ATLAS Alternator rotor/stator/charging problem

... is a common occurrence on theearlier rotors where the magnets are just cast into the aluminium alloy. Later ones are welded to avoid the problem. It's a good job you caught yours in time!

Rex's speedshop show the welded rotor in stock: https://www.rexs-speedshop.com/product/genuine-lucas-rm20-rotor-lu54202299/

Working on  a 750 motor  ( p11 Ranger possibly) I had to go through 4 used rotors till i found one the fitted the shaft nicely and felt right. You may need to get a new key or even an oversize key and fettle it to achieve a play free assembly . The so called "welded" rotors are not actually welded but of an improved design. Might be best to buy rotor and stator from the same source. Some new stators come with oversize holes for mounting ,so some form of stepped studs or sleeving will be needed.

Lucas stopped manufacture in the mid 1980s The name is still being used by the Wassell empire on goods made in the far east.

The 54212006 rotor we have here was the original part number (and is the one that comes apart) was used throughout the 1970s on the commando etc.the later part that replaced it was 54202298. These are both Lucas numbers from the 1980s so how relevant to the 'modern part' now sourced from the far east, that is any ones  guess. We watch with interest.

Roger mentioned sleeving the larger stators, please consider the advantage these holes will offer by allowing more wriggle room to achieve a rotor stator clearance of .008"  minimum.

I've quoted Norman Whites suggestion before  on this site but I see it could be of use here.

Norman suggests that the stator bolts be machined down to the core diameter of the threads to enable a tad more clearance to be obtained around the rotor.

15ft lbs is the figure quoted in my Routine Maintenance manual.

If the bolts snap they are not of the correct material or are fatigued.

The most usual method to get the gap to equalise is to give the offending studs  a "bump" !  in the required direction. But i did not tell you that !.

Hitchcocks sell a laminated plastic strip that is the right length to go round the rotor and the thickness to give the requisite air gap apparently.

insert, tighten the stator nuts, remove - voila (in theory).

For Doris, I packed the gap with old broken feeler gauges at the stator fixing points and tightened as you did, which did the trick.

Good luck with it Graham.

When I spent quite a while in the hydraulics repair industry tie rods invariably came with the main length the same core diameter as the threaded ends.

Sizes could have been from 5mm O/D to and beyond 32mm in my experience.

These tie rods/bars had to contain anything from 100psi to 4,000 psi.

I only ever had one malfunction from a 16mm tie bar when the nuts were forced off along the threads under 250 bar pressure! 16mm tie bars would have a core diameter of circa 14mm as an example.

To understand the working of this phenomena consider this if you will. The thread is only there to keep things together the main strength is from the core diameter of the whole system which will be constant along the length.

The tolerances of newly produced rotors and stators are much finer than the originals, so out of the box, the air gap is less.

In my opinion, it’s not enough.

I don’t like the idea of waisting the alternator studs or hogging out the holes in the stator, so I take a light skim of the rotor in the lathe.

https://youtube.com/shorts/OULRRNfaRpE

I aim for a 12 thou air gap rather than the 8 to 10 that the factory workshop manual calls for.

It’s peace of mind for me, and after lot’s of testing over many years on several engines, I have seen no less power output, which is why I’m comfortable sharing this recommendation with others.