Engine Rotor

I have been trying to find a machine shop in the Raleigh-Durham area that will skim my rotor and nobody wants anything to do with it.Anyone have any suggestions where I could have this done on the east coast of the US?

Thanks,
Mike

YING said:

I have been trying to find a machine shop in the Raleigh-Durham area that will skim my rotor and nobody wants anything to do with it.Anyone have any suggestions where I could have this done on the east coast of the US?

Thanks,
Mike

Click to expand...

Mike
Are you talking Alternator Rotor?
If so, they're probably worried about a magnet flying out.
At $118USD (AN price) I'd just get a new one. You would likely spend a big part of this on machine shop repair - which could, depending on factors, make it more prone to a VERY expensive future failure.
Just my two bob's worth.
Cheers

Assuming you want to gain some clearance the other option is to take a Dremel with emery cloth drum to the Stator inner steel sections. Don't do one at a time to reduce the height but partially do one before moving to the next one and repeat until you have gained the required clearance. This reduces the risk of heat building up at one coil.

Probably telling granny how to suck eggs but...
I use 3 pieces of 0.010" brass shim stock, equally spaced, between the stator and rotor while finally tightening the stator.
Has always worked for me.
Increasing the gap will come at the expense of lower alternator output.

YING said:

I have been trying to find a machine shop in the Raleigh-Durham area that will skim my rotor and nobody wants anything to do with it.Anyone have any suggestions where I could have this done on the east coast of the US?

Thanks,
Mike

Click to expand...

No problem, let me have the part and I'll have my NASCAR buddy do what you need or want. He made the shim/spacer I needed to fit the RGM front floating disc.

Jim

Why ?
Is it scored or burnt or ...
Just buy a new one , they are improved and you get good solid magnets that won't drift outwards to possibly contact with the stator .

Norman White suggests reducing the diameter of the mounting studs. Chuck them into a drill, use a file and Bob's your uncle!
Much less drama than trying to skim the rotor or grind the stator.

Thanks for all the suggestions.Much appreciated
Mike

SteveBorland said:

Norman White suggests reducing the diameter of the mounting studs. Chuck them into a drill, use a file and Bob's your uncle!
Much less drama than trying to skim the rotor or grind the stator.

Click to expand...

I file the stator mounting holes in the direction the stator needs to go

robs ss said:

Probably telling granny how to suck eggs but...
I use 3 pieces of 0.010" brass shim stock, equally spaced, between the stator and rotor while finally tightening the stator.
Has always worked for me.
Increasing the gap will come at the expense of lower alternator output.

Click to expand...

Yep but that's just the first part
You then need to rotate the engine and try in at least the 12 / 3 /6/9 o'clock positions for a minimum 8thou gap
As the rotor is not always central

Torontonian said:

Why ?
Is it scored or burnt or ...
Just buy a new one , they are improved and you get good solid magnets that won't drift outwards to possibly contact with the stator .

Click to expand...

+1

A new welded rotor is clearly the way to go. If magnets have started moving outwards (and thus impairing neccesary stator clearance), why risk complete damage of the stator if the rotor explodes?
If you have to pay someone for trimming the old rotor, keeping it makes even less sense.

- Knut

I’ve made it my standard practice to turn the rotor down in order to ensure a 20 thou gap. All 3 of my current Lucas alternator equipped bikes are running like this.

Fast Eddie said:

I’ve made it my standard practice to turn the rotor down in order to ensure a 20 thou gap. All 3 of my current Lucas alternator equipped bikes are running like this.

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Nigel, I'm interested as to how you arrived at 20 thou. Is there science to it?
What made 10 thou or 15 thou not good enough?
Cheers

robs ss said:

Nigel, I'm interested as to how you arrived at 20 thou. Is there science to it?
What made 10 thou or 15 thou not good enough?
Cheers

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Science?
Me?
Ha !

At 10 thou I had signs of rubbing on my Commando, I assume this is down to crank flex at higher rpm?

Also I’ve struggled getting proper adequate clearance with only a 10 thou gap before.

I read in Stan Shelton’s ‘Triumph Tuning’ that they ran a 20 thou clearance so thought I’d give it a go.

I’ve never measured the output, but never had a problem. It was explained on here by someone that the effect would be inconsequential.

A 20 thou gap means I can use a strip of plastic milk bottle wrapped around the rotor as a spacer when tightening everything up.

I’ve had no rubbing and no issues, so do this now as ‘standard’.

I am in now way suggesting others do the same !

Fast Eddie said:

Science?
Me?
Ha !

At 10 thou I had signs of rubbing on my Commando, I assume this is down to crank flex at higher rpm?

Also I’ve struggled getting proper adequate clearance with only a 10 thou gap before.

I read in Stan Shelton’s ‘Triumph Tuning’ that they ran a 20 thou clearance so thought I’d give it a go.

I’ve never measured the output, but never had a problem. It was explained on here by someone that the effect would be inconsequential.

A 20 thou gap means I can use a strip of plastic milk bottle wrapped around the rotor as a spacer when tightening everything up.

I’ve had no rubbing and no issues, so do this now as ‘standard’.

I am in now way suggesting others do the same !

Click to expand...

Success rules.

That said, the air gap affects reluctance (resistance for magnets). *IF* Lucas did anything scientific, they measured the spot where the magnetic flux lines were still plenty strong enough and the rotor would not hit the stator; or, they just said that .008" was the minimum to keep them from hitting and still providing sufficient current. I can't remember the formula, but .020" will produce less EMF and therefore current. However, in general, the Lucas stator and rotor at riding speeds produce significantly more than is needed.

My only concern is people thinking about .020" minimum clearance and nothing else. On most Commandos simply skimming the rotor to have a diameter that is .012" smaller means that you will have .020" at the 1-2 o'clock position and probably .040" at the 7-8 o'clock position. Having .020" all the way around is fine I'm sure.

So, I recommend getting .008" all the way around before skimming. Then if worried about the rotor and stator touching, skim off up to .006" (.012" smaller diameter).

I don't do any of that!

1) I check to be sure that the inner primary is properly shimmed!
2) I check the inside of the stator for material protruding past the cores and fix that if found.
3) I check the gap all the way around measuring at the outside and inside of the stator to see if the stator is not sitting parallel to the rotor. I often find that the spacers and/or inner primary bosses are not consistent, so the stator is not parallel to the rotor (perpendicular to the crankshaft). Usually, moving spacers around or swapping spacers can correct that. At that point, a feeler gauge that fits at the outer edge of the stator/rotor should slide all the way in with no difference in resistance.
4) Then:
On a Commando, I do whatever is needed to get a consistent gap - often opening one or more stator mounting holes slightly.
On a unit construction Triumph or BSA if there is anything needed for a consistent gap something is wrong, so I figure that out and fix it (unit construction is more precise in stator location).

BTW, pretty funny that the Commando workshop says minimum air gap of .008" to .010". How in is there a range attached to "minimum"?

The inner primary chaincase alignment is critical on a Commando. If there is the slightest movement when you tighten the nut that holds the outer chaincase cover on, then the clearance for the rotor will change.

When my Commando was relatively new I had problems with the rotor touching. Replaced under warranty but did it again. Dealer then skimmed the rotor. This reduced the already pathetic 110 watt output and as the bike was my daily transport, I was having to charge the battery every couple of days. Eventually I figured out that it was not having the inner case shimmed properly that was the problem. I also now put a spacer on the outer cover stud and fit the nut before setting rotor clearance.

Grant Tiller (whom I trust on everything involved with British electronic issues) skims every rotor on his bikes.He even has a video showing the procedure.My inner primary is shimmed properly and system is working fine. I have a new stator and rotor and when I go to install it, I don’t want to fight it to get the clearance I am after. I have had this problem on this bike for over 30 years with various stators and rotors.

On another note, I was helping my friend install a new CNW Estart and it came with an adjustable mounting stud that holds the outer primary case and eliminates the shims. I thought it was a great idea and simple to adjust.
Thanks again for all your responses
Mike

^^^ Just Googled the stud to see it in the flesh so to speak and found a CNW Etsart installation video, yes the stud is a cracking idea.
The Estart also looks rather good in its own right.