Motor Rips Loose From Mounting Plate

(Much delayed posting due to holidaze and circumstances; was started thanksgiving night but not finished till the 28th)

Last week, on the way up toward Arrowhead along the canal, about 3 miles from home, the motor mounting plate gave way along the only rightside mounting bolt it had.

It looks much worse in person than I could capture on camera. The largest hole in it on the right rear of the plate is for the old motor's clutch lever to pass thru, and that weakened the plate enough in that area that the hole for the rightside mounting bolt of the new motor, right next to it and partly intersecting it, finally expanded and let the bolt pass thru it.

It took a small chunk of the plate out with it. This was during uphill travel on one of the under-road tunnels on the canal path; they're pretty steep. Not sure of the grade, but steeper than I can pedal up from a stop on my other unpowered bike, the DayGlo Avenger (the upright aluminum bike), without hurting my knees pretty badly even in the very lowest gear, and even that only at just enough speed to stay barely upright (if wobbly); perhaps 1-2MPH.

I didn't have any thicker steel plate, so I just cut another plate of the same material and same shape to weld to the existing one. First I had to hammer and bend the other plate back mostly flat, then I clamped them together, welded one edge (where it joins the frame), then clamped along the flat portion of the plates and welded thru the various holes in the plates (mounting screwholes from whatever they originally came off of) to the plate underneath, to join them more thoroughly. Not as good as a single thickness, most likely, but good enough for this, I hope. Sorry there aren't any pics of this process; again I didn't think to do it until too late.

After welding them, I did a lot of comparing, holding, marking, placing, and test-fitting of potential chainlines before I drilled any new holes, and before cutting the new slot for the chain to pass thru on the left edge of the plate (it's only major weak point now that there will not be slotted holes nor clutch lever hole).

Eventually I decided to do two things differently than before. First, to move the pedal crank chainring to the *right* side of it's spider, since it is a bolt-on to a flat plate.

This moves the pedal chainline right far enough to completely clear the motor chainline, even if I move the motor chainline more right as well. Then I did that, too, by flipping the hub over, cutting off more of the hub the same way I did it before (hacksaw while spinning it on lathe), and using the removed parts as spacers on the left.

This also allows me to center the motor better between the cranks, and it straightens the motor's chainline--part of the problem I had with it coming off (besides flex from the motor plate prior to failure) was that the chain had to be super-tight due to the chainline passing from left at front to nearly 1/4" out of line at rear, with no guide or jockey wheels to keep it lined up where it met the bottom of the receiver sprocket. So under the right circumstances (left turns with a lot of tilt, especially on bumpy roads or rough intersections, etc), it would come off, and sometimes tangle.

Now that won't happen, as the motor's chainline is as close to straight as I can see, as is the pedal chainline. The pedal chainline doesn't even need the tensioner/guide wheel anymore; even under bouncy conditions it stays on, so far, despite still being about 1/2 link too long.

I left the plate to bolt the wheel onto in case I have problems on the road; the wheel and bolt is in my toolkit.

While I was at it, I also welded up some battery retainer strips, just to give them some guide at the bottom, so I don't have to keep using the wood blocks (which deform over time and have to be readjusted) to keep the batteries from shifting around. For the front battery, I just used the bottom tray from a small standard computer UPS (the kind that uses a 7Ah battery), and cut a piece just long enough to tack weld onto the bike frame and still keep the bottom of the battery from moving side to side.

I cut a small slit for the hose clamp that secures the batteries to pass thru, for more clearance to the chain. No rubbing problems, even in a hard right turn. It does rub if the bike is tilted far enough to lift the rear wheel off the ground, using the right cargo pod as a "stand", but that's not relevant to riding it.

For the rear battery, which was the most problematic on the road, I took the two triangular strips left from cutting the new motor mount plate, and notched them to fit the frame and be out of the way of the motor bolts.

Then spot-welded to the frame and motor plate (as this also stiffens the motor plate some), and can now clamp the battery down without worries of it moving. Due to chain clearance, the clamp only goes around the rightside plate, but it is very secure and doesn't shift around even with that.

A quick shot of the PDA used as a bike computer, showing the readings at the time.

22MPH was unpowered gliding down into the tunnel that I had to walk the bike back out of due to the motor plate breakage. Usually (in daylight when I can see in the tunnel and it's entrances better) I can keep gliding until I am most of the way back up the other side, as long as there is no other traffic (normally there is not) or anyone sleeping in the tunnel with a cart full of their belongings (this happens more than encountering other traffic), and then I can engage the motor in a low gear and continue up the rest of the way.

This time it didn't work out like that, because when I engaged the motor, almost instantly the motor pulled out of the plate on the right side, which allowed it to be pulled left and back by chain tension, getting in the way of even the pedal chainline, which made me just stop right there, and set the parking brake lever (taken from the scooter) on the left, to the rear wheel. Then I saw what had happened, and just ended up walking the bike the rest of the way uphill, then walked it home via the surface paths.


Some new full-bike pics, including the headlight/taillight. First is the room light (same 15W/60W CFL that's in the HL/TL) and camera flash.

Next is just the room light, flash, and HL/TL.

Just the HL/TL

Just the room light, HL/TL. No flash.

Just the room light, no flash or HL/TL.


I've now gone another 31 miles, for 905 total, and the only thing I had to change (at 882 miles) was to weld the longer piece of hub that I'd cut off and used as a spacer, to the end of the hub it now sits against.

This is because the little pin that rests in the groove of both the hub and gearbox axle isn't long enough to totally fill the space from one to the other, and apparently can work it's way loose. The original one *was* long enough, but I managed to misplace it during my original modification of the hub, and had to make a new one; for whatever reason I no longer remember, I did not make it the same length. Now it's welded, *and* has a hardened torx-head bolt threaded into the groove for the rest of the length, to ensure full contact and power transfer between the axle and hub.

I was very lucky that it failed where it did, less than 1/4 mile from a friend with a welder and the large 19mm wrench it takes to undo that locknut, or I would not have made it home in any reasonable time that night--the motor couldn't transfer any torque to the drivetrain, and I could not have gotten the nut off to put the pin back in place (the washers block the pin from coming out, and thus anything I have from going in!). So my thanks to him for letting me barge in after turkey-day dinner and use his tools!