Pedal threads - non-standard size
 

I am trying to get SPD clipless pedals on an old department store bike. The thread pitch is the same, but the diameter of the bores is a hair less. I did not have anything to measure with at the time so I do not know what the size is (I can find out).

My question is if anyone knows if there is a way to adapt pedals to work.

I would be tempted to drill and tap the crank, but from what I saw I don't think a proper size drill bit to cut the larger threads would get down past the original threads to full meat. That, and if I could, I don't have a left handed thread tap that size (I don't have any left handed thread taps period).

Replacing the crank would mean replacing the chain rings also. There again, I don't know what the BB size is. With everything else that's been "odd-ball" sized I would expect the BB to be a strange size also at this point.

1 piece cranks use 1/2" pedals instead of 9/16".
Reason: There isn't enough metal left in the arm if drilled for 9/16".
Get some 1/2" pedals at xmart.

Pedal threads are "non-standard" pitch for the diameter at 9/16x20TPI and the L sided crank is threaded L hand. In your
scenario if the pitch really is 20TPI then best bet is to find an LBS with pedal tap set and have the cranks rethreaded.
A drill out may not be needed, or only a minimal drill out.

I think there are adapters that screw into the 1/2 thread, and have a 9/16 thread.

This ?

https://www.ebay.com.au/itm/NEW-Bike...-/293129834400

"A hair less"?? Like actually how much less is a hair? Is that a red hair or a blond one?

As others have said 1/2" pedal threading is common on cheaper bikes. But so to is poor manufacturing in general. Most SPD pedals are from manufactures that take more QC and production care then the cheapest bikes available (as in big box built for the lowest price point ones). If the threading isn't 1/2" but is 9/16" I will suggest that the crank arms were not well made, as in an old/dull tapping tool was used.

An experienced person can figure this out real fast if they are allowed to get their eyes and hands on the cranks. Andy

I know, right? My father was a tool-and-die maker used to working to precision of 0.0005" (half a thousandth) and less, and one of his Scottish co-workers would drive him nuts asking for a "wee" drill.

...yes, they are available on Amazon and e-bay. I have a set I used to put better pedals on a Fauber crank equipped DBS bike here.

....just look up the adapters on Amazon and buy a pair. They move the pedal surfaces out a little bit, but in many cases that's an extra bonus feature.

A black pubic hair. Curly, round at the root.

Thanks for the adapter suggestion. I will look in to it.

When I found the threads were different I was prepping the bike for a ride with a friend. I didn't have anything to measure with, all I know is the pedals I was putting on are the same thread pitch and too big to screw in - not by much. Pedals were Shimano's. Same size as my regular bikes, not sure what size that is off the top of my head.

In fact... I think the pedal threads on my mountain bike (department store variety, 25+ years old) are the same threads as my regular bikes. It seems to me I had put different pedals on it at one point.

If it's that close I would suspect a boogered thread. Bicycle pedal threading is about as universal a standard as there is. If the cranks are aluminum: 9/16" x 20tpi. If the cranks are steel: 1/2" x 20tpi. It's been that way for about the last 35 years.

1/2"-20 is a common SAE Fine thread size.
Buy a bolt at your local hardware/xmart.
See if it fits the R. arm. I'm pretty sure it will.
Lot's of 1/2" pedals here on just a couple second search.
https://porkchopbmx.com/pedals/1-2-p...-piece-cranks/

This well not worth your time. I would never want to be clipped in to a Wally-mart bike for fear it falls apart underneath me and I am still attached. There a bodges that will make it work sure but do you really want to do this? The pedals are probably worth more than the entire bike.

French pedal threads are a hair less than 9/16, though I can't imagine a dept. store bike having these.

Try installing the pedals from the backside of the crank arms. If the starting threads were mashed a bit form the previous pedals the back sides will be clean. A quick test. Any decent service focused LBS should have pedal taps to clean up the threads with. Be careful as many taps can be slightly tapered and one can cut the threads too much oversized if not tested after a small bit of chasing. Andy

How "old"? French bikes were 14 mm x 1.25, but probably not since the 1980s. Really old (1960s?) British bikes are 9/16" x 20 TPI BSC (British Standard Cycle) which are about .004" smaller than the current 9/16" x 20 TPI UNT.