Fixing buggered crank threads

[lindy46]

I picked up a 1972 Johnson 25hp for $10. Pretty rough shape but lots of good parts. The crank threads are buggered up and the flywheel nut won’t thread on. I was wondering if anyone has tried re-tapping/re-cutting the threads. Powerhead has good compression and may be worth trying to save.

[frankr]

I hate it when that happens. Sure, most of us have dealt with it–usually with limited-if-any success.

[Tubs]

If it were me- I would take a file and taper the
first couple of threads. Then run a die over
the threads. If you file the first thread down
to where it’s not distorted the die should
follow the threads. If it were me. Let’s see
what others come up with. We both may
learn something.
Tubs

A "Boathouse Repair" is one that done without having tools or the skills to do it properly.

[Bob Wight]

I had the same issue on my ’72 25hp. I also did exactly what Tubs described – carefully filed the first couple of threads just to get the die engaged. The die was then able to get started straight and cleaned it all up. However, I did not have the same success on a ’57 18hp with bad threads. That crank was pretty much junk otherwise so I just found a good quality used crank – you may have to do the same.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[dave-bernard]

always put a nut on before you put on the puller. that said take a die and break it then put it on below the bad threads use a vice gip to hold it together and turn it off. may take a few times.

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amuller

[crosbyman]

try a small triangular file …. maybe a hack sawblade could open things up

Joining AOMCI has priviledges 🙂

[Buccaneer]

You don’t show how bad they threads are, but one trick I’ve seen
and used was to take a good nut the correct size and thread,
and cut through it with a hacksaw vertically. That way it will
expand some, and may start onto and help clean up the
bad threads. Your could expand the nut even more before
you try, so you can get it past the bad threads easily, then
once past, clamp the nut kerf tight with a vise grips, and unscrew it.
Only out a nut by trying it.

Prepare to be boarded!

[Mumbles]

You can buy a thread file in either SAE or Metric with the proper thread count to clean up the threads. The advantage here is it has the correct pitch and no threads are removed from the shaft. A thread file usually has eight different thread surfaces so it can be used on lots of other things to. A quick chase with a dye after filing will ensure the threads are good for service.

1 user thanked author for this post.

opposedtwin

[lindy46]

I should have mentioned the threads are pretty much gone. I was thinking of trying to cut new threads of a lesser diameter and get a smaller nut to go on.

[fleetwin]

lindy46 wrote:

I should have mentioned the threads are pretty much gone. I was thinking of trying to cut new threads of a lesser diameter and get a smaller nut to go on.

What happened that would take out all the threads? What brand/hp crank is it? I would hesitate to advise rethreading the crank to smaller threads….Sounds risky

[Author]

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