggested using the newer shadow+ 10 speed in a special way that hopefully allows it to work with fewer speeds.)

 

[magicsound]

If there is no resistance from the trainer/stand.
Or perhaps the slap from the slack in the middle chain (and first chain) is feeding through to the final chain.

The stand is a CycleOps with fluid resistance and flywheel, so there is some load anyway. Could be chain slap, though very unlikely since it only happens in 5th gear. The motor RPM and thus chain speeds are the same for all gears.

 

[FurryOnTheInside]

it only happens in 5th gear.

5th gear and above?
How many rear sprockets are there?
What are the sizes of the largest and smallest of them?

Do you have a freehub with cassette, or a freewheel cluster?

Which of the rear sprockets is the front drive sprocket lined up with?

Did you attach both front sprockets to the inside of the flange of the BB freewheel?

 

[magicsound]

This could be a chain line problem. Which rear cluster sprocket is the front output sprocket lined up with?
How many sprockets are on the rear cluster? What exact model of chain do you have?
View attachment 80812

Thanks for the nice chart of the model range. The chain line is pretty good, lined up with the 3rd sprocket. The cassette is a 7-speed SRAM PG730 (32, 26, 21, 18, 16, 14, 12). Chain is a fresh SRAM PC850.

So I will look for a better derailleur, maybe an XTR if I can find a good used one.

 

[FurryOnTheInside]

Thanks for the nice chart of the model range. The chain line is pretty good, lined up with the 3rd sprocket. The cassette is a 7-speed SRAM PG730 (32, 26, 21, 18, 16, 14, 12). Chain is a fresh SRAM PC850.

So I will look for a better derailleur, maybe an XTR if I can find a good used one.

XT would be stiffer, XTR is just lighter.
If you want to keep/use a Shimano compatible shifter you would need to use an older version of the XT RD, from before 2009, before ten speed, before shadow plus. But then that would still suck. One of the SRAM derailleurs and shifters would probably be better for ICE (although the better ones are expensive).

I would advise you don't trust my plan to get the ten speed to work with fewer speeds on an ESP gripshifter, but do look into it, because I believe it will work.
I suppose you could change everything over to ten speed and double click every shift.
Either way you would have the shadow plus "clutch" to hold the tension much better than the old tech does, something that I think the ICE driven derailleur chain needs.
The Zee (RD M-640) rear derailleur is cheap in reasonable used condition on the auction site and they have easily enough capacity for your cassette.
http://bike.shimano.com/content/sac-bike/en/home/components11/mountain/zee1/rd-m640-ss.html

Or just put in new jockey wheels and take a link out of your chain.