The repair was inspired by the photos that Davide Andrea posted on his repair. He put a bolt all the way through the axel. The way through the axel of my Sparrow is blocked by a pin. I used the pin to hold one end of the bolt.
The weld broke a month before the sprocket fell off. I noticed a slight bump when starting out after reversing direction. I looked for the source of this play in the drive train but didn't find it. From the photos on the sparrow_ev yahoo group it looks like at least 4 Sparrows have had this weld break.
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The end of the axle where the drive sprocket was attached. The weld only involved the outer millimeter or two. There is hole through the axle. A pin in this hole fit in to the back of the sprocket. This pin was sheared off on both ends. |
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The slot in the back of the drive sprocket where the pin fit in. |
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I bought a 3 inch long 5/8 inch diameter bolt, cut off its head, and drilled a 1/4 inch hole through the bolt. The bolt will be holding the sprocket onto the axle. The only reason the diameter of the bolt is so big is so it wouldn't be too weak after drilling a hole through it.
The bolt is a little too long. If the body panel is tight and I go over a bump, the end of the bolt grazes body. A bolt just a little shorter would be better. |
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I replaced the 1/4 inch diameter pin with two inches cut from the shank from a quarter inch drill bit. A saint at the Ace Hardware store cut both the bolt and the drill bit for me with the cutoff saw they had in the back room. I used the rest of the drill bit to make the hole in the 5/8 inch bolt.
I don't know what the best material for the pin is. A drill bit is hardened steel. I worry that it will be too brittle to hold up. A softer pin might last longer. |
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The new bolt extends through the hole in the sprocket. Click the picture to zoom in on the broken weld. |
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The finished repair.
The sprocket slips a few degrees when I switch from forward to reverse or the other way. |