Thread size for standard pedals & cranks?

KC said:

I have to fix an old exercise bike in a lab at the university where I
work. Some student removed the pedals, then tried to put them back
on... on the wrong sides. Fortunately, the only one that got really
fouled up is the right-side pedal, so at least it's not a left-hand
thread.

So, what size tap do I need to get to clear out the threads on the
crank? They are pretty mashed up, but I think that there's enough
there that if I just re-tap them, they will hold well enough for the
uses of this stationary exercise bike.

Also where can I order a tap of this size? (A die might come in handy
too, although it's a lot easier to clean up external threads by hand
than internal threads). Are they standard enough that a typical
hardware store would have them?

Thanks,
Kieran.

I should have searched first:
http://tinyurl.com/tbn27

9/16 x 20, available from Park Tools retailers. Thanks Jobst.

-Kieran

KC wrote:
< I have to fix an old exercise bike in a lab at the university where I
work. >

Check the crank of this machine, as it might have a one-piece crank.
These use a single piece of steel that is bent and fit through the
bottom bracket shell. See the type at
http://www.parktool.com/repair/readhowto.asp?id=150

The one-piece crank commonly uses a smaller pedal thread, 1/2" x 20 tpi
threading. However, if each arm attaches separately to a spindle, it
is more likely the 9/16" x 20 tpi. Both standards use a left side,
left hand threading.

KC said:

I have to fix an old exercise bike in a lab at the university where I
work. Some student removed the pedals, then tried to put them back
on... on the wrong sides. Fortunately, the only one that got really
fouled up is the right-side pedal, so at least it's not a left-hand
thread.

So, what size tap do I need to get to clear out the threads on the
crank? They are pretty mashed up, but I think that there's enough
there that if I just re-tap them, they will hold well enough for the
uses of this stationary exercise bike.

Also where can I order a tap of this size? (A die might come in handy
too, although it's a lot easier to clean up external threads by hand
than internal threads). Are they standard enough that a typical
hardware store would have them?

Try www.biketoolsetc.com for the taps. No, they are not common sizes.
If the crank is a one-piece unit, the pedal threads are usually going
to be 1/2" in diameter, while multi-piece cranks usually use 9/16"
diameter threads.

If the unit is portable and not too large, your best bet may be to
toss it in the back of a vehicle and take it to the nearest large bike
shop. If it's bolted down to something or otherwise not possible to
haul off, I'd take an old pedal shaft of the correct size, grind or
cut a slot in the end of the threaded section, grind away the shoulder
behind the threads, and then use that as a thread chaser from the
other end of the hole. Cheap pedals are easy to get; a big bike shop
might even have a scrap pedal of the right diameter that they'd give
you.

Good luck.

--
Typoes are a feature, not a bug.
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KC said:

KC said:

I have to fix an old exercise bike in a lab at the university where I
work. Some student removed the pedals, then tried to put them back
on... on the wrong sides. Fortunately, the only one that got really
fouled up is the right-side pedal, so at least it's not a left-hand
thread.

So, what size tap do I need to get to clear out the threads on the
crank? They are pretty mashed up, but I think that there's enough
there that if I just re-tap them, they will hold well enough for the
uses of this stationary exercise bike.

Also where can I order a tap of this size? (A die might come in handy
too, although it's a lot easier to clean up external threads by hand
than internal threads). Are they standard enough that a typical
hardware store would have them?

Thanks,
Kieran.

I should have searched first:
http://tinyurl.com/tbn27

9/16 x 20, available from Park Tools retailers. Thanks Jobst.

In my experience, it's not a given that your local Park sources will
have one for sale.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Chances are the pedal was not tightened very far before it jammed, so only
the first few threads are damaged. Try inserting the pedal from the back
side of the crank. It should start okay--then if you run it all the way in,
it probably will push enough metal back into place to allow you to start the
pedal from the front.

Leo Lichtman said:

Chances are the pedal was not tightened very far before it jammed, so only
the first few threads are damaged. Try inserting the pedal from the back
side of the crank. It should start okay--then if you run it all the way in,
it probably will push enough metal back into place to allow you to start the
pedal from the front.

I did try that, and couldn't thread it all the way through, although
most of the threads are good (maybe 2/3~3/4 of the threads are okay) the
mashed ones are really mashed. I was actually going to run the tap
through from the back for this reason, because I wouldn't be confident
that I was cutting the threads in the right place if I tried to start it
on the mashed up side.

FYI for others who replied: the threads are standard 9/16th, not 1/2".
I know this because I have put my own clipless pedals in the cranks when
I did a VO2max test on this bike. (I just wasn't aware of what a
standard pedal thread size was... now I know, it's 9/16"x20)

Thanks for all the advice,
Kieran

"KC" wrote: I did try that, and couldn't thread it all the way through,
(clip)
^^^^^^^^^^^^^^^
Take an old junk pedal and strip away or grind away anything that is in the
way, and thread IT in from the back. If it refuses to move through the
ruined threads, take it back out and make a couple of hack saw cuts across
the threads. This will make it into a sort of fake tap.

Leo Lichtman said:

"KC" wrote: I did try that, and couldn't thread it all the way through,
(clip)
^^^^^^^^^^^^^^^
Take an old junk pedal and strip away or grind away anything that is in the
way, and thread IT in from the back. If it refuses to move through the
ruined threads, take it back out and make a couple of hack saw cuts across
the threads. This will make it into a sort of fake tap.

LOL... interesting technique. I like it. I'll see if I have an old
junk pedal around... don't think I do, but the LBS might.

Thanks,
Kieran

"KC" wrote: LOL... interesting technique. I like it. I'll see if I have
an old junk pedal around... don't think I do, but the LBS might.
^^^^^^^^^^^^^^^^
When you go to the LBS, take the crank arm with you. "Kuz here is my
prediction: You'll ask them about a junk pedal, and explain why you need
it. The mechanic will say, "We have that tap. Why don't I just do it for
you? It'll only take a second."