The best JRA stories are from mountain bikers with cracked drive-side chainstays and shattered rear derailleurs .

I know a lot of folks have weighed in on this, but I thought I'd add my thoughts as a long-term wrench.

1. It would have been helpful if the LBS had advised you to check your cranks and pedals for tightness after 50 miles or so. NOT touching the pedals is not necessarily a good thing, but it's the LBS job to advise you, and to assume you don't know automatically to check. It's similar to the written warning you will typically get on your repair receipt when you have work done on aluminum wheels on a car.

2. One thing I have seen stress pedals, cranks and BB's is what I call the "Roy Rogers" method of mounting/dismounting. That is, placing your foot on one pedal, pushing off and then swinging your other leg over the bike. Dismounting is the reverse process. The problem is that you can exert force in excess of your body weight, in one spot on the rotation, over and over. Heavy persons especially can stress things enough to cause problems.

Yes, it's quite possible to do the above without damage but I saw a high correlation between that method and various crank/bb problems. 90% of the pedal and crank arm problems I saw were with the left side, which is where the great majority of folks mount their bike.

As I said in my earlier post, go in and talk to them about it, and give them a chance to tell you what they will or won't do, before setting yourself by anticipating the worst.

After-thought on the possible cause of the problem, not the solution. Two stripped cranks on the same side in short order is too much of a coincidence for me to swallow, and I suspect there might be something else at work, such as a problem pedal.

The right/left threading on cranks and pedals is configured to keep a functioning ball bearing pedal tight. Unfortunately a pedal with excess bearing friction will tend to unscrew. Once it unscrews about half way out it'll tear out the rest of the way stripping the crank arm. Whenever I see a crank stripped about half way, I assume that's what happened. Don't strip a third crank, have the shop check that the pedal spins freely and the bearing is properly lubed so it'll spin freely under load.

If it turns out the pedal is the problem, it's up to you and the shop to work out who's fault it was for not having checked this last time, but at least there won't be a third time. Just in case, make it a habit to glance at your pedals once in a while to make sure they're threaded in all the way.

+1 I refurbish old, neglected bikes, usually 25 to 35 years old, and I have not seen this problem in the last 150 bikes. Maybe I have been lucky. To have it happen back to back, with two different sets of pedals, and two different cranks, is way out on the probability curve. It will be interesting to hear what the cause was in this case.

This is a good reason for trashing any part that is not usable right away or at least putting a label on it noting what is wrong with it if you want to salvage any of the parts on it.

+1 I'm not an expert bike wrench; but it takes some significant toolage and intent to strip a pedal out of a crank arm......and twice at that.....a likely scenario is that the first pedal was crossthreaded at installation (destroying the thread intregrity) and it failed........and who knows about the used one...you get what you pay for with any used parts.

As you say, you're not an expert. Stripped cranks are fairly rare, and the scenario of a person cross threading one crank, then somehow getting a defective crank stretch credulity. Two different cranks stripping on the same side is rare enough that you should be searching for a common denominator. Either the OP is lying and is cross threading his pedals (possible), or the pedal has a damaged thread and is damaging the crank when installed (though a mechanic should have felt the resistance and caught it) or the pedal is unscrewing halfway then stripping under load, which is the most common cause of stripped cranks.

nothing incredulous at all.....especially if the second crank is used and from an unknown source.........

but you ARE an expert and your assessment is probably correct......

I have seen a few stripped cranks in my time... the causes were (1)pedal not properly tightened; (2) cross-threaded or forced left side into right cranks; (3) excessive bearing friction.

(1) is always my first guess. But if the OP rode 100 miles then this is unlikely. Generally, an improperly installed pedal will pull out on the first few miles. It's not impossible, but just not how it has happened in my experience.
(2) is usually obvious, except where the threads are ripped out clean and no 'evidence' remains, but if someone is determined and careful it is possible to get a pedal in to a crank of the wrong thread type and ride it like that for a while. But the rider would notice or feel the pedal being crooked as it is usually pretty bad.
(3) does not happen too often, in my experience. If a pedal is properly tightened from the beginning, the amount of torque required to unscrew would easily be noticed by the rider as the pedal flips over under his foot.

I agree the first was my fault..the second one was not....awwwe it is so frustrating because that is my good bike!

I can't imagine that you can't get back on the road for $50 at the most....parts and all.....in my region there are donor bikes on CL and at thrift stores all day; everyday for cheap.......it won't be Campy; but it'll work.......

Which crankset are we talking about?, i can understand the op might not have money but a crankset is not that expensive now a days. Rather get a crankset than a pair of brifters.

All I can say is: if you came into our shop with this problem, I 'd have a very hard time swallowing the JRA angle...

Do you really think the OP removes his pedals just for fun daily? Who takes their pedals off with any regularity? No one.

ok........I give........JRA?

I had to research it..."Just Riding Along" I believe.

https://www.jrabikeshop.com/

The first crankset was a BD bike...I went to Mentor Ohio and had to palace my bike in a trunk of a car...I took the pedeals off so it would fit....My fault.....The second crankset was a used one from the LBS...I rode around 100 miles on their repair and had the same problem...strange?

Thank you! I take the pedals off only when I need to...and that is a rare occasion!

Did the problem pedal spindle threads have alot of grease or anti-seize on it?

I think that was the over enthusiastic rookie move I made when I slathered the spindles of my replacement pedals, placing on my current 15 year old beater, with anti-seize, and noticed about 100 miles after the rebuild I had lost probably 75 percent of the torque I put on onto the non-drive side thread. Went down from like 36 N-m to about 10 N-m. The drive side was perhaps 25 percent down then. I attribute it to over-lubing and new pedals whose seals seemed to have fair bit of dynamic drag twisting the spindle loose. Bottom bracket fixing bolts loosened a little too. I re-tightened checked again another 100 miles, pretty much stayed 100 percent tight. Relief - glad I didn't taer threads out my new Sugino XD600 cranks. 900 miles - nicely spinning cadence 90-110 continues.

Telecom commercial "Don't make me get off this bike: Alphonse, no man over the age of 30 should ever include emoticons in his messages."

When I work on my bikes, I make sure to grease just about every nut and bolt. I've dealt with way too many stuck/rusted/sheared off bolts on bikes. The grease actually allows you to tighten them down more. Getting off stuck pedals is especially painful.