FSA MegaExo Crank arm adjustment
 

I have a Co-motion Speedster with FSA MegaExo BB-7000 bottom brackets installed. I've had to replace bottom brackets more frequently than anticipated, at about 5,000 mile intervals. The bb in the front has less than 2,000 miles and there is a new wavy washer installed. I'm having some trouble adjusting the front crank arm torque. If I tighten the crankarm enough to crush the wavy washer (on the non drive side), I begin to detect a little drag/resistance in the bearing. However, backing off on the nut slightly results in the crankarm loosening during the ride. I have one metal spacer installed on the timing chain side, two metal spacers sandwiching the wavy washer on the non drive side. If I remove one washer or replace it with a thinner washer the crankarm bottoms out on the spindle and does not fully compress the wavy washer. What could be wrong with my assembly? Should I just accept the increased drag/resistance with the higher torque? Is there a different compatible brand bottom bracket that I should consider for the Speedster?
Dave Fritsch,

This sounds like a crank issue, not a BB issue. What crankset do you have?

WVDave: I suggest you take a look at the installation instructions for the FSA crank set; they should specify the correct arrangement of spacers. Two things: 1) the wavy washer will not necessarily be compressed even when the correct torque is set on the crank arm bolt, and 2) it's expensive, but it's best to set the torque on that bolt with a torque wrench rather than guessing. Finally, I think the installation instructions will indicate there should not be a spacer between the wavy washer and the crank arm. If your particular installation requires a spacer it should not be outboard of the wavy washer, I don't think. Again, I'd refer to the crank set installation instructions from FSA. Good luck!

It is the original stock FSA Gossamer tandem timing crank.

What width is the bottom bracket shell and eccentric? 68mm or 73mm?

My front and rear fsa crankset had a little too much drag with the chains removed I just adjusted the spacer width until it spun freely but still had a little compression on the wavy washer and no sideways play. Keep in mind when its under load the drag will be negligible, I have never liked the wavy washer system but there isn't a lot of affordable choices in the tandem market

73 mm

Thanks for the suggestion. I did find what I think are the relevant instructions on the internet. It helps to know the wavy washer doesn't compress completely. We were able to take a ride this afternoon. Although at the start of the ride I had tightened the crank arm bolt to the point that it was slightly impeding the pedal stroke I had to stop three times on a 13 mile ride and tighten the bolt on the pedal arm. I only had a quick tool so I didn't have a lot of leverage, but I was surprised how quickly it loosened again. I did use my torque wrench afterward to set 33 ft. pounds of torque which is within the FSA recommended range. At that torque I couldn't detect any hindrance on the bearing. I suspect I had more than 35 lbs. torque when it loosened. I was fortunate that the stoker's bottom bracket and crankset were installed by a bike mechanic with experience with FSA cranks and it has never loosened or restricted the bearing. I took it apart to make sure I had the same number of spacers on the captain's crank. They were the same. The FSA instructions show the wavy washer immediately next to the pedal arm, on the outside of the alloy spacer washer, next to the pedal arm. The mechanic who installed the stoker's crank had the wavy washer inside of the alloy washer so I am going to replicate that with the stoker crank and see if it makes any difference. It is interesting to note that the alloy washer has "outside" printed on one side of the washer. Does "outside" refer to the position on the crank the direction it faces on the crank? There is only the smallest difference on the inside hole on each side. I hope to get in another ride this Friday and I'll see if it loosens up during the ride. If it still loosens, I thought about cleaning out the grease on the pedal arm bolt and out of the interior threads of the crank and applying Blue Locktite thread adhesive on the threads. Would that amount of additional resistance to unthreading be sufficient to keep it secure without ramping up more torque on the pedal arm bolt, or am I creating another problem the next time I try to take off the pedal arm.
Dave Fritsch

extra spacers
 

[QUOTE=My front and rear fsa crankset had a little too much drag with the chains removed I just adjusted the spacer width until it spun freely but still had a little compression on the wavy washer and no sideways play. Keep in mind when its under load the drag will be negligible, I have never liked the wavy washer system but there isn't a lot of affordable choices in the tandem market[/QUOTE]

Sounds like we dealt with the same issue. I've been through every configuration I can think of. While chasing down a creaking noise I thoroughly greased everything including the pedal arm bolt and the threads inside the crank. I wondered if that grease is what allows it to unthread so easily. However, I greased the stoker crank at the same time and didn't have the problem with that crank. The rational part of me realizes that the increased bearing resistance from an overly tightened crank results in less physical effort than even 2 lbs, of extra weight on me. However, while toiling up a hill, the irrational (and compulsive) part of me forgets that and I worry that I'm causing premature wear on the bearing.
I'm going to fix this, even if it causes my long suffering stoker to lose her temper. I'll let you know how it goes.
Dave

Random thoughts...

Good to know it is a 73mm width shell. That configuration uses no spacers under the bottom bracket cups and there are likely none given the stated visible spring action left in the wave washer. If spacers for the 68mm shells are installed, the bearings will be ruined right off when tightening down the arm and the spring washer is squished flat, real flat.

A crankset should never be ridden without the arm torqued down properly as the soft alloy arm will be ruined right away. Once it comes loose, the mating machined surfaces are no longer flat as the alloy is wallowed out (how much depends on how long it was ridden) and it will never stay tight again, generally. In other words, the flat platform is no longer flat after ridden loose.

If the spring washer has not been compressed all the way, there is no way the bearings will be squeezed and put into a bind any tighter than that allowed by the spring tension, no matter the torque applied to the arm fixing bolt. Why? There is still room for the spindle to be forcibly shifted sideways given the gap remaining in the visible wave of the washer.

Another rare issue would be if the mating surfaces of the bottom bracket shells are not faced properly, that may cause the cups to not be perfectly in line or parallel with one another. But then that would be noticed from a difficult install when trying to slide spindle through 2 holes that don't line up perfectly.

The orientation of the spacers and washers will make no difference.

The 'outside' term is to the outside of the bike. It really only mates with the seal on the arm with the spindle which is what the groove is for on the inside to mate with. It makes no difference which way it faces on a non spindle side given there is no spindle seal on those arms.

I have the same crankset on our Calfee since 2011 and have not had any problems or had to touch it.
I agree do not ride it without the crank bolt arm torqued down.

TandemDr & HeadAsunder,
I neglected to thankyou for your suggestions. We did get to ride for 13 miles today with the torque set at 35 ft. lbs. I was happy that the crank arm bolt did not loosen on the ride and upon return the torque wrench revealed the bolt was still within specifications. I decided to tighten both the stoker and the captain crankarm bolts to 40 ft. lbs. which is still within the specification range and ride it for a while but checking it often. If it loosens again, I'm going to try using some Locktite thread sealer on the bolt threads. It will take me some time before I won't feel like I have to check it every five miles.
Dave Fritsch

My experience confirms this. We were on a tandem tour in 2018 and one of the other captains was having a problem with the crank arm loosening. The tour mechanic made a temporary fix by disassembling a Mach 3 razor blade and using individual blades as shims on the spline. A few days later the same problem developed on our bike. The mechanic used the same fix and advised me to avoid removing the crank in the future, but I need to remove it to pack it into travel cases. His opinion was that thread lock compound would not solve the problem.

The bike is a 2005 Speedster. I ended up calling Comotion about a possible replacement and it so happened that they had a captain’s crankset of that vintage lying around in inventory that they were willing to send to me for an attractive price compared to any other alternative. This is a good reminder for me to double check that my crank bolt is still torqued to spec.

Warped crank arm
 

Two questions. Was it an FSA crank? Could you visually detect the warped edge when laying on a flat surface? If the crank arm metal is so soft it makes me wonder if it is a good idea to have the wavy washer against it. Seems like the greater surface area of the alloy spacer would be more likely to limit damage to the crank arm face. Perhaps I’m way overthinking this.
:) Dave

I’m attaching pictures of the crank that was loosening under use. FSA SL-K. Once I solved my problem by finding a replacement, I stopped trying to understand root cause, but my impression was that it had to do with some wear or deformation of the spline interface detail. I can’t imagine that the washer or spacer had anything to do with it.
https://cimg5.ibsrv.net/gimg/bikefor...235c1c905.jpeg
https://cimg6.ibsrv.net/gimg/bikefor...ac912dffb.jpeg

Reburn, thanks for taking the time to post the detailed picture. I'm going to take a close look the next time I take the pedal arm off. I may go ahead and purchase a replacement crank to have here in reserve.
Dave