While working on my first build, I found a simple and repeatable way to true the rear rag mounted sprocket. The rubber discs included in my kit were not cut consistent in thickness. And after initially mounting the sprocket, a spin of the tire rewarded me with a significantly wobbly sprocket. I tried to true it by eye for a few frustrating hours then sat back and thought there must be a better way.
Tools needed in addition to your sprocket parts and wrenches:
Scrap piece of 1x2 about 7 inches long or similar scrap wood.
Machinist dial indicator. You can get one from HarborFreight for about 15 bucks.
2 to 3 inch C-clamp or other small clamp.
Refer to my photos below to make sense of the abbreviated instructions.
1) Loosely mount sprocket on wheel with the nine bolts just lightly tightened and mount wheel back on bicycle.
2) Cut about 2 inches off the scrap of wood. Cut a vee grove in the scrap of wood an inch from one end to enable clamping to the upper chain stay. Also cut a vee groove in the short piece of scrap.
3) Now using the c-clamp, clamp the long scrap to the upper chain stay as shown in the photos below.
4) Position your dial gauge on the wood so that the point is near the top of the sprocket and the plunger has been depressed two rotations of the needle. Secure the gauge here to the wood. I used a screw to secure it.
5) Now you can rotate your tire and watch the gauge to find the spot on the sprocket that is closest to the spokes. Zero your dial face here.
6) Now rotate your tire so that the next bolt in the sprocket is lined up with the plunger. Tighten that bolt until the dial reads zero. This will not require much tightening. This is okay.
7) Continue rotating the tire for the other seven bolts tightening each one until the dial reads zero. At this point, your sprocket is very close to true but your bolts are not very tight.
Repeat the following two steps until you have the bolts tightened to your satisifaction:
8) Now tighten the bolt you are on (doesn’t matter which bolt) a few turns and zero the dial indicator face again.
9) Repeat the process of tightening the next eight bolts until the needle reads zero for each one again. At this point the sprocket is very true and the bolts are a little bit tighter.
Last step after tightening all the bolts to your satisfaction is to spin the tire and watch the gauge. If the needle moves more than a few thousandths, you can stop the tire on the high spots and tighten those bolts to really true the sprocket.
On my build, I decided to use nyloc nuts to hopefully keep the sprocket true in use since every bolt is not tightened to the same torque. This meant I was removing the original nuts from an installed and trued sprocket so that I could install the nyloc nuts. But now that I can true the sprocket so reliably, I didn’t mind the task one bit. Later if I decide to remove the sprocket for any reason, I won’t hesitate in the task because I know that installing the sprocket will not involve any trial and error. By the way, my initially very wobbly sprocket trued to .003" with the nylocs. Watching the sprocket spin by eye looks absolutely perfect. You can't see the .003 that the dial indicator measures.
Tools needed in addition to your sprocket parts and wrenches:
Scrap piece of 1x2 about 7 inches long or similar scrap wood.
Machinist dial indicator. You can get one from HarborFreight for about 15 bucks.
2 to 3 inch C-clamp or other small clamp.
Refer to my photos below to make sense of the abbreviated instructions.
1) Loosely mount sprocket on wheel with the nine bolts just lightly tightened and mount wheel back on bicycle.
2) Cut about 2 inches off the scrap of wood. Cut a vee grove in the scrap of wood an inch from one end to enable clamping to the upper chain stay. Also cut a vee groove in the short piece of scrap.
3) Now using the c-clamp, clamp the long scrap to the upper chain stay as shown in the photos below.
4) Position your dial gauge on the wood so that the point is near the top of the sprocket and the plunger has been depressed two rotations of the needle. Secure the gauge here to the wood. I used a screw to secure it.
5) Now you can rotate your tire and watch the gauge to find the spot on the sprocket that is closest to the spokes. Zero your dial face here.
6) Now rotate your tire so that the next bolt in the sprocket is lined up with the plunger. Tighten that bolt until the dial reads zero. This will not require much tightening. This is okay.
7) Continue rotating the tire for the other seven bolts tightening each one until the dial reads zero. At this point, your sprocket is very close to true but your bolts are not very tight.
Repeat the following two steps until you have the bolts tightened to your satisifaction:
8) Now tighten the bolt you are on (doesn’t matter which bolt) a few turns and zero the dial indicator face again.
9) Repeat the process of tightening the next eight bolts until the needle reads zero for each one again. At this point the sprocket is very true and the bolts are a little bit tighter.
Last step after tightening all the bolts to your satisfaction is to spin the tire and watch the gauge. If the needle moves more than a few thousandths, you can stop the tire on the high spots and tighten those bolts to really true the sprocket.
On my build, I decided to use nyloc nuts to hopefully keep the sprocket true in use since every bolt is not tightened to the same torque. This meant I was removing the original nuts from an installed and trued sprocket so that I could install the nyloc nuts. But now that I can true the sprocket so reliably, I didn’t mind the task one bit. Later if I decide to remove the sprocket for any reason, I won’t hesitate in the task because I know that installing the sprocket will not involve any trial and error. By the way, my initially very wobbly sprocket trued to .003" with the nylocs. Watching the sprocket spin by eye looks absolutely perfect. You can't see the .003 that the dial indicator measures.
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