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Lucas magneto self extractor not working #536877
04/06/14 2:59 pm
04/06/14 2:59 pm
Joined: Mar 2007
Posts: 88
San Pedro CA
Lenos Offline OP
BritBike Forum member
Lenos  Offline OP
BritBike Forum member
Joined: Mar 2007
Posts: 88
San Pedro CA
This is a pre-unit tr6 with a K2FC magneto. I'm unscrewing the center bolt and it just keeps turning without the gear going anywhere. It came off fine the last time I removed it. Getting desperate, any suggestions?

Thanks,


'64 Atlas/'60 TR6 Triton
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Re: Lucas magneto self extractor not working [Re: Lenos] #536889
04/06/14 4:13 pm
04/06/14 4:13 pm
Joined: Sep 2007
Posts: 1,110
Ottawa, Canada
gREgg-K Offline

BritBike Forum member
gREgg-K  Offline

BritBike Forum member
Joined: Sep 2007
Posts: 1,110
Ottawa, Canada
I'm assuming your mag is the type that has an automatic advance device (ATD) integrated with its drive gear, right? Lucas ATDs have a built-in extractor, and as a result it should first appear to jam as it unscrews, and then pop the drive gear off, if all is proper.

The hex-headed center "bolt" of the ATD is actually a tube nut, the open end of which is threaded 3/8" BSF to match the male thread of the K2FC's armature. The shank of this tube nut is threaded with a reverse thread, which is fundamental to the operation of the extractor function.

It works like this:
- As you undo the tube nut, it unscrews from the male armature thread on the mag
- The tube nut will unscrew until the reverse thread contacts the (hidden) underside of the ATD's yoke
- At this point, the tube nut will stop turning because it has jammed between the two threads
- You unscrew the tube nut with as much torque as you can muster by hand, which pre-loads the taper
- if you can't pop the ATD off the mag's taper at this point, a light rap on the hex head of the tube nut will shock the ATD off

It is vital to be gentle when tapping the tube nut, as you can damage the mag's internals ... this works only because the taper has been pre-loaded by the extractor mechanism.

I suspect your extractor is not functioning because the reverse thread on the tube nut is stripped, or some other problem is preventing the extractor from functioning as it should.

I hope this explanation makes sense ...

.. Gregg


Spyder Integrated Technologies
Lucas, BTH, & Miller Magneto & Dynamo Restoration
SMITHS Chronometric Restoration
magneto@spyder-it.com
Re: Lucas magneto self extractor not working [Re: Lenos] #536897
04/06/14 5:13 pm
04/06/14 5:13 pm
Joined: Mar 2007
Posts: 88
San Pedro CA
Lenos Offline OP
BritBike Forum member
Lenos  Offline OP
BritBike Forum member
Joined: Mar 2007
Posts: 88
San Pedro CA
Thanks for the response.

It all makes sense, but the question arises as to what to do now.

As I'm unscrewing it I can feel when it goes onto the reverse thread, but as I continue turning the gear and advance mechanism don't budge.

Assuming the reverse thread is stripped, what next? I can't be the first guy this has happened to.

Any ideas?


'64 Atlas/'60 TR6 Triton
Re: Lucas magneto self extractor not working [Re: Lenos] #537023
04/07/14 12:09 pm
04/07/14 12:09 pm
Joined: Sep 2007
Posts: 1,110
Ottawa, Canada
gREgg-K Offline

BritBike Forum member
gREgg-K  Offline

BritBike Forum member
Joined: Sep 2007
Posts: 1,110
Ottawa, Canada
I take it that the center tube nut, when backed off fully, is loose in the ATD and does not wedge between the ATD and armature? That being the case, the extractor function can not operate.

If the integral extractor is non-functional, you have few other options but to use a claw-type puller on the center tube nut and the back side of the ATD, being careful not to bend anything.

So, apply pressure with a claw-type puller, and if the ATD does not pop of its taper, a tap on the center post while pressure is applied should do the trick.

Once it's off, you should determine why the extractor stopped working. If it is the reverse thread on the OD of the tube nut is stripped, you should be able to replace it as long as the female thread in the ATD body is still serviceable.

.. Gregg


Spyder Integrated Technologies
Lucas, BTH, & Miller Magneto & Dynamo Restoration
SMITHS Chronometric Restoration
magneto@spyder-it.com
Re: Lucas magneto self extractor not working [Re: Lenos] #537051
04/07/14 3:10 pm
04/07/14 3:10 pm
Joined: Mar 2007
Posts: 88
San Pedro CA
Lenos Offline OP
BritBike Forum member
Lenos  Offline OP
BritBike Forum member
Joined: Mar 2007
Posts: 88
San Pedro CA
Thanks again. I may need to get creative here as there is almost no room for a puller.

Wish me luck.


'64 Atlas/'60 TR6 Triton

Moderated by  Alan_nc 


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