Buggered threads on new crankshaft

[reelfishin]

I have a new old stock crank for a mid 70's 115 hp which came to me with a dented/mushroomed top end. It looks to have been dropped on the threads or hit with a hammer.
Does anyone know the thread diameter and pitch?

Any suggestions? If I can fix the threads, I'll check it further for any damage and maybe use it on a rebuild I am doing.

(I got it for free, so there's no loss if it's trashed but it don't look that bad, just bad enough that you can't get a nut on it. I may even have the die needed for it if I am sure of the correct size.

 

[F_R]

Re: Buggered threads on new crankshaft

I don't know the size offhand, but that is the result of some cretin trying to remove the flywheel by hammering on the shaft and nut. There should be a suitable punishment for those people.

My guess is that it is a standard SAE (fine) thread, fractional. So, measure it as close as you can. Probably 9/16 or 5/8.

 

[jonesg]

Re: Buggered threads on new crankshaft

I've fixed the same damage by grinding a taper onto the beginning of the threads, a dremel or angle grinder with a grinding disk will work, then clean it up with a file and work the nut on and off a few times.

 

[CATransplant]

Re: Buggered threads on new crankshaft

Take the crankshaft and nut to a machine shop. Seriously. They can fix it quickly and correctly. All you have to do is get a die aligned improperly on the damaged threads and you'll hose the threads and ruin the crankshaft. It's a minor job for a machine shop and shouldn't cost all that much.

If you have lots of experience with dies, then ignore this advice. But, if not, I recommend taking the safer route and let someone else do it.

 

[R.Johnson]

Re: Buggered threads on new crankshaft

Read my post on the other crank, but that mushroomed top is another problem.

 

[freddyray21]

Re: Buggered threads on new crankshaft

machine shop

 

[reelfishin]

Re: Buggered threads on new crankshaft

I called a few machine shops, none wanted to mess with it. They had no listing as to what the thread was supposed to be. My guess is 3/4" SAE but the threads look even finer. I have a full assortment of taps, dies and a lathe that can roll new threads in it. None of the local machine shops have that.
I have more equipment in my shop than some of the local automotive machine shops when it comes to odd threads. I don't have another from the same era here to take a measurement on. I'll have to pull one off another motor to get a measurment. I think the crank nut, #0314209 is common to many motors. The nut is still in the package, the flywheel also looks untouched, but its just tagged, not boxed. The crank was in a box with one end pushed out the side. It's my guess it got dropped. All of the parts I'm dealing with are new old stock, even the block, heads, rods, and pistons are new.

 

[jonesg]

Re: Buggered threads on new crankshaft

it doesn't take a machine shop full of tools, just a bit of common sense.
Clean the mushroom end up until you can thread a nut on by finger.

Being hardened/ground and polished , those parts must be ground as the metal is no longer free machining. I've fixed worse in 20 minutes.
And I'm a cook.

 

[EN2]

Re: Buggered threads on new crankshaft

Take the nut you have and try a sae bolt on it. then youll know.

 

[F_R]

Re: Buggered threads on new crankshaft

I called a few machine shops, none wanted to mess with it. They had no listing as to what the thread was supposed to be. My guess is 3/4" SAE but the threads look even finer. I have a full assortment of taps, dies and a lathe that can roll new threads in it. None of the local machine shops have that.
I have more equipment in my shop than some of the local automotive machine shops when it comes to odd threads. I don't have another from the same era here to take a measurement on. I'll have to pull one off another motor to get a measurment. I think the crank nut, #0314209 is common to many motors. The nut is still in the package, the flywheel also looks untouched, but its just tagged, not boxed. The crank was in a box with one end pushed out the side. It's my guess it got dropped. All of the parts I'm dealing with are new old stock, even the block, heads, rods, and pistons are new.

And you don't have a caliper or micrometer and thread pitch gage?

 

[reelfishin]

Re: Buggered threads on new crankshaft

The crank is damaged and the nut is self locking with three crimp marks making it impossible to get an accurate measurement on the diameter. It looks closest to 15/16" x 20tpi. The problem is that the original threads are most likely rolled or formed threads, and not knowing the thread depth percentage, a caliper reading can vary.
The crank damage is slight enough that I could probably grind off the first two threads and it would still work but it would look suspect.
I also don't want to start a die on the bad threads and end up out of sync with the existing threads. I will most likely turn the mushroomed section down to size and try to re form the threads with a forming die on the lathe.
The only thing that gets me is that I keep hearing that the size of the crank threads are 5/8", I even checked my twin cylinder motors and even they use a larger diameter crank thread. 15/16" also seemed like an odd thread size as well for some reason.

 

[CharlieB]

Re: Buggered threads on new crankshaft

1. Use a thread pitch gauge to determine the pitch, make sure you have the correct thread file.

2. Use a flat file (or your lathe) turn/grind/file the mushroom down to size.

3. Use the correct thread file (or lathe) to restore threads from existing thread on out to end.

 

[dingbat]

Re: Buggered threads on new crankshaft

The crank is damaged and the nut is self locking with three crimp marks making it impossible to get an accurate measurement on the diameter. It looks closest to 15/16" x 20tpi. The problem is that the original threads are most likely rolled or formed threads, and not knowing the thread depth percentage, a caliper reading can vary.

15/16-20 UNEF
Basic Major Diameter = 0.9375
Basic Pitch Diameter = 0.9050
Minor Diameter = 0.8762
Lead Angle at Basic Pitch = 1 degree - min. 0

Personally, I'd taper the first couple of threads then file to shape. If worst comes to worst get a good set of thread files and file the threads back in by hand.

Been there, done that...too many times

 

[Tim Frank]

Re: Buggered threads on new crankshaft

The crank is damaged and the nut is self locking with three crimp marks making it impossible to get an accurate measurement on the diameter. It looks closest to 15/16" x 20tpi. The problem is that the original threads are most likely rolled or formed threads, and not knowing the thread depth percentage, a caliper reading can vary.
The crank damage is slight enough that I could probably grind off the first two threads and it would still work but it would look suspect.
I also don't want to start a die on the bad threads and end up out of sync with the existing threads. I will most likely turn the mushroomed section down to size and try to re form the threads with a forming die on the lathe.
The only thing that gets me is that I keep hearing that the size of the crank threads are 5/8", I even checked my twin cylinder motors and even they use a larger diameter crank thread. 15/16" also seemed like an odd thread size as well for some reason.

15/16" is an odd thread as is a pitch of 20 TPI. If they were going to use an EF series, I can't imagine why they would not have gone 7/8" or 1"....they are both 20 TPI.
Also, is there a nut on the crankshaft now?

 

[CATransplant]

Re: Buggered threads on new crankshaft

Here's a spendy solution to the problem. I want one:

http://www.amazon.com/exec/obidos/t...103610709/sr=1-196/ref=sr_1_196?v=glance&s=hi

Comes with dies for all thread pitches. You could start this on the good threads, then back it up to clean up the buggered ones, I think.

$72 isn't all that much. It could be a lifesaver in many situations.

 

[karlow1]

Re: Buggered threads on new crankshaft

Nice tool, a single tread die, or maybe it has 4 or 5 threads.

 

[rjezuit]

Re: Buggered threads on new crankshaft

I've used them. If the thread is short, they look like they work much better than they work. The major diameter (outside diameter)of an external thread does not depend on what the techniques use to form it (O.D.). If it is 1" it should be around .005-.010 smaller than 1" regardless of the forming method. Percentage of threads only comes into play on internal tapped threads in nuts etc. The correct way is to measure the outside diameter, and get a thread pitch gauge. If you can operate a lathe and cut single point threads you can chase the threads. If you have no idea what I am talking about, or are not sure do not even try it. Either way measure the O.D. and post the size. Maybe we can help from there. Rick

 

[R.Johnson]

Re: Buggered threads on new crankshaft

The size is 7/8- 14, or .875 dia. with 14 threads per inch. This is a standard thread. The crank I just checked can hardly be scratched with a file, so trying to recut with a die, or thread chaser would probably not be possible. To do this in a lathe will require a carbide cutting tool plus a very rigid lathe with the proper tooling to make the crank run dead true. Set-up time would take longer than cutting the thread, and most places, it probably would not be cheap.

 

[reelfishin]

Re: Buggered threads on new crankshaft

I pulled the flywheel off my 135 today and got the same, 7/8" x 14 tpi. I don't see this crank being that hard, its mushroomed so it has to be somewhat malleable. I chucked it up in the largest lathe this afternoon and ran a thread rolling die over it till the threads were again square. The nut fits fine now.
It took about an hour to get it set up, about 10 minutes to fix.
It was actually my impression that the crank was pretty soft, at lease where the threads are. The weight area and bearing surfaces are most likely much harder.

The adjustable thread rolling die head I have sold for over $2300 about 15 years ago, they're probably gone up a grand or so by now. I actually got mine used at an auction when a local shop sold out. I bought the remaining contents of the shop for a song which included quite a bit of specialty tooling. I sold off the screw machines and one of equipment and kept only two lathes and two knee mills. They were making billet suspension parts so much of the equipment wasn't of much use outside of a manufacturing operation and I had no intention of manufacturing parts.
I downsized what I had here a few years ago as well, it just didn't pay to house several of the larger machines which might get used once or twice a year. Back when I started building up my equipment assortment I was more into automotive restoration and custom fabrication and doing some production run lathe work on the side which helped support the hobby and pay the rent.

As far as the rethreading tool;
http://www.amazon.com/exec/obidos/tg...?v=glance&s=hi
these are good for thread clean up where a normal die cannot be used, the dies are about 1" wide, and these do not 'cut' threads very well. These are a good choice for repairing a threaded shaft in the center or to repair isolated threads.
Snap-On tools also sells a version of this.
http://buy1.snapon.com/catalog/item...&group_ID=1150&store=snapon-store&dir=catalog

These are sold mainly as a thread repair tool but have limited uses. The fact that the back side of the thread drags against a bronze plate and not a facing die creates much friction and on occasion thread damage.

 

[R.Johnson]

Re: Buggered threads on new crankshaft

Sounds like a great repair, and you certainly had the tool's to make it possible. I wonder what the cost for that repair would be at the average shop.