Bicycle Mechanics - Shimano 105 & Ultegra Hollowtech II crank arm interchange

I have a complete 105 series FC- 5600 standard double crankset that is in excellent condition, but not in use.

I have found a used Ultegra FC-6603 triple crankset with a stripped pedal thread on the non-drive side arm. The drive side of the crank looks very good. I need a triple for my next build project.

Both cranks are a 175mm size.

Will the 105 non-drive side arm install correctly on the Ultegra crank?

It doesn't exactly answer your question, but the stripped pedal thread can be economically repaired with a threaded insert known as a Helicoil. The damaged threading is drilled out and tapped oversize with a special thread, then the insert is threaded in. It will make the repaired thread stronger than the original.

It will work, any Shimano HT2 drive side will match with any Shimano HT2 non drive side, may not look pretty but will work.

I may be wrong but the helicoil solutions I've used would not work very well. The problem would be the drilling out the hole from the non threaded side would ruin the step the screw seats against. If you drill it out the other way then installing the helicoil would be a problem as the tang that installs it would be in the way. if you reverse the helicoil and try to put it in that way then you're trying to expand the coil and it would drag. They may have another helicoil solution I'm not aware of though.

I was just thinking that's probably a M6 screw. A 1/4"-28 is just a little bigger. My chart says a #3 drill bit for the 1/4-28. A M6 would be a #8 so it's not much larger but it should be enough for new threads. Don't use cutting oil on Aluminum and tap it vertical for the chips to fall out. Another question would be if the socket that the screw sits in is big enough for the 1/4" -28 head to sit down in.

OOPS Pedal thread never mind.

"the tang that installs it would be in the way." It shouldn't be a problem with a genuine Helicoil brand insert. The driving tang is broken off after the Helicoil is driven in. It shouldn't interfere with threading from either direction.