New Rotor/Stator Installation

I was having an issue achieving the recommended minimum spacing of 0.008” between a new rotor and new stator on my 1974 Commando. I did some research on the Forum (an amazing resource) and elected to ream out the three stator bolt holes as several posters had recommended. This method worked and provided the required clearance when I tested the new stator by putting it back on the mounting studs alone with no spacers or washers. The issue arises when I put the spacers and washers on the studs for final mounting of the stator. It looks like the OD‘s of the spacers and the washers are slightly larger than the diameter of the indents in the potting epoxy? (not sure if that’s the right term) where the three bolt holes are in the stator, and the spacers and washers are catching on the potting epoxy and not sitting flat against the plates of the stator. I think the fix would be to grind a small amount of the potting epoxy off to permit the spacers and washers to sit flat. I think about 1/16” should do it. My question is whether it is possible to remove this much of the potting epoxy material at the indents without compromising the stator?

Hi,
You will have no problem doing what you plan.
The epoxy is pretty thick.
Even if you did go to deep by mistake.
A bit of epoxy putty would fix it right as rain.
So go for it.

blaisestation said:

Hi,
You will have no problem doing what you plan.
The epoxy is pretty thick.
Even if you did go to deep by mistake.
A bit of epoxy putty would fix it right as rain.
So go for it.

Click to expand...

Agreed. Once you're sure that problem is fixed, if you still have trouble try moving the spacers around. I've seen times where they were not all the same length. A few thousands length difference can cock the stator and give spacing problems.

I have no stators used or new that are hindered by the potting at the location of the stock spacers and use wave washers under the three special nuts that hold the stator.
With a new stator the spacers had at least 0.010" movement in any direction before hitting the potting.

(It would be taken for granted in your case a previous owner had not been one of those stud benders to try and position the stator)

It seems some folk go crazy oversizing the holes, stock is around 8 mm, I opened them to 8.2 mm (or another 0.004" radial movement.
There are plenty of pictures here (I also moved the rotor and stator inboard due to the duplex conversion which also allowed aligning the two vertically)
A machined crank mounted push fit plastic disc made setting the gap easy, the wave washers meant no radial movement when the nuts were tightened.
0.009" / 0.010" all the way around.


I doubt taking some of the potting away will hurt in that area ( I had the same thoughts when I machined the ignition timing marks into the stator and wondered how far a way I was to seeing copper wire)

Personally I like to see a lot more than the minimum recommended figure. I’ve had the rotor rub at .010”. Whether that was due to heat expansion, crank flex, etc I do not know for sure (I suspect a bit of both).

I now get rotors turned down to ensure a .020” gap and have noticed zero downside to this.

But back to that potting material, which is frankly unfit for purpose, smaller 12 point nuts are commonly available that take the next size smaller socket than is usual for the thread size. I’ve used these to get around the issue:

Fast Eddie said:

Personally I like to see a lot more than the minimum recommended figure. I’ve had the rotor rub at .010”. Whether that was due to heat expansion, crank flex, etc I do not know for sure.

I now got rotors turned down to ensure a .020” gap and have noticed zero downside to this.

But back to that potting material which is frankly unfit for purpose, smaller 12 point nuts are commonly available that take the next size smaller socket than is usual for the thread size. I’ve used these to get around the issue:View attachment 21948

Click to expand...

There´s no problems turning the rotor, with the magnets?

No problem.

WEM said:

I think the fix would be to grind a small amount of the potting epoxy off to permit the spacers and washers to sit flat. I think about 1/16” should do it. My question is whether it is possible to remove this much of the potting epoxy material at the indents without compromising the stator?

Click to expand...

You'll likely find that you need less than 1/16 inch. A 1/2" sanding drum on a Dremmel works well for that.

Thanks to all for the suggestions. I’ll report back with any progress..

Good news. Before attempting to dremel away some of the potting material on the stator, I figured I’d have another go at trying to get the recommended air gap. After two days of no satisfaction and lots of frustration, the alternator went together this afternoon with surprisingly little effort. I used the plastic pop bottle shim trick. I now have an air gap of 0.009“ between the rotor and stator. I rotated the rotor 60 degrees several times as recommended and had the 0.009” gap each time. I guess the fifth (or sixth) time’s the charm. However, when you get a good look at it, although within spec, an air gap of 0.009” really isn’t much. There really isn’t much space between the rotor and the stator. I’m thinking of following Fast Eddie’s recommendation of getting another 10 thou turned off the rotor. Has anybody who has done this noticed any reduction in the electrical output of the alternator?

Maybe the manufacturer comes into it, the Lucas boxed three phase stator and rotor I fit had no problem as far as the spacers.



The rear of the stator had more room and neater finish than the front.
I had considered machining the front pockets for a better fit on the reduced hex nuts but it was doable just, as is.