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  #1 (permalink)  
Old 01-19-2014, 10:59 AM
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Drive Alignment Problem, please help

First of all, sorry for the long post:
Drive Alignment Issue, final drive belt walks to the left on an RSD tranny.

I am having a heck of a time getting my final drive belt to track to the outside of my transmission pulley. I will start with the basics of the setup and then let you know what I have tried to fix it.

Hardtail frame
Demon 114 motor
Ultima 6 speed RSD
1.5 Gates Poly belt 139 tooth
Vulcan works transmission pulley with offset built in

I have been working on this problem for over a week and can't seem to get it straightened out. I have:
1. Zero'd all the motor mounts and the rear axle on a digital level to 0.0 degrees. Everything is level, square and straight.
2. Attached the primary to the engine and tranny and locked them down tight.
3. Installed them into the frame
4. squared them up to the frame taking measurements off the frame rails
5. Dropped in the rear axle and tire without spacers for now
6. Ran a straight edge from the tranny pulley to the rear sprocket pulley, squared them up
7. Checked the tranny pulley face it's both level and the face is a perfect 90 degrees
8. Also checked the rear drive pulley, it is also at 90 degrees
9. Put on the belt, correct tension and....

No dice, I can't get it to track. I always wants to pull in towards the frame (moves right to left).

Note: When I spin the wheel backwards, it will rotate towards the outside of the pulley so it moves left when the tire moves forward and right when it moves backward.

Things I have double and triple checked.
1. I checked the transmission pulley to make sure it didn't have a taper to it, driving it toward the bike, the pulley teeth have no taper, they are square.
2. I have opened up the tranny mount holes and swung the motor to the left and to the right and no matter what position the drivetrain is in, the belt still walks to the left on the tranny when the tire is rotated forward.
3. I have tried pulling the spacers out from the rear axle so that only the wheel is on, giving me free reign to move the tire back and forth from left to right to try and force the belt to on the tranny pulley to walk right and I can't do it without binding the belt on the rear pulley.
4. I have tried different tensions on the belt both overly loose and overly tight and right in the middle, still walks toward the frame (left).
5. I have taken the tranny pulley off and checked the level of the drive spline itself compared to the other side of the tranny, both are running level.
6. I have double and triple checked the distance from the center of the tranny to the center of the axle on both sides and they are perfectly even and square. I purchased a 5/16 solid rod and I run it through the middle of the transmission so it sticks out both sides, then I measure from the rod to the center of the axle bolts. Its square.

So, all the math, physics and geometry tells me that if the engine and transmission are square in the frame and the transmission drive is perpendicular to the centerline of the frame and the rear axle is both level with the transmission and square to the transmission and the pulley faces on the transmission and final drive are flush with each other, there is no possible way that belt should walk...but it does every time.

My final resort was having a piece of plate glass cut that was 1.5 x 25. I laid it on the face of both pulleys. The glass tells me that I am square but there is a tiny bit of rock to it. Maybe .005 so there is an extremely slight twist. When I measure the depths of the groove on the final drive pulley to the runoff guard I do find there is approximately a .010 difference from side to side which is where the twist might be coming from but I can't image that a twist in the belt, that small over a 24 span would make the belt walk.

I am completely out of ideas. I have read leagues of threads on everything pertaining to belt alignment and tried everything I can think of. Hopefully someone out there has some clue as to what is going on.

Thanks in advance.

Shadetree
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  #2 (permalink)  
Old 01-19-2014, 01:44 PM
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Looks like u have checked everything...this may sound silly but did you try flipping the belt around and installing it the other way...in other words if the lettering on the belt is facing u so I came be read..flip it around so it reads backwards...I know shouldn't make any diff.. but just something to try.
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Old 01-19-2014, 02:20 PM
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Here's what I recommend, center the rear wheel within the frame, set the transmission on the trans mount without tightening the nuts on the studs and determine what it takes to get the trans pulley to track straight with the rear wheel then go from there. You want to work from back to front, get the rear wheel centered, get your belt/chain alignment correct, install your engine, then your primary goes on and you may have to shim the trans at this point.
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Old 01-19-2014, 04:23 PM
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Quote:
Originally Posted by barl View Post
Looks like u have checked everything...this may sound silly but did you try flipping the belt around and installing it the other way...in other words if the lettering on the belt is facing u so I came be read..flip it around so it reads backwards...I know shouldn't make any diff.. but just something to try.
Barl,

Yup, thanks for asking, I knew I was forgetting something to add to the "things I have tried" list but yeah, I read a few threads that said they weren't directional but I flipped it anyway, just to rule it out.

Good thought.

Thanks,

ST
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  #5 (permalink)  
Old 01-19-2014, 04:33 PM
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Quote:
Originally Posted by Captain America View Post
Here's what I recommend, center the rear wheel within the frame, set the transmission on the trans mount without tightening the nuts on the studs and determine what it takes to get the trans pulley to track straight with the rear wheel then go from there. You want to work from back to front, get the rear wheel centered, get your belt/chain alignment correct, install your engine, then your primary goes on and you may have to shim the trans at this point.
Thanks Captain,

Will do. I have set it up from the rear a couple times already. I use a tight string and run it up to the front forks, then drop a weighted line off the side of the forks and measure from there. Once the rear wheel is adjusted so that the string is barely touching on either side of the tire, I marked the frame and the axle adjuster plate so that I could go back and bring it into alignment at any time.

To get the drive pulley and the tranny pulley flush with each other, I have to move the tire over to the left side of the bike 1/4" to get the engine and tranny to line up, if I leave it perfectly centered in the bike, I can't get the pulleys flush. But even when I cheat the wheel to the right to try and use the left side of the drive pulley to pressure the belt over to the right on the tranny pulley, it begins to bind and make noise before it walks over, so its no bueno.

Here is a question that might help. After researching this topic I have found two different threads that have said opposite things regarding the angle of a pulley and which way the belt will run. One thread said that the belt will always try and "climb the hill" or go to the end of the pulley that is farthest away from the other pulley. The other thread that I read said the opposite, that the belt will always go toward the path of least resistance or "down the hill" (towards the side of the pulley that is closest to the other pulley). Since my pulley always goes to the left whether I have the engine and tranny slightly canted to the left or right, I don't know the answer to the riddle. Any ideas?

Thanks,

ST
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Old 01-23-2014, 07:56 AM
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Any ideas guys??? Still struggling with this.

Thanks
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  #7 (permalink)  
Old 01-23-2014, 08:53 AM
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very few things will make a belt walk. defective belt, as said, turn it around and it'll walk the other way if its defective. worn sprocket teeth, belt to tight or loose, sprockets not aligned or sprockets not square.
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Old 01-23-2014, 03:57 PM
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Thanks Redwings.

That is what is so frustrating about this problem and probably why there has been little feedback. The belt is brand new, the pulleys are brand new, the tranny pulley is new, I tried running the belt the other way and it was the same, tried it loose and tight, etc.

I think I might order another belt, I just don't know what else to try at this point.

Thanks,

ST
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