drewfio

Hello, I have installed an fsa vero square taper crankset on my bike, and torqued the arms to the same amount, but they seem to sit at different depths on the taper, and also the end of the arms are different distances from the frame. I realize there are asymmetrical spindles and perhaps this one, but I assumed the taper would be the same shape/length, just starting further out on one side. Is that assumption incorrect and these cranks are installed correctly? Or is this a symmetrical spindle installed incorrectly? See pictures below. Thanks!

(Also I know the crankset is not classic or vintage, but the bike is—a 1985 Trek 500—and I find the folks on this forum to be very knowledgeable).

AdventureManCO 

Hmmm...do you know what the BB said on it before you installed it? Could it be a 70mm BB instead of a 68mm? That would set the correct protrusion on the drive side (with the chainrings) since the cup is fixed on that side (and thereby the sprindle length sticking out) which would leave any discrepancy in sizes to be noticed on the non-drive side. When I have undoubtedly installed 70mm BBs in 68mm shells, I usually see the threads of the NDS cup sticking out just a bit. Yours is not. If you remove the cranks, do the spindle ends stick out the same amount on each side? If so, the issue is likely with the cranks. But if they stick out different amounts (according to a measurement against the chain stays) then its probably not the cranks but the BB.

Hope that helps! Others will be along soon to explain much better!


EDIT: Also, we cannot properly help you without full, glorious pictures of your very nice Trek!

juvela

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first step:

remove fixing bolts so you can examine how much freeboard you have between spindle end and floor of removal threads

it "should" be the same on both sides


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drewfio

Oof, I hadn't thought of the shell size! The cranks were given to me (in a lot of free parts someone was giving away on FB marketplace for whatever reason) along with the matching bottom bracket. Because of this I'm not sure I looked closely at the specs, and assumed they'd install without issue since they were matched. And the BB installed easily, as did the cranks.. besides this unevenness. But I don't know what bike they were previously installed on or its shell size, so that could be it! I've actually ridden the bike a couple hundred miles like this, and only noticed when I was inspecting chainline to see if it was the cause of some noise that was bothering me.

dddd

Eyeballing your installation, it appears that there is not much L/R discrepancy at all, given that the same reference is applied on both sides of the BB shell at the shell mating surface, not at the outer face of the fixed cup.
It really looks like the same ~7mm or so is (about equal) on both sides.

I can't see the taper flats and transition bevel on the right side photo, but as juvela just posted that can be checked from underneath the fixing bolts.

What torque have you applied? It is often the case in my experience that left-side cranks, if anything, tend to expand more and thus go on just slightly further than driveside cranks. This I believe is due to the additional metal surrounding the square hole on the right crankarm.

How is your chainline? There is typically supposed to be about 43mm from the center of the seat tube to the center of a single ring on a derailer bike or singlespeed conversion, and the two crankarms should equally clear their respective-side chainstay.

If that isn't a narrow-wide chainring you might find this setup prone to dropping the chain at the worst possible moment when the chain is maximally crossed, which can be very dangerous.

drewfio

Oh and here are pics, as requested
I've been enjoying tinkering with this one. Usually I keep things pretty vintage, but I decided to have some fun with more modern components, experimenting with a 1x10 setup. And it takes pretty big tires, which is nice.

SurferRosa

Instead of measuring this distance using your thumb and the chain stays, use a metric ruler and the seat tube.

AdventureManCO 

Very nice retro build / restomod! I bet it rides like a honey.

juvela

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one variable not as yet mentioned is that of Q-factor

if you remove the NDS arm and remount 180 degrees from it present position you should be able to easily measure the Q-factor of the assembled chainset

this could be compared with posted value from a technical publication, which should be findable online


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drewfio

Thanks for the reply. To answer your questions:

Yeah, in that photo it is tricky to see, but the little bevel/curve at the inside end of the taper is further from the crank on the NDS, and on the drive side the crank sits just about at that curve. I'll have to do as suggested and remove the bolts to check from the other side.

I applied about 36nm (I say "about" since I'm using a beam type wrench which I find a little tricky to hit a specific nm 100% accurately) based on Park's guidance of 34-39nm for FSA square taper cranks. I'm pretty confident they are both within that range.

It's a double crank so the chainline is not perfect. I found the inside spot to be a bit smoother, in most gears, but too extreme in the small/high gears such that it was catching the neighboring cog slightly. I moved it to the outside and it no longer does that in any gear, but the low gears are predictably a little noisier than before, and the angle looks more extreme. But with a 40t ring and 11-36 cassette, I find I'm in the mid to high gears most of the time, and haven't needed that 36 yet with the hills around me. A different crank or BB with a few mm difference might get it dialed in better, but I'm still debating whether I want to keep this 1x.

It is in fact a narrow wide, though it is a cheapie Deckas one from eBay. I have a nicer wolf tooth ring I tried, but for some reason it was causing the chain to stick to the wide teeth, like the teeth were barely too wide for the interior of the link (and I did double check that I had narrow and wide links properly matched with the right teeth). The Deckas doesn't have this issue.

Bad Lag

Is this as simple as the asymmetric spindle is installed backwards?

Chuck M 

^^ That was my first thought.

drewfio

Excuse the imprecision. I was just being lazy since I could feel/see in person it was off. But to confirm I just took out the caliper, and the NDS is about 2mm farther from the seat tube than the DS. Smaller difference than I thought.

repechage

While the crank arms show displacement.
The chainline is not reported.

there really is not enough info to work with here.

my first notion as Bad Lag mentioned- a flipped cartridge.

drewfio

That crossed my mind. But it's a cartridge bottom bracket with the spindle and one threaded end connected to the unit, and I think the left hand threading would prevent me from installing backwards in the shell, correct?

AdventureManCO 

Is the threaded (drive side) cup removable? If so, it is very possible that it may have gotten reversed. But this would only be the case if one side of the spindle is longer to compensate for a certain crank side. If they are the same, it would matter. But, It might be easier to see when it's out. If you have the tools to pull it out and snap pictures, that would help a lot, but could be a bigger operation than planned. Some BB tools would make for great stocking stuffers, and then the whole process becomes more approachable.

drewfio

Just measured the chainline and on the outside position the ring is nearly 50mm, and on the inside 43mm (it is a pretty thick ring). I feel like somewhere in the middle would get the best performance based on the actual setup I have now. Would need to change the crank or BB I think to get to that though.

drewfio

I can't say with 100% certainty it is not removable, though if so it was pretty snug on there at least, definitely not just falling off. And I do have the tools, but yeah it is becoming a bigger investigation than I'd hoped, ha. Not sure I have time today to disassemble, so I'll have to report back when I can get to it. Thanks for the suggestion.

79pmooney

My first thought - does it matter? I have probably owned a bike or two that has had cranks that sit evenly over my 50 years of using tapered spindles but I never either checked or noticed. When I have thought about it, it was in terms of getting the Q-factor down to what my knees like and that almost always means the left crank siting closer to the frame than the right.

I can guarantee you the bike doesn't care. Where the right crank sits matters in terms of chainline and derailleurs. Needs to not hit the chainstay (rarely an issue) and likewise clear the bottom bracket cup and bike's BB shell. Left needs to clear the chainstay. Those of who raced way back when raced bikes where there was perhaps half the clearance on the left to the chainstay as on the right. Some of us took pride in having left cranks that nearly scraped the paint.

And last - tapered bottom bracket spindles and the tapered aluminum cranks. Tolerances, both when made and as evolved over repeated mountings. Small errors in cross section size (these are machined parts) make considerably bigger difference in where those parts sit relative to each other simply because of the shallow taper. Say the taper is 10:1. (I just pulled that out of a hat.) A 0.1mm error in either spindle taper size or crank taper size would make a full 1mm difference in where the crank sits. Where cranks sit relative to the bike frame is one of the least precise measurements on the whole bike. And since it really doesn't matter, no one sweats it very much. You can pay twice as much for higher end parts and get a little better. (Better machining tolerances, perhaps harder steel/aluminum.) Plus, the variations of your torque, the grease or no on the spindle, perhaps the polish on the spindle and maybe whether it is Monday, Thursday or Saturday when you tighten the fixing bolt ...

drewfio

This is all making a good point—it might not matter and might be fine. That is really just what I was hoping to confirm. After all I've ridden it a couple hundred miles without a noticeable problem. I didn't think the 2mm offset needs to be corrected for its own sake, I was just wondering if it was a clue to something I should worry about. My main concern was if I somehow installed something incorrectly in such a way that it could damage anything (eg the crank taper, the frame shell, etc), and/or break while riding in a way that might cause me harm. So I do very much appreciate all the thoughtful replies!

repechage

that would make a 7mm thick ring. Derailleur equipped bikes do not use a ring like that. Almost assuredly your measures are not to a meaningful surface.
toss that aside and take a known straight edge with the chain off the ring and strike a line using the inside and outside surface of the ring toward the cog set.

oneclick 

Not bad - 14.3-ish.

And as is bigger, that issue is worse.

merziac

This is negligible IMO, stretch, wear, torque, lube, stiction and more all come into play here, no way to know how many times they've been installed, removed and could be uneven.

Spindle penetration will tell a lot but none of this is life threatening absent cracking or "bottoming out" in the arm.

Check BB cartridge orientation when more convenient and correct if necessary.

Chuck M 

Speaking of thinking about it... If I knew something was off, I wouldn't be able to stop thinking about it. Fortunately I'm so old my eyesight would never notice what the OP did. And the older I get, the fewer scratches my bikes have.