laser sprocket alignment

jaguar

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#1
I thought I was using a good method of front/rear sprocket alignment by using a tape measure to get equidistant the right/left side of rear axle from the swingarm pipvot bolt. BUT when I double tested the results with a pen laser light I found out the light beam (aligned with rear sprocket) was pointing about 7mm to the left of the front sprocket!
So then I adjusted them accordingly. I expect much longer chain life now.
HOW I DID IT:
I cut off the top of a quart sized clear plastic water bottle where the neck meets the body. I put that (bottom end down) on the top of the rear sprocket and (in dim lighting) shone the red laser light through the bottle top in alignment with the rear sprocket (by keenly eying it). The light leaves a pinpoint reflection where it goes thru the plastic. Then of course I was able to see the dot of light to the left of the front sprocket (whereas it should of been shining on the front sprocket).
I bought the pen laser here for $2 but I think Radio Shack sells them in the states for $20.
Let me know if you try it and what results you get.
 
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Jaybird

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#3
I have tried, but cannot for the life of me picture what you are trying to explain with the bottle.
What does the bottle have to do with anything? If you shined the lazer through the plastic, is there any chance the light was slightly refracted?
7mm is quite a bit to be off and should have been easily apparent by eyesight that it was not in alignment.
I would double check my method if I were you.
I will stick to a straight edge running from the side of the rear to the front. Much easier and reliable. (no keen eyeing is involved, it either hits the side of the CS or it doesn't) A 50cent dowel rod or even a broomstick will do the trick.

I won't take anything away from laser alignments though. I've done a few of them in my day. When warranted, they are the ONLY method to use.

http://www.hamarlaser.com/systems/s600/600rotosys_3810.htm ;)
 
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#4
Yeah Jaguar I gotta say I’d need drawings & diagrams to follow that. If you laid the laser against the edge of the Rear sprocket you would have to be sure it was aligned straight,

which I guess you could do by laying it on a long flat edge (if the pencil shape was thin & flat) & rotating it to see if it touched the edge.

This would be a convenient way as it should point to the sprocket nut & a bit of thickness of the housing accounted for. I’ve always used the straight edge approach but it can be a bit of a pain when chain & frame rail gets in the way as you need the correct size edge but sturdy enough not to flex (or warp).

Convince me, I need a new gadget. :)
 

Houndog

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#5
How do you adjust back to alignment? I assume the snail 'thingys' will end up being on different numbers?
 

Smit-Dog

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#6
Originally posted by Jaybird
... A 50cent dowel rod or even a broomstick will do the trick.
I'd be leary of using anything made of wood, especially a broom stick that is frequently leaned against a wall. Wood warps.

I also question how to correctly align using the snail/cam/lobe type adjusters found on the KDX. Screw adjusters allow for very granular adjustments, but not the KDX adjusters. I always just keep the cam adjusters on the same number, and make sure the cam recesses are butted up tight against the little nub stops. Seems like the only adjustment option in this case is to increment/decrement to the next number on the cam plate, when the possibility is that the perfect alignment falls between two numbers.

While I agree that screw adjusters give you the ability for very fine adjustments, I'd also guess that because of that, there is a greater likelihood for the sprocket planes to be out of alignment. Seems to me that with the appropriate manufacturing tolerances in place, the cam/lobe type chain adjusters found on the KDX should provide sufficient sprocket alignment. I'd think that this would be especially true considering the relatively small surface area of the C/S sprocket. Also, given the fact that a pair of sprockets can be out of alignment on 3 separate planes, a bike's chain adjusters only accounts for 1 of these planes.

Thoughts, comments, corrections? Be easy on me, Jay!
 

Jaybird

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#7
Well, I can tell you don't shoot pool, Smit! :)

If you do use a wooden dowel,you can lay it on a flat surface and roll it. If it doesn't wobble at all, it is still true. And yes clearance can be a problem if your dowel is too thick.
You could also use a 2' steel rule.

We can only adjust on two axis'. In a perfect world our CS sprocket will be in the same plane as the rear, but as some of us know, spacers need to be used on occasion with some set-ups.
The other axis is what we adjust for with the chain adjusters. Once we get the sprockets true with each other and running in the same plane, we then need to adjust axis B for tension.
That is where the controversy between cam/lobe type and screw type adjusters comes into play.
With screw type adjusters you can precisely keep your chain tension adjusted in any given situation, with a cam type adjuster this is impossible to do.
I do not like cam type adjusters. They leave room for chain tension error and there is no way to correct it.
You are either too tight or too loose with a cam type adjustment...well yes, you can be spot-on by using them, but it will not stay that way when the chain does (and it eventually will) elongate. Being exactly correct and having the precise chain sag is a crap shoot at best with a cam type adjuster. Kaw (as well as other mfg's)should seriously think about changing this.
 

Smit-Dog

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#8
Originally posted by Jaybird
... You are either too tight or too loose with a cam type adjustment...well yes, you can be spot-on by using them, but it will not stay that way when the chain does (and it eventually will) elongate. Being exactly correct and having the precise chain sag is a crap shoot at best with a cam type adjuster.
I think that you're overplaying the fact that a cam-type adjuster is either too tight or too loose. Considering the amount of swingarm travel, and setting the correct chain slack, the incremental adjustments provided by the KDX cam adjusters are small enough to get the right amount of chain slack. I don't believe that it is a crap-shoot at all.

And regardless of the type of chain adjuster, the proper tension will not stay that way forever. Both types of chain adjusters are subject to this same issue. Can't single out the cam-type on this one!

Given good manufacturing tolerances, wouldn't you agree that cam-type adjusters would be easier/quicker to align sprockets, *if* the cams provided a sufficient amount of granularity? Do you really need the precision of a screw adjuster, given the environment and setup (i.e. swingarm travel, flying over whoops, flexing/twisting forces)?
 

Jaybird

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#9
See, the correct adjustment for the chain is only when the chain is in one position...it's tightest. Which for most is when the swingarm is in a straight line between CS and rear shaft. In all other postions the drive train will be looser than when it is in the condition I describe. You must be certain that your tension is correct for the tight situation or else jeapardize the components of the drive.
If you set your tension spot-on with a screw adjuster and it loosens just a bit during your ride, you can effectively get the exact adjustment back. Not so with a cam type adjuster. You may well be in between adjustment. And for that reason I CAN single out snail adjusters. Granted it's not of great concern that you are a bit too loose, but being a bit too tight, which can easily happen if you aren't careful, can and will be a problem.
Remember that on a sprocket take-up, when you move the adjuster only 1/16" you are actually removing 1/8" of travel. (1/16" on a side = 1/8" chain distance)
It doesn't take much screw at all to make the chain drastically move. The snails aren't precision enough for this.
Yes, I do feel you need the precision of the screw type adjusters, but only if you want to be correct. So many live with being less than, and thats OK if you are happy with it.
 

tedkxkdx

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#10
I really have a problem with my snail adjusters considering the sprocket sizes and chain length I am dealing with. My chain is a couple links short in the fact that I have the snail at 3.5 and it is a bit loose and at 4 it is tight.
I think if I had a couple more links I could better adjust for the 13-48 combo I am running. I think I am at 108 links.
 

Smit-Dog

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#11
Originally posted by Jaybird
... If you set your tension spot-on with a screw adjuster and it loosens just a bit during your ride, you can effectively get the exact adjustment back. Not so with a cam type adjuster. You may well be in between adjustment. And for that reason I CAN single out snail adjusters. Granted it's not of great concern that you are a bit too loose, but being a bit too tight, which can easily happen if you aren't careful, can and will be a problem.
Granted, the chain will be it's tightest, and at it's most correct tension, when the centerline of the CS sprocket is farthest from the CL of the rear sprocket. Consider then that the "most correct" tension is only in effect a minority of the time. At all other times it varies between correct tension, and acceptable slack (according to bike specifications).

Now, if the CLs of the sprockets were a fixed and constant distance, then I would totally agree with you that the precision of screw adjusters just can't be beat.

FWIW, I have yet to stop and adjust my chain during a ride. In fact, I have yet to adjust the chain at all (but it only has around 900 miles on it - O-ring type). Still in spec. Well, at least as close as a cam-type adjuster will get it... which happens to be in-spec.

Please keep in mind that I am usually pretty anal about things, but in the case of "correct" chain tension being an absolute, I'm tempering that with the reality of acceptable chain slack on a dirt bike. I don't have the manual in front of me, but I even think that the chain slack spec calls out a acceptable range, as opposed to an absolute. Given a range spec, I think that the cam-type adjuster works fine. My next bike, however, will most likely have screw adjusters.... but I don't think my chain slack maintenance approach will change.

... But then again, you're talking to a guy that doesn't compensate for barometric pressure, humidity, and ambient temperature when putting air in my tires! :scream:

I'm sure you've forgotten more about chains than I'll ever know, but these are my thoughts to date.... ignorant as they may be. ;)
 

Smit-Dog

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#12
Originally posted by tedkxkdx
I really have a problem with my snail adjusters considering the sprocket sizes and chain length I am dealing with. My chain is a couple links short ...
Now there's a compelling reason for screw adjusters. Although I still think given a cam design with enough grandularity, it'd work fine.
 

jaguar

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#13
I forgot to mention that you have to first take off the chain.
I tried to use the laser pointing such that it just grazed the side of the rear sprocket but that didn't work out. So then I wanted to have a way to point the light beam above the rear sprocket and align it by sight. But unless the light is hitting something (and therefore sending off some reflection) you can't see it. So then I came up with the clear plastic idea. Important also is head position. Close one eye and situate your head above and to the rear of the rear spocket. Move left or right until your eye can't see any of the side of the rear sprocket. Move vertically until you can see the two points of light (reflecting from the close side and the far side of the plastic) and the sprocket under them so that it will be obvious how to move the light to get it more in line with the sprocket.
Another way would be using smoke. Have a buddy blow smoke above the rear sprocket while you get the light in alignment with the rear sprocket.
Any true straight edge would work also but would it be as true as light? NO
 
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#14
Ok for starters re the snail cam adjuster debate my (poor old abused) KDX had worn the bumps off the snail so I had to re-file them. If they didn’t align straight one could modify the locator on the sw to correct for this.

Re tension, just to rark Jay up ;) My GasGas has snail tensioners which are infinitly adjustable. They just didn’t put any bumps on them. Having said this; it’s a trials bike & only in possession of several horsepower so it works just fine.

How about lube though? I’ve made a chain tensioner out of a block of lard, :scream: which is easy on the chain, subscribes to Jays dry lube theory & you can just slice a chunk off for a barbeque, but this can annoy the vegetarians. :flame:
 

Jaybird

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#15
Jaguar, I have no doubt that a good straight edge is MUCH truer than what you are describing. How in the world do you know you are true to the plane of the sprocket with your $2 laser and plastic bottle set-up? You don't.
Are you trusting that the body of the light is true? Perhaps truer than a machinists rule? Hmmmm.....

Smit, what Ted is describing is exactly what I'm talking about. And yes, this could be overcome if there were no detents in the adjusters, like David describes.

When you say "in spec", are you saying that the three finger method still holds true? Trust me, no bike manual goes indepth with chain tension. They simply give the comman rider an easy way to get close. Yes, even in good engineering books there is an acceptable range for sag and cantenary tension, but on dirt bikes, being just one bit too tight means disaster for the drive components.
The guy who takes his snail adjuster to the tight side instead of choosing the loose side, when the adjustment is in between, is in trouble. It only takes a few times of the shock compressing and the chain placing undue force on the chain, bearings, sprocket teeth, etc. before damage can and will occur.
But like many, get close and hope for the best. :)
I'm not quite certain, but is your argument that close is far better than being spot-on and correct? If so, then I have to agree....close is far better than being correct. (shakin head)

David, there is something that can be said for those who barbeque lard. Not sure what it is, but something can surely be said. LOL