Wandering chain tension

[Vintagewannabe]

So I have a 520 conversion kit on my 73 RD350, bought from economy cycle with a DID ert3 chain. The setup has about 500 miles on it.
So my problem is that at one point in the chain, my slack will be at 1 1/4", another 1 3/8, and at its tightest 3/4".
I thought at first that it was the chain, but I am beginning to think rear sprocket. I marked the sprocket, and as I roll the wheel around, every time the sprocket is at the same point, the chain gets tight, regardless of where it falls on the chain. If I just spin the wheel around say 180°, the chain loosens up.
Has anyone experienced this? I talked to economy cycle and he said they have never run into this issue.
 The wheel is aligned, chain is straight, tire is centered in the swingarm.
I checked the runout of the sprocket by putting a ziptie on the swingarm, and a section of about 12 teeth would contact the ziptie, then the rest would be about 1mm or less from touching. I dont know if this is acceptable because I have never checked one, just trying to see if I can find my issue. I can include pics if someone thinks I may have something there

[m in sc]

sounds like might be the cush drive rubbers failing. also check the carrier bearing

[quocle603]

I had this similar issue on another bike. I believe it was a warped sprocket. Ended up changing it and it resolved it. Your conversion kit is probably new, but doesnt hurt to check if its true

[Vintagewannabe]

The cush drive is new, and is pretty tight. I checked the drive for any play around the axle or any deflection,  but I can check again.
quocle603, the conversion kit is new, but how do you mean to check if its true?
I am also considering just getting another sprocket and trying that as well

[pdxjim]

Pretty common in my experience.

Make sure the axle adjusters are even, the chain run is straight, and split the difference.

The tight bit will wear faster than the loose bit, and it'll all even out in the end.

[Vintagewannabe]

Pretty common in my experience.

Make sure the axle adjusters are even, the chain run is straight, and split the difference.

The tight bit will wear faster than the loose bit, and it'll all even out in the end.

all of that is even, and the chain and sprockets are all straight and aligned.
How many times have you seen tjis work out? The only time I have run into it was a worn out chain that was not maintained.

[paul1478]

for my bike, it was the swingarm bushings...

[RDnuTZ]

I've had it many times with worn chains on my dirt bikes. As noted above chains don't always stretch evenly.

[1976RD400C]

That doesn't seem like something to worry about. I would adjust the chain so it has 1 1/2" at the tight spot. Then put it on the center stand and spin the wheel by hand and watch the lower run of the chain and if it's not moving up and down more than 1/2" I think you're good.

[m in sc]

I agree.  if everything else is good just lube it and run it.

[klaird]

Check you front sprocket too.  I had a similar problem and it turned out the splines were not in the center of the front sprocket.

[Simoniz]

I had this on my RD250LC back in the 1980s, and was puzzled by it too. Turned out the rear wheel bearings were collapsing. Get your back wheel off and put in new bearings to correct it.

[sav0r (CL MotoTech)]

This thread deserves a sticky. It's a good resource for chain tension issues. Many great places to look that don't necessarily come to mind immediately. At least for me.

My two cents is that I always adjust tension to the tight spot. If the tight spot is egregious, then I try to spot the issue. A sticky link for example. Though eccentric sprockets have been found too. 

[Vintagewannabe]

I will doulbe check the bearings and front sprocket. One of my worries about just adjusting for the loose spot, is that it would be so loose on other spots it might drag on the swingarm, and these are not set up for that. Also if the sprocket is the problem, would it. Not just continue making the chain worse?
I haven't found any sticky spots in the chain yet, but I can double check.

[quocle603]

The cush drive is new, and is pretty tight. I checked the drive for any play around the axle or any deflection,  but I can check again.
quocle603, the conversion kit is new, but how do you mean to check if its true?
I am also considering just getting another sprocket and trying that as well

You can always put a dial indicator to it to see if there is any major run out. I would just lay it on some glass to see if it isnt warped.

Good luck. It seems like there other possible reasons from others.