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Sugino crankset difference, GP vs AT

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Sugino crankset difference, GP vs AT

Old 03-31-22, 01:47 PM
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Duke of Prunes
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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?
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Old 03-31-22, 02:00 PM
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You could do either. Get a longer bottom bracket spindle or another GP.
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Old 03-31-22, 02:18 PM
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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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Old 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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Old 03-31-22, 02:51 PM
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I don't know if it makes a difference, I think the AT is forged and the GP is cast.
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Old 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

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Old 03-31-22, 03:43 PM
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And the spindle length for the Sugino AT should be 127.5

Sugino AT Triple bottom bracket question?

Asymmetrical Woes and the Sugino AT
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Old 03-31-22, 03:46 PM
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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.
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Old 03-31-22, 04:15 PM
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Originally Posted by Duke of Prunes View Post
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.
That seems surprising, but you’re the one seeing it. I’m sure you know that the recommended chainline for a triple is 45mm to the middle ring. Mine are slightly less, but my FD have enough clearance to not hit the ST when shifting to the granny.

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.

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Old 03-31-22, 05:42 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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Old 03-31-22, 07:00 PM
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Originally Posted by ThermionicScott View Post
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.
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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Old 03-31-22, 08:18 PM
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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.
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Old 03-31-22, 08:54 PM
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Originally Posted by Duke of Prunes View Post
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.
Older Sugino cranksets were asymmetrical. Sugino did not move the left crank outboard on the longer spindles so all (or at least most) of the length difference was on the drive side, Sadly, I never documented the many that passed through my hands. As one who has needed low Q-factor cranksets the past 40 years, I took it for granted that the left crank nearly hit the chainstay. The past 15-20 years I've been going to more modern cranksets and sealed BBs. My feet got moved outboard, bike by bike until my knees said "enough". Now I seek out those old Suginos or get asymmetrical Phil Woods.
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Old 03-31-22, 09:07 PM
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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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Old 04-01-22, 06:25 AM
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Originally Posted by ThermionicScott View Post
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.
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.
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