veganbikes

After seeing those pedals and not recognizing them I can see why they might send 2 left pedals, they are some cheap-o pedals from Alibaba and his 40 thieves or from Billionaire Jeff Bezos presents Amazon where you can buy crap at low low prices every day.

You can ask a shop and see if they can Helicoil it or repair it in some way and ask them for some pedals and ask them to install them and bring them some nice beer or cookies or candy and then go ride your bike. Everyone is probably good at something but not everyone is good at everything and that is OK you just have to "know when to hold 'em, know when to fold 'em, know when to walk away, know when to run..."

Andrew R Stewart 

Work in a service strong LBS and you'll see all kinds of boo boos. There's a reason why more and more big box bikes are coming with "L" and "R" stickers on the cranks and pedals. The amount of added effort to thread a LH pedal into the RH arm (if the arm is Al) is less then what some think. Especially if greased threads and a long lever arm is at play.

Iride01- I figured that the pro that the OP brings the bike to will get the thread directions correct Andy

trrrrrev

Why else would the pedal fall off whilst I'm cycling? I would assume forward motion on a bike would increase resistance between pedal and the crank, not loosen it? Come to think there was a bit of resistance on the R pedal's spindle when rotating it, it was not turning as easy as the L pedal. I tried to lube it up but still the same. I guess it doesn't matter now lol so I will just get a new pair.

Does anyone recommend a place to get reasonably priced vintage pedals for a pinarello? These were from eBay..

Sy Reene

Do we know the OP didn't already have two L crankarms installed, and that was the problem?

Iride01 

Well now that you say the word vintage, then you bring up the possibility that these may not be threaded as most every bike has been since the 80's. Though I don't know that Pinarello ever used those other standards.

cxwrench

It doesn't matter what brand of bike it is...what matters is what kind of crank you're trying to install them in.

woodcraft

We're pretty sure that's not the issue or the OP would have complained that the bike didn't go because no chainrings.

trrrrrev

No the crank arm is fine - I have changed the pedals in previous years and didn't have any issues. I think it's likely these dodgy eBay pedals and not the bike, and I probably did try force the pedals in which messed up the crank..

Phil_gretz

My first impression is that the crank, bottom bracket shell and chain are filthy. This bike need proper servicing and cleaning. It's way past due.

Don't do anything until the crank is removed and cleaned. Check the chainrings for wear, gouging, etc., and make a determination whether or not to replace worn parts (bolts or chainring(s)).

Test the cartridge BB bearing for wear or play. Likely it's okay, but verify this.

Thoroughly clean the bottom bracket shell area, front derailleur, and below BB shell cable guides (which undoubtedly are equally filthy).

Take the [now clean] right crank to a bike shop and ask whether they have the Helicoil kit to make a repair of the threads. If so, have them do it.

Bring the repaired crank home and re-install to the correct torque spec (in the neighborhood of 35-40 N-m).

Get a new set if pedals and inspect the thread direction on each BEFORE attempting an install. Carefully, grease and hand thread them, use a wrench to bring them to tightness.

Pause and consider the lessons you've learned from this. Remember the lessons.

3alarmer 

...I'm genuinely uncertain of your expectations at this point. But I can tell you from your description of the issue that a new pair of pedals by themselves, no matter their quality, are unlikely to now repair the damage you've encountered. I have wide feet, so I use the quill pedals that used to be made and sold by SR. But there are plenty of flats (like the ones you show), that will fit your crank on a Pinarello. They are unlikely to have a crank that uses French standards.

It does look and sound like it's probably a crank that is worth repairing.

The reason one of your pedals pulled out is any body's guess without an in person examination. I'll save speculation for someone who likes to do that.

Andrew R Stewart 

Precession is the term for the forces that rotate pedal axles within the crank arm threads. The threading directions used are those that make the axle self tightening. By using a reversed from the convention threading direction (as in the OP's LH axle in RH arm) that pedal axle will tend to self loosen. Once a pedal axle is slightly loose then the next type of forces kick in. The pedal will be wiggle this way and that way within the arm and the hard steel axle bearing the full weight of the rider will auger out the arm's hole. IME it's his two step process that causes the real damage, removal/flowing away of the arm's material. Andy

2old

As stated above, it's because Newton's third rule predominates.

jccaclimber

Unlikely, but every now and then a right arm with no chainrings from the front of a tandem gets mixed in as a normal left arm.

woodcraft

You learn something new every day!

3alarmer 

...speaking of physics. If we are all headed toward the heat death of the universe anyway, why bother to repair it ?

trrrrrev

That was enlightening, thanks.

Andrew R Stewart 

Our lives are more about our paths and time alive then where we are when we die. Andy (who thinks riding a bike is about more then a Strava record)

zandoval 

Sounds like the crank was messed up to begin with. This is the one area of the bicycle that takes an incredible amount of torque forces. Buy a new set of pedals and a new crank. Then as you ride your bicycle consider the repair of the crank. "Heli Coils" come to mind. Filling the hole with "Aluma Weld" then re-tapping to 9/16ths. Of course all of this is unproven but just think of what fun...

This is a long video but worth the time just to know for further applications...

Crankycrank

I've used the Aluma Weld and it's great for some things but I wouldn't recommend it for this as you've got to get the aluminum extremely hot which could ruin any heat treating and the "soldering" is very hard to control meaning trying to machine and cut threads that are perfectly positioned and square afterwards would take some decent machining skills. The helicoil or threadsert would be my choice.

3alarmer 

...for your sake, I hope no one from the road forum sees this.

Yelbom15

I’m seeing a lot of pretentious comments. Like we haven’t seen this happen a million times in bike shops from people trying to install pedals themselves. Don’t read the negative comments. Happens all the damn time.

If there’s enough meat, a bike shop can tap and clean. You may have lost a couple threads but it’s better than none.

Someone mentioned heli coil which is the go to if there’s no meat left at all. Most bike shops should have these but I remember when we couldn’t get our hands on them for months for some reason.

I see it’s a an old 105 crank. These guys go for cheap. If a bike shop isn’t too big of jerks, square taper cranks can be slapped on and off within thirty minutes(if they’re not busy…) Maybe take a look around on Ebay if everything else is too troublesome.

Again, ignore the “you’re stupid” comments. Happens all the time.

By the looks of the poll, it’s time for some new cranks. Usually the case.

cxwrench

No, it really doesn't happen all the damn time. I see it maybe once/twice a year. (pretentious comment on) It should be painfully obvious something is wrong and you should stop. You have to force the pedal into the threads, most of the time you can't even get the thing started. (pretentious comment off) And no way you can clean that mess up with a tap...not gonna happen and be anywhere near safe.

Yelbom15

Yikes. Got a bit defensive in here.

ign1te

Can you show us a close up on the pedal threads, the new ones you bought? It is possible to tell the threading if the image is detailed enough. Will be fairly easy to determine if you have recieved two "left sided" pedals. I think such an image would interest most people in this post, and it can also be the basis for a return claim.
In the OP's defence, aluminium crank threads can strip even if not abused. Especially if the cranks are old, as aluminium does not age gracefully. It may be the case that the original pedals was tough to remove (cheater bar tough). When such forces are involved you can end up stripping the crank thread regardless. Talking from experience.

grizzly59

The big problem with thread repair of a crank- the pedal has to end up aligned with the BB spindle when the pedal is installed. You will get a very weird feeling as you pedal if it’s just a bit off.