Fouled 12mm x 1.25 crank thread

[mofosheee]

Hello Forum

I've acquired a motorcycle crankshaft with fouled 12mm x 1.25 TPI threads. Cleaned up the "mushroomed" section, purchased the correct die.
Currently having difficulty in getting the die to capture the first threads. I know there is someone out here in forum world with a trick up their sleeve
and would love to be enlightened.

Thanks!

 

[Ulma Doctor]

Use a file to bevel the first couple threads and flatten any high spots
Or
Use a thread file to clean up the high spots

 

[toprecyler]

You can also use a small triangle file to hand file in individual threads. With practice, you should be able to work backwards from the good threads to make bad area good enough to start the die.


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[markba633csi]

Sometimes helps to use a nut of that size with a slot cut in it as a "persuader" to help ease over the bad section, then follow with the die.
You can also get fancy and make a pivoting split nut with a hinge if you have a welder. Clamp the pivoting nut over the good section and unscrew
over the bad. I had to do that once.
You could probably dispense with the hinge and just clamp two halves of a nut with a hose clamp then grab the whole assembly with Vise-Grips and spin it off. Never tried it but it should work.

 

[Illinoyance]

There are spit dies that allow you to place the die over the good threads, then cut backward to clean up the damaged threads.

 

[mofosheee]

Split die.............

https://www.amazon.com/dp/B08DK1QYPC/ref=twister_B08GZWYLMH?_encoding=UTF8&th=1

Thank you everybody!

 

[Jake M]

A split die is going to be your best option. It can be opened, installed on the good thread, and then run OFF of the thread. Kinda the opposite way that you normally would. They can be a life saver, but they are not "necessarily" as good of a finish tool as the real thing. Typically (repair work has no hard rules....), but typically if I use a split die to save a thread, it will absolutely be close, so a "regular" die can start in the normal way, but it kinda (usually) likes that second pass with the regular die.

A close second place solution is to use just a standard flat file and a set of calipers. Use the flat file to bring the "mushroomed" end back down to the actual diameter of the actual good threads so they'll fit inside of the correct die. Use the caliper not so much to measure (although that's useful too), but clamp that thread in the jaws from the end, so the jaws go not "across" it as you normally would to measure it, but so they go over the whole length of it- It's a parrallel set of guides to tell you where to file from. Unlesss it's "horrible", that's almost always enough to get a die to pick up the actual thread. Providing there's "some" thread exposed when the nut is fastened, there's also no harm in filing, grinding, dremmeling, or otherwise removing a thread or two to get a fresh(er) start.

 

[mofosheee]

A split die is going to be your best option. It can be opened, installed on the good thread, and then run OFF of the thread. Kinda the opposite way that you normally would. They can be a life saver, but they are not "necessarily" as good of a finish tool as the real thing. Typically (repair work has no hard rules....), but typically if I use a split die to save a thread, it will absolutely be close, so a "regular" die can start in the normal way, but it kinda (usually) likes that second pass with the regular die.

A close second place solution is to use just a standard flat file and a set of calipers. Use the flat file to bring the "mushroomed" end back down to the actual diameter of the actual good threads so they'll fit inside of the correct die. Use the caliper not so much to measure (although that's useful too), but clamp that thread in the jaws from the end, so the jaws go not "across" it as you normally would to measure it, but so they go over the whole length of it- It's a parrallel set of guides to tell you where to file from. Unlesss it's "horrible", that's almost always enough to get a die to pick up the actual thread. Providing there's "some" thread exposed when the nut is fastened, there's also no harm in filing, grinding, dremmeling, or otherwise removing a thread or two to get a fresh(er) start.

The threads weren't too bad to begin with, but they wouldn't accept a new standard die. By the attachment you might understand my concerns about things going sideways. I've never used a split die before and knew it was the ticket as soon as Mr. Illinoyance mentioned it. Yes, I'll do a second pass with a regular die after using the split. Great advice from all. Thanks again everybody!

 

[Brad_C]

In the absence of a split die, I've often cut a nut in half and clamped both halves over the thread before backing it off. That has often been enough to allow me to get a conventional die on.

 

[Mrben144]

I have also had good luck with an OTC 7402 chaser working from the good section backwards.