jgf310

in 2013..,i posted about trouble with getting my FC 6703 crank on to my 2007 specialized Roubaix with a BB 6700 installed.

https://www.bikeforums.net/bicycle-m...wrong-one.html

Basically.., with the spacer in place, the spindle did not seem to protrude far enough through the BB to securely fasten the non-drive side crank arm. The cap that pre-loads the bearings only barely engages with the threads on the spindle.

Anyway, i rode it for 1000's of miles.., eventually replaced the chain rings because i wore them out.., and rode it for many miles again...

now, this season.., the crank arm will not stay on

At this point.., I am pretty sure I have stripped the splines or ridges inside the hole on the crank arm.., so i am ordering a new one. It looks like the splines on the spindle are fine.

I am thinking of installing it without the spacer - the crank arm will fully mate with the spindle without the spacer.

In fact - there is a little play without the spacer, and I am afraid it will lead to poor shifting, as the chain rings could move in and out slightly. So, maybe i could get a washer that is thinner than the spacer and use it instead.

any suggestions?

Crankycrank

Here is a diagram of your crankset with spacers and their widths listed. Check that yours has all the proper parts and installed in order. BB for double and triple are the same. It should fit if everything is correct. https://si.shimano.com/pdfs/ev/EV-FC-6703-2979A.pdf

jgf310

I plan to take it all apart and check - but i did that before, and it seemed everything was correct.

One thing i never understood, is the role of part #4 in that diagram - the "plate". What does it do?

MudPie

I believe it's a go/no-go indicator that your NDS crank arm is pressed in adequately onto the axle. If The crank arm is sufficiently engaged, you are able to pivot the plate and its little pin will fall into the hole in the axle. If the crank arm isn't fully engaged, the pin will not fall into the hole in the axle and the plate will not be flush with the crank arm and indicates something is wrong.

Crankycrank

#4 also keeps the crank arm from coming off if the pinch bolts come loose and the #1 "crank arm fixing bolt" loosens up or falls out which almost never happens if the pinch bolts are torqued properly.

jgf310

it's difficult to see how #4 could do that very well... there is a tiny tab on it that i guess is supposed to go in the hole on the spindle - but it seems too small to do anything.

is that how it's supposed to work?

Crankycrank

Yup, fits in the hole to prevent the crank from sliding off the axle. Not meant to hold up for miles on end but is a short term safety device. Try pulling your crank off with it in place and the pinch bolts and crank fixing bolt loosened and you'll see. As I mentioned this is a very rare occurrence but might save somebody some grief at some point.

jgf310

So, I have all the parts, and no extra parts...

I have measured my BB width with a micrometer - it's 91.3 - 91.4 mm.., does that seem right?

This seems to me to be a possible source of my problem - if the BB when mounted on the bike is too wide, then the spindle will be too short...

jgf310

My part #4 - the stopper plate is plastic, and is cracked - it is apparently also missing a metal pin

is it supposed to look like the one in this ebay ad?

https://www.ebay.com/itm/Shimano-Hol...oAAOSw50VeAkRU

it doesn't seem possible that this tiny pin could really hold it on - my arm comes off when i am out of the saddle climbing a hill - so really loading the pedal arm up...

In any case - on my bike, that little metal pin is not going to be near the tiny hole on the crank - at least i don't think it will - because i can't get the arm on the spindle far enough with the spacer in place

Here is a picture showing the arm fully seated on the spindle with the 3mm spacer in place - note how the end of the spindle is recessed into the arm. I believe the little metal pin on the stopper plate would be outboard of that hole.

jgf310

well, I am still having trouble - the crank arm will not stay on

i did manage to lengthen the interval between failure though.

So, i experimented with simply removing the 3mm spacer, to get more of the pedal arm over the drive side spindle. It was obvious that this would not work because the spindle was now about 1/2mm too long - with the crank arm on as far as it would go, there was a tiny gap. The spindle would be free to slide back and forth, and the with the chain rings moving in and out by 1/2mm, the shifting would not be very good.

I fact, one of the first signs that the arm is coming off is that i can no longer shift to the large chain ring - as the pedal arm loosens and begins to slip off, the chain rings move outboard, and the large ring gets beyond the limit stop.

anyway, i next experimented with a home-made spacer of about 1/2mm, made from a takeout food container, installed without the 3mm spacer. This seemed to work better - certainly I got the pedal arm on to the spindle much further. It was tight and shifting was good.

I then found these delrin spacers made for shimano BB's by Wheels Manufacturing

https://wheelsmfg.com/products/botto...-brackets.html

they have a 1mm and a 1/2mm spacer.

I installed a 1mm spacer in place of the 3mm spacer.

I also bought a new part #4 , and a new crank arm

on closer inspection of the crank arm and spindle it seems they are fine, so i did not use the new crank arm yet.

everything goes on fine - i get the arm seated well on to the spindle. Shifting is good.

but after say 100-150miles, i notice the shifting problem - it gets hard, then impossible, to shift to the large chain ring, as the arm begins to slip off the spindle and the whole crank is free to move side-to-side a bit.

I carry the tools, and can fix it on my ride - but it sure is a pain.

I am thinking of trying the new crank arm.

shelbyfv

Seeing the pic in post 9, I'm not surprised the arm came off. What's surprising is that you thought it was OK to ride it that way. My advice is to take it to a shop before you waste any more time or money. Clearly this isn't something you need to be messing with yourself.

trailangel

BB width is not measured with bearing installed.

jgf310

i agree it looks terrible (that's why i started the first thread years ago) - but i wore out one set of chain rings, and got maybe half way through the next set - so thousands and thousands of miles - before having an issue.

in any case, it doesn't look like that anymore - with the narrower 1mm spacer.., the pedal arm is seated quite far on to the spindle - about as far as it will go. recall that with no spacer, it doesn't go all the way on...,

WizardOfBoz

Yeah, that spacing in post 9 seems way off.

You might find the Park Tool's video by Calvin Jones useful:

https://www.parktool.com/blog/repair...ession-slotted