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Sprocket Weld Repair

In November of 2006, the big sprocket on the real axel of my Sparrow fell most of the way off. It was stopped by the belt guard and the bottom edge of the body. I had to take the body panel off before towing my Sparrow the two blocks home.

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.

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.

The slot in the back of the drive sprocket where the pin fit in.

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.

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.

The new bolt extends through the hole in the sprocket. Click the picture to zoom in on the broken weld.

The finished repair.
The sprocket slips a few degrees when I switch from forward to reverse or the other way.

August 2008 Update

The pin through the axle breaks and the sprocket spins on the rear axel. I suspect that the drill bit shank I used as a pin almost 2 years ago broke in the first few weeks, but the force of the 5/8 inch bolt kept the sprocket from spinning earlier. I think it may have broken earlier because the sprocket would rock just a bit every time I switched between forward and reverse.

I replace this 1/4 inch pin with one I cut from spring steel. It breaks right away.

I replaced the 1/4 in pin with a 3/8th inch pin. This involved drilling out the hole through the axel, drilling out the hole in the 5/8th inch bolt, and having the back of the sprocket machined out to be both wider and deeper to accept the new pin. The guy at the machine shop found a tempered pin that was longer than what I started with and so the slot in the back of the sprocket had to be made longer too.

Below is the new 3/8th inch pin, and the remnates of the previous two pins.

	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.
	The slot in the back of the drive sprocket where the pin fit in.
	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.
	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.
	The new bolt extends through the hole in the sprocket. Click the picture to zoom in on the broken weld.
	The finished repair. The sprocket slips a few degrees when I switch from forward to reverse or the other way.