Bicycle Mechanics - Mega Exo help!
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09-01-08, 03:05 PM
I just installed a 2007 SL-K (double) with Mega Exo BB to manufacture's specs. Somehow, the non-drive side crank arm is 2.2 mm further away from the bike midline than the drive side. I did not have this problem with Ultegra Hollowtec. The bb shell is within 0.2 mm of 68mm.
It seems the issue is with the non-drive BB cup, which does not thread in to being completely snug with the frame. Is this how the BB is designed? It seems possible that the middle spacer is too long and prevents the non-drive BB from threading fully into the shell. I'll check this when more loctite 241 arrives.
Any other suggestions?
Anyone else deal with this issue?
FSA has not been helpful.
09-01-08, 03:38 PM
Does this help?
With the Mega Exo BB, both cups should thread completely into the frame. If not, something is either wrong with the threading on the frame or the BB cup or both. It's also possible that your BB area needs to be faced, though 2.2mm sounds like an extreme alignment issue.
The middle spacer (at least the ones I've seen) are plastic as their only purpose is to provide a dust/dirt shield. If it was too long, it would be crushed when the BB cups were installed. On my Iron Horse MTb with an FSA Mega Exo crank, the assembler forgot a 2.5mm spacer which not only caused the spacer to be crushed, but the bearing preload could not be adjusted properly, leaving a bit of play in the cranks.
Have you tried using a rubber/plastic mallet to insure that your crankarms are fully seated in the bearings? I had to do this on a friend's bike when installing a Shimano outboard bearing crank. The crank spindle was a really tight fit in the drive side bearing (as it should be).
09-01-08, 04:14 PM
i installed the bb/crank according to specs. on pdf, triple-checking did not identify problem. The center spacer and sleeve are both alloy, so they do not crush. I am considering cutting off ~2 mm from the center spacer, but my fear is that the spindle will be too long.
I also tightened the left crank arm to the max torque specified by fsa, so the arm should be seated properly.
I really don't think this is a frame issue, since I had been riding ultegra hollowec (similar outboard design) on same frame without any problems. I only changed cranks because I decided to change crank arm length.
09-01-08, 04:32 PM
Ok, I was looking at the wrong crankset installation specs. In the K-Force Light instructions it notes the alloy shell spacer.
In looking at how that crankset assembles, it appears as though the non-drive side BB cup must align with the alloy shell spacer on the drive side cup. Have you verified that this is occuring? If the alloy spacer was somehow out of alignment, it could be blocking the non-drive side cup from fully screwing in. As you have already torqued the cup, you might even be able to see the damage on the spacer from this misalignment.
A quick way to check to see if the alloy spacer is the issue is to remove both BB cups and hold them in your hands the same way that they would be installed on the bike. Measure the distance between the two cups and see if it matches your BB width. If it's too big, the issue would seem to lie in the spacer. If it measures correctly (something less than 68mm), I would inspect the frame to see if possibly the BB was crossthreaded resulting in the misalignment.
09-01-08, 04:38 PM
I ran into sort of the same issue when I tried to install an MTB external BB into a 68 shell. I found out that MTB EXO's are 72 while it seems that the usual road setups are 68. Is it possible that your crankset is actually a 78mm? The 2 mm crank spacing difference to the stays and the NDS cup jamming against the internal seal would seem to support that option (exactly what happened to me in both cases first time around). If so then you need the two BB cup spacer rings or a 68 specific setup.
09-01-08, 05:55 PM
good points BCRider & joejack951.
I had confirmed that I have the correct parts for a road bb 68mm shell. I am out of loctite 241 - necessary to insure that the NDS arm does not fall off. More should arrive tomorrow - when I will take this thing apart again and check some measurements.
09-01-08, 07:29 PM
Well as part of that take it all apart and leave out the center shield and see if the two cups will thread in all the way on their own. If not then it's something in the threading and not due to the shield.
09-03-08, 06:39 PM
It turns out the middle spacer is too long. Somehow FSA must have mixed up Italian and British parts. I have the correct cups, incorrect spacer. I hope those at FSA finally respond to my email. In the mean time, an Ultegra spacer sits between the fsa cups.
Simple things shouldn't be so difficult.
09-03-08, 06:41 PM
Oh, and of course the new BB bearings grind.
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