Repairing F'ed up crank treads

[super3]

Ya I know what the fk is a crank tread? One of you mods change the spelling for me.

I've had to repair the threads on several cranks over the years for whatever reason they were damaged. Ham fisted flywheel removers, piss poor packaging and dropped in shipping, flywheel remover used with nothing to keep the end of the crank threads from getting mushroomed and one I fked up and knocked off the bench.

After checking to make sure they still run true this was the simplest way that I have come up with to get a re thread die to start right and not make things worse than what I started with.

1st I use a sanding roll to take out the bulge on the end and give it a bit more taper.
2nd I file just a bit any spots where the threads were pushed together and would not let a die start.
3rd I hacksaw a slot in a nut(grade 8 or better), drive a carb screwdriver in the slot to expand it ( this gives it enough clearance to get over the f'ed up threads) and thread it on the crank far enough to get to the good threads. Remove the screwdriver and use a small pair of vise grips on the flats to put just a bit of drag on the nut.
Work it out to the buggered up part of the threads and turn back and forth about a 1/4 turn at a time until you feel it getting easier to turn and keep working your way to the end of the crank. Back it up periodically and blow off the small shavings.

The slot that was cut in the nut also creates a bit of a softer cutting die as of sorts, just enough to let you shave the threads to get a re thread die started on correctly. If it won't start easily repete step 3 until it does.

 

[Al Smith]

Since you brought it up,an old blacksmith trick .Do the nut like you said then heat it up to about cherry red and toss it in a can full of brown sugar.It will set it on fire but that's okay .After it cools heat it to about orange and toss it in a can of oil .

This is how it goes .sugar is c6 h12 o6 .You burn off the hydrogen and oxygen the carbon gets infused into the steel,it gets a hard like as a rock once it's heated to critical (1400 degrees F ) and quenched .

 

[CR888]

Interesting stuffs...

 

[Mattyo]

Interesting about expanding a nut just enough to fit over threads....then locking it back in place and using it as a die as you back it off...

 

[decableguy2000]

They also have split dies for re-threading. You start them at the back and work your way out. I have a metric and standard set I picked up cheap off Ebay.

 

[Mattyo]

Never knew that, thanks!

And cool idea for makin one!

 

[XP_Slinger]

Very cool trick. Another thing Ive done is cut 8 notches in nut threads with a hack saw, basically makes the nut function as a die if you don't have the right one in your kit. This obviously only works if there's no bulge on the end of the threads That prevents the nut from threading on. I used this technique to fix severely damaged threads on a trailer axle spindle. Using anti-seize during the process helps A LOT also. Don't know if it's the lubrication or semi abrasive properties in the anti-seize but it works like a charm. It's a trick my dad showed me when I was a teenager, he was a machinist for 33 years.

 

[MattG]

Back in the day me and my mates ended up having repair a lot of f'ed stuff on motorbikes. Wheel axles bolts etc. that were belted too hard in the process of extraction, you know how seized up that sh!t can get.

Yes filing a taper was a common technique. Other times, we weren't clever enough to think of dies in those days.......we'd just look at the thread and carefully use a hacksaw blade to re-define the troughs in the thread spiral, and saw down those bits where the crests of the spiral might've got bent slightly off the helix.

 

[XP_Slinger]

Been there too. I've had many long sessions tapering then cutting new threads with a Swiss file.

 

[redtractor]

I saw someone use one of these to good effect. He was working on something larger but it did the job.

https://www.google.com/#q=thread+file.

 

[fearofpavement]

Anyone else use thread files? I have one in both metric and sae. Pretty handy when needed.

 

[NCFarmboy]

I use thread files have for 40+ yrs. I have a large one I bought to chase threads on Ford F600 rear axle.
Shep

 

[Al Smith]

The morel of the story is don't be beating on the crankshaft end with a big ball peen hammer .Use a dead blow,plastic ,rawhide hammer or use block of hardwood .The only metal might be a lead head hammer.Never brass,steel, babbit .

 

[MattG]

The morel of the story is don't be beating on the crankshaft end with a big ball peen hammer .Use a dead blow,plastic ,rawhide hammer or use block of hardwood .The only metal might be a lead head hammer.Never brass,steel, babbit .

Good advice - until you pick up some sh!t some primitive lifeform has left you with...then you need every trick in the book!

 

[Al Smith]

I suppose there's many ways to skin that cat .I must admit the OP has a good method considering what he has to work with .If you had a lathe plus the knowledge to operate it and if it can cut metric threads you could always "chase" the treads left to right by running in reverse .It's gong to be a pain in the behind because the rod is connected but I suppose with some creative thought it could be tied fast so it doesn't flop around like chicken with it's head cut off .
Then again if you aren't familiar with threading on a lathe ,to chase a thread first you have to "find" it .Meaning everything has to be set to properly follow the original thread form else it will be screwed up .It easy once you know a few tricks but it isn't something for the novice .I've never done so on a chainsaw crank shaft but I have on a drag link pin on a big dump truck somebody got medevil on with a BFH .Beat on a tapered pin with an 8 pound sledge,good grief .

 

[super3]

I have a lathe Al.
This is just faster and it works with the crank still in the cases. A bit of a challenge to get the needle file in there.

Yep, I f'ed up a quite a few yrs ago. Got a crank from another member and didn't look it over close enough.
Mushroomed threads. I think it was dropped in shipping. I know it wasn't that way b4 he sent it, he is someone we all here trust.

This was a saw I was building for myself and is still in service.