Chainring bolt wont tighten

[Kestevan]

I've had several issues with chainring bolts working loose. I've now got 1 that wont fully tighten at all. The threads engage for a couple of turns, but it then simply goes slack again before nipping up.

This is on a shimano 105 5800 chainset so unfortunately the bolt isn't the older 2 part device, but simply screws directly into the spider.

What's the best way to fix this (preferably short of replacing the chainset)? I'd thought of wrapping ptfe tape round the bolt, or using glue/threadlock but not sure if either will work.

 

[Kestevan]

Have you tried swapping the bolts? It probably isn't the bolt, as they are normally harder than the thread in the chainset but it is worth a go to see.

Yeah, tried that.. it's the thread that's gone I'm afraid.

 

[Cycleops]

Bit of a bummer. The only way short of replacement is to find the next size up allen bolt and re tap the thread.
BTW I have noticed these bolts come loose quite frequently, always worth checking and maybe using loctite.

 

[fossyant]

Knackered I'm afraid. Had that happen on a SRAM MTB chainset, but fortunately the thread was in the chain ring, but it meant a new chainring. Much prefer the bolt and nut setup.

You might be able to try one of the permanent threadlocks, but it's unlikely to last.

 

[Kestevan]

Looking at it, it may actually be the outer ring that's threaded....not that it matters price is pretty comparable between ring and whole new chainset....

Arse!

 

[Yellow Saddle]

Let's have a look at a photo. Perhaps there's a work-around. I just can't picture the angles involved.
Note that stripped threads cannot be retapped as is often suggested here. Once the thread is stripped, there's no meat left for retapping. The only solution is to go oversize.

 

[Illaveago]

As above a picture might help us to come up with a solution. The old chain rings used a nut and bolt system Which might not be ideal but might be a way out. You say that it grips to begin with and then goes slack. To me that sounds like it is the shoulder end of the bolt that might be stripped. Would it tighten if you were to fit a washer to the bolt?

 

[Kestevan]

Well, didn't plan on spending lunchtime dismantling a crankset armed only with a mini tool and an Ikea teaspoon*... but I've managed to get it rideable enough to get me home.

As suggested by Fossy the threaded portion is actually in the outer ring. Removed the cranskset and all the chainbolts. Cleaned all the threads and could see that the loose one was damaged. Wrapped a goodly amount of ptfe tape round the bolt in the "dodgy" position. Carefully re-assembled and it's now tightened up enough to ride.

Think I'm going to order a new one, though I might Araldite the bolts in place and see how long this lasts in the interim...

Not sure about the Shimano 4 bolt crank design. The spaces between the bolts are so big, that once a bolt works loose, there's very little to stop the ring "twisting" and allowing the chain to unship.



The teaspoon handle was used as a temporary crankarm preload spanner as strangely enough this was missing from my mini tool.