What could cause the chain to be tight then loose as the wheel spins?

I am perplexed by this ongoing safety issue. I noticed that the chain is tight then loose then tight and so on as the wheel spins. My first thought is that something is bent. I took it all apart and I have found nothing is bent. I used a laser level to see into the drive sprocket, I have checked that the wheel is true.

Could it just be a bad chain adjustment on my part? The crazy thing is that everything seems good but this is an obvious safety issue and I am looking for any help on it. The one thing that I have yet to check is that I installed a license plate holder and it goes on the left side like a washer on the axle. Could this thing be making it out of alignment?

Any help is much appreciated, as always.

Pnedac

All chains will do that to sum degree. The chain should be adjusted when it's in the tightest part of the run. Set it there and forget about checking at differing locations in the run.

i know what your talking about and i think that is just how it is. Growing up with bmx bikes there is a tight and a loose side. I think its normal

Sprockets out of round, or good 'ol chain wear. If you replace both sprockets and the chain, it goes away for a good while. Using a new chain on worn sprockets makes it seem worse if it's the sprockets, but it's not unusual for them to wear that way anyway as a set, even if you do everything right and keep it clean and well lubed and don't adjust it too tight.
If it's killing you, get new sprockets and a new chain, but as I said, it's not unusual for a set to wear like that. The only way it's a safety issue is if the "loose" part will let you lift a link on the back side of the rear sprocket far enough to see the roller depression in the sprocket. If you can do that, it's beyond worn out. Here's more than you ever wanted to know about chain.
http://tsubaki.ca/pdf/library/the_Complete_guide_to_chain.pdf

Going on some bicycle experiance (the theory should be the same). Frozed link(s), depends on how old/worn the chain is. The tire is crooked, Make sure the chain adjusters are in the same location on both sides. The wheel is tracking forward and back, Make sure the axle is completely tightened down to specs. The sproket is out of round, see above.

Thanks everyone for the responses. I guess I feel better seeing these. I even brought my wife out to make sure I am not losing my mind. I just finished the build, the bike is great, but I noticed this last weekend while out riding and it caused concern. I do know a few things that make me more comfortable that these could be the driving issues: the chain is old, the sprockets are old. Perhaps the problem is solved. I will order up a new chain and and sprockets if for nothing more than the peace of mind.

the big mistake people will make with a new chain is to immediately go out and do a hole shot this stretches the chain in one spot, it should be run several hundred miles to stretch normally over the entire lenght of the chain and readjusted accordingly before any heavy load is put on it, it's also better to run a chain a little loose than to tight

jayel said:

the big mistake people will make with a new chain is to immediately go out and do a hole shot this stretches the chain in one spot, it should be run several hundred miles to stretch normally over the entire lenght of the chain and readjusted accordingly before any heavy load is put on it, it's also better to run a chain a little loose than to tight

Click to expand...

Both good points. In the Tsubaki bible I posted in the section on wear on a transmission chain (which is what we are dealing with) there is a graph that shows the initial high rate of wear as a break-in kind of period, when the chain will stretch further per service hour than it does for the rest of it's useful life, Which is 1.5% elongation for a power transmission belt. After that initial stretch is a prolonged plateau, consistient with proper care, (the useful service life) then a rapidly steepening point in the curve for wear, and loss of ultimate strength. For reasons of fit over the sprocket (also in the book) and the way it contacts the sprocket throughout it's life, looser is better than tighter. When in doubt, a little looser wins. The chain and sprockets wear together. As the chain elongates, so do the ramped areas of the teeth. As they explain in the book, the roller "collides" with the ramp of the sprocket tooth, and the chain has a natural resonance that creates vibration, which is perceptably, and mathematically worse with smaller sprockets, because there are more free links to flop with smaller sprockets. Great book, if you enjoy any form of mechanical engineering studies.

I've had "tight spots" in a chain before and it's often down to corrosion or dirt inside the link, generally the only proper fix is a new chain and new sprockets too if they're worn. Depending on how bad it is it can cause premature failure of the gearbox bearing and/or rear wheel bearing as the tight spot continually puts a load on it before letting it go slack again.

I've seen many people with chains adjusted too tight in my 45 years of working on motorcycles. The swingarm arcs and as the countershaft sprocket, the SA pivot and the axel line up, the chain is at maximum tightness. The initial adjustment must be loose enough that the chain doesn't bind tight when riding two up or hitting bumps. Driveline parts bend, break, slip and wear uneven if the chain is not adjusted properly.

You would think everyone knows this but I know from experience that way too many chains are misadjusted!

Tom

Lets start at your rear hub. Is the hub bore where the bearings seat perfectly centered so it spins true around the axle?
Is the flange the sprocket mount to perfectly centered around the bearing seats and does it run true around the axle?
Now on to the rear sprocket, is bore where it meets the flange perfectly centered to the teeth? Are all the teeth exactly the same size and distance from center.
The chain has 104 links, are they all the same length? The pins and rollers all the same size?
The front sprocket, the same applies here as the rear. The shaft the sprocket mounts on. Are the splines centered around the shaft center?
All the questions have the same answer, no they are all a bit off. Manufacturing tolerances let all these parts vary to a small amount.
Niow if you wanted to you can buy try moving the rear sprocket around one bolt hole at a time, checking for tight to loose variations and possibly get the offsets to cancel each other out. You can also do this on the front sprocket one spline at a time.
It's possible you might find a spot for each sprocket that minimizes the tight and loose spots.
Is it worth the time and trouble to do this? I don't think so. Check for chain and sprocket and chain wear. On the rear of the rear sprocket can you lift the chain off the sprocket more than 1/2 of a tooth? If so your chain and sprockets are worn to a point they should be replaced.
As others have said putting a new chain on old sprockets or new sprockets with old chain is not a good thing. The worn parts excessively wear the new parts.
Replace as a set. Keeping the chain properly lubed and adjusted will keep it working well for many thousands of miles.
Your repair manual should tell you how to inspect the chain and sprockets for wear as well as how to adjust it.
Leo

I have 22,000 miles on my current (Parts Unlimited) X-ring on my SV650, and it does not measure even 1% stretch yet. I lube it every 250-350 miles with 30W. It's a little messy, but the quietest running and longest lasting I've experienced. Will probably make 25K and change the set anyway. That's good miles to dollars. Parts Unlimited sealed chains are made by EK, not sure about the unsealed chains.

As well as you maintain your chain I'd bet you can get at least 50k on that chain. A friend ran a CC Rider o-ring chain for about that on his 74 FXE with a 93 inch Shovel head. The main reason he put a new one one is the clip type master link broke. He figured at 50 k he didn't owe the chain much.
It broke as he was pulling in to get gas, He gassed up and the bike wouldn't move. He looked and saw his chain was gone. He looked back the way he came and saw the chain layed out on the ground just where he pulled of the street, a hundered or so feet father he found the master link. Couldn't find the side plate or clip. The clip probably broke miles away and it took awhile for the for the side plate to fall off. As soon as the link fell out the chain just rolled off the sprockets.
He had some safty wire in his saddle bags, Put the chain back on, used the safety wire to twist around the pins and made it the 35 miles home.
Very lucky the chain didn't lock up the wheel.
Leo