Need help on rear wheel alignment

[pa-powerstroke]

So here's the deal, I have a 74 frame with a voodoo vintage hardtail on it. We did the hardtail ourselves, not the first time we have done one and we measured a million times to make sure it was on straight. So now the motor is in and we are trying to get the rear wheel lined up on the axle so the chain is perfectly straight. We got the chain straight, the back wheel seems to be in line with the backbone of the bike but when we measure from either side of the hardtail to the wheel, the wheel seems to be sitting about 1/2 inch to the left of center. If the sprockets are lined up perfectly I don't understand how this could be. Does anyone have a sure fire way of ensuring the back wheel is in line with the front? If it is a half inch off what is going happen when trying to ride/turn? And finally what does everyone use as wheel spacers because my stock ones won't work. This whole issue has me puzzled and if I can make sure the back wheel is inline with the front I'll be happy and continue on.

 

[chizler62]

what I'd do...
Roll the rear wheel several times and where ever you check. The chain is centered on the sprocket. Slight space between tooth and inner chain plates. Regardless of axle plate, drop out indexing marks, chain adj etc
Snug axle
Run a small string, like yarn or the like from one axle plate face leading up around the head tube and back down to the similar place on the other axle plate. Be sure the string doesn't hit anything along the way, cables etc especially around headtube, and has good tension. Measure from the string to the top edge of the rim where it meets the tire on both sides. Given the rim is true. Spin it and do it in several spots to ensure you don't get a dent or the like giving a false reading.
that will let you know if the rear wheel is in alignment with the head tube, which is aligned with the front wheel unless the axle spacing of the front wheel is screwed up?

As far as axles spacers? I don't know. I make my own on a lathe. I'd suspect that's polly what you'll end up doing. Be glad to help out if you can't get it done locally.

From your post you seem skilled and I hope this gets the ball rolling for you!

 

[chizler62]

I should also add, before I ever even mock up a rear wheel you must ensure that the drop outs or axle plates are in alignment themselves. Basically they must be parallel to each other. I made a tool that does it easily and quickly.
if one side is in plane with the headtube and the other is off 12 degrees you'll be in a mess.
I'd remove wheel and check for that before my suggestion above.

 

[chizler62]

I should also add, before I ever even mock up a rear wheel you must ensure that the drop outs or axle plates are in alignment themselves. Basically they must be parallel to each other. I made a tool that does it easily and quickly.
if one side is in plane with the headtube and the other is off 12 degrees you'll be in a mess.
I'd remove wheel and check for that before my suggestion above.

 

[pa-powerstroke]

Thanks for the help, I think I will end up getting a guy I know that has a little machine shop to lathe me some spacers.
But I believe my hardtail to be on straight from all the measurements Ive done, so this doesn't worry me too much. And from all the research I have been doing the sprockets lining up is the MOST important thing, seems obvious right? Checking the space between the sprocket and axle plates like you said seems like the best way to go about this. Apparently it is not uncommon for the offset on the front sprocket to make the rear tire not "truly centered".

From "Two Wheel Terror" on thechopperunderground.com
"Normal. Before you buy/make/steal any spacers, mock uo the chain. Many motors have the drive sprocket offset from the actual "centerline" as you think of it.

Thus you may need a short and a long spacer to get the chain or belt straight.

Dont woory, it will still track true with two slightly different wheel placements. That is as long as everything else was welded up true, straight and plum."

 

[TwoManyXS1Bs]

Maybe you're experiencing that same slight frame offset/cant that Steveair2 ran into:

http://www.xs650.com/forum/showthread.php?t=36707