Bicycle Mechanics - Chainring Bolts Loosening

What could be causing the chainring bolts to loosen up every week or so? The bike is a fixed gear conversion and I'm using the bolts that came on the bike with an extra spacer on each bolt. 5 bolts and 10 spacers. There is a space on each side of the chainring.

They come noticable loose to the point where they almost fell off the day when I first noticed that it was happening, but now I just tighten them every week or so when I notice them getting looser, but I'm wondering what is causing it?

Is it loosening up because of the spacers?

Or are the bolts just old? Its an 80's steel frame bike and I'm guessing that its original from then.

Two possibilities:
1) You're just not tightening them enough. (Unlikely, no?)
2) The overall bolt length is too great.

Why are you using two spacers? In most application with a space there is one spacer between the ring and the spider.

Two possibilities:
1) You're just not tightening them enough. (Unlikely, no?)
2) The overall bolt length is too great.

Why are you using two spacers? In most application with a space there is one spacer between the ring and the spider.

1) Without using a machine of some sort they are not going to be getting any tighter, so that is rather unlikely.

2) Most likely

I'm using two spacers because it is a fixed gear conversion. The bolts that were originally on there held one spacer and two chainrings. I eliminated the one chainring and was required to add a spacer to still use the original bolts. With just one spacer the bolts will hit each other and therefore cannot be tightened anymore and the chainring is then loose.

definitely check the bolt length. If it is even (apparently) flush, that is too long. Grind a bit off the end of the bolt? Or, if there is a machined depression for the bolt head or nut to fit into, you could slip the fing around so the overall thickness of the spider arm/ring was a tad more.

Properly tightened, spacers should not be an issue. However, they do add some leverage to the mix where you don't want it, so they could be a contributing factor.

Riding fixed just adds a lot of stresses to the ring/crank interface. Crank those bolts down tight. Maybe put some locktite on them. Or, alternatively, add some grease to the threads, counterintuitively it lets you get them a bit tighter.

jim

problem should be solved by buying a set of 5 single stack chainring bolts from LBS or online. should cost about 3 - 5 bucks. make sure to grease the threads and tighten them well when you install...

problem should be solved by buying a set of 5 single stack chainring bolts from LBS or online. should cost about 3 - 5 bucks. make sure to grease the threads and tighten them well when you install...

Agree. Hell my LBS just gave me some.

Oh!! I think I firured something out. Perhaps mechanical precession. The bolts on a chainring are right-hand threaded so mechanical precession acts in the tightening direction. Now that you're fixie, The mechanical precession of pedaling backwards would act to untighten the bolts.

Unless he is a circus rider, I doubt he is doing much backwards pedaling. Perhaps backpressure, but would not have the same effect.

jim

Oh!! I think I firured something out. Perhaps mechanical precession. The bolts on a chainring are right-hand threaded so mechanical precession acts in the tightening direction. Now that you're fixie, The mechanical precession of pedaling backwards would act to untighten the bolts.

The OP's problem is caused by incorrectly spaced out chainringi bolts or incorrect torque.

Most likely the cranks are worn. That is the hole that fits over the BB spindle may be rounded; hence the cranks won't stay tight because there is play in the interface.

I had a similar problem with a single chainring. I fixed it using a spring washer.

Alright I'll see if I can get some from my LBS.

I'm not doing any backwards pedaling at all, just back pressure to slow down and stop.

The torque is most definitely correct or over tightened.

Cranks being worn would not have anything to do with a chainring being loose. The cranks are not loose, just the chainring.

Shorter bolts seems like the way to go on this one, so I'll be trying that one first.

Hang on, we keep talking about "bolts" but it's not the bolts that define the effective length of the fastener. It is the "nuts" - the female bit. The bolts just have to be long enough to catch in the nut. The nuts are through-threaded so the bolts can be as long as you want.

But the nuts cannot be longer than the depth of (spider + spacer(s) + ring(s)). Get shorter nuts or grind them down. Also, a spacer that bottoms on a nut - has an inner diameter smaller than the nut outer diameter - will cause the same type of problem.