Bicycle Mechanics - chainwheel binder bolts- how tight?
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12-26-05, 11:16 PM
I'm cleaning up and assembling a beater bike. It's got an Atala cottered crank and Simplex derailleur that seems to be ubiquitous on 70's vintage 10 speeds. In Eugene Sloane's book, he claims that chainring binder bolts (on presumably high quality bikes) should be tightened to 70-90 inch/lbs. The wussy 8mm bolts on my chainring don't look like they ever could have been tightened much beyond 30-40 before they strip. How tight should I make them? Judging by how many of these drivelines I see still on the street, they can't be total garbage, but am I taking my life in my hands? Thanks in advance :)
12-26-05, 11:27 PM
I'd probably err to the light side. Barnett's gives a range of 48-72 in-lbs. I might think 50's a good number.
The other option is to put blue loctite on the threads and just snug 'em up to something like the 35 in-lbs that your instincts are telling you, then check 'em periodically.
12-27-05, 07:28 AM
70-90 inch-pounds isn't that tight. I tighten the chainring bolts about as tight as I possibly can with a regular length 5 mm allan key. You can't get too much force on a wrench of that length so you aren't going to hurt anything.
12-27-05, 07:58 AM
Tight enough, but not too tight. Seriously though, if its an 8mm, 70-90 in-lbs is way below what that size bolt is rated for. I'm assuming that the bolt goes through the chainrings and then is held on by a steel nut on the other side. If thats the case, it is not too much torque. Just be sure all the threads are clean and oil the entire nut and bolt.
12-27-05, 08:35 AM
I'd just use tools no longer than 3-4 inches and crank it as tight as reasonably possible with your bare hands. Then check it again after an hour or two of riding. Loctite is good, but I've found that it is not needed and makes removal more of a pain.
12-27-05, 08:37 AM
Thanks for all the replys, folks.
These are non-graded hex head 8mm bolts. Tiny and wimpy looking. They pass thru the large chainring and thread into the smaller chainring, no nut on the back. I'm new to bikes, but I've spent a lifetime around other stuff that use bolts, and as I'm tightening these, I'm getting that familiar twinge in the gut that tells me there isn't far to go before they strip. Good advice on the locktite, though.
12-27-05, 10:15 AM
OK, the bolts you describe aren't typical of most chainring retaining bolts. If the hex is 8 mm, the threaded bolt is probably only 5 or 6 mm and the thread engagement depth on the small chainring probably isn't much. Use your judgement on these but get them good and tight. If you overdo it, there's your excuse to upgrade. :)
12-27-05, 10:24 AM
Be careful. You have a steel bolt threading into aluminum, its very easy to strip the aluminum and if you do, you goobered a chainring. Double check the torque spec you looked up to make sure it is for aluminum threads. Then check the size of the bolt, the diameter of the threaded part, not the size of the hex key that fits it. Its easy to check with a socket set, just put the bolt inside successive sockets and the one it just goes into is the size of the bolt. If all the above checks out, then use a torque wrench, its very easy to strip Al threads.
12-27-05, 12:47 PM
San Rensho says :Be careful. You have a steel bolt threading into aluminum, its very easy to strip the aluminum and if you do, you goobered a chainring.
Actually, this bike probably pre-dates Roller Disco, and has steel chainrings. The bolts aren't allen, but hex, and according to my vernier caliper, the diameter measures 4.8mm. Fairly fine threads, and not-so-high-grade looking steel. So, if anything's going to give, I'd imagine it'd be the bolts. Like Hillrider says, if they do, there's my chance to upgrade, but I thought this would be a fun opportunity to see first-hand what the old technology was like and why the new stuff might or might not be better. Mainly, I'm just a cheap bastard.
Also, it probably wouldn't be too difficult to replace the crappy bolts with some higher grade Allen head screws.
12-27-05, 05:19 PM
I rode a probably similar japanese 10-speed as a commuter for a couple months that had a 3-bolt steel chainring and cranks with the same wimpy little bolts...threading directly into the chainring. I had it set up with only the small ring, ends of the bolts passing just a little through the back of the chainring. So one night i was riding along, downtown at night, and all of the sudden i hear a loud snap/click/metal sort of noise and feel something through the pedals. I pull off the road a few seconds later and see that one of the 3 chainring bolts snapped off at the head and the remaining two weak little arms of the spider had torqued themselves out of true when it happened. Pretty much the end of that bike, though i bent the spider back as best i could and used different bolts; it still rode for a few days before i realized it probably wasnt a good idea to have a ghetto singlespeed whose chain tension dramatically changed throughout the rotation of the cranks...and freaking cottered cranks are impossible to remove.
Anyways, i torqued those chainring bolts about the way you're describing you did, tight, but a little looser than i thought would make them snap...
I'd reccommend some new allen-bolts, probably look nicer and also give you some confidence about them. Granted, that bike lived outside and was thoroughly abused every day, its up to you.
12-27-05, 07:26 PM
[QUOTE=mattduth] I pull off the road a few seconds later and see that one of the 3 chainring bolts snapped off at the head and the remaining two weak little arms of the spider had torqued themselves out of true when it happened.
Mine's got 9 bolts in total. It looks a lot like the chainring on this page:
and is the same one apparantly used on lower end Peugeots from the late 60's- early 70's, as I've got one of them with the same Atala driveline as this dumpster beast.
If I decide I love this bike, maybe I'll swap in some heavier duty bolts.
12-27-05, 10:31 PM
I'm dealing with a similiar situation as frankenbike. My son's old HOO KOO E KOO had a bolt come loose from the granny gear chain ring. He was pedalling when it came out and he rammed it into the stay right where it meets the seat tube. What a mess. I'm sorry, I should have taken pictures to share with everyone. I just started to reassemble the chain wheel. I'm going to try 50-60 in-lbs and use loctite as recommended by neil0502. Thanks for this thread frankenbike, it was great timing for me.
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