Nonboost cranks on boost frame question

pkovo

pkovo

Well-Known Member
Picked up a boost spaced frame on deep discount which I am budget building using parts I have on hand. Planning to use a set of shimano deore non-boost cranks with a nonboost RF 4 bolt ring. This frame has a 73mm threaded bb shell. Im
Installing a Shimano mt501 BB designed for 68 or 73 bb shell. My question is:

If I need to space the cranks/chainring out a bit, can I just use the extra bb spacers that would typically only be used if my bb shell was 68mm? Any issues with doing that?

I imagine the spacing may end up too wide for that plastic tube between the bb cups to seal properly, but if thats my only concern, I can live with that.

Guessing I might not even need to use spacers to get this to work, but I’m starting out with a 2.6” rear tire on plus rim and want the ability to potentially step up to 2.8 or even 3” tire down the road so I may need extra chain clearance. Thx!
 
pkovo said:
Picked up a boost spaced frame on deep discount which I am budget building using parts I have on hand. Planning to use a set of shimano deore non-boost cranks with a nonboost RF 4 bolt ring. This frame has a 73mm threaded bb shell. Im
Installing a Shimano mt501 BB designed for 68 or 73 bb shell. My question is:

If I need to space the cranks/chainring out a bit, can I just use the extra bb spacers that would typically only be used if my bb shell was 68mm? Any issues with doing that?

I imagine the spacing may end up too wide for that plastic tube between the bb cups to seal properly, but if thats my only concern, I can live with that.

Guessing I might not even need to use spacers to get this to work, but I’m starting out with a 2.6” rear tire on plus rim and want the ability to potentially step up to 2.8 or even 3” tire down the road so I may need extra chain clearance. Thx!
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Ha. This is how I end up with 7 bikes.
 
Is it a 104BCD ring?

I can't imagine that running a non-boost 104BCD chainring on the inside position of a Shimano non-boost crank would hit a tire, even a 2.6" And it should give you a good chainline with a non-boost rear.

If you add spacers you'll have less of the splines engaged into the non-drive crank-arm. In reality assemble it and see if it works.

Both my mountain bikes randomly have Shimano non-boost cranksets and are boost frames. No issues whatsoever. SRAM 11 speed and Shimano 12 speed.
 
Santapez said:
Is it a 104BCD ring?

I can't imagine that running a non-boost 104BCD chainring on the inside position of a Shimano non-boost crank would hit a tire, even a 2.6" And it should give you a good chainline with a non-boost rear.

If you add spacers you'll have less of the splines engaged into the non-drive crank-arm. In reality assemble it and see if it works.

Both my mountain bikes randomly have Shimano non-boost cranksets and are boost frames. No issues whatsoever. SRAM 11 speed and Shimano 12 speed.
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It is indeed a 104bcd ring. This is great to hear, thanks!

I’ll slap it all together without the spacers and hope it works.
 
pkovo said:
It is indeed a 104bcd ring. This is great to hear, thanks!

I’ll slap it all together without the spacers and hope it works.
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Adding an extra spacer between the BB cup and the frame reduces the number of threads securing the BB to the frame, I wouldn't do it and you shouldn't need it.
 
A spacer works fine, you can get different widths. like others have said you really just need to try it and as long as your cranks not hitting the chainstay, you’re good to go.
 
Patrick said:
i'll lend him my compressor. 😉
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overmyhead.gif
 
I have non-boost cranks on my boost Giant XTC. Works fine, but the 32t oval chainring is super close to the chainstay. Can't go bigger than 32t ring.
No problem with 2.8 tires. Might have had 3.0 at one point, but might have been front only.
27.5 x 2.8 in 1st pic.
29 x 2.4 in 2nd pic, currently on the bike.

1698704879023.png

1698705032098.png
 
Sven Migot said:
I have non-boost cranks on my boost Giant XTC. Works fine, but the 32t oval chainring is super close to the chainstay. Can't go bigger than 32t ring.
No problem with 2.8 tires. Might have had 3.0 at one point, but might have been front only.
27.5 x 2.8 in 1st pic.
29 x 2.4 in 2nd pic, currently on the bike.

View attachment 226211
View attachment 226212
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You can go bigger than a 32 but you have to do it in steps.

Put on a 33T. It'll be noisy at first but the noise goes away. Once that happens you put on the 34T and after some initial noise it's ok.
 
Santapez said:
You can go bigger than a 32 but you have to do it in steps.

Put on a 33T. It'll be noisy at first but the noise goes away. Once that happens you put on the 34T and after some initial noise it's ok.
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No way. The grease from the chain already touches the chainstay. Just barely not scratching the paint. The problem is the chainring hitting the chainstay.
 
El Stache, the boostiest-boost bike that ever boosted (okay, not really, my Lenz is worse, but not by much), easily clears a "regular" crank.

If you have parts, I'm a huge proponent of 'see if it fits'. If you are paying someone to 'see if it fits', that's stupid. Likewise if you 'found a great deal' on something.

Since neither of those seem to be the case, go nuts.

(fyi, my original Cross Check had ~.25mm of clearance between the crank arm and bottom bracket [it was square taper], and ~1mm clearance between the chainring/chainstay. It was fine, because nothing actually hit in use)

If the tire is too close to the chain, grow a pair of ovaries and single speed it 😎
 
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