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Cheap, welded chainrings?
#1
Hi. New member.
I working in Cambodia, riding a 2011 Giant Escaper 26" 24SP.
It's not a great bike, but it's what they gave me, and it works OK for what I need.
But now my large chainring is well worn, and has some broken teeth.
Looking to change out the one ring (since the others and sprockets all
look pretty good still), this set looks like nothing I've ever seen before. (Maybe because most bikes I've ridden in the past were of noticeably higher quality.)
There are no bolts/screws holding the rings together! It appears this Shimano set has all the rings welded together as one solid unit! Really? What's up with that?
Am I missing something? Or am I going to have to replace the whole set? Cranks too?
And I'm wondering if it's a good idea to maybe replace the chain as well.
I've got about 36,200km on the bike already - DANG! I just did the math on that so I could offer the data. Never realized it was that much already.
Suggestions welcomed. But know that I'm a volunteer on a very small budget. So I'm hoping to get through this as cheaply as possible. Help!
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#2
Hi;

They are riveted together, not welded. In the USA, the Shimano riveted triples cranksets (whole thing with both left and right arms and chainrings) are less expensive than purchasing a single chain ring. The individual rings are not replaceable.

They are so inexpensive because they are stamped and assembled in a single progressive die. Every 15 seconds or so, another complete chainring assembly comes out of the machine. Then the assembly is swaged on to a right crank arm - also not a process that allows replacement.

http://www.amazon.com/Shimano-FC-M171-Altus-Crankset-170-mm/dp/B003ZMFNX4/
http://www.amazon.com/Shimano-M131-Crankset-170mm-48/dp/B003ZMDJW6/
Nigel
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#3
Wow!
Not just fast, but really good, detailed info - just the way I like it! :-)

Thank you so much, Nigel.
I'm not psyched that the bike's components are so cheap. But then having precious little money to put towards it is a relief.
And it did get me around covering an awful lot of territory in the past three years. So it gets a little bit hard to complain too much.

Thanks again.



(04-17-2014, 01:07 PM)nfmisso Wrote:  Hi;

They are riveted together, not welded. In the USA, the Shimano riveted triples cranksets (whole thing with both left and right arms and chainrings) are less expensive than purchasing a single chain ring. The individual rings are not replaceable.

They are so inexpensive because they are stamped and assembled in a single progressive die. Every 15 seconds or so, another complete chainring assembly comes out of the machine. Then the assembly is swaged on to a right crank arm - also not a process that allows replacement.

http://www.amazon.com/Shimano-FC-M171-Altus-Crankset-170-mm/dp/B003ZMFNX4/ref=sr_1_4?s=cycling&ie=UTF8&qid=1397740100&sr=1-4&keywords=m131
http://www.amazon.com/Shimano-M131-Crankset-170mm-48/dp/B003ZMDJW6/ref=sr_1_1?s=cycling&ie=UTF8&qid=1397740155&sr=1-1&keywords=m131
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#4
Low end chainwheels are often riveted together - it's not just Shimano that does so. What's up with it is that it allows a lower price and less maintenance in return for less flexibility. It takes a lot to wear out chainrings, but if the teeth are very pointy and curved toward the back side (often called "shark fin" - pic 1) then it is indeed worn. Be aware that broken teeth are very rare, and you may just be looking at some teeth that are intentionally shorter or differently shaped to allow easier shifting - pic 2,3

If the entire drivetrain has that many miles and the chainwheel is very worn then you will need to replace chain and rear cassette/freewheel as well. If the bike is low end a newer used replacement bike may be lower cost than replacing the entire drivetrain, especially if you do not already have the requisite tools.
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#5
Understood. And thanks for the added info.
I've been MTBing for about 25 years. Rode Fishers ("pre"), Specialized, Konas, etc...
I'd just never seen a crankset done this way before.
Sharkfin?? Dude, I've got bluefin tuna here - sleek and low! Broken teeth - 7, two groups of two (not where you'd expect them) and another group of 3 teeth down. Chain slip is an ever increasing problem.
I'd love to be able to bring everything up to spec. But the bike is the property of the organization, issued to us to use. Yet we are often responsible for repairs, even normal wear and tear maintenance. Sounds rough. But their sponsorship means I get to try to do some good, giving back to the world some of what it has brought me. So it's fine. I just have
to stay below the fiscal radar.
I might be able to get them to swing for a new chain. I've already replaced the original once about a year ago. Maybe they'll accept that it's their turn this time. :-)
Thanks again.


(04-17-2014, 01:16 PM)cny-man Wrote:  Low end chainwheels are often bolted together - it's not just Shimano that does so. What's up with it is that it allows a lower price and less maintenance in return for less flexibility. It takes a lot to wear out chainrings, but if the teeth are very pointy and curved toward the back side (often called "shark fin") then it is indeed worn. Be aware that broken teeth are very rare, and you may just be looking at some teeth that are intentionally shorter to allow easier shifting.

If the entire drivetrain has that many miles and the chainwheel is very work then you will need to replace chain and rear cassette/freewheel as well. If the bike is low end a newer used replacement bike may be lower cost than replacing the drivetrain.
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#6
Check the chain for wear - very easy to do with a ruler. Just google "measure chain wear" and note that any result from sheldonbrown.com or parktool.com is reliable. If the chain is OK and you don't get skipping/slipping under pressure then the rear cogs are OK for now. If it is worn then you will know when you replace it whether some of the rear cogs have problems also.

Entire new crankset is the best option, as the BB spindle and crank have to be compatible with each other. Need to check whether BB shell on frame is 68 or 73 mm across.
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#7
I hardly ever use the middle ring. And the small ring, I think I've been on it once. That's it.
So far, it's only chain slip - try to crank hard, chain slips - sometimes even off the chainring. The cogs seem OK. They even sound like they're in OK shape. Rear sprockets look OK too. When I go to the shop to see about parts, we'll take apart the BB (that's the only tool I don't have with me) and see what's going on there.

I remember in my teens riding motocross - motorcycle sprockets are way expensive for a kid. When the sprockets got too worn, we'd just file off the bent-over points, turn the sprockets around so the chain would be putting pressure on the unworn part of the tooth. Got a few hundred miles more out of them that way!!
Can't do that here though.

Thanks for all the help.

(04-17-2014, 01:34 PM)cny-man Wrote:  Check the chain for wear - very easy to do with a ruler. Just google "measure chain wear" and note that any result from sheldonbrown.com or parktool.com is reliable. If the chain is OK and you don't get skipping/slipping under pressure then the rear cogs are OK for now. If it is worn then you will know when you replace it whether some of the rear cogs have problems also.

Entire new crankset is the best option, as the BB spindle and crank have to be compatible with each other. Need to check whether BB shell on frame is 68 or 73 mm across.
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#8
I know one can get into a habit, but your legs, heart and drive train walk do much better if you tromp less on the pedals (lower gears, higher rpm). Your terminology is confusing - you say cogs are OK (sound good?) but then say rear sprockets look OK too. The rear are usually called cogs and the front chainwheels. The BB has nothing to do with slipping, and is cartridge type, can't be OH'd.
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#9
(04-17-2014, 03:13 PM)cny-man Wrote:  I know one can get into a habit, but your legs, heart and drive train walk do much better if you tromp less on the pedals. Your terminology is confusing - you say cogs are OK (sound good?) but then say rear sprockets look OK too. The rear are usually called cogs and the front chain weeks. The BB has nothing to do with slipping, and is cartridge type, can't be OH'd.

Hehe!
I don't power-pedal often. Usually just when I need to get out of the way of either a bus that just popped up from out of nowhere or a runaway ox cart.
But that's when I need things to hold together the most!
Mostly my use is just getting around. Most days it's steady riding (paved and dirt roads) between 7 to 35km, and then back again that day. With some pieces donated by friends, I've turned it into a bit of a hybrid - stem raiser, more comfortable seat, narrower tires... It's the rainy season that makes having a MTB really important. Plus, I'm not a fan of the riding position of road bikes.

The cassette & hub contains the rear sprockets and the inner drive/coaster mechanism. Right?
I've always understood that the "cogs" were the internal, spring-loaded pieces that catch inside the hub to push the wheel forward, but ride over the catches in the hub when the wheel is turning faster than the sprocket cluster. ie; coasting.
Maybe my nomenclature is off. Sorry. But they sound very positive with a solid, higher pitched "click" like when new rather than a softer (kind of rounder) sound once they are worn and can begin to not engage as sure anymore.
The teeth on the rear sprockets still look pretty decent. 4 through 8 are the only ones I use. So 1 through 3 are pretty much new condition to compare to.
I only mentioned the BB because you did. And I figure that if we're taking the cranks down, might as well inspect, have a look around while we're in there.
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#10
Another reason it's best to ride in a bit lower gear is the very problem you mention. In a higher gear acceleration is much more difficult. It's much easier to accelerate out of the way with the greater torque of a lower gear.

The things that click are called pawls. With bicycles the most common terminology is to call the individual gears in the rear, whether on a freewheel or cassette body, by the term COGS. The most common terminology for the front is CHAINWHEELS or chainrings, though some still call them sprockets. At least that's the case in the U.S. The only thing to check with the BB is whether it is fairly smooth and has no significant play. If so then the entire unit is replaced. If you replace just the crank/chainwheel you have to make sure the length of the BB spindle is compatible, which is the reason it's simpler to order it all together.
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#11
(04-17-2014, 06:57 PM)cny-man Wrote:  Another reason it's best to ride in a bit lower gear is the very problem you mention. In a higher gear acceleration is much more difficult. It's much easier to accelerate out of the way with the greater torque of a lower gear.

The things that click are called pawls. With bicycles the most common terminology is to call the individual gears in the rear, whether on a freewheel or cassette body, by the term COGS. The most common terminology for the front is CHAINWHEELS or chainrings, though some still call them sprockets. At least that's the case in the U.S. The only thing to check with the BB is whether it is fairly smooth and has no significant play. If so then the entire unit is replaced. If you replace just the crank/chainwheel you have to make sure the length of the BB spindle is compatible, which is the reason it's simpler to order it all together.

Again, thanks.
Yes! "Pawls". Soon as I read the word I remembered.
I like your suggestion that lower gears are good for accelerating. Yes, if, in an emergency situation, you happen to be in one of them.
But if you need to high-tail it right now, you go in whatever gear you happen to be in since downshifting is going to take a few seconds to get there, and you're still working in whatever gear you started.
Besides, for me, if I'm not on some major hill climb (not many of those here) the smaller rings below 4 or 5th gear are useless to me since I don't take a spinning class. (grin)
Seriously. Just because there are so many of them, doesn't mean they have to be used. It doesn't even mean they're actually useful. I think the lowest I've needed on the steepest hill I've been on here is middle ring 3rd gear. Everything below that is just dead weight.

Thanks again, both of you for your help. There's a Giant dealer in the capital city. I can check with them and make sure they have the proper parts to bring things back up to spec. Can't reach them by phone. So I'm glad I was able to find the needed info on the cheapie chainrings here before I have to make that journey into town. Major bonus.
Have a great one!!!!
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#12
To be honest on my road bike I seldom go above the middle (39 t) chain ring. I can easily spin that out to 50 km/h, which is fast enough if you ride solo (and don't want to accelerate down the hills). On flat terrain I average about 30 km/h most of the time (not longer than 100km rides), so the middle chain ring sees most action.
So: The large chain ring should be considered the dead weight - unless you have much more power than I do (which is not unlikely).

Safe riding!
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#13
(04-22-2014, 07:23 AM)Joe_W Wrote:  To be honest on my road bike I seldom go above the middle (39 t) chain ring. I can easily spin that out to 50 km/h, which is fast enough if you ride solo (and don't want to accelerate down the hills). On flat terrain I average about 30 km/h most of the time (not longer than 100km rides), so the middle chain ring sees most action.
So: The large chain ring should be considered the dead weight - unless you have much more power than I do (which is not unlikely).

Safe riding!

Hey Joe,
I guess it's comes down to a matter of what you like, the kind of riding you do, and the actual, and relative sizes of the various rings and "cogs". ;-)
Personally, I don't like spinning. It feels clumsy, and like a lot of energy is being wasted. I like a steady, even pace that covers some ground.

For me, riding a hybridized mountain bike on roads ranging from pavement to (not kidding) 5'-deep-wooptydoos-everywhere dirt roads after monsoon season, I'd gladly scrap the smallest ring for about 8 to 10 more teeth on the large ring for better top-end on some of my longer, easier rides.
Oh - and downhills are just for going all out that much faster!!!! :-)
Have a great one ---
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#14
(04-19-2014, 08:16 AM)Far Away Wrote:  I like your suggestion that lower gears are good for accelerating. Yes, if, in an emergency situation, you happen to be in one of them.
But if you need to high-tail it right now, you go in whatever gear you happen to be in since downshifting is going to take a few seconds to get there, and you're still working in whatever gear you started.

My point is that it's helpful to spin at least a bit faster in lower gears as a general practice, so that if you face a need for acceleration you would already be in that gear.
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#15
Actually it is a matter of whether you like your knees and joints or not. Spinning is also more efficient. But on the potholes and stuff it is easier to crank on a higher gear. I have pavées on my commute...
I recently read somewhere that you need to be trained on all ranges of cadence, to not be fatigued so easily. You need to train the spinning, I need to train the lower cadence (also because my commuting bike has... too high gears for the hills, damn the glacial valleys!)
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#16
The OP and others can do as they wish, but I have never seen that tromping on the pedals helps with "potholes and stuff," - quite the opposite in my experienct.

It's flat out untrue that more teeth equals a higher top end (speed) unless you're talking about downhill and a tailwind, and the fact that one thinks energy is being wasted when spinning is irrelevant. Spinning is also a relative term. I rev at around 100rpm but I would consider anything about 80 to be a good cadence, and not necessarily the higher the better. I have also seen that persons with heavier legs tend to have more problems and less benefit spinning.
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#17
(04-28-2014, 05:20 PM)cny-man Wrote:  The OP and others can do as they wish, but I have never seen that tromping on the pedals helps with "potholes and stuff," - quite the opposite in my experienct.

It's flat out untrue that more teeth equals a higher top end (speed) unless you're talking about downhill and a tailwind, and the fact that one thinks energy is being wasted when spinning is irrelevant. Spinning is also a relative term. I rev at around 100rpm but I would consider anything about 80 to be a good cadence, and not necessarily the higher the better. I have also seen that persons with heavier legs tend to have more problems and less benefit spinning.

OK - got the front crankset, chain, and rear cogs replaced. Considering that this is not exactly a top-line bike, things are well again. At least long enough until I finish my volunteer service. Once I'm actually salary-employed again, I'll again be riding a bike far less than 30lbs, with quality components, proper geometry, and a bloody-well comfortable seat!!

I want to thank those who offered useful input that actually aided in resolving the issue. You help is what I came to this forum for.
As for the couple of trolls picking out singular bits of discussion out of context, and not relevant to offering forward momentum to an eventual solution, well, they're always going to be a part of dealing with the internet community. So, no big deal.

Hope you're all having as much fun biking as I am. Whatever your style is.
Thanks, again!!!
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