Rotor (Crankshaft End) Threads

[MikeG]

Amazon.com: UTR - Universal Thread Restorer. External Thread Repair Tool. Easily Replaces hundreds of Dies. Automatically chases threads within range 5/32" - 1/2",4-13 mm. All In One Patented Universal Solution! : Automotive https://share.google/gImeeLM4XCUNF8q9Q perhaps something like this? The cutting bits could be reground to 55 degrees if needed?

 

[marshg246]

Amazon.com: UTR - Universal Thread Restorer. External Thread Repair Tool. Easily Replaces hundreds of Dies. Automatically chases threads within range 5/32" - 1/2",4-13 mm. All In One Patented Universal Solution! : Automotive https://share.google/gImeeLM4XCUNF8q9Q perhaps something like this? The cutting bits could be reground to 55 degrees if needed?

Only works to 1/2" - this is 5/8". If I can find one larger, it should be a nice addition to the tool chest.

 

[Johnny0]

I just went through fixing the crankshaft threads on the primary side of my 75 Commando MkIII. I was never able to get the exsisting rotor nut torqued properly and the loose rotor nut might have contibuted to my 3 phase alternator melting down from the contacting rotor. I think the rotor nut might have been over tightened in it's past life which started the problem.
I started out by ordering a new rotor nut from Andover, part # 06.0387. It would not even start to screw on the crank threads. I then ordered another rotor nut from Steadfast Cycles in Washing because the picture of the rotor nut on their website looked a like the machining was a little different than the the Andover rotor nut. It screwed on the crank about 3 threads.
I found a BSC Die size 5/8 x 20 TPI from British Tool and fasteners (https://britishfasteners.com/). It had a screw adjustment to be able to tighten the threads once I made the 1st pass with an adjustable
1 1/2" die stock. The 5/8 x 20 die was $125 but they were the only ones I could find that had one. I figured it was worth it because I had only one shot of repairing the threads without further ruining the exisisting threads on the crank shaft.
I was able the clean the threads up moving very slowly back and forth using plenty of cutting oil. The rotor nut from Steadfast cycle was able to thread completeley on to the crank threads. I tightened the rotor nut to 50 ft lbs once the rotor was installed. I did not want to go any higher on the ft lbs torque being that the threads were certainley in somewhat of a weakened shape after everything they had gone though.
So far all is good after a 50 mile ride!

 

[MikeG]

Look at this product I found on google.com https://share.google/xgzjnwdBzmREAEuPT. This one might work for you Greg

 

[mdt-son]

So, I'm trying to decide whether to keep working with the UN die and if I can get it started, rethread it. If there is there some other die (or better, thread chaser) available for the crank end I would like to know as this comes up often.

Maybe there is a company who can change the thread angle of your UN die? Minor diameter of UN class 2A is 0.5675" while the Whit form should have a minor diameter of 0.5770" so the die doesn't need altering wrt. depth of cut.
The rounded thread form is fatigue resistant, which may be the answer why NV chose to keep using this special thread.

- Knut

 

[marshg246]

Update - I wish it were more definitive.

The 5/8"-20 UN die I have threads onto other crankshafts without needing tools. Cannot get it started on the MK3 crankshaft I'm working on.

The 5/8"-20 UN Tap I have easily cleaned up threads in several used rotor nuts I have, most using no tools, just bare hands.

I cannot find a 5/8"-20 Whit Form die.

I spent a lot of time with a thread file and a triangular needle file and I have the threads well enough in my used nuts. The damage was only at the first 2 threads. I'm going to order a new nut and see if there is any difference.

I thought about using the 5/8"-20 BSC die British Fasteners has but it is also 60 degree so I'm not sure it make sense to spend $115+shipping.

So, I believe that the threads are Whit Form (55 degree) but there is no problem using UN.

 

[Deets55]

Update - I wish it were more definitive.

The 5/8"-20 UN die I have threads onto other crankshafts without needing tools. Cannot get it started on the MK3 crankshaft I'm working on.

The 5/8"-20 UN Tap I have easily cleaned up threads in several used rotor nuts I have, most using no tools, just bare hands.

I cannot find a 5/8"-20 Whit Form die.

I spent a lot of time with a thread file and a triangular needle file and I have the threads well enough in my used nuts. The damage was only at the first 2 threads. I'm going to order a new nut and see if there is any difference.

I thought about using the 5/8"-20 BSC die British Fasteners has but it is also 60 degree so I'm not sure it make sense to spend $115+shipping.

So, I believe that the threads are Whit Form (55 degree) but there is no problem using UN.

Greg,

If you know a good machinist he (or she) should be able to grind (or even buy) a 55* single point thread cutting tool and chase the threads on a lathe. Unfortunately finding someone who will take that job on, and be reasonably priced is hard now days.

 

[marshg246]

Greg,

If you know a good machinist he (or she) should be able to grind (or even buy) a 55* single point thread cutting tool and chase the threads on a lathe. Unfortunately finding someone who will take that job on, and be reasonably priced is hard now days.

I normally check all threads before assembling things, but I didn't on this as they looked fine at a glance - won't make that mistake again! Now the engine would have to come out of the frame and apart to use a lathe. Also, there are no capable machine shops anywhere near me and I don't have a lathe.

 

[batrider]

I like the clamping a split nut idea.