22t Freewheels slipping/jumping
09-24-10, 10:44 AM
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22t Freewheels slipping/jumping
I have been trying to change the gear ratio of my polo bike and I have been having lots of trouble with 22t freewheels. This size gives me a good drive ratio, but I have tried 3 different 22t freewheels and all of them slip or jump under heavy load.
The first two were low-cost versions sold under Pyramid and another brand, but that turned out to be identical. They are 'non-easy off', bronze colored, and I tried tightening the lockring to see if that helped. The current one is a 22t ACS Claws and it jumps as well.
Can I file the pawls to make them catch better, or is there an adjustment I can make to prevent the jumping?
I weigh 240 lbs, the drivetrain is a 34t front ring and a bmx hub with a derailleur set to a fixed position to act as chain tensioner. Chain line is good. Chain is new 1/8 inch. The first two generic freewheels were 1/8 inch, the ACS is 3/16. 19t freewheels work fine with no skipping. I can make the freewheel skip by pedaling fairly hard, and a 170 lb friend can get it to slip when he is accelerating as hard as he can.
I don't really want to buy a $100 freewheel, at that point I could replace the cranks and go to a smaller chain ring. Any ideas on fixing the freewheel?
The first two were low-cost versions sold under Pyramid and another brand, but that turned out to be identical. They are 'non-easy off', bronze colored, and I tried tightening the lockring to see if that helped. The current one is a 22t ACS Claws and it jumps as well.
Can I file the pawls to make them catch better, or is there an adjustment I can make to prevent the jumping?
I weigh 240 lbs, the drivetrain is a 34t front ring and a bmx hub with a derailleur set to a fixed position to act as chain tensioner. Chain line is good. Chain is new 1/8 inch. The first two generic freewheels were 1/8 inch, the ACS is 3/16. 19t freewheels work fine with no skipping. I can make the freewheel skip by pedaling fairly hard, and a 170 lb friend can get it to slip when he is accelerating as hard as he can.
I don't really want to buy a $100 freewheel, at that point I could replace the cranks and go to a smaller chain ring. Any ideas on fixing the freewheel?
09-24-10, 11:05 AM
#2
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I don't have anything specific to offer for brands or setups but from the sounds of the 34t front and 22t rear it seems like you are using the bike in the same sort of explosive way with sudden snaps of power that are used by bicycle trials riders. In your case the only difference would be the duration of the bursts to get yourselves across the playing field. But the level of torque load on the freewheels sounds like it would be about the same. Try searching out some of the setups that they use for options.
You mention about changing the cranks and going to a smaller chainring. But it's the combo that is putting the load on the rear. Going to a smaller chainring with a smaller rear will still have the same ratio and still load up the freewheel as hard. If you're blowing out the pawls then just altering the gearing won't help as long as you use the same ratio. And that ratio is the one you need since it is that which sets up the drive to top speed range that you require. Going smaller in the sprockets will just load down the chain more while keeping the same load on the freewheel mech.
I hate to say it but one bike trials rider I know uses a Chris King hub just because he had no luck with the other options. Another possible out may be the BMX hubs that have the cartridge style driver with the freewheel outer pawls in the hub itself. You'd have to look into it.
As for internal mods you'd have to look at the pawls with a magnifying glass to check the angles. But yeah, if they don't seat on the ratchet teeth with a nice flat manner then very lightly altering the shape would help them sit better on the drum teeth. They are hardened though so you can't file them. You also need to be careful to remove only the minimum of material. So I'd suggest you make up a bit of a jig and use a sharpening stone to hone them to the right contact angle. Don't even THINK about trying it just hand held as the small size of the pawls will guarantee that you end up with a ruined bit of misshapen metal. You need to make up some form of a block with alignment pins that hold the pawls securely with just the end jutting up a hair and the sharpening stone is guided by the surrounding block to produce a nice flat and accurate angle. Gunsmiths use such jigs for doing trigger jobs. Try a Google on "sear honding jig" for some examples of these. Go for maximum contact instead of a sharper angle. They don't "dig in". They rely on surface contact. But stoning them even slightly will also increase the angle that they sit at which will help as well. On top of this if you can slightly reform or swap out to springs to get a little more reset pressure this should aid in holding the pawls in contact even with harsh torque loads. To swap out the springs you'd need to find slightly thicker spring material. If it's round wire then using a slightly heavier gauge of wire would do the job. You can find different sizes of music wire at hobby shops which can be formed into the shape(s) you need. And finally try playing with the shims typically used to set up the bearing clearance in freewheels to go for a fit with less slop. You may need to canabalize some extra shims from old broken freewheels to do this. A freewheel with less slop will certainly let the pawls do their job more effectively.
Of course a little more tension in the pawl springs will make the freewheel a little more draggy when coasting and the ratchet sound will be more powerful. But that sort of stuff is what it'll take to avoid the big buck wheel hubs.
You mention about changing the cranks and going to a smaller chainring. But it's the combo that is putting the load on the rear. Going to a smaller chainring with a smaller rear will still have the same ratio and still load up the freewheel as hard. If you're blowing out the pawls then just altering the gearing won't help as long as you use the same ratio. And that ratio is the one you need since it is that which sets up the drive to top speed range that you require. Going smaller in the sprockets will just load down the chain more while keeping the same load on the freewheel mech.
I hate to say it but one bike trials rider I know uses a Chris King hub just because he had no luck with the other options. Another possible out may be the BMX hubs that have the cartridge style driver with the freewheel outer pawls in the hub itself. You'd have to look into it.
As for internal mods you'd have to look at the pawls with a magnifying glass to check the angles. But yeah, if they don't seat on the ratchet teeth with a nice flat manner then very lightly altering the shape would help them sit better on the drum teeth. They are hardened though so you can't file them. You also need to be careful to remove only the minimum of material. So I'd suggest you make up a bit of a jig and use a sharpening stone to hone them to the right contact angle. Don't even THINK about trying it just hand held as the small size of the pawls will guarantee that you end up with a ruined bit of misshapen metal. You need to make up some form of a block with alignment pins that hold the pawls securely with just the end jutting up a hair and the sharpening stone is guided by the surrounding block to produce a nice flat and accurate angle. Gunsmiths use such jigs for doing trigger jobs. Try a Google on "sear honding jig" for some examples of these. Go for maximum contact instead of a sharper angle. They don't "dig in". They rely on surface contact. But stoning them even slightly will also increase the angle that they sit at which will help as well. On top of this if you can slightly reform or swap out to springs to get a little more reset pressure this should aid in holding the pawls in contact even with harsh torque loads. To swap out the springs you'd need to find slightly thicker spring material. If it's round wire then using a slightly heavier gauge of wire would do the job. You can find different sizes of music wire at hobby shops which can be formed into the shape(s) you need. And finally try playing with the shims typically used to set up the bearing clearance in freewheels to go for a fit with less slop. You may need to canabalize some extra shims from old broken freewheels to do this. A freewheel with less slop will certainly let the pawls do their job more effectively.
Of course a little more tension in the pawl springs will make the freewheel a little more draggy when coasting and the ratchet sound will be more powerful. But that sort of stuff is what it'll take to avoid the big buck wheel hubs.
Last edited by BCRider; 09-24-10 at 11:09 AM.
09-24-10, 02:14 PM
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It turns out it was not the freewheel at all. I took it to the LBS at lunch and he suggested that the chain could be slipping over the teeth. He took 7 links out of the chain (now it's almost straight, before the derailleur sat slightly behind the hub) and it works great. Playing around in the parking lot I could stomp as hard as possible with zero slipping. If I'd only figured that out on the first freewheel...
