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Old 01-19-08, 09:26 AM   #1
wroomwroomoops
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BMX cranks and chainrings.

I read on a webshop that some of their BMX chainrings are "For 1 Piece American Cranks". Does this mean that those chainrings wouldn't work with three-piece cranksets, like the ones that use 19mm axle? I have seen 1-piece BMX cranks as well as various types of 3-piece BMX cranksets, and they all seem to take the same kind of BMX chainring - the one with a hole a few cm from the center. Are there actually different types of these chainrings, or is the shop only using this term "For 1 Piece American Cranks" to differentiate the chainrings from the 5-arm 110mm BCD chainrings that are also popular in BMX?

I have another question, regarding BMX 3-piece cranks, but I am transfering the picture right now. In a few minutes I'll post it.

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Old 01-19-08, 10:05 AM   #2
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So, here is my question regarding cranks. I thought that all BMX 3-piece cranksets use a 19mm axle with some tiny splines/serrations at the ends. I bought rather cheap this crankset a BMX crankset and realized that I got a different beast. Please look at the axle:

It's not 19mm but about 21mm at the center (even thicker elsewhere, like at the threaded section), it has some strange threads followed by hexagonal ends! What the heck did I get, how is it called? I guess this is not compatible with "Euro" bottom brackets, but is it compatible with "US" or "Spanish"? (and what is a "Spanish" BB in terms of size?).
And is there any more types of BMX three-part cranksets?

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Old 01-19-08, 03:35 PM   #3
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Most of the modern BMX cranksets (Primo, WTP) use proprietary spindles that fit their crankarms and bearings. You can either find crankarms to match what you have, or find a spindle that matches your BB shell and crankarms. Hope this helps..
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Old 01-19-08, 03:52 PM   #4
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Originally Posted by wroomwroomoops View Post
I read on a webshop that some of their BMX chainrings are "For 1 Piece American Cranks". Does this mean that those chainrings wouldn't work with three-piece cranksets, like the ones that use 19mm axle? I have seen 1-piece BMX cranks as well as various types of 3-piece BMX cranksets, and they all seem to take the same kind of BMX chainring - the one with a hole a few cm from the center. Are there actually different types of these chainrings, or is the shop only using this term "For 1 Piece American Cranks" to differentiate the chainrings from the 5-arm 110mm BCD chainrings that are also popular in BMX?
A chainring bolts to a spider.

A BMX chainwheel is manufactured as one piece and (usually) has the center spindle mounting hole bored to the largest standard spindle size. There are adpaters available to fit these chainwheels to a smaller size spindle, like the common 19mm.

To fit a chainwheel bored to fit an american one piece crank to a 3/4" (19mm) spindle, you'd need a 15/16" to 3/4" adapter -- like this:http://www.danscomp.com/457004.php?cat=PARTS
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Old 01-19-08, 04:10 PM   #5
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A chainring bolts to a spider.

A BMX chainwheel is manufactured as one piece and (usually) has the center spindle mounting hole bored to the largest standard spindle size. There are adpaters available to fit these chainwheels to a smaller size spindle, like the common 19mm.

To fit a chainwheel bored to fit an american one piece crank to a 3/4" (19mm) spindle, you'd need a 15/16" to 3/4" adapter -- like this:http://www.danscomp.com/457004.php?cat=PARTS
Great, thanks!

On this page, it looks as if ALL BMX chainrings are bored for a 15/16" spindle. Is it so then that the chainrings with the smaller, 3/4" hole are much more rare/hard to find?

I am now going to order these adapters. Your advice has been very precious. Was it you who also informed me about the EURO bottom bracket availability, so I can use BMX cranks on a non-BMX bike?

Another question: is the spindle that is pictured in my second post, what is usually called a 22mm spindle? I see at the link you provided, a Primo chainwheel adapter, which "Fits chainwheels with 15/16" (1-pc) hole to crank with a 22mm spindle."
EDIT: I measured the axle at the point where the chainring should sit, and it's 23.5mm in diameter. So, it does not need any adapter to fit a "one piece american" chainring. I wonder if BMX chainrings for 19mm spindle are produced, or if everyone relies on adapters.

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Old 01-19-08, 07:27 PM   #6
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I wonder if BMX chainrings for 19mm spindle are produced, or if everyone relies on adapters.

There have been a few, but for practical purposes most BMX chainwheels are produced with the larger bore. It makes it easier for retailers to stock one product that will fit a variety of cranks with an adapter.

I don't recognize that spindle. If you know the maker, you might want to search the web for a euro conversion BB kit.
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Old 01-19-08, 07:50 PM   #7
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There have been a few, but for practical purposes most BMX chainwheels are produced with the larger bore. It makes it easier for retailers to stock one product that will fit a variety of cranks with an adapter.

I don't recognize that spindle. If you know the maker, you might want to search the web for a euro conversion BB kit.
It's some no-name stuff I bought for cheap from a German eBayer. But my measurements are conrirming that it is the same size as a 1-piece american (which I also happen to have), eccept that it's in three pieces - I hope I am making sense. It uses the same (american) BB as the 1-piece crank.

OK, so now I gots to order that adapter. It sucks that Dan's Comp has such shipping policy, that a $3.99 item will cause me a $38 shipping charge. That's nuts... but I scanned the 'net and couldn't find anyone else selling these adapters. Yet. More scanning ahead.
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Old 01-21-08, 10:54 AM   #8
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That spindle should work with a euro, spanish, or whatever other bb without a problem. You just need to get bb bearings with the proper inner diameter (22mm from the looks of the picture). Cranksets with 19mm spindles are used about equally as much as 22mm are in BMX. Profile has always been one of the most popular cranks used, and they have 19mm spindles as well as the many other Profile-style copycats.

A spanish bb just has a different outer diameter. The bearings press directly into a frame made specifically for a spanish bb without the use of any cups. It saves on weight (no cups & smaller bb diameter, so overall less metal used) and makes installing/uninstalling real quick and easy.
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