Sugino crankset difference, GP vs AT
03-31-22, 01:47 PM
#1
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Sugino crankset difference, GP vs AT
I have an '85 Miata 610 and had a problem with the chainrings moving relative to the derailleur. I remounted that crank different ways and determined the Sugino GP spider must be bent. I have a nice AT crankset in my bins and tried putting that on, but the depth of the spider where it seats on the square taper is too close to the frame. Picture shows the difference. Is this AT from another planet?
Should I use a wider BB, say, 118 vs the 113mm, or do I just need to give up & find another GP spider?
Should I use a wider BB, say, 118 vs the 113mm, or do I just need to give up & find another GP spider?
03-31-22, 02:00 PM
#2
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You could do either. Get a longer bottom bracket spindle or another GP.
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03-31-22, 02:18 PM
#3
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How badly bent is it? I've had decent luck correcting a couple millimeters of runout by bending the spider ears with an adjustible wrench. A clothespin attached to the FD cage can help you detect which spider ears need to move in or out.
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03-31-22, 02:50 PM
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The AT is a nicer crank for what it's worth.
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03-31-22, 03:42 PM
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I’m using a 126mm SKF BB with my AT. Added 2.5mm DS spacer for proper chainline.
Sheldon Brown’s database has three entries for AT BB length: 127.5+2mm spacer (probably most correct); 122.5+2mm spacer; 115mm+2mm spacer, but that one gives a narrower 42.5mm chain line than typically recommended for triples. Great crankset.
https://www.sheldonbrown.com/bbsize.html
Sheldon Brown’s database has three entries for AT BB length: 127.5+2mm spacer (probably most correct); 122.5+2mm spacer; 115mm+2mm spacer, but that one gives a narrower 42.5mm chain line than typically recommended for triples. Great crankset.
https://www.sheldonbrown.com/bbsize.html
Last edited by Dfrost; 03-31-22 at 03:58 PM.
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03-31-22, 03:43 PM
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And the spindle length for the Sugino AT should be 127.5
https://www.bikeforums.net/classic-v...-question.html
https://www.bikeforums.net/20846056-post6.html
https://www.bikeforums.net/classic-v...-question.html
https://www.bikeforums.net/20846056-post6.html
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03-31-22, 03:46 PM
#8
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Thanks. And since the extra width is on both sides, I may need to go to 122.5. I tried a 127, but that put the chainrings too far out.
03-31-22, 04:15 PM
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Surely there are a few bike coops in bike friendly Madison, WI that have used sealed BB, assuming you don’t have one already. (Also probably an excellent place for the purchase.) If so, do a quick fit check there, including DS spacers with a 122.5 to ensure that granny rings and it’s bolts clear the frame. No need to fully torque BB and crank in this fit check, but expect that the crank will seat inwards close to 1mm when the bolts are fully torqued. You’d would be wise to quickly confirm that the NDS crank arm clears, but that’s rarely a problem.
Last edited by Dfrost; 03-31-22 at 04:18 PM.
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03-31-22, 05:42 PM
#10
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Thanks. No, you’re right - it makes sense that the left side clearance would be the same. Good idea on the coop for a used cartridge BB to try. Since the 127.5 is about 5 mm shy of allowing the FD to get the chain to the top ring, I’m hoping the 122.5 is what I need. I may see is they have a drive side spider similar to what I have so save some fiddling.
03-31-22, 07:00 PM
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We used a rubber mallet at my last shop job. I routinely had to whack cranksets on low level specialized to keep them from rubbing on the fd. Satisfying.
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03-31-22, 08:18 PM
#12
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align the chain rings
In my experience it is more likely that the chain rings need a bit of restorative bending.
It is unlikely that the spider on this specific model crank set has become misaligned.
It is unlikely that the spider on this specific model crank set has become misaligned.
03-31-22, 08:54 PM
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Thanks. No, you’re right - it makes sense that the left side clearance would be the same. Good idea on the coop for a used cartridge BB to try. Since the 127.5 is about 5 mm shy of allowing the FD to get the chain to the top ring, I’m hoping the 122.5 is what I need. I may see is they have a drive side spider similar to what I have so save some fiddling.
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03-31-22, 09:07 PM
#14
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If it is the spider and not the chain ring, you could consider using a shim to make the mounting surface co-planar (eliminate the wobble).
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04-01-22, 06:25 AM
#15
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It's pretty bad. I first thought it was the chain rings, so I swapped them out with the AT's, but the wobble was just as bad. I'm guessing the spider's too out-of-whack for tweaking but I may give it a try, just for upper Midwest late-spring, basement shop kicks.
