Cycling UK Forum

I lent a friend a bike with an 8 speed MTB drivetrain, albeit running a 9 speed Deore FC-M530 triple chainset. Drivetrain had very few miles on it and worked perfectly.

The bike has just come back to me after the chain “went a bit rusty”. It was in fact rusted solid and there’s lots of corrosion on the plated steel parts of the drivetrain. Front mech was completely seized up too.

Having cleaned and lubricated everything and fitted a new Shimano HG-71 8 speed chain, it’s all good again except... there’s some chainsuck on the middle ring. Happens in all rear sprockets and gets worse with increased load. No sign of it when running on the stand. The teeth on the chainring don’t appear worn or hooked, but they are a bit crusty due to the corrosion event.

So my question is: is there a chance of this settling down after a few miles? Having spent a fair bit of time working on this today I’d like to just hand it back and say “it’ll sort itself if you keep it lubed”, but is that realistic?

This is a classic example of the horrors of road salt. The friend doesn’t use it much but must have ridden it in the wet in the winter and then left it for a while.

You could replace the middle chainring. You could also attach a few cable/zip ties on the chainstay with some excess tie sticking out so that if the chain "sucks up" it is knocked down by the cable ties. See last photo on this article https://reviews.mtbr.com/workbench-how-to-un-suck-your-chainsuck

LinusR wrote:You could replace the middle chainring. You could also attach a few cable/zip ties on the chainstay with some excess tie sticking out so that if the chain "sucks up" it is knocked down by the cable ties. See last photo on this article https://reviews.mtbr.com/workbench-how-to-un-suck-your-chainsuck

Yeah, just wondering if the lack of ‘normal’ wear on the chainring means I might get away with letting it all run in a bit. Hadn’t seen that cable tie trick before, cheers.

If the chainring isn't badly worn then you should be able to clean it up with a wire brush, well enough that you can at least inspect it properly. Chainsuck can be caused by

a) burrs on the tooth sides and/or
b) slight hooking of the teeth.

since the latter occurs under load only, I'm assuming that this is what is happening. The teeth will eventually wear down but it is debatable if this will happen before something dreadful does. You can also 'de-hook' chainrings with a file, which at the least can speed this process up, even if it doesn't cure it immediately.

New chainring is easiest.

cheers