Shimano XT M737 Chainset issues

[DoctorRad]

Second on my list of potential issues with retro kit...

I'd been having problems with chainsuck with an M737 chainset for a while but didn't realise until yesterday exactly what was going on. Using an 8-speed SRAM chain and the particular combination of chainrings I was using, it's possible for the chain to get jammed behind the granny ring when shifting down from the middle ring. I had to loosen bolts on the granny ring to free the chain.

The middle ring on my setup doesn't have any ramps or pins, so the chain just drops straight off the side. It appears that there is a large enough gap next to the granny ring for the chain to get jammed in, but that the original Shimano middle ring had ramps and pins long enough to ensure that the chain wouldn't ever drop into this gap. Without the pins (i.e. with many other chainrings) the chain will drop into the gap and jam.

Anyone else encountered the problem?

 

[legrandefromage]

change the chain ring then or fit spacers to suit. Its not just 'retro' either I get the same on a Truvativ chainset.

A worn chainring can look ok but literally 'suck' the chain up as you pedal too. Seen this on a Kona Dr. Dew where it was commuted just on the middle ring day in day out. After 6 months the chain had ground its way deeper into the soft alloy ring and ended as the perfect chain suck device. It was only noticeable under load. It would present itself on a bike stand.

The cure was a new ring and chain.

 

[DoctorRad]

Hadn't though of spacing the middle ring in a little... doh! Never had to use chainring spacers before...