tadawdy

In question: FSA MegaExo BB, with about 800 miles on it.

Got on the trainer tonight, and something was popping like crazy. No problem whatsoever on last ride. Determined it to be BB-related. A pop on each downstroke; BUT if it pops with left crank , and you soft pedal the right, it won't happen again on the left (until you do make he right pop) . This would indicate to me something is shifting from side to side. I can also demonstrate this by hand (with a lot of force) off the trainer, and feel it very slightly when riding. It probably wouldn't bother me if I didn't notice it on the trainer, though.

So, it seems like something is not seated correctly, or is loose (?)
Alternatively, the BB could be dead, but it's only had a very short life so far. But why would it be 100 times worse on the trainer?

I did look for cracks, and didn't find any. I was hoping if someone with knowledge of this type of BB could tell if it is simply an omen of my BB's demise (it feels perfectly smooth) or if some other issue is probably present.

tadawdy

I don't know why my post isn't showing...basically, is there any reason, other than the BB simply being toast, an FSA MegaExo BB (800 miles) would be popping with each downstroke? And why would I only notice it on the trainer, where it's suddenly atrocious? Could it just be loose, or something?

operator

Instead of speculating, why don't you pull the crankset/bb and reinstall while inspecting the parts...?

tadawdy

Lack the necessary tools to pull the crank and BB; should probably invest in them. I have the ones for a square-taper BB, but this is my first BB of this particular type. Just trying to figure out what to expect when I go into the LBS.

I thought someone with knowledge of the internals might know what is likely going on.

rm -rf

Megaexo cranks tend to get loose on the non-drive side. You don't need any special tools to take it apart and reassemble. Just a 5mm wrench for the two pinch bolts, and probably a 3mm ( or an 8mm for some caps) for the adjusting axle cap.

On mine, it sounds like a click and doesn't happen on every downstroke. I can be "just riding along" and then it suddenly starts making the noise.

The first time, at about 1000 miles, my LBS cleaned the axle splines, greased them, and used loktite on the two pinch bolts. I've had to do it again at least once a year.

I also had a creaking noise from the bottom bracket itself, so I bought the tool, unscrewed the cups and used teflon tape on them. I've since had one of the sealed bearings seize up. The LBS replaced the bearings in the cups and I reinstalled them.

See the Park Tool repair guide here.

tadawdy

I have had the issue with the non-drive crank being loose and have fixed that before. This happens on the downstroke of botrh pedals.

This seems like an issue with the spindle rocking around, or something similar. I just mounted the arms parallel (pedals across from each other) and applied pressure with my hands to test the bearings. I was able to produce the loud click by alternating force on them.

I will try removing the spindle and reinstalling it. I suppose I should check the chainring bolts while I'm at it.

stevemtbr

FSA BB's are horrible, replace it with a shimano model and all your problems will go away. I have a shimano7900 BB with my FSA crank and it runs super smooth.

wesmamyke

It is very common for the little blue washer/seals to become worn or lost and have to be replaced. I would pull the cranks and check both sides for them. They will tend to feel a little loose without them. And +1 on everything said above.

operator

We could spend the entire day discussing what if's and possible scenarios. A huge amount of what-if's are eliminated by actually taking it apart and reassembling, noting if anything is missing, out of place, worn or improperly installed etc. etc.

tadawdy

Fair enough.

Having removed the cranks, but not the BB (don't have the tool), and reinstalled them, my issue seems to have been solved for now. The spindle does look a little worn, but serviceable, and the noise is gone. Basically, I think the spindle wasn't seated against the bearings properly, probably from the left crank coming slightly loose.

In any case a follow-up question: What is the proper way to adjust/check bearing preload on this type of BB? I'm new to these, having only really messed with square-taper. The videos I see online basically have the guy putting the spindle as far in as it will go, sometimes with a mallet. So, that is basically what I have done. My first goal was to eliminate the noise I had, but now I need to make sure the bearings won't disintegrate.

How do I make sure the adjustment is good? On square taper it's really easy, but I can't just adjust the play out like that on this BB.

onbike 1939

The same principles apply. Take up the slack until there is no rocking movement but the spindle turns relatively freely, then lock off. FSA does recommend certain torque settings but it amounts to the same thing. Keep an eye on those outboard bearings as they seem to wear very quickly. Certain of FSA outboard bearings can be replaced by Shimano ones.