Wierd Chain Tension Discovery

Kevin B · Feb 20, 2023

It seemed like the wheel nuts were slipping or something on my 2009 Schwinn cruiser. I'd set the tension then it would be too tight or loose. Checking it out I found the chain would tighten and loosen during a revolution of the crank. It was going from too tight to too loose. Wheel cog is new, chain is low mileage, bottom bracket seems to spin true. I figured it had to be the front sprocket. Replaced it and all is good. This sprocket has better than 5k on it. Inspection shows the sides of the teeth are galled and the teeth gaps are worn on the side that gets the power applied. I think it has worn eliptical somehow. Would not have expected that.

rickpaulos · Feb 20, 2023

I see it all the time one cheap wallyworld kids bikes with not very many miles. Chain going tight & loose is usually due to worn out bearing cups, cones and ball bearings. . I have to teach the newer volunteers at the local coop how to adjust the chain. Look for the tight spot and adjust from there. When the chain goes tight it puts excess pressure on the bearings in the rear hub too and can trash the hub cones and bearings. And the chain will wear out fast too.

outskirtscustoms · Mar 14, 2023

I have seen this happen in BMX bikes from bent axles and bad bearings. Might give them an inspection just to see.

Kevin B · Mar 14, 2023

Thanks, just to be sure I went ahead and replaced the bottom bracket too.

Ulu · Mar 14, 2023

And here I paid good money for an elliptical sprocket.

Son of Kradus · Mar 14, 2023

rickpaulos said:
I see it all the time one cheap wallyworld kids bikes with not very many miles. Chain going tight & loose is usually due to worn out bearing cups, cones and ball bearings. . I have to teach the newer volunteers at the local coop how to adjust the chain. Look for the tight spot and adjust from there. When the chain goes tight it puts excess pressure on the bearings in the rear hub too and can trash the hub cones and bearings. And the chain will wear out fast too.

WOW, Thanks! if your super thrifty and rebuilding with scraps, remove the bearing cups and spin them 180, maybe try n even the wear out..... ive never noticed this coz most of my rebuilt stuff has gears with derailleurs, but I do rebuild from junk so ,,,,Hmmmmm very interesting topic!