stripped crank threads

[auraslip]

This is a common problem. Well, common for bike newbies like me who don't know that the left pedal is LH threaded

There are some options:

Ebay a new crank. Ebikers want road cranks with a 110BCD to fit larger 52 tooth chain rings, but don't want light weight aluminum. Vintage steel it is then.

Get a bike shop to repair the threads with a helicoil. None of the LBS do this in my area, and the machine shops don't have left hand threaded helicoils. The repair kit is available but it's $130.

http://cgi.ebay.com/Bicycle-Pedal-Extenders-Trike-Road-Recumbent-18MM-steel-/160446631141?pt=Cycling_Parts_Accessories&hash=item255b5d4ce5
These little darlings stick the pedals out by an ~ inch. Those of us with integrated battery boxes in the triangles will find these useful. In the mechanical field they are known as standoffs. These are custom made just for bicycles, so don't bother looking in hardware stores for them.

In order to save the cranks I have now, get the benefit of the pedal extenders, and get a cool tap and die set I'm considering making my own custom jig.

Tap out the cranks to 10/16"
Die the male end of an OTC standoff to 10/16"
Die the pedal threads to 1/2"
Tap the female end of the OTC standoff to 1/2"

Yes it'll be RH threaded on both sides, but locktite should keep it from coming unscrewed.

Now I just need the appropriate tap and die set, and the appropriate standoff.

Or I could use a sex bolt through the crank and screw that on to the pedal threads.....

 

[neptronix]

Yeah, but if the pedals are spread out, you will end up pedaling a bit weird with your legs spread out, potentially.
You can buy a new crankset for $50 or less, even cheaper off a used bike.

Also, some cranksets outwards a bit too; Some are totally flat, some curve outwards & may just achieve what you're looking for.
Just thought i'd throw that out there.

 

[FMB42]

Forget about the loctite.

You'll save both time and money by just replacing the cranks.

BTW, most pedals have either an "R" or an "L" stamped on the end of the threaded shaft.

 

[dogman dan]

For the cheaper bikes, a replacement crank is a dumpster away. But meanwhile, I'd try the JB weld, or PC 7 on it. Use a junk pedal as your tap. Lots of pressure and just make sure you get it started straight. You can ream out the first thread to get started with a bent nail. Then use the Jb weld on the pedal when you permanently screw it in. Maybe even drill a hole and put a roll pin though the pedal. Nothing to lose by trying. The cranset is wrecked already.

I understand what you want to replace might be harder to find, but keep hunting at the garage sales and thrift stores with a max price of $20. You'll find it eventually. You can make do for awhile with a cheap bikes 48 tooth.

Did you wreck both sides? or just the left. Replacing just the left is easy as pie.

Post a pic of your crank. My local used bike shop owes me about $50, and has piles of cranks.

 

[dogman dan]

Another thing you might try, Take the cranks off the bike, ( easier said than done if you don't have a puller), and then use a pedal to screw in fron the backside. If you have a couple good threads left at the bottom of the hole you'll be able to get it started straight, and perhaps chase out the hole good enough to get a pedal back on it from the front side, and epoxy the thing in permanent. I have a good crank that I saved that way, when it had a couple stripped threads on the front side.

I can also source you a free crank, off an old vintage roadbike. If one of those would fit. Often they will rub frame on a MTB

 

[auraslip]

Made by TPI. I don't think they're steel. Fridge magnet wouldn't stick. 110 BCD...so they can fit the 60 tooth chain rings =) http://www.vueltausa.com/components/chainrings/se-flat-chainrings/se-chain-ring-110mm-34-60t.html (if price was no issue )

Stripped right crank threads.

What I originally did was greased the pedal threads, and then JB Welded the crank threads. The plan was for the JB weld to form around the threads, but not bind to the pedal threads. I don't think it worked, but either way it turns out there is now some threads at the very back of the crank. So I went head and tried it again. This time I got the pedal as tight as it would go without a pedal wrench (I used tiny vise grips). We'll see....

In other news I'm wondering if a machine shop could tap and die the pedal, crank, and custom standoff. I figure I'm going to have to buy the $20 pedal extenders any way at some point. If a shop charges $40 to fix the crank, and make the pedal extenders It'd be worth it.

 

[spinningmagnets]

Please contiunue with the experiment and keep posting the pics, this is useful to discuss. That being said...

On a fairly regular basis, people bring in an old/damaged bike to the LBS to get a quote for repairs, new-tubes, brake-pads, and/or a tune-up. Unless the quote is very cheap (it rarely is) the customer is often persuaded that using their credit card to get a a new bike of the type they've always wanted is the thing to do. This results in old and damaged bikes being thrown into their dumpster out back on a regular basis.

You'd be suprised at some of the good parts attached to these trash-day bikes. Stop by in the evening after closing time the day before trash pick-up. I've gotten cargo-racks, seats, tires, brake-pads, etc...they look a little used, but still in good shape. Cranks are one of the easiest parts to source...best of luck with whatever you choose.

 

[TylerDurden]

Craigslist is also good for cast-off bikes.

Also check to see if your area has a bike co-op (or "bike kitchen")... usually lotsa freebies or cheapies just for helping out a bit.

 

[neptronix]

Yeah seriously. I just picked up a disc brake + front disc brake wheel + disc rotor + shifters for $25 at my local bike co-op. They had a bucket full of cranksets.

 

[auraslip]

I love that these bike co-ops are popping up every where =)

Unfortunately, mine is closed till december.

 

[dogman dan]

Re the crank extenders. I'd expect the extra leverage would put even more strain on the pedal to crank connection. So you might want to hunt down a new crank before adding those.

 

[amberwolf]

http://finance.groups.yahoo.com/group/Dentonfreecycle/
I'd check the posts for stuff myself but it's members only, and I'm sure they wouldn't approve me since I don't live there. Sign up, and keep an eye out for bike stuff, and/or post a Wanted for what you're after.

Between that, CL, and local bike shops' dump bins or used parts shelves, you can probably find something before the co-op reopens.

 

[Kingfish]

On my California trek, I was late getting to the train and missed the opportunity to board by 5 minutes; I had the bike already tore down when they told me. In my anger and angst I insufficiently tightened the pedals down and they came loose on the way home. REI was close by and they installed a helicoil for $30. This is a temporary fix, and I had problems with it right away.

Later on the road when I had to stop for repairs to replace the rear rim I had the shop scrounge through the parts bin and they found a left-arm that fit; the replacement cost was buried in the $60 bill for the complete effort which included a new tube as well.

Though this worked out in the end, it's better to replace the arm; if you're not picky and find one in the parts bin they're cheaper than a helicoil.

~KF

 

[neptronix]

Park tool for removing cranksets: $10-$15

http://www.google.com/products/catalog?q=park+tool+crank&hl=en&client=firefox-a&rls=org.mozilla:en-USfficial&biw=1280&bih=619&um=1&ie=UTF-8&cid=5984402427979282416&ei=eHLlTPqQEIH2tgOay6CxCw&sa=X&oi=product_catalog_result&ct=result&resnum=10&ved=0CGsQ8wIwCTgK#

Cheap crankset: $20-$50

http://www.google.com/search?q=crankset&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-USfficial&client=firefox-a#q=crankset&hl=en&client=firefox-a&sa=N&rls=org.mozilla:en-USfficial&biw=1280&bih=619&tbs=shop:1,p_ord&fp=5df4fea6b90678f1

Knowing that you didn't spend even more on a crappy fix that won't last: priceless