Quick question(s) about installing a chainring/crankset I just received.
Bought a new crankset with the understanding that it would be an easy swap. Unfortunately, after my first attempt at installation, I found that the frame facing bolts that attach the small chainring to the large chainring do not clear the driveside chainstay (2013 Cervelo P2). While the crankset is the exact same, the chainrings are not, hence the issue.
This leaves me with a few questions:
What is the minimum chainring/chainstay clearance you are generally comfortable with (not sure if it matters, but the stock crankset did not provide much clearance at all)?
1a) Is there any flex down there at all?
Is it ok to use spacers to obtain more clearance?
2a) If I were to use spacers, should I be using them on both sides to maintain symmetry?
2b) Any drawback or negatives to using spacers on the BB (in doing some cursory searching, I read about issues ranging from chainlines to bearing wear to compromising stiffness)?
Is there a difference between using spacers between the bearing cup and the frame as opposed to the bearing cup and the crankset (not even sure this is an option but it came up in one of my searches as a potential solution)?
Since I didn’t have any spacers available to experiment with, I switched the wavy washer to the driveside. This allowed *barely *enough space for the small chainring bolts to clear the chainstay (maybe a credit card to a dimes width). Any issues with doing this? I.e. is the wavy washer on the non-driveside for a reason? Again, not sure if it matters, but my stock crankset did not have one on either side, or any washers, for that matter.
I’m picturing this in my head. I don’t really see how spacer would work. It depends on the crank, but with newer cranks I think the spindle length is what it is. Spacers are not going to increase this, unless for instance, with a Hollowtech crank you attach the non drive side arm not all the way on the spindle end, but that doesn’t seem like a solution, I’d assume there’s not alot of extra real estate for spacer. With like a square taper or ISIS you could put spacers between the BB and the BB shell but then the BB is not screwed in all the way. Neither sound like great solutions. What crank do you have this problem with?
Pictures would be helpful to get an idea of what is going on. Also, the specs on the original crank and new crank would be helpful too. Leaving too many holes to give a proper answer. I have a couple of suspicions but won’t guess until more info is provided.
I would imagine from 2-3 mm would be the minimum clearance you’d want from your chainstay. Can you swap the chainring bolts to something with a smaller head so it doesn’t protrude as much? maybe like a set screw (http://www.mcmaster.com/#set-screws/=1090ttc)
I’ll try to get a pic up shortly - I have a few, but it was tough to get the proper angle because its in a tight spot.
The old cranks were the stock FSA Gossamer that came on my 2013 P2. The new cranks are the same but have Praxis rings instead of the stock FSA rings. This is where I think the problem is.
The bottom bracket is a mega exo that came stock, as well.
Not sure if I can swap screws (since the new crank and rings came with a P2M installed), but I’ll look into that. I’m not hopeful, though, because if I install the wavy washer on the non-drive side, like I’m supposed to, it probably would result in the same clearance. In other words, the space I gain by changing the bolts to ones that were flush with the small chainring would be lost when I reinstall the wavy washer correctly on the non-driveside instead of the driveside.
Yes, that is one of my concerns. Using a spacer where I shouldn’t really need one would result in having less of the non-driveside spindle end screwed into the non-driveside crank arm (albeit by millimeters).
The old cranks were the stock FSA Gossamer that came on my 2013 P2. The new cranks are the same but have Praxis rings instead of the stock FSA rings. This is where I think the problem is.
Is there a reason you can’t pull the new rings and put them on the crankset that has already fit? That seems like the least bad option. If you’re going from 110BCD to 130 or the opposite, fine (although 52/38 is really close and doesn’t need a BCD change if you’re going up).
That doesn’t seem possible that you took Part A #1 off and installed Part A #2 and it doesn’t fit. Did you look at both cranksets to make sure they’re exactly the same? Sometimes spacers can get jammed on and look like a generous boss on the spider.
Also, fun stuff since you have a newer Cervelo. BBRight is pretty picky about spindles, specifically length, because the shell is comparatively wide.
In general, I’ve found that “normal” cranksets don’t have enough spindle length to run spacers with the BBRight shell. My Quarq has no spacers, and doesn’t work with any spacers. I just put a stock BBRight Gossamer on my S5 and for whatever reason the Rotor bearings that were installed are a slight bit inset, so I’ve got to run ~10mm of spacer plus the wavy washer. Spacers - within reason - should be no big deal.
The other option, if you have calipers or a good scale (ruler). Measure the distance between the external faces on the pressed bearings, then measure the length between the spider face and the start of the crank splines on both cranksets. Something has to be different, report back, IMO that is probably more useful than pictures since we’re talking about a handful of milimeters of difference which we won’t really see in a picture.
As you’ve probably already realized, you don’t want to add any spacers between the bottom bracket cups and the frame. If you have existing spacers behind the cups you could reduce the spacer thickness behind the NDS cup and increase the thickness behind the DS cup to gain chainstay clearance. Same goes for spacers between the crankarms and the outside of the bottom bracket cups. If you have any on the NDS, try moving them to the DS and see if it gains you enough clearance for the new chainring bolts. The wavy washer can be moved to DS. I haven’t kept up with what FSA currently uses to take up spindle lash w/o infringing on Shimano’s hollowtech patent, but as long as your spacers allow the NDS crankarm to fully seat or connect to the spindle the rules are up to you. The only difference in the end would be a small asymmetry on the crankarm distance from bike centerline - slightly offset q-factor.
One other consideration is that when I ran FSA carbon cranksets for several years the MegaExo bottom bracket specs changed at least a couple of times. I never looked into exactly what changed, but it likely included the outside face to face distance because they changed from using rubber coated crush washers or o-rings to something else. It could be that you have a slightly wider BB vs. the current Gossamer crank. It might help to drop FSA USA a note and see which MegaExo BB they recommend for your crank.
Both cranksets “fit.” Its the new chainrings that result in the clearance issues (specifically the frame facing bolts on the small chainring not clearing the chainstay).
How do you know if you have enough spindle length for the non-driveside crank arm if I end up placing spacers on the driveside? Just thinking about it, I don’t see why or how 2-3mm of spacer would result in not enough spindle (for what its worth, the new FSA Gossamer cranks have that integrated bolt thing instead of the pinch bolt on my old FSA Gossamer).
I’m guessing you’re saying its not a big deal if I ran, lets say, 5 mm of spacers on the driveside (giving me about 2.5 mm of breathing room between the chainring and the chainstay)?
Thanks Summit, I think this answers my questions/concerns.
Would there be any problems with adding a 3mm spacer to both the NDS and the DS to maintain the centerline? I’m thinking that 3mm of q factor isn’t really something that anyone could actually perceive (though I have nothing to back this statement up). And if I use a 3mm spacer on the NDS to maintain the symmetry, how would I actually know if the crankarm has enough of the spindle? 3mm of spacer on the NDS would result in 3mm less of the spindle for the NDS crankarm to grab, though I’m not sure if that even matters.
I’ve got an e-mail out to FSA as well. Thanks for the suggestion.
Knowing nothing else about this BB and crank combination your safe bet is to only move spacers from one side to the other so the distance between the back of crankarms doesn’t change. Because the FSA (AFAIK) cranks only seat on the spindle by being torqued down (rather than clamped on like Shimano) you don’t have much flexibility.
I imagine that any lack of spindle grab will show up as severe lateral bearing pressure/drag when the crankarm bolt is fully torqued.
I imagine that any lack of spindle grab will show up as severe lateral bearing pressure/drag when the crankarm bolt is fully torqued.
You mean spline seating, right?
I’m having the same issue on my S5 right now, which is to be expected. If I don’t dump all the bolt torque into bottoming the spine out on the NDS arm, then it’s all taken up by the spacer into the bearing and contributes a ton of friction.
I’ve seen Gossamer cranks with both styles - spindle centerline mounting fastener or pinch bolts (although they were on both on a 24mm spindle, so I can’t say if that’s the case on a 30mm).
The good news, relatively, is an incorrect installation will show up as obviously wrong. Too many spacers and you’ll have a ton of BB friction, too few and (if you have a light or no pressfit between the bearing and spindle) the crankset will slide longitudinally on the spindle. I would just keep playing around with spacer locations until the chainring bolts clear, and there isn’t one of the aforementioned assembly error flags. As far as biasing the crankset to one side or the other, it’s hard to say if it will make a difference or be perceptible. Everyone has some power balance between legs and this slight offset may have a similar ‘effect’ - FWIW, I’ve never measured to see if my crankset is centered on any of my bikes and it’s never bothered me.
The good news, relatively, is an incorrect installation will show up as obviously wrong. Too many spacers and you’ll have a ton of BB friction, too few and (if you have a light or no pressfit between the bearing and spindle) the crankset will slide longitudinally on the spindle. I would just keep playing around with spacer locations until the chainring bolts clear, and there isn’t one of the aforementioned assembly error flags.
The BB friction due to lack of spindle length is what I was imprecisely describing above (assuming for the centerline mounting fastener style crank). With the year of the P2 I was assuming 24mm crank and threaded bb cups rather than BBRight and 30mm.
As far as biasing the crankset to one side or the other, it’s hard to say if it will make a difference or be perceptible. Everyone has some power balance between legs and this slight offset may have a similar ‘effect’ - FWIW, I’ve never measured to see if my crankset is centered on any of my bikes and it’s never bothered me.
Agreed. I’ve seen a lot of variations on asymmetric offset with mtb’s and fatbikes for chainring and chainstay clearance tweeks. Lots of riders sit offset to one side of the saddle or other without issue.
For what its worth, Pioneer and Shimano told me that running a spacer on my Pioneer DA9000 power meter would not have any adverse effects on crank performance or power meter reliability/performance.
I have a 24mm spindle. New cranks had the centerline mounting fastener and old ones had the pinch bolt. Hopefully, the spacers wont result in any of the red flags you pointed out and if they do, then I’ll have to deal with the fact that this particular crank/chainring combo won’t work for me.
Very informative answers, appreciate you taking the time.
Ugh, going from pinch bolt to centerline… I know the pain, I couldn’t ever get the centerline to work to my liking on my Soloist (24mm external BB) and ended up going to the pinch bolts where I could gingerly - and directly - change bearing preload.
Get everything spaced out so you have 5-10mm of gap between the bearing/spacer/whatever face and the spline termination, throw in a wavy washer, torque the crank arm on, check for too much friction or longitudinal play. Knowing that’s what you’re trying to do, playing around with different stacking sequences should net success - definitely space the crank to clear the DS chainstay first, then play on the NDS.
Give that a go, post back if you’re still having issues.