Hi, I think I have damaged the threads on my pedals. I have tried so m
any times to install the pedals but have had no luck. Any thoughts on what I can do? Thanks.

I assume you are installing in AL crank arms. If so then the softer crank arms are FAR more likely to suffer damage then the steel pedal axles. The photo shows what looks to be the AL deposits on the pedal threads.

Common reasons tom fail to be able to thread in pedals are- trying to thread in the LH pedal into the RH arm (and RH into the LH0, the threads are reversed side to side. The AL arms have the initial threads damaged so that the first curl ot thread can't catch and lead into the arm. The pedal axle is not coaxial with the arm's threads, the pedal is crooked. The threads don't match, French threads or 1/2" ones in the arms.

What to do? First try to clean up the pedal axle threads with a pick or thread file. Try to confirm the threading matches between the pedals and arms. Run a thread tap/chaser through the arms. (from the arm's backsides as these ends are usually not damaged).

Which is more vital to you? The pedals or the arms? Andy

If the crank threads cannot be chased back into usable condition, a Heli-Coil insert will repair them stronger than new.

I used a park tap tool but still cannot install it. That is why I think maybe it is the pedal threads and not the crank threads. Left right is easy to determine so I am pretty sure I didn't do that. The bike is older and I didn't have much luck searching for replacement cranks. The cranks are Truvativ Elita, which are isis with 130CBD.

You're holding the left pedal, so that threads in counter-clockwise.
If you ran the correct taps through the cranks, pedals should thread in by hand, only needing a wrench for final tightening.

As already mentioned, steel pedal threads rarely get damaged. It's the softer crank arms that suffer.

Do you have different pedals you can try ? Some pedal threads have a bit more tolerance and are not quite as tight a fit, so you can test the crank threads with them.

Run a toothbrush or such through the crank threads to clean them out. Do they look damaged ?

Please define "cannot install." Are you unable to get the threads started, or do they not hold when tightened? A tap will pass easily through threads which have been stripped out. Can you try installing a different set of pedals?

The picture below shows steel threads gummed up with aluminum. That needs to be removed BEFORE attempting to put these pedals into any crank.

A stainless steel wire brush in a motor tool will clean them up nicely. Pedal axles (the good ones anyway) are CroMo, which will not be significantly damaged by the stainless steel wires brush. Stainless steel wire brush is much more effective at removing the aluminum than brass wire brushes or other metal wire brushes because aluminum likes to gall stainless steel more than other metals.

After the pedal threads are cleaned up, coat with a very thin layer of grease. (apply then gently wipe off, a nice thin layer will be left behind.)

[MENTION=391685]Andrew R[/MENTION] Stewart covered the cranks already.

Really difficult to see the threads from that photo. Clean them up and post a new photo. It sort of looks like the first thread on the axle may be damaged but too hard to see with all the crud on it.

Thanks everyone. to clarify a bit, I mean I can't get it to thread in. I will try a dremel with a wire brush and see if I can clean up the pedal threads tonight.

I am pretty sure I used the correct tap on correct side. The crank threads looked good to me but I will take some better pictures.

That may be a little overkill. Just a good wipe with a rag should be all that's necessary.

yup, or old toothbrush.

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Sometime back, I did encounter a pair of Speedplay pedals that fit entirely too snug after a couple of turns. Not wanting to risk damage to vintage Campy cranks, I retreated, and measured the OD of the pedal threads.... right at 0.5625 inches. Entirely too big by almost two thousandths. I called Speedplay, they scoffed at my notion of over-sized axles, so I mailed the pedals in and eventually got replacements!
So try some different pedals....

Thanks for all the replies. Embarrassingly, I had the pedals reversed. I was trying to install the left pedal on the right crank. Not sure what I was thinking.

Nice to see someone humbling themself and admitting to a mistake like that. Glad you got it figured out.

On the positive side, you did use the correct taps for each side.

Yes, thank goodness I didn't do that backwards.

I've had this same problem installing Shimano pedals in old Campy cranks. It's not the diameter but the shape of the thread. The angles of the "slopes" and "valleys" (no doubt someone will correct me on that) are just slightly different, enough that installing the pedals required a hefty wrench after the first couple threads. They threaded in fine and the cranks and pedals worked fine, even after reinstalling older pedals.