apollored

When I was out on Sunday last:

https://www.bikeforums.net/showthread...=#post15827719

I was riding my bike down a slope and into a small stream ( to create a splash for a photo which involved riding down a stony slope and then off a small lip into a stream and then riding up a slope, turning round and coming back down.

I did that twice and then rode back up the small slope and got off my bike to hold a piece of fingerpost of the Pennine Bridleway for another pic.

When I got back on my bike I found I couldnt pedal it forward and it felt like the gears had slipped. I changed gear but it still wouldnt pedal so I jumped off and turned the bike upside down to find out what was wrong.

I found that the chain had come off the front chainring and jammed itself between it and the frame also becoming twisted in on itself.

I couldnt free it so had to finish the ride on foot and then take my bike to the LBS who have freed it up for me and I will pick it up tomorrow.

What could have caused that?

Have never known it to happen before, tho the chainring is worn and needs replacing the chain is new as are the rear chainring and jockey wheels.

Before those were replaced the chain used to jump off regularly but never jammed like that before.

Would appreciate any advice thanks.

Hopefully will be able to replace the chainring tomorrow.

FBinNY 

This could be classic chain suck, where friction keeps the chain from disengaging at the bottom of the chainrings and it gets carried up and jammed into, or past the chainstay where there's limited clearance.

It could also be that you somehow dropped the chain and got it jammed in there.

Wet conditions stream crossings and loose mud are notorious for causing suck, because water washes out lube, and carries fine silt into the chain. When the water evaporates it leaves the silt behind which increases the chain's internal friction and causes suck.

There could also be other causes, so this is simply a general analysis. Better or more specific analysis, would require seeing the bike.

fietsbob

there are accessory chain minders that backstop at the top, keep the chain from going past the 3rd ring while you rude.

apollored

FBinNY 

A photo, taken at the distance isn't what I meant. You have to let an experience mechanic take a look at it in the flesh.

Or at the very least, check the chain for any sign of stiffness, binding or stiff links. The condition of the chainrings is also a factor, as is whether this happened randomly or while shifting.

apollored

I have left in Halfords for a mechanic to check it and possibly replace the rear mech if thats what is needed, he wasnt totally sure that was the problem.

It happened when I tried to pedal away on a slope, first I couldnt move the pedals, then I tried to change gear to move the chain to another ring but it felt worse.

I probably should have jumped off when it first felt wrong, the chain may have jumped off as it did when I had the old chain on and worn rear chainring but since I had them replaced I didnt think it would do it again.

Mmm didnt help the situation I dont think

apollored

Mechanic in Halfords said there isnt anything wrong with the rear mech or hanger.

So it was prob the water or silt as you say which caused it, will need to be more aware of that when out on rides.

FBinNY 

Without mentioning names or brands, a decent chain lube keeps water and the silt it carries out of your chain.

gyozadude

Another tip to avoid possible chain suck is to think about tension on a chain and if you plan to take a lot of bumps and ride rough, you may want to keep more tension on the chain. So keep the chain in big rear, if you're on the small front, or better, middle front, big rear to yet more tension. The chain has some mass and inertia. If you jolt the bike, you might not feel like it's sharp impact because you're standing on the pedals with bent knees and can absorb it. But the chain is heavy metal and can get thrown unless tension keeps it on the gears. On MTBs with long-armed rear derailleurs, if you're in the small chainring up front and somewhere in the middle in the back, there's a lot of stretch left in that RD arm and it doesn't exert much tension on the chain.

timvan_78

LOL, I think I see some silt in there! Also, looks like some of the lube washed off.

apollored

LOL well she didnt get wet till a lot later in the day, then she got well soaked lol

apollored

I'll do that, also the chain did look loose when the hanger was moved so possibly a link out of the chain might be a good thing, esp as I may be going to MTB Trail Centres more often now, up to blue and red level so I need to think about where I'm keeping the chain on the rough stuff