Alternator Advice

To repair my broken starter sprag clutch, I of course had to remove the alternator rotor and stator. While I had it apart, I sent the rotor to Joe Hunt Magnetos to be reconditioned. I put everything back together today. I have no extra parts and the starter works fine. I do have an assembly question though.

A long time ago I either read or dreamed there is a tolerance in the clearance between the rotor the stator. Around the large majority of the rotor I can get a .004" valve adjustment gage in. At one point I have a tight measurement of .002". Is that okay, and how do I adjust it if that is not okay?

I have checked my shop manual and do not find any mention of a clearance measurement.

I just found the thread, "How Bad Is It?" First, I forgot to list I have a 75 MKIII. As mentioned in the other thread, there is a bracket for some of the starter gear around the stator. That plat appears to be milled to trap the stator even before you tighten the nuts. I still don't see how you can adjust the air gap. I assume the .010 listed in the other thread is the correct gap.

The manual calls for 0.008-0.010 inch allthe way around.

I believe the studs can be tweaked to adjust the air gap. Not sure about the best process, but I've heard of it done.

I just did this today. To adjust the gap I would fit the alternator on an check with (.010) gauge in all places and if it need adjusting I would take it off and with the nuts on the studs I would slowly and carefully put pressure on the studs with my socket and ratchet to bend them. Then assemble and recheck the gap and repeat as necessary. To fine tune the gap I used a soft rubber mallet and taped the alternator in the proper direction. when I got the gap the best I could I then rotated the engine slowly with the gauge in place and made sure it was ok. then repeated the rotating check in all the locations. When I was done I had a gap of .014 all around it.

blipJC said:

I just did this today. To adjust the gap I would fit the alternator on an check with (.010) gauge in all places and if it need adjusting I would take it off and with the nuts on the studs I would slowly and carefully put pressure on the studs with my socket and ratchet to bend them. Then assemble and recheck the gap and repeat as necessary. To fine tune the gap I used a soft rubber mallet and taped the alternator in the proper direction. when I got the gap the best I could I then rotated the engine slowly with the gauge in place and made sure it was ok. then repeated the rotating check in all the locations. When I was done I had a gap of .014 all around it.

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I'd advise extreme caution when attempting to bend a mounted alternator stud, I'd go one step further and advise against bending a mounted stud as they are screwed into a much softer aluminum boss that does not have much meat on it or tolerance for stress (inner primary covers are not inexpensive). Given that the studs have a tolerance I suggest that you first try swapping them around and see if the clearance doesn't fix itself.

If you determine that you must bend the studs to achieve uniform tolerance I would recommend that you set repeatable torque, mark the studs in the direction you need them to move, remove them, bend them in a vice, using a fulcrum opposite your mark while protecting the threads, refit then check again. Keep in mind that if you bend one stud you should really bend all the studs, keeping stress as low as possible; your initial measurements will show you which way to "vector" the stator.

Hope this helps,

Bill.

My manual (a Norton Publication) states "There should always be at least 0.005" clearance between rotor and the pole pieces on the stator ...". I read that as saying it is unnecessary to be equal all around. The manual does not suggest how to adjust.

Slick

With the rotor nut torque to spec. I use a 0.010" brass shim stock that I cut to fit the rotor with no overlap around the diameter. With the Stator loose, I fit the shim in between and then tighten the three-stator nuts with new star washers. Recheck with the engine nudged by the rear wheel (plugs out helps) in various positions with your feeler gauge to make sure there is no contact or you will burn out the stator. Use a new rotor star washer every time and use blue loctite. When they come loose they damage your keyway on the crank and rotor.
Cheers,
Thomas
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