Thread stripping in crank arm?
#1
Full Member
Thread Starter
Thread stripping in crank arm?
I just picked up a 1977 Super LeTour for tooling around town on a weekly Taco Tuesday ride of about 10 miles. It was priced right, seems pretty bulletproof, and it's the full-chrome version, so it's nice and shiny. Perfect for days I don't want to be the guy in lycra. I'm swapping out the brake pads for something made in this century, and I'll probably recable it, but otherwise, it's in great shape.
I took it for a test spin at lunch today, about a mile in each direction. I wasn't pedaling particularly hard (it was in a spinny gear), and I'm 165 pounds, but the non-drive side pedal popped off. I went back, piced it up, and saw what looked like a teeny bit of silver metal in the threads. I was only 500 yards from home, so I cleaned off the threads on the spindle and in the crankarm with my finger, screwed it back by hand (seemed to move freely--no crossthreading), and started pedaling home slowly in my second-lowest gear. 200 yards later, the pedal popped out again, and this time, there was an obvious semicricular piece of crank in the spindle thread:
The crank arm looks like there's some stripping, but not a TON:
Any thoughts?
Options I've considered:
I took it for a test spin at lunch today, about a mile in each direction. I wasn't pedaling particularly hard (it was in a spinny gear), and I'm 165 pounds, but the non-drive side pedal popped off. I went back, piced it up, and saw what looked like a teeny bit of silver metal in the threads. I was only 500 yards from home, so I cleaned off the threads on the spindle and in the crankarm with my finger, screwed it back by hand (seemed to move freely--no crossthreading), and started pedaling home slowly in my second-lowest gear. 200 yards later, the pedal popped out again, and this time, there was an obvious semicricular piece of crank in the spindle thread:
The crank arm looks like there's some stripping, but not a TON:
Any thoughts?
Options I've considered:
- Clean everything, grease everything, reinstall, and just torque the absolute crap out of it.
- New pedals?
- New crank arm (probably a whole new crankset -- there's a NOS-ish pulloff on eBay for $58 with shipping)
#2
Senior Member
Join Date: May 2003
Location: Mountain Brook. AL
Posts: 4,002
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 303 Post(s)
Likes: 0
Liked 136 Times
in
104 Posts
One possible reason is the pedal(s) are an uncommon French threading which is 14Mx1.25mm, these are about 0.050" or more undersized
compared to the usual 9/16x20TPI pedal thread so they screw in easily and 'seem tight' but under pedal pressure will ruin the threads in
an aluminum crank. From your pix most of the threads look ok, so you might substitute another set of pedals and see how it goes.
Fr threaded pedals are extremely uncommon these days but lurk on 60s-early 70s era French bicycles (and a few in my basement, which
is how I know this). That pedal will cut rubber soled shoes in half after awhile anyway and platform pedals are inexpensive.
One other thought that might support this opinion, if the pedals are Lyotard, risk of Fr threading goes way up, if Japanese or east
Asian then maddog34's opinion may be more likely. I personally have never had a pedal come loose when screwed in by hand.
and minimally torqued with a wrench but have had cranksets come loose from axles.
compared to the usual 9/16x20TPI pedal thread so they screw in easily and 'seem tight' but under pedal pressure will ruin the threads in
an aluminum crank. From your pix most of the threads look ok, so you might substitute another set of pedals and see how it goes.
Fr threaded pedals are extremely uncommon these days but lurk on 60s-early 70s era French bicycles (and a few in my basement, which
is how I know this). That pedal will cut rubber soled shoes in half after awhile anyway and platform pedals are inexpensive.
One other thought that might support this opinion, if the pedals are Lyotard, risk of Fr threading goes way up, if Japanese or east
Asian then maddog34's opinion may be more likely. I personally have never had a pedal come loose when screwed in by hand.
and minimally torqued with a wrench but have had cranksets come loose from axles.
Last edited by sch; 04-05-23 at 03:31 PM.
#3
Senior Member
Join Date: Jul 2015
Location: NW Oregon
Posts: 2,975
Bikes: !982 Trek 930R Custom, Diamondback ascent with SERIOUS updates, Fuji Team Pro CF and a '09 Comencal Meta 5.5
Mentioned: 15 Post(s)
Tagged: 1 Thread(s)
Quoted: 1299 Post(s)
Liked 739 Times
in
534 Posts
that piece of thread you saw was from the crank arm.. it would have been pulled out as the last thread of the steel pedal reached the end of the threads in the crank arm.
Pedals need to be tightened in fairly well... screwing it in by hand or even using a short open end wrench will not be enough. My pedal wrench is 16" long and is a better design than a standard open wrench.
do you feel any bad roughness in the pedal's bearings when it's not attached to the crank arm? that can help the pedal to unscrew from the crank arm.
Pedals need to be tightened in fairly well... screwing it in by hand or even using a short open end wrench will not be enough. My pedal wrench is 16" long and is a better design than a standard open wrench.
do you feel any bad roughness in the pedal's bearings when it's not attached to the crank arm? that can help the pedal to unscrew from the crank arm.
#4
Senior Member
Join Date: Jul 2015
Location: NW Oregon
Posts: 2,975
Bikes: !982 Trek 930R Custom, Diamondback ascent with SERIOUS updates, Fuji Team Pro CF and a '09 Comencal Meta 5.5
Mentioned: 15 Post(s)
Tagged: 1 Thread(s)
Quoted: 1299 Post(s)
Liked 739 Times
in
534 Posts
One possible reason is the pedal(s) are an uncommon French threading which is 14Mx1.25mm, these are about 0.050 or more undersized
compared to the usual 9/16x20TPI pedal thread so they screw in easily and 'seem tight' but under pedal pressure will ruin the threads in
an aluminum crank. From your pix most of the threads look ok, so you might substitute another set of pedals and see how it goes.
Fr threaded pedals are extremely uncommon these days but lurk on 60s-early 70s era French bicycles (and a few in my basement)'
compared to the usual 9/16x20TPI pedal thread so they screw in easily and 'seem tight' but under pedal pressure will ruin the threads in
an aluminum crank. From your pix most of the threads look ok, so you might substitute another set of pedals and see how it goes.
Fr threaded pedals are extremely uncommon these days but lurk on 60s-early 70s era French bicycles (and a few in my basement)'
#5
Senior Member
Agree with maddog, you gotta get that sucker in there tight with a long handle. If it falls out after that then I think you're looking at new (old) cranks.
#6
Full Member
Thread Starter
Likes For cormacf:
#7
Full Member
Thread Starter
OK. So based on the above:
- Step 1: Install a new set of MKS touring pedals I have in the car (because shiny) that I never got around to putting on my old Rivendell before I gave it away.
- Step 2: If there's still a problem, buy the new crankset.
#8
Senior Member
If you can find a LBS that will do it (or want to try it yourself), there is a 3rd option: a helicoil repair for the crank arm.
But if done at a LBS, depending on the LBS that may cost nearly as much as replacing the crank. And many LBSs may elect not to attempt this anymore because of either concerns about liability or lack of a mechanic with the necessary skills.
But if done at a LBS, depending on the LBS that may cost nearly as much as replacing the crank. And many LBSs may elect not to attempt this anymore because of either concerns about liability or lack of a mechanic with the necessary skills.
Likes For Hondo6:
#9
Half way there
Join Date: Sep 2015
Location: North Carolina
Posts: 2,957
Bikes: Many, and the list changes frequently
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 987 Post(s)
Liked 880 Times
in
527 Posts
With luck the new pedals will solve your issue, but I'd advise in any case that you examine the crank carefully for cracks. The cranks are presumably close to fifty years old and it would not surprise me to see that metal fatigue is occurring. If there are any cracks, they may be difficult to see at first but if you use magnification and bright light they should be apparent. Installing the pedal from the rear of the crank and stressing it during your exam may help.
Good luck.
Good luck.
#10
SE Wis
Join Date: Apr 2005
Location: Milwaukee, WI
Posts: 10,516
Bikes: '68 Raleigh Sprite, '02 Raleigh C500, '84 Raleigh Gran Prix, '91 Trek 400, 2013 Novara Randonee, 1990 Trek 970
Mentioned: 40 Post(s)
Tagged: 0 Thread(s)
Quoted: 2747 Post(s)
Liked 3,401 Times
in
2,058 Posts
A good shop can repair it with a helicoil
Likes For dedhed:
#11
Old fart
Join Date: Nov 2004
Location: Appleton WI
Posts: 24,790
Bikes: Several, mostly not name brands.
Mentioned: 153 Post(s)
Tagged: 0 Thread(s)
Quoted: 3590 Post(s)
Liked 3,401 Times
in
1,935 Posts
The crank arm threads appear to be mostly intact, so a helicoil repair would be over kill. The first thing I'd try is threading the pedal into the arm from the back side; this will allow the pedal axle threads to chase the damaged area and will usually clean things up enough to allow the pedal to mount properly from the front side. If this doesn't work, then try the helicoil option.
N.B. while it's possible to do this without removing the crank arm, it's much easier if you remove the arm and hold it in a vise to chase the threads.
N.B. while it's possible to do this without removing the crank arm, it's much easier if you remove the arm and hold it in a vise to chase the threads.
Likes For JohnDThompson:
#12
Junior Member
Superglue.
Gorilla glue.
JB Weld.
There isn't much better surface for gluing something than threads.
I probably will use JB Weld for attaching a nut to the spindle of Milwaukee's cordless mud mixer, for my next electric bike. The glue being necessary because the drill will run in reverse, on the left side of the bottom bracket. I will correct this if it doesn't work. I used JB Weld once before, but the lesser drill burned up, so it was a short test.
Gorilla glue.
JB Weld.
There isn't much better surface for gluing something than threads.
I probably will use JB Weld for attaching a nut to the spindle of Milwaukee's cordless mud mixer, for my next electric bike. The glue being necessary because the drill will run in reverse, on the left side of the bottom bracket. I will correct this if it doesn't work. I used JB Weld once before, but the lesser drill burned up, so it was a short test.
Likes For trailangel:
#14
Happy With My Bikes
Join Date: Sep 2020
Location: Oklahoma
Posts: 2,187
Bikes: Hi-Ten bike boomers, a Trek Domane and some projects
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 884 Post(s)
Liked 2,308 Times
in
1,118 Posts
Likes For Chuck M:
#15
Senior Member
Join Date: Oct 2022
Posts: 1,378
Bikes: a couple
Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 563 Post(s)
Liked 863 Times
in
456 Posts
This LeTour crankset holds pedals fine and the threads don't look that much better than yours, maybe the thread depth on the pedals you're using?
#16
Full Member
Thread Starter
Not sure. They're the original pedals, but anything could have done wrong in 45 years.
New MKS pedals are on, and they have enough of a similar look to the old ones (in my hand) that I feel pretty good. They SEEM to be in there solidly. Planning on riding a couple miles tomorrow to confirm or deny.
New MKS pedals are on, and they have enough of a similar look to the old ones (in my hand) that I feel pretty good. They SEEM to be in there solidly. Planning on riding a couple miles tomorrow to confirm or deny.
Likes For cormacf:
#17
Senior Member
Join Date: Apr 2011
Posts: 7,068
Mentioned: 41 Post(s)
Tagged: 0 Thread(s)
Quoted: 4409 Post(s)
Liked 1,566 Times
in
1,028 Posts
Superglue.
Gorilla glue.
JB Weld.
There isn't much better surface for gluing something than threads.
I probably will use JB Weld for attaching a nut to the spindle of Milwaukee's cordless mud mixer, for my next electric bike. The glue being necessary because the drill will run in reverse, on the left side of the bottom bracket. I will correct this if it doesn't work. I used JB Weld once before, but the lesser drill burned up, so it was a short test.
Gorilla glue.
JB Weld.
There isn't much better surface for gluing something than threads.
I probably will use JB Weld for attaching a nut to the spindle of Milwaukee's cordless mud mixer, for my next electric bike. The glue being necessary because the drill will run in reverse, on the left side of the bottom bracket. I will correct this if it doesn't work. I used JB Weld once before, but the lesser drill burned up, so it was a short test.
Likes For Kontact:
#18
Senior Member
Join Date: Mar 2019
Posts: 1,606
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 581 Post(s)
Liked 921 Times
in
518 Posts
Superglue.
Gorilla glue.
JB Weld.
There isn't much better surface for gluing something than threads.
I probably will use JB Weld for attaching a nut to the spindle of Milwaukee's cordless mud mixer, for my next electric bike. The glue being necessary because the drill will run in reverse, on the left side of the bottom bracket. I will correct this if it doesn't work. I used JB Weld once before, but the lesser drill burned up, so it was a short test.
Gorilla glue.
JB Weld.
There isn't much better surface for gluing something than threads.
I probably will use JB Weld for attaching a nut to the spindle of Milwaukee's cordless mud mixer, for my next electric bike. The glue being necessary because the drill will run in reverse, on the left side of the bottom bracket. I will correct this if it doesn't work. I used JB Weld once before, but the lesser drill burned up, so it was a short test.
There's a first time for everything, I guess.)
Please stop posting responses to questions in the bicycle mechanics subforum. You have no idea what you are talking about and your advice is bad and dangerous.
#19
Junior Member
#20
Junior Member
(I don't like saying this, and while I have thought about saying it a few times in the past, I have always refrained.
There's a first time for everything, I guess.)
Please stop posting responses to questions in the bicycle mechanics subforum. You have no idea what you are talking about and your advice is bad and dangerous.
There's a first time for everything, I guess.)
Please stop posting responses to questions in the bicycle mechanics subforum. You have no idea what you are talking about and your advice is bad and dangerous.
#21
Junior Member
Looks like the lesson is to inspect bikes and test ride them before you buy them, and after you buy them check them over to make sure the previous owner did not do something like take their clipless pedals off and put the old flat pedals back on the bike without tightening them etc.. The reason for the different threads for the pedals on the two sides of a bicycle is they are supposed to be self-tightening, but if the bearings in the pedals are bad in some way then they switch to being self-loosening.
#22
Happy With My Bikes
Join Date: Sep 2020
Location: Oklahoma
Posts: 2,187
Bikes: Hi-Ten bike boomers, a Trek Domane and some projects
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 884 Post(s)
Liked 2,308 Times
in
1,118 Posts
Forums fascinate me. It has been four months and the OP hasn't indicated that he solved his problem, but someone dug this back up to defend their highly questionable advice.
__________________
"It is the unknown around the corner that turns my wheels." -- Heinz Stücke
"It is the unknown around the corner that turns my wheels." -- Heinz Stücke
Likes For Chuck M:
#23
Senior Member
Join Date: Apr 2011
Posts: 7,068
Mentioned: 41 Post(s)
Tagged: 0 Thread(s)
Quoted: 4409 Post(s)
Liked 1,566 Times
in
1,028 Posts
#25
Senior Member
Join Date: Apr 2019
Location: UK
Posts: 1,404
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 682 Post(s)
Liked 453 Times
in
338 Posts
Forgive my ignorance but why is glueing the pedal in so dangerous? (Not that I’d want to do it)
and yeah, I really want to know if the OP got on ok with his other pedals.
and yeah, I really want to know if the OP got on ok with his other pedals.