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
sounds like might be the cush drive rubbers failing. also check the carrier bearing
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
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
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.
Quote from: pdxjim on September 17, 2025, 01:37:17 AMPretty 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.
for my bike, it was the swingarm bushings...
I've had it many times with worn chains on my dirt bikes. As noted above chains don't always stretch evenly.
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.
I agree. if everything else is good just lube it and run it.
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.
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.
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.
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.
Quote from: Vintagewannabe on September 16, 2025, 09:53:52 PMThe 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.
To rule out manufacturing issues (defects) with the chain you can measure sections of 10-14 links with calipers in different spots around the chain. Compare the section where it's tight to where it is looser. If it's not the chain then you have radial runout on one (or both) of the sprockets.
Quote from: SoCal250 on September 17, 2025, 02:27:59 PMTo rule out manufacturing issues (defects) with the chain you can measure sections of 10-14 links with calipers in different spots around the chain. Compare the section where it's tight to where it is looser. If it's not the chain then you have radial runout on one (or both) of the sprockets.
This is my plan for my next move, as well as putting the wheel on a truing stand and checking sprocket runout in all directions, and checking bearings.
So I pulled the rear wheel, and checked the sprocket, and bearings. Wheel bearings were perfect, cush drive is still good, looks like my carrier bearing has a bit of play, like if you were to try and twist the carrier on the axle, same way you check wheel bearings on the bike.
So once I had the wheel on the truing stand, I checked the sprocket and it acted out of round. Sat the wheel on the ground, and realized that around the carrier, inside the center bore of the rear sprocket there was a large gap on one side and none on the other. The taller area fell between the two green dots I made, which falls in line with all the slack in the sprocket being on that side.
So I pulled the rear sprocket and the center bore of the sprocket was 1mm larger than the hub on the sprocket carrier. Any other sprocket I have fitted has been a tight fit, but this one is definitely not, but I did not think much of it at time of install.
I have it back together, and now there is a much smaller variation in chain tension. About 1/4 in or less, vs the 3/4 it was.
Has anyone else had a sprocket that loose on the hub? I'm thinking of just ordering a custom one from sprocket specialists.
actually, no but that def explains it. you always want the sprocket to be hubcentric. if that's from economy, reach out to John. also, look into rebel gears, they may have one as well
Quote from: Vintagewannabe on September 23, 2025, 10:30:43 AMSo I pulled the rear wheel, and checked the sprocket, and bearings. Wheel bearings were perfect, cush drive is still good, looks like my carrier bearing has a bit of play, like if you were to try and twist the carrier on the axle, same way you check wheel bearings on the bike.
So once I had the wheel on the truing stand, I checked the sprocket and it acted out of round. Sat the wheel on the ground, and realized that around the carrier, inside the center bore of the rear sprocket there was a large gap on one side and none on the other. The taller area fell between the two green dots I made, which falls in line with all the slack in the sprocket being on that side.
So I pulled the rear sprocket and the center bore of the sprocket was 1mm larger than the hub on the sprocket carrier. Any other sprocket I have fitted has been a tight fit, but this one is definitely not, but I did not think much of it at time of install.
I have it back together, and now there is a much smaller variation in chain tension. About 1/4 in or less, vs the 3/4 it was.
Has anyone else had a sprocket that loose on the hub? I'm thinking of just ordering a custom one from sprocket specialists.
Based on what you have posted previously, it appears to me that the sprocket has been the issue.
Not sure if you turned it 180 degrees when you reinstalled it, but there's a chance that could improve the inconsistent tension.
It seems like that sprocket is out of spec in a few ways.
I am pretty dead set that the sprocket is my problem.
I didn't spin the sprocket, I just centered that extra slop that it has. I am going to make some calls to see if the numbers I got line up with the specs that economy cycle has, and the manufacturer rebel gears.
It certainly shouldn't have to rely on the bolts to center it, it needs the hub to fit, like rotors and wheels on a car.
automotive wheel lug nuts are tapered on 1 end which does help center the wheel :umm:
there used to be bolt centric wheels,, or were more common vw vugs come to mind. but the taper nuts are there so the load is spread out better. and not against the threads. also a tapered nut has less chance of backing off. hub centric, way better 0.02
Good to see you found the solution to the weirdness. It's unusual to see one like this that is too big in the center. At least sprockets are easy to replace.