BMX or MTB cranks?

PB Forum :: Dirt Jumping & Street
BMX or MTB cranks?
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flag am-shaegar
Posted: Apr 18, 2016 at 4:50 Quote
Hmm, so you say that 165 mm could be too long?
flag cmc4130
Posted: Apr 18, 2016 at 6:15 Quote
am-shaegar wrote:
Hmm, so you say that 165 mm could be too long?

6" = 152.4mm

I think the 165mm spindle is for Downhill bikes which have 83mm wide bottom bracket shells.
flag am-shaegar
Posted: Apr 18, 2016 at 23:09 Quote
Ok, so I got it apart, again, just to make sure I have the right measurements.

My frame is a 68mm
But, with the external BB, I get 93mm, so basically I need a flush part of the spindle of 93mm:
photo

But, my spindle has a flush part of only 74-75mm:
photo

I need it to be like this in order to avoid the play:
photo

photo

So, would it be ok to get the 165mm spindle and add some spacers between the crank arms and the sprocket/conic spacer, if it's too big? Because the chainline is good now.

Because I think that the flush side is the right length...
flag FaithUSA
Posted: Apr 19, 2016 at 12:23 Quote
am-shaegar wrote:
So, would it be ok to get the 165mm spindle and add some spacers between the crank arms and the sprocket/conic spacer, if it's too big? Because the chainline is good now.

Because I think that the flush side is the right length...
I would add the spacers on the non-drive side so that you don't mess up your chain path.
flag cmc4130
Posted: Apr 19, 2016 at 12:55 Quote
am-shaegar wrote:
Ok, so I got it apart, again, just to make sure I have the right measurements.

My frame is a 68mm
But, with the external BB, I get 93mm, so basically I need a flush part of the spindle of 93mm:

But, my spindle has a flush part of only 74-75mm:

I need it to be like this in order to avoid the play:

So, would it be ok to get the 165mm spindle and add some spacers between the crank arms and the sprocket/conic spacer, if it's too big? Because the chainline is good now.

Because I think that the flush side is the right length...

I'm not sure it matters if the splined part of the spindle goes through the bearings rather than just the "flush" or smooth part.

http://www.profileracing.com/tech/installing-the-profile-outboard-bb/
flag Metro-Gnome
Posted: Apr 19, 2016 at 14:28 Quote
Me either. When I made that recommendation earlier, I was picturing an 8-spline spindle (a lot of my previous cranks have been 8 spline opposed to 48, so I just assumed)

With an 8 spline, it would matter, with a 48, it really shouldn't. Either way, I think an internal euro bb would be cheaper than almost any spindle (at least where I live it's like $40 for bb vs. $78-80 for a spindle) so why not just replace the bb?

I think the reason your cranks have play is that there isn't enough 'spline space' to hold the cranks on properly. This is the only possible explanation now, as normally bmx bbs (68mm) with threaded shells are usually run with normal, internal euro bottom brackets. You are running and external, which is usually how someone with an aluminum frame would run a threaded bmx bb, so that they can use deity vendettas or octane one 2 or 3piece 19mm cranks.

What I'm saying is, when you tighten your bolts all the way, the crank arms aren't held by enough spindle, so they wobble.

The other reason I'm saying this is because, you generally want the crankarms to clear the frame by at least 5-6mm, but you don't want them too far out. If you get a spindle made for 83mm bbs, your bike might feel a bit different.

Idk, I like my feet as close to the frame as possible, personally.
flag cmc4130
Posted: Apr 19, 2016 at 18:19 Quote
am-shaegar wrote:
Howdy!

I'm a new user, but have been browsing this forums for a while now Big Grin

I have a small problem.

Currently I have a dirtjump bike with bmx cranks, bmx BB but with external bearings, made to fit mtb frames.
The cranks have a 19mm 48 spline chromoly spindle and a chainring of 28t, because I have a driver of 9t, everything brand new...made the bike myself and my local bike shop Big Grin

The problem is that ... the chainring appears to be off-center ... on both axes!
So I have a point where the chain is stretched to the maximum, and another in which it hits my frame because of how loose it is.

I went to fix this at my local bike shop, but they couldn’t do too much and the problem began to worsen Frown
The chainring is perfectly round and flat, so I know it's not from it.
And the spline seems alright, but it appears to move a little inside the BB..
Now, I do not know if the problem are the cranks (xposure infinity) or the BB (Octane One External) ... but I am thinking about changing them both, with something better.

And now comes my question ... should I go for another BMX crank and BB ... or should I get a MTB set like the Hope Spiderless cranks?
What do you think?

Thank you in advance.

I think the hat washer in the sprocket may be incorrect or missing. This would explain a crooked sprocket or one where the chain gets super tight then super loose.
flag Aaronz25RS
Posted: Apr 19, 2016 at 21:23 Quote
Maybe this will help..
Unsecure image, only https images allowed: http://img.photobucket.com/albums/v108/sublimewind/Bike%20Pics/20160419_175750.jpg
Unsecure image, only https images allowed: http://img.photobucket.com/albums/v108/sublimewind/Bike%20Pics/20160419_175724.jpg
The cone washer is on the non drive side, I have the thinnest washer I had on the drive side and my chain alignment is perfect..

Do you have a way of adjusting alignment in the rear? Spacers moving or something, my SS kit allows 2 positions and inboard and an outboard option

Also, im sorry if it's been gone over, do you have a spacer between the bearings?
flag cmc4130
Posted: Apr 20, 2016 at 6:56 Quote
Aaronz25RS wrote:
Maybe this will help..

The cone washer is on the non drive side, I have the thinnest washer I had on the drive side and my chain alignment is perfect..

Do you have a way of adjusting alignment in the rear? Spacers moving or something, my SS kit allows 2 positions and inboard and an outboard option

Also, im sorry if it's been gone over, do you have a spacer between the bearings?

Nice bike!! So, what length spindle is that? 6" (152.4mm) ? What is the bottom bracket shell width? 68mm or 73mm?
flag am-shaegar
Posted: Apr 20, 2016 at 10:55 Quote
Guys, sorry for not posting these days, I have some problems at work Frown

Many thanks for all your replies ^_^

I want to keep the external BB because I heard it's more durable...is that true?
And yes, I also like the crank arms as close as possible to the frame...

I'm waiting for the spline-drive sprocket to arrive, and I ordered a 150 mm Subrosa Bitchin spindle.
I'll post some pictures and a video once they get here Big Grin
flag Aaronz25RS
Posted: Apr 23, 2016 at 6:40 Quote
cmc4130 wrote:
Aaronz25RS wrote:
Maybe this will help..

The cone washer is on the non drive side, I have the thinnest washer I had on the drive side and my chain alignment is perfect..

Do you have a way of adjusting alignment in the rear? Spacers moving or something, my SS kit allows 2 positions and inboard and an outboard option

Also, im sorry if it's been gone over, do you have a spacer between the bearings?

Nice bike!! So, what length spindle is that? 6" (152.4mm) ? What is the bottom bracket shell width? 68mm or 73mm?

68mm ... 5 5/8 (143) spindle
Unsecure image, only https images allowed: http://img.photobucket.com/albums/v108/sublimewind/Bike%20Pics/20160420_184441.jpg
Unsecure image, only https images allowed: http://img.photobucket.com/albums/v108/sublimewind/Bike%20Pics/20160420_184450.jpg
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