Front freewheel DIY chain guide.

[Retrorockit]

Some people add front motors and drive them through a front freewheel like the ENO. Another situation is disabling the rear freewheel to use the front one in a mid drive to allow shifting w/o pedaling. The ENO needs a straight chain line due to it's one row bearing, and the front freewheel needs a low friction guide to place the chain onto the chain ring in an overrun situation. Any friction form a solid guide, or front derailleur cage will make things worse. Cross chained bikes will benefit form this solution also. Hats off to the guys with milling machines who can make their own stuff. But there are off the shelf parts that can do this also.
Part #1 The Terra Cycle 15t Sport idler. 8MM shaft to run next to a big mid drive. Options for 10mm bearings for bigger stuff. Steel cog and double 608 bearings.

SportPlus 15 Tooth Power Idler

With a CNC-machined 7075 aluminum cog and bearing carrier, fiberglass reinforced nylon 6/6 sideplates, and high performance ABEC-7 bearings, the SportPlus Power Idlers from T-Cycle are the sleek, beautiful, light and quiet must-have upgrade for your chainline.

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Part #2- The Terra Cycle battery mount frame clamp. The idler clamp they sell is too weak. The battery clamp comes in many sizes to fit various frame tubes and uses 2x 6mm bolts to attach the load to it.

Frame Clamp

The heaviest duty clamp we offer! It's the clamp that holds the Battery Mounts, the SPRING Mini Fairing Mount and the WINTR Fairing Mount in place! Sporting twin 6mm bolts, this 5/8" thick beast stays where you put it and holds what you need it to hold. Made in an ever-growing list of sizes...

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part #3 T-Cycle spacer kit. get a couple jam nuts and ss washers form the local hardware also. An 8x50mm allen bolt will have enough unthreaded shank for the bearings to run there. The T-Cycle bolts are cut too short for fine adjustments.

T-Cycle Idler Spacers Kit

These are 8mm ID aluminum spacers, custom cut on a C&C lathe specifically for T-Cycle idlers. Kit Includes: 2x 0.09in spacers 2x 0.30in spacers 1x 0.60in spacers You can use a 0.09in spacer between a Power idler and a flat surface, like a chain keeper or an idler mount. The 0.09in spacer can...

t-cycle.com

The DIY part- A piece of 3/8"x1" or 3/8"x 1 1/2" Aluminum bar stock. (My local metal supplier has no minimum order and sells by the pound and the first cut to length is free.) Drill 2-1/4" holes 1.97" apart centered 1/4" in from the edges starting at one corner. This will bolt to the frame clamp, and is reversible up and down.
The drill and tap the 8mm hole in the opposite corner centered 8mm in from the edges. The offset can help clear water bottle bosses on the frame if needed. The 1 1/2 inch size allows more offset, or angle drilling to be level when mounted on a seat tube. A few minutes on a drill press is all it takes for this
This part can handle wheels up launched on a 1500W BBSHD. I broke a lot of other stuff before coming up with this.
Pictures in this thread.

DIY BBSHD 15t Chain Guide - Electricbike.com Ebike Forum

This chain guide came to be out of another DIY project here The Mid Drive Cassette Zip Tie Mod. This guide solved some problems peculiar to that mod. But also solved some more common ones too. AS you can see form the flat 50t chain ring and no Wide/ Narrow feature this bike has chain line...

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