Trouble with chain alignment and tensioner stability.

New Tensioner Design, Check It Out!

Hi BlueDestiny.

After building my first motorized bike I ran into the same problem. I wasn't really thrilled with what was available so I designed and fabricated my own tensioner. As you can see in the pictures it's a captured idler gear 10 tooth. The plastic on either side of it is high density, whats used for making jigs, cut to size with hole saw and keep the chain on track without damaging it. The reason the plastic and steel washers are so big is to provide tracking in case the chain moves away from the gear. Just cut some scrap steel to make large washers for strength. The bolt is a 3/8 standard and of coarse locknut. The chain was replaced with a 41, the hub assembly is a clam shell with 36 tooth sprocket. As it is it's way too fast, so my next build I purchased a 44.
The plate bar is just scrap steel about 1/8 inch thick cut to length and width and drilled.
To fasten the assembly to my bike I chose to use pipe clamps that I threaded all the way down cut to length and again locknuts.
I have ridden with this design for over 300 miles. No adjustment or failure but I check every bolt and nut on my bike before every ride.
With this setup it's very cheap to build and impossible for the chain to come off track or the tensioner to hit the wheels or anything else.
Feel free to copy it if you like, total cost for the tensioner was around $15. I love to recycle. LOLOL

Idler

http://www.ebay.com/itm/141348808023?_trksid=p2060778.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Chain

http://www.agrisupply.com/agmate-single-roller-chain/p/84987/&sid=&eid=/

Buy the master key at the same place very cheap and will give you 2 chains for less than $10.

Clam shell hub and sprocket.

http://www.bicycledesigner.com/motorized-coaster-wheel-brake-kit.html

Tensioner full view.

http://imgur.com/O3sHfG0

Captured idler gear closeup.

http://imgur.com/MeXXfE5

This is a Kent La Jolla Wally World Bike. Over 500 miles total and zero failures causing down time. However the bike and engine have many upgrades some of my own design and fabrication.
Hope this helps. Have Fun Be Safe!

AssembleThis

crassius said:

I refuse to build a coaster brake bike, so that over-priced adapter is not used here.

Click to expand...

You can get reducer bushings. Seeing as a manic mechanic adapter will outlast a hundred bikes and a dozen shift kits I'd say it's worth the cost.

I rarely build, as I'm mostly a repair shop & I sometimes get 4 or 5 chain problems a day. I never have anyone come back after I straighten it out for them. My customers are quite poor & won't pay that much extra. Good running bikes are often on CL here for $150 - $250, in fact, there are 2 on right now at $75 & $90, but they need minor work.

While I appreciate the information for building my own components, my tools and supplies are limited to wrenches and screwdrivers (so no metal cutting/drilling/welding). I'll see about finding some way to fix the bracket to the frame securely, and I'm going to double check the chain length.

Safety First!

If your limited to basic tools I would highly recommend getting the needed tools to take apart both wheel hubs and crank. When I started my first build I decided to take mine apart because of all the stories I read on wheels and cranks locking up. I'm extremely glad I did as all of my bearings were dry. There was a small dab of grease on each, there is no question after about 30 minutes of riding I would have had major failures. Something else to consider, the cost to repair or replace a destroyed bike hurts. Granted but what cost would it be to replace your life? Or broken bones from a catastrophic failure? At just 20 miles an hour you can be seriously hurt or killed. If you plan to build and ride a motorized bike do yourself a favor and get the knowledge and tools needed to keep it maintained so your rides are fun and safe. I have ridden motorcycles for over 50 years and have been hurt on a few, so I plan to limit the possibility of a hospital visit again. I hope you do what you can to also ride safe. The stock chain tensioner is an accident waiting to happen.

butre said:

they shouldn't have to steer the chain anywhere, you should have a perfectly straight line between the sprockets

Click to expand...

That is exactly it.
A tensioner will not re-direct chain around something, they are only meant to make chain adjustment easier once the chain is in perfect alignment and as tight as possible.

Also note the tensioner has a long side and short side, try the long side on the outside of the chain stay.

With some help from a few friends, I got the chain working. To start with we shortened it as much as possible using the dropouts for maximum tension. Then we cut a piece of old bike inner tube and used it as a gripping pad for the pulley clamp. The pulley itself is positioned closer to the front of the wheel, so if it does move the worst that will happen is a slipped chain and scraped tire rather than jamming the spokes. The pulley has held its place so far while cranking the engine by hand, so I'll call it fixed for now.

I wonder if the sprocket is indexed correctly to the rear wheel ? If in doubt, measure from sprocket teeth to wheel rim. Take many measurements to circle the wheel . If index is spot on, all measurements will be the same