petflunky

Hey All
So I gave my sons friend my old Raleigh M-30 (early '90's mountain bike. It's a really nice bike, and he kept it inside and everything, but unfortunately, he damaged the crank. What happened it the sprocket side pedal pulled out of the hole, stripping the threads. So I have 2 questions.

1. Can I fix the hole somehow? Is there something I can put in the hole to rebuild the threads so that it will hold (jbweld, etc)?

2. If not, where can I get a crankset (tapered) really cheap? I bought a crankset from nashbar, but the gearing is too high. I think it was 28,38,48, and the current set is 18,28,38. The problem with this is the front derailleur is connected to the bottom bracket, and is not adjustable up or down. Otherwise I would use the new crank and buy a new chain.

So, if someone can point me in the right direction, I would appreciate it.

petflunky

Ok, I searched the threads here and found information on helicoils. Is this something I might be able to do myself?

petflunky

Never mind. I did some more searching and found the info in helicoils as well. I feel like such a noob.

Bill Kapaun

"the current set is 18,28,38"

I doubt that!

petflunky

I probably misremembered the numbers. Either way, I forgot the fact my father in law owns a machine shop, and can easily fix it for me. How's that for a noob mistake??

twobikes

I have the same problem with an alloy crank on a road bike. I posted on it last week. Perhaps you read my post.

I will probably keep the bike nearly forever. The crank is holding right now and I have a good 100 miles on the damaged threads with no movement. The excitement will come when I want to change pedals or sell the bike. Changing pedals is more likely. In that event, I think I will grind the threaded part of the pedal back and chamfer it. Then I will chamfer the end of a 9/16 inch x 18 threaded stud. I will weld the stud to the end of the pedal threads. I will remove whatever thread remnants still exist in the crank arm and place a nut on the stud where it comes through the crank arm. I will need to make the nut a little thinner in order to keep it from catching the chain when the crank arm comes around, should I be in a very high gear. By the time I would seriously need to replace the crank arm the chainrings will likely be shot, too. Then a replacement will make some sense.

I phoned a local bike shop (or "lbs") and they said helicoils in alloy crank arms will eventually fail, too.

Do not worry about feeling like a noob. We are all noobs about something, and often about many things.

petflunky

Thanks for the words of encouragement. I think I did see your post when I was rummaging around. I't thinking my father in law should be able to do something with it. He's been doing machining work since before I was born.

BCRider

The pedal threads are not a standard size. Unless Helicoil makes inserts for the bicycle industry I seriously doubt you'll find the right inserts. Just buy new cranks. Basic square taper stuff is pretty cheap these days.

Bill Kapaun

9/16" pedals use a non standard 20 pitch thread instead of the common 18 pitch.

MnHPVA Guy

Helicoil may not but a bike tool outfit called Unior does. They sell a kit with the proper taps and several sets of inserts. Many, if not most, shops will have the kit but I don't know what they would charge to use it to repair your crank.

petflunky

I did buy a new set of cranks, but the sprockets didn't fit correctly with the front derailleur. The front derailleur on the older Raleigh M-30 i connected to the bottom bracket. Therefore, if I were to use the new crank, I would need to remove the front derailleur and replace it. Probably replace the chain as well. I'm not willing to spend a lot of money on the bike because
1. It's not mine any more.
2. I don't have a lot of money to spend.

I will just wait and see what it looks like when I get home tonight.

petflunky

Well, it's finally repaired. What my father-in-law did was drill out the crank, and make a plug that tightly fit in the hole, then thread it. Then he had it welded it in place. Here is a picture. It's also welded on the pedal side.

twobikes

Congratulations. The sleeve your father-in-law inserted must have been an aluminum alloy, too. Otherwise he would not have been able to weld it to the parent metal in the crank.

tellyho

When you replace cranks, you need to replace the bottom bracket as well, for future reference. Hope the repair works!