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3mm gap between the crank arm and chain stay: too little?

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3mm gap between the crank arm and chain stay: too little?

Old 09-24-20, 09:40 PM
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orangeology 
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3mm gap between the crank arm and chain stay: too little?

just dry-assembled a single speed setup. chainline seems fine, straight. but the distance between the chain stay & crank arm seems too tight.
drive side is fine, well with about 5.5mm—where they encounter closest—but the non-drive side is like about 3Īmm. it seems rolling fine, just wondering if 3mm is 'too close' ish too tight, when some kind of distortion happens when ride. before trying a bit longer spindle, would like to collect your insights, what's the limit here.

fyi, the spindle is DA 109mm pista, symmetrical. what i suspect is that the non drive side arm has slightly more stretched taper as i see less room between the BB cup & the arm joint. if 3mm becomes a prob, i can simply source 112 - 113mm spindle, opening up a couple more mm on both sides.


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Old 09-24-20, 09:43 PM
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If that’s the clearance on a dry fit, i.e., without tightening the crank bolt, you’re too tight. If the bolt is already cranked down, I could live with that just fine.
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Old 09-24-20, 10:27 PM
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Originally Posted by nlerner View Post
If thatís the clearance on a dry fit, i.e., without tightening the crank bolt, youíre too tight. If the bolt is already cranked down, I could live with that just fine.
both bolts are totally cranked down.
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Old 09-24-20, 10:39 PM
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Agreed, I wouldn't have an issue with that clearance either.
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Old 09-25-20, 01:48 AM
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You're good to go. Ride and enjoy!
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Old 09-25-20, 02:03 AM
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just in case you might want to put down a couple of turns of black tape or cloth tape, take it up a steep hill, get on the gas and see if you scrape the tape,
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Old 09-25-20, 03:51 AM
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Originally Posted by cjenrick View Post
just in case you might want to put down a couple of turns of black tape or cloth tape, take it up a steep hill, get on the gas and see if you scrape the tape,
Yes, I agree! It would be ok if there's no lateral flex in the chainstays, but, do you really know?

Does the chainset need a DA spindle? If you could find something not just with more spindle length but a little longer on the non-drive side it would be better insurance. Bring both sides up to maybe 6 mm (ľ inch) if you can. Spindle 6 mm longer but on the drive side only 2 mm longer. I don't know what kind of spindle will get you these dimensions. This is where consulting a Sutherland's handbook would be useful.

If you're using a Campy Record Pista chainset and have the Campy Record Pista BB, you get even L/R spacing and very low Q.
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Old 09-25-20, 04:27 PM
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Originally Posted by Road Fan View Post
Yes, I agree! It would be ok if there's no lateral flex in the chainstays, but, do you really know?

Does the chainset need a DA spindle? If you could find something not just with more spindle length but a little longer on the non-drive side it would be better insurance. Bring both sides up to maybe 6 mm (ľ inch) if you can. Spindle 6 mm longer but on the drive side only 2 mm longer. I don't know what kind of spindle will get you these dimensions. This is where consulting a Sutherland's handbook would be useful.

If you're using a Campy Record Pista chainset and have the Campy Record Pista BB, you get even L/R spacing and very low Q.
it's a DA7400 NJS Pista BB + Campy Strada (road) cranks combo, and yes. it has to be a DA spindle. the bearing interface for early DAs are kinda proprietary, not interchangeable*. ITA pista spindle is 109mm, but the road spindle in 113mm is readily available if needed. Campy pista is not a bad idea, but there possibly can be some complications. early DA spindles have JIS-ish square tapers, thicker/shorter than Campies. while even spacing can be achieved, good possibility of the arms' too close to the BB due to thinner, longer sq tapers.

*early DA stuffs are, understandably, stupid. it's like they tried too hard not to copy/resemble the dominating marque, Campy. unique and thoughtful same time almost obsoletely strange... IMO.
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Old 09-25-20, 05:48 PM
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I would put your intended pedals and shoes on it and check for heel strike
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Old 09-25-20, 06:05 PM
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Iíd say no worries. I put road cranks on my RockHopper to go 1x and reduce Q-factor and I have maybe 1mm clearance on the non-drive side and have ridden many thousands of miles without a problem.

I should perhaps add... when I undo the U-brake straddle to pull the wheel, the brake arms block the crank arms, but it would take a fair amount of chain stay clearance to prevent that, and itís pretty much inconsequential.

Otto

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Old 09-25-20, 09:11 PM
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thanks for all the inputs, folks. at this moment, i've decided not to worry about it. a few bits still incoming, almost there. can't wait to ride the heck of it...
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Old 09-26-20, 08:30 AM
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With those cranks, I doubt you'd cause them to flex into the frame. Now if you're running some NR-knockoff Saavadera cranks, then yeah, it would probably be kissing the chainstays.
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Old 09-26-20, 11:23 AM
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when you climb a steep hill out of the saddle, the rear stays will flex.

this is what shifts your real derailleur on thin frame or Vitus type bikes.

in this case, you would be pulling the stays to the right, (chain on the right) which means nothing to worry about on that left hand crank.
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Old 09-28-20, 10:31 AM
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I thought I posted this last night, but I'm not seeing it now, so here goes again. Apologies if this is somehow a dupe.

If I'm seeing your photos correctly, I'd be more concerned about the drive-side clearance between the chainstay/bb shell and the inner chainring ledges and the back of the outer chainring bolt. From the photo it looks like you've maybe only got 1-2mm clearance there. Is it really that close?

Might be I'm just seeing it wrong, might be shadows, camera angle weirdness, "fork is bent" lens distortion/weirdness, or whatevs, but it looks very, very tight to me.

All's you'd need would be a bit of flex, a little bb slop, maybe that Ital fixed cup loosening just a hair, and you're maybe shaving paint, or worse...
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Old 10-01-20, 11:24 AM
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Originally Posted by droppedandlost View Post
I would put your intended pedals and shoes on it and check for heel strike
+1, and the clearance between your foot (or the pedal) and the chain.
I have this problem once in a while, on a specific frame with that type of clearance.
The R inner heel of the shoe doesn't noticeably strike the chain, but ends up greasy after a ride.
I don't remember to check while riding, and maybe I don't really want to know.
I do have extenders for the pedal spindle if it worries me.
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