Chainwheel center hole size

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biknut

Well-Known Member
Sep 28, 2010
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Can anyone explain the difference between a chainwheel with a 19mm center hole, and one with a 23.75mm center hole.

Is there a way to tell which one your bike uses by looking? More spicificly which size fits a felt beach cruiser?
 

mybike1

New Member
Dec 21, 2011
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Michigan City, Indiana
19mm is pretty standard for modern bmx bikes 22mm is odd but I come across them once in a while... I've never seen a 23.75 that I'm aware of.
I'm guessing you're felt could be that 23.75 because I've never actually measured the center hole for a one piece style crank chainwheel... I'm just guessing about that.
Your best bet would be to unassemble what you have and measure it with a set of calipers... you can find them pretty cheap at the big box stores... even the cheap ones are a great measuring tool to have for us bike guys. they take the guesswork out of everything.
 

biknut

Well-Known Member
Sep 28, 2010
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19mm is pretty standard for modern bmx bikes 22mm is odd but I come across them once in a while... I've never seen a 23.75 that I'm aware of.
I'm guessing you're felt could be that 23.75 because I've never actually measured the center hole for a one piece style crank chainwheel... I'm just guessing about that.
Your best bet would be to unassemble what you have and measure it with a set of calipers... you can find them pretty cheap at the big box stores... even the cheap ones are a great measuring tool to have for us bike guys. they take the guesswork out of everything.
Thanks for the reply. What you suggest is exactly what I did, but unfortunately not till after buying a 41T chainwheel that doesn't fit.

And you guessed is right, the Felt chainwheel does have a 23.75 mm center hole. Unfortunately I bought a 41T sprocket that only has a 19 mm center hole. But I noticed in the picture it had a spacer pressed into it's center, so I thought if I knocked it out it would fit. Wrong again. After knocking out the spacer, it's 22 mm. D@%n!t why does everything have to be so complicated.

What I'm finding out is locating a spicific size sprocket is difficult when you're picky. I want alloy. I want black, but now I'm willing to paint my own. I want a 23.75 mm center hole. I want 3 different sizes, 41, 42, 43.

So far I found a 40T, and I have the stock 44T. I wonder it I can get someone to bore the 41T I bought that doesn't fit, out the 23.75 mm? If not I found a 41T I can buy, but I'll have to paint it.

That's all I've been able to find. A 40T, a 41T, and a 44T which I don't need, and some even bigger ones. There just doesn't seem to be much verity.
 
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mybike1

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Dec 21, 2011
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Michigan City, Indiana
I'm not always a patient person and in the past I've taken a 19mm and turned it into a 22 just by getting out the old dremel tool and carefully marking the hole and grinding it out to size... if you take your time you wont have any issues keeping the hole centered... your next best bet would be to find a local machine shop and see if they will do if for you... even some high schools with a machine shop program would do it for you... usually for free :)
Oh, and if all else fails check this place for a variety of chainwheels... last time I looked they had a bunch to choose from. http://www.fnrco.com/
 
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biknut

Well-Known Member
Sep 28, 2010
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Find someone with a set of adjustable reamers.

Good Luck,

Chris
AKA: BigBlue
I'm not always a patient person and in the past I've taken a 19mm and turned it into a 22 just by getting out the old dremel tool and carefully marking the hole and grinding it out to size... if you take your time you wont have any issues keeping the hole centered... your next best bet would be to find a local machine shop and see if they will do if for you... even some high schools with a machine shop program would do it for you... usually for free :)
Oh, and if all else fails check this place for a variety of chainwheels... last time I looked they had a bunch to choose from. http://www.fnrco.com/

Thanks to everyone that replied. I was trying to decide if there would be a way for me to enlarge the hole myself. BigBlue I think you saved the day. I never actually heard of an adjustable reamer. After googling them to find out what they are, that's the ticket. Harbor Freight to the rescue. They have a set of adjustable reamers in the correct size range for $70, which is about the same as 2 sprockets, but I'm sure I'll figure out a way to get my money back with them in the future.
 

rustycase

Gutter Rider
May 26, 2011
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IMO

:)

at the speed & power level here, tolerances are not so extreme that this part could not be dressed with a half round file to gain the clearance required for a fit.

but i'm a real cheapskate and darn sure wouldn't spend $70 for a china-made adjustable reamer to work on a china project!

Good luck!
rc
 

biknut

Well-Known Member
Sep 28, 2010
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409
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IMO

:)

at the speed & power level here, tolerances are not so extreme that this part could not be dressed with a half round file to gain the clearance required for a fit.

but i'm a real cheapskate and darn sure wouldn't spend $70 for a china-made adjustable reamer to work on a china project!

Good luck!
rc
I think my wife would like to talk to you about a possible husband swap lol.
 

biknut

Well-Known Member
Sep 28, 2010
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Problem solved. I went to Harbor Freight this afternoon, armed with a coupon for a free flashlight and 20% off. A complete set of adjustable reamers, out the door was $60.

Not being familiar with this tool, it took me a few minutes to figure out how to use it. I think you're supposed to chuck it up into a drill press, or maybe a mill, but I was able to make due by putting the sprocket in a vise, and turning the reamer with a wrench. It was easy on my first try to ream the 22mm sprocket hole out to 23.75mm and end up with a tighter tolerance than the stock sprocket has. In all, once I got started it took about 15, or 20 minutes.

This is going to greatly increase my options in the future when buying sprockets, because now I won't have to worry about the center hole size.
 

BigBlue

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Nov 29, 2011
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biknut

Well-Known Member
Sep 28, 2010
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Dallas
Glad it worked out for u. I was wondering if you were going to figure it out before I had a chance to show how to adjust. Here's a YouTube video that shows u how to adjust them:
https://www.youtube.com/watch?v=qxxU0I_gvPE

A tap handle (wrench) or a T-handle will work, but a wrench will work too. I don't know if this set is big enough to hold the reamers:
http://www.harborfreight.com/3-piece-t-handle-tap-wrenches-38560.html

Chris
AKA: BigBlue
Thanks again. I guess I'm ahead of the game. I already installed my new sprocket, and serviced the BB.