chainring bolt confusion
05-06-15, 04:40 PM
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chainring bolt confusion
I have a Shimano FC-M391 Acera triple crankset and I need to replace all of the chainring bolts. I have seen various sizes on amazon butI am not sure about which sizes or ones to get. I need 8 of the bolts and 4 of the connecting backs.
05-06-15, 04:48 PM
#2
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Why do you "need to Replace them"? You can drop by a Bike shop and be shown in person.
Outers are double length
the granny if the Back side of the crank has the spacer built in does not need to be as long as one with a removable spacer ..
Outers are double length
the granny if the Back side of the crank has the spacer built in does not need to be as long as one with a removable spacer ..
05-06-15, 05:07 PM
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Most common are the bolt and nut sets for double rings, which are just about universal. The same design is used for single and some triples with only the length changing.
The separate screws that attach grannies to threaded holes in the arms, come in a few threads and are specific to the crank.
But, like Bob, I'm curious why you think they need replacing.
The separate screws that attach grannies to threaded holes in the arms, come in a few threads and are specific to the crank.
But, like Bob, I'm curious why you think they need replacing.
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FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
05-06-15, 05:24 PM
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i've come across three different lengths, single, twin, and triple, of what i would call standard chainring bolts/nuts and two different materials, steel and alloy. the length always seems to make a difference. the short ones are too short for anything but single chainrings. the twin chainring bolts are too long for singles and too short for triples and the triple chainring bolts are too long for anything but triples. i've found some exceptions too.
sometimes, the washers that show up on some crank's chainring bolts are useful.
recently, shimano on their new road hollowtech cranks don't use the nuts, and the heads on the bolts are designed for use with a torx headed wrench. they are a soft alloy and the heads, i think, are designed to strip before the threads. i think, in order to avoid destroying the crank altogether. looking at that crank, i don't think it should be a problem.
sometimes, the washers that show up on some crank's chainring bolts are useful.
recently, shimano on their new road hollowtech cranks don't use the nuts, and the heads on the bolts are designed for use with a torx headed wrench. they are a soft alloy and the heads, i think, are designed to strip before the threads. i think, in order to avoid destroying the crank altogether. looking at that crank, i don't think it should be a problem.
Last edited by hueyhoolihan; 05-06-15 at 05:54 PM.
05-06-15, 06:11 PM
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Besides searching the interweb and asking others there's the time proven method of discovering what size anything is needed. Take a chain ring bolt apart and measure. Andy.
05-07-15, 07:52 AM
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