tahoeeddie

I have a friend who has a beach cruiser that keeps slipping when high torque is put into the pedals. specifically riding up hills. for example, he can pedal normally on flat or descending roads. but when he puts power into the pedals, they'll slip and he can't generate any power into the rear wheel.
the bike shop initially said that it was a dirty bottom bracket. i didn't buy that. they cleaned it out and sent him on his way.
that did not fix the problem.

now they say they can fix it by replacing the 1-arm crank because the nipple broke off.
I'm familiar with traditional road bikes. and the only thing that is called a crank to me is the crank arm. and i don't know what a 1-arm crank would be. and nipples, to my knowledge, are only the nipples on the wheel spokes.

what does the braintrust here think a possible problem is? and/or what do you think the bike shop is talking about?
i have not talked to the bike shop directly. my friend is very intelligent, but not particularly familiar with the workings of bikes. so he's only relaying to me what he remembers of their conversation.

so far none of what the bike shop has said makes much sense to me.

thanks in advance for your thoughts and ideas.

tcs

Hmm. Most likely...

The hub is out of adjustment.

or

The shift cable is no longer moving freely in its housing.

or

The hub needs to be cleaned and relubricated.

Service manual:
https://si.shimano.com/pdfs/sm/SM-IHG-INTER3_ENG.pdf

Russ Roth

One piece crank arms on the drive side have a shoulder that the chainring pushes up against and then the cone is threaded onto the arm to lock it into place. On the crankarm is a tab, which I guess could be called a nipple, that helps to keep the chainring in place. On nicer cranks the tab will be tapped and threaded and the ring bolted to it. On some cheaper ones it'll just stick through the hole in the chainring, with the cone threaded down as tight as it should be the chainring probably wouldn't move under normal load but if you put down power it could possibly move, the action of the chainring moving would help to tighten the cone more but powering down with legs I wouldn't be surprised, if the tab is gone, if the ring could move.
A shop should have an easy time diagnosing an internal hub, they're pretty self-explanatory with clear red or yellow markings and shouldn't easily be able to slip if they're adjusted.

Bill Kapaun

If he pin is broken or not engaging, that could cause a slip on a 1 piece (Google Ashtabula crank) under load.
See pic for pin.

However- A worn chain/cog could slip under load.

He definitely should avoid that LBS if they indeed say it was a "dry BB".

Me thinks there's some communication error involved?

tahoeeddie

Folks, thanks for the thoughtful replies.

to clarify, the slipping he's experiencing is almost as though the chain is not catching on anything. it's not actually sliding or skipping over the teeth on either the chain ring or the sprocket. it's like he puts the pedals down, the chain moves, and the sprockets move, but there's no translation into power in the hub. so it's totally confusing to me why the shop would assume anything up front. it seems like it'd be something internal in the hub. but i also can't figure out why it would happen under load and then pick up again (like it gets reset) later. based on the manual that TCS linked, in the troubleshooting page, its recommendation is sort of a general "internal assembly malfunction" "replace the whole thing". without any real explanation. which maybe is the TLDR of "save yourself the headache and just start over". but I'm guessing a lot of you in this forum can understand the desire to know exactly what's going on even if you admit that the faster, more economical solution is to replace and move on .

i did a search for the words "nipple" and "crank" in the manual and nothing came up for nipple. but apparently, there's called a bell crank unit, which appears to be where the shift cable comes into the hub assembly. and i suppose if that's malfunctioning, it could cause the hub to slip into a weird spot where the pawls don't catch. maybe that's what tcs is trying to say?

oh, additional information. it's a beach cruiser. so not a kids bike or anything like that. I've never worked on beach cruisers. so don't know much about them.

tahoeeddie

yeah, i don't think they even really tried to listen to him when they described the symptoms, nor did they try to test ride it. he's taken it back to them twice. it's still under a 1-year warranty with the shop.

tcs

Replace the whole thing? Again, and this will be the last time:

The hub is out of adjustment.
Adjust it.

The shift cable is no longer moving freely in its housing.
Clean it or replace it.

The hub needs to be cleaned and relubricated.
It's a dunk, swish and drain. See the manual.