Another Stator/Rotor Question

I've studied all the methods used to obtain the required clearance and have decided to go with LAB's method of trimming the stator using a flap wheel.
Question is; Do you resurface the shaved portion of the stator with anything?

Saber,
Not familiar with L.A.B.'s method but;
you need about 0.009" thou of an inch clearance all around. I normally use a piece of brass shim stock of that thickness, which fits the diameter of the rotor as a fit up shim before I tighten the stator stud nuts up tight. Brass being non magnetic. (beer cans are too thin) Then I rotate the engine at various points to check clearance around with a feeler gauge. If you find a really tight spot at one of the three points of a stud, you can massage it with a hide mallet to the required clearance.
Cheers,
Thomas

Ive never done the shave routine but as you likely need only a few thou I suppose it is doable. Id be very careful
with tapping the studs as they are strong but the alloy base less so especially if, like many, the chain at some
point had eaten into the alloy bosses.

I have always used Canuck's method with no problems at all obtaining sufficient clearance with OEM or the Lucas 3 phase system. I HAVE had some issues with aftermarket parts in that regard but was able to get enough clearance using the bolt-tapping method.

I drilled the stator holes with whatever number or letter drill was a few thousandths bigger to allow some movement on the studs,

Upgrading my MKIII with a Lucas 3 phase. A very tight fit, will try the Canuck hide mallet method to get the correct clearance. More than a little nervous about wacking my baby with a hammer. Well got to do it, this has held me up for a week.

Onder said:

Ive never done the shave routine but as you likely need only a few thou I suppose it is doable. Id be very careful
with tapping the studs as they are strong but the alloy base less so especially if, like many, the chain at some
point had eaten into the alloy bosses.

Click to expand...

I mark the side of the stud which needs "persuading", then remove the stud, thread two nuts on the end that screws into the chaincase, clamp the nuts in a vice, use a length of steel tube over the stud and "persuade" the stud. Screw the stud back in and recheck. Truly a PITA.

I bought a new three phase Lucas rotor (RM20 LU54202299) and stator (RM24 LU47244) a few weeks ago.

The clearance between rotor and stator off the bike was less than I was happy with, so I sent them both back and got replacements sent out.

The replacements were exactly the same, so in the end mounted the rotor in the lathe and skimmed a few thousandths off.

It cut really nicely and left a great finish - we blew air on it as we cut, as obviously it’s magnetic so the swarf would have clung.

gtiller said:

I bought a new three phase Lucas rotor (RM20 LU54202299) and stator (RM24 LU47244) a few weeks ago.

The clearance between rotor and stator off the bike was less than I was happy with,

Click to expand...

What was the clearance that made you uncomfortable? I have had no issues running .008" I don't have the service manual here (I'm in the UK until November; the bike and all my reference material is in Mexico) but I don't remember that there is a spec for that clearance in the service manual though I certainly could be mis-remembering that. IOW, when we are installing an alternator and looking for a specific clearance, what is that clearance spec based on? Is it actually in the service manual or is it an arbitrary clearance that, over time, has become "the spec?"

I guess what I'm thinking now (and I never really thought about it before) is, since the stator does not have any adjustment capability, it leads me to believe that Norton/Lucas were confident that the parts fit with sufficient clearance as delivered. Why do we think it has to be carefully adjusted/set to some figure?

I want to emphasize that I have always done a clearance check since I bought my current Commando in '06. it is only now...as in 'while composing this post' ...that I'm wondering about the process.

I'm an absolute heathen. I put a long socket over the mounting tower and bend the alloy in the direction I need it to move.

Well maybe not absolute. I put the nut on at the very tip to help torque it in the desired direction.

Does anyone know how important the clearence is to function?

What I mean is, can we open up the clearence a lot? Imagine having .020” or even .040” clearence, you could ask your kids to fit it, blindfolded, and it’d still be fine!

Anyone know what the impact of doing this would be?

"you could ask your kids to fit it, blindfolded, and it’d still be fine!

I suspect that was essentially the factory method!

What yer doin’ over ‘ere Mike ?

Yes but what happens if the rotor "runs aground"? Even if it just contacts a bit?

Years ago I had a feeler gauge set that had a brass blade at 10 thou among all
the other steel ones. Suddenly occurred to me to use it whilst installing the
stator and rotor one day. Cannot say Ive seen a set like this since.

Sure, too little gap is bad.

But can we have too much?

How much can we have and not affect functionality ?

Fast Eddie said:

What yer doin’ over ‘ere Mike ?

Click to expand...

We actually purchased a house in Bath late last year and will be spending about 5 months/year here - Jun through Oct. Originally we were planning to buy Motos here but the house has no garage or even street parking (listed cobblestone street - only loading or unloading - so I'm not sure how we would keep them. We'll be going to the IOM for a week for the Manx and, as we have done previously for the IOM, are hiring bikes for that. We could probably rent/buy a garage within a mile or so which would be workable but I don't think we want to add the expense.


"Yes but what happens if the rotor "runs aground"? Even if it just contacts a bit?"

Well, that would be a bad thing, of course! But, again, the question is (in my mind) does that ever happen with an OEM/Lucas system/replacement parts? OTOH, my experience with modern "exact replacement" parts is that frequently they are not. I have interchanged all sorts of parts between old Nortons with no issue BUT have purchased quite a few new AN parts that do not fit without some fiddling. So maybe in the old days there were no issues with rotor/stator clearance but now there are? Doesn't seem to make sense since I ASSUME (you know what they say about assumptions) that modern machinery would make for more accurate tolerances than already-old machinery did back in the 60's-70's.

FWIW I replaced the standard alternator with a Lucas 3-phase on at least 5 different Commandos many years ago and we never paid any attention to the clearance - did. We just removed the old parts and installed the new parts. Never had any issues. I suppose that could have been luck, I guess, but again, I don't recall that Norton said anything about checking the clearance.

When I got back into Commandos in '06, it was a thing to check so I didn't give it much thought as to why we do now and didn't then. I figured that back then we were just stupid! But I'm not sure of that now...

@MexicoMike I have a plastic shim that I wrap around the rotor when I’m installing the stator.

The Commando manual calls for a minimum air gap of 0.008 to 0.010 inches

My shim is 0.25mm which equates roughly to somewhere between the two, and I couldn’t get the stator over the rotor with the shim strip in place.


When I measured the diameter of the rotor, it was a tad over 74.1mm
So on the lathe, I took the rotor down to 73.9mm

Once everything was buttoned up on the bike, I could get a 12 thou feeler gauge all round.
My shim strip slided in easily - and I’m happy there will be no fouling.


@Fast Eddie obviously, the bigger the air gap, the more lossy the alternator output will be, as the effectiveness of the magnetic field is lessened.
But I think because we are talking thousandths of an inch, that the difference will be negligible.

Cool! Good that someone found what it says in the manual...it was ME! Sad when you forget that a few years ago you knew the answer to your own question.

Here are the excerpts from the manuals.

From 1970


MK3


Interesting to see they discovered Loctite!

Onder said:

Yes but what happens if the rotor "runs aground"? Even if it just contacts a bit?

Click to expand...

The rotor heats up and explodes. Catastrophic failure ensues. I had such a failure years ago that I attributed to not checking clearance, though it could just have been a bad rotor. But ever since then I'm careful to check. IMO the number isn't all that important, but contact must be avoided.