Dead rotor - best options to fix / replace?

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Buccaneer

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Hi all,

I've been doing up and then riding around a little XS400SE, while my search for a decent XS650 went on and on, 2+ years in total. The 400 is now all done up with loads of new parts and all works well except for difficult starting; a second carb clean needed, think I missed the 'hidden' fuel feed passage for the Pilot jet (it's the Capped jet type) in my first carb boil.

BTW, for some reason the XS400 seems significantly more prone to carb issues than the 650; seems rather strange, anyone know why?!

Anyway a few weeks ago I finally dived in and bought what looked like a very nice XS650 Special, USA import ages ago, from a guy in Devon. It's on an age-related UK plate 'V-reg' which I think puts it at 1979 or 1980. It has cast wheels, factory CDI (I think, but wouldn't know for sure how to differentiate from a Pamco), a solid state finned regulator unit mounted low, black paint job, and 'Special' logo on sidepanels. The alternator rotor brushes are the 'later' type where they are both the same and neither goes to chassis / ground. Frame & Engine numbers are the same, 2F0 201 xxx. Can anyone confirm the most likely model number? XS650SG?

Knowing (owned a UK XS650SE 'US Custom' from '86 to '95 and 45,000 miles) how the charging system fails when the rotor brushes wear out, I'd checked the charging system before buying and it seemed to work. PO had it on a battery conditioner so the battery Volts were very decent to begin with (13.8 ish @ idle IIRC), but did see some rise going from idle to 2000 rpm and was satisfied with that. Rode it home 200 miles, pretty much OK (1 fuse died but replacing with spare got me back on the road with no hassle apart from the embarrassment of it dying at a roundabout). (And yes, replacement blade fusebox is here already, awaiting installation).

Anyway a week later riding it home late from work (all lights on) the lights started out a bit dim, then after 10 mins very dim, then it started missing. A sinking feeling at that time of day! I JUST got it home (semi-) safely, with creative minimisation of lights usage etc and lots of (invisible) smiling and waving at all the drivers flashing me for being poorly lit. Yes I know I KNOW I KNOW, but I don't fancy pushing this bastard 4 miles home ... or leaving it to get scratched or nicked!!!!!:banghead:

So, I got & fitted new brushes, thinking that would be it (old ones still showed the limit lines, with about +1mm on the Outer, but know from past experience the brushes can fail with the limit line still showing). Anyway, NO! The battery Volts goes from 12.4 off load, to 11.8 IGN ON, to 11.9 idling and (erratically) 12.0 to 12.1 with headlight on an 2000rpm up.

So I've now checked the excellent 'Charging System Guide' on here (thanks ggggGary, nice work) and done all the checks I should have done before parting with my readies. The Rotor resistance measurement is erratic but can be seen as low as 1.3 Ohms, so, seems like the rings need a careful dress down & cleaning and, more importantly, the rotor windings have a serious short anyway.

So to the question: I need either a new, recon, or used OEM rotor in UK, (TCI compatible type with magnet). What is my best option? I already was feeling cautious about jumping straight to eBay and comments on here seem to confirm some of those 'New' ones are rubbish ... however, what about this one?: eBay item number: 331239130326. Sounds good. Then again although it does sound good I'm well aware that is all just words at this point!

Maybe look around for the best used OEM I can find, then keep fingers crossed as $200+ goes to buy some 30 year old component that can be prone to cooking? ... doesn't sound very enticing!

BTW, my initial reaction to PMA plus Pamco is I'd really rather not ... loads of money and quite a lot of faffing about to install the whole lot. But maybe I can be talked into that as the best option for a complete, long term fix.
 
Sorry I should have made clear, that eBay ref is for the 'RaceTech Electric' pattern version. Amongst all the blurb is reference to 'precision cut', 'each individual unit being dynamically computer balanced', etc. They give a 1yr g/tee for what it's worth (less than the hassle cost!) and the price seems reasonable at US $100 (and with reasonable international postage cost).
 
I had the same problem with my XS 2. The rotor was damaged and not working .when tested with a meter it was showing no ohms at all .After much searching I found one on E bay last week for £15.00 .It is testing at 5.9 ohms and it appears to work ok and is charging the battery at 13.5 v.They can be found eventually,keep searching.
 
Well to start the XS650 never ever used a CDI, it uses a TCI, very different beast.
I would look around the find a place that can rewind the rotor you have.
Places the fix alternators and starters.
I think getting a rotor rewound is the best way, you know it fits and runs true. A lot of "new" rotors don't always run true.
Sometimes when a rotor gets rewound it's magnetic field can overpower the magnetic field of the TCI magnet. Easy fix is to "glue" a new magnet on top of the old.
Here state side Radio Shack sells a 4.5 mm round rare earth magnet that is a perfect fit.
Most use an epoxy glue, I like JB Weld, very strong if used right, everything has to be immaculately clean.
Up in the XS650 TECH section you will find VIN to year charts to help ID your bikes year. The one I like your bike is an 80.
In 79 the US bikes had points and the BS38 carbs and a separate reg and rec, in 80 they used the TCI, BS34 carb and combo reg/rec.
Leo
 
Last edited:
Custom Rewind
2014 Pratt Hwy.
Birmingham, AL
35214

800 798 7282

Ask for Gary. I had my rotor on my '81 rebuilt from Gary years ago and it's still going strong, but I have a PAMCO ignition and do not use the trigger magnet.

There are a number of things that can cause a rotor to fail, but the #1 cause is the rectifier, especially the original rectifiers. They have a greater voltage drop than a more modern rectifier and this means that the rotor uses more current to overcome this voltage drop. More current in the rotor means that it will run hotter, and that is the killer, so anytime you change the rotor, I would suggest also changing the rectifier or even the combined reg / rectifier to get the maximum life out of your new or rebuilt rotor.
 
I agree with the poor rectifier as part of the reason for rotor failure.
The main reason is heat.
A weak or bad battery causes excess heat build up in the rotor because the regulator keeps the current through the rotor on more than it should trying to keep a poor battery charged.
I think a bad battery is more common than a bad rectifier.
Custom Rewinds is a good place for state side rewinds but being in the UK the shipping costs would be too much. That's why I recommended a more local place.
Leo
 
Ok, I'll except that I do make mistakes every now and then, I'm only human.
I'll correct it.
My 81 has the drum brake rear mag.
Leo
 
Yep, I knew you had one so it was just a slip. BUT, as you have stated in other posts,
regardless of the reason, a slip needs to be pointed out. And with the hard fast rules
you set for others. . . . . . Like the Op's slip on CDI which he corrected to TCI later in the same post. . . .
Jus sew ya no bro, Iam hear to hav yer bac. No pity no slack.
 
Hey everyone thankyou so much for all those fast replies! This is a coooool site!

CDI, TCschmi, thanks for the headsup Leo. You are pedantic but I'm not complaining! (The world probably needs more rigour, not less, as a rule). Local rewind may be a good idea, especially as now I live next to a likely area for finding such small businesses. Even knowing about the TCI magnet and its registration with the rotor, and passing that info on, I'd be a bit nervous that a non-bike guy may make some error that causes problems.

Pamco Pete thanks for that idea but as Leo points out the shipping 2 ways will be a real pain. Also it seems Gary can get busy this time of year and it might take time to get the job loaded...


Yellowdog ... yeah, if I see a used rotor on eBay that looks OK for that sort of money, I would jump at it. I suspect you may have been quite lucky!

Weekendrider - great link, thanks. Seems like RaceTech Electric are bike enthusiasts who have properly tested their products in real 650s, so that option is looking good to me..

FWIW my bike has the disc rear brake not a drum.

Thanks too for all the 'root cause' comments. I think I'll go with the full Race Tech solution and use their rect/reg while I'm at it. And maybe even a new battery for good measure, although I have loaded tested the current one and it is clearly not a terrible battery. Since it was freshly charged before I ever rode it and the PO was using a battery conditioner, suspect the damage may have been caused long ago, but who knows.

Thank you all again.
 
Motorcycle reg/rect's are quite expensive. We've managed to round up auto regulators and electrical industry rectifiers that work and are much cheaper. Do a search, there's many threads on this. You can save about half the cost of a motorcycle specific unit. I just picked up a couple of these rectifiers to have on hand for updating local guy's 650s .....

http://www.amazon.com/gp/product/B00E1IP228/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1

Auto regulators can usually be had for somewhere in the $20 to $30 range, sometimes cheaper if you shop around. I got mine off eBay for about $10.
 
Thanks 5twins, will check out those ...

A possibly fairly obvious follow-up question ... has anyone had trouble with the RaceTech Electric alternator rotor?

cheers:thumbsup:
 
I bought 2 and ohmed them out at 5.4 they look good, lightly sanded the slip rings phenolic to get rid of some flash. I have not put one on a bike yet. On their web site for $90 with US shipping, expect some more $ to the UK
 
Hi everyone,

Firstly thanks again for all the advice and a great site, which made changing out my alternator rotor quite easy in the end - not a job I would have attempted without knowing about it!

I ordered the Racetech rotor and it arrived pretty quick. Price seems quite reasonable for a new part.

There is a good video of how to fit the rotor on Racetech's site here:

This is confidence-inspiring. They have a pro shop with compressed air tools so the only difference for me was working out how to do those jobs with hand tools.

One other point is in the video they removed the brushes from the stator before pulling the stator basket off, but I couldn't see any need to do this and left the brushes in place ... did not notice any problems as a result. I did clean up around the brushes on the inside of the stator basket to remove all the carbon dust that had built up. (My old rotor was measuring only around 1 Ohm so there was probably excessive current going through those brushes for the last 2 months). Cotton buds and electronic cleaning fluid are good for that clean-up job.

So far, the new rotor works fine. It measured at 5.1 Ohms (allowing for cable and contact resistances) which seems spot on. I did not need to replace rectifier / regulator. Quick end-of-swap test at base confirmed battery voltage (freshly charged from the mains, ~12.7V engine off) reaching around 13.8V @ 3000rpm, which seemed encouraging enough to venture out.

Output seems fine, went for a 2.5 hour ride 2-up with GF yesterday late afternoon, started without lights (as per dead alternator riding style!), gradually ran lights for longer and longer with eyes and nose for any problems... and ran full lights the whole way back (over an hour) which would definitely have drained the battery before. Battery volts after we got back (everything off) 13V. Good, so far!

I don't have facilities for easily checking the runout on Racetech's part, but assuming that is OK (and IIRC others have checked it and found it good) then I'd say it is a good buy.

The only problem with the rotor was the keyway for the Woodruff key being a bit too small. This caused quite a panic initially as the key was a very smooth fit in the OEM rotor and would not go into the new one at all. Firstly I had to scrape out some varnish in the keyway which I did with screwdriver and volatile cleaning fluid (ECS in fact). The key still didn't fit! Drat. So in the end I had to use a small hacksaw blade as best I could to erode the edges of the keyway. With patience I probably got a total of around 0.3mm away with reasonably straight edges and square corners, and it took 20 mins or so, carefully cleaning away the swarf with cotton buds and more ECS fluid. The key still didn't fit and I didn't think I could get much further with the saw blade without the edges and corners ending up rounded or out of true. So then I got some sheets of fine emery and sanded down the key by hand. I was afraid the key would be super hard but it sanded down OK. Another 10 minutes or so and I had the key fitting nicely.

The only other points to report are regarding removing the retaining bolt, pulling the old and refitting the new rotor without the use of an impact wrench. On my bike it could be done, with a bit of hassle. The method relies on locking the rear wheel and putting the bike in 2nd gear, then you can work against the drive train. You can keep the bike on the centre-stand and complete the work on your own, but do be careful not to push the bike over if something is hard to shift!! There is a bit of give in the train of course, but you can work around it. I found an ordinary claw hammer with rubber covered handle was perfect for locking the rear wheel. Getting the first nut off needed building up the tension with the socket handle by hand first, then tapping the socket handle with another hammer. You have to be fairly brave and hope nothing gets bent, stretched or broken, but it works!

You do need the special rotor puller (about 15 quid from Yambits on eBay) to pull the old rotor off the shaft, I wouldn't attempt that without the special tool. The rotor can be pulled easily (at least on my bike) using an ordinary socket on the puller tool, I only had to tap the socket handle fairly gently and the old rotor popped off sweetly.

Finally for tightening down you have to reverse the direction of your rear wheel lock, and then use a combination of arm power and hammer taps to get the new rotor firmly seated on the shaft. Don't forget you can rotate the shaft using the bike's kickstart (before applying the rear wheel lock, of course) to align the Woodruff key slot on the shaft to be pointing upwards, which makes refitting a whole lot easier if it happened to lie the other way up on disassembly (...mine did, of course!).

OK so hopefully that's it - if there are any problems I'll report them back later. It's not 100% easy job, but not too difficult either... if you are patient you can tackle this without any worries.:thumbsup:
 
Here is a video of a rotor mounted on a lathe to check for runout:

Too much runout:


Here is a video of a Custom Rewind rotor:

Runout is very important because if there is excessive runout, the "valleys" will collect the carbon from the brushes and create a high resistance and the "peaks" will cause excessive and faster wear of the brushes so you end up with a low output voltage and you have to change the brushes often. The roller coaster ride that the brushes take also results in uneven contact between the brushes and the slip rings further reducing the current in the rotor.

brushes.jpg

You can check for runout with the rotor installed by removing the brush holder and holding the eraser end of a pencil close to the copper rings with the engine running.

The first video is of a rotor that I bought on line instead of using my better judgement and getting a Custom Rewind. Fortunately, the seller gave me my money back except for shipping costs. The bad rotor also had a defective slot for the Woodruff key.

Custom Rewind
2014 Pratt Hwy.
Birmingham, AL
35214

800 798 7282
 
Buccaneer;

Good to see you have things working better now. Don't forget to use a torque wrench to torque that large rotor nut to the correct spec.

13.8 volts is getting close, but is not a full charge voltage. The stock incadescent tail light
bulb(s) draw a lot of amps. If you replace it with the LED type, you may get the charging voltage up to 14.1 volts, where it should be.
 
I had the same issue with the keyway in the Racetech rotor I bought being too narrow - some hand filing on the key itself, then dressing it smooth with emery paper, required for proper fit. I use a band-type oil filter wrench on the rotor circumference to hold it while loosening or tightening the locknut - the band is wide enough to span both halves of the rotor assembly evenly, so no risk of damaging the rotor in this process. With clean slip rings and good brushes and battery, I get 13.8-13.9 VDC showing on my analog voltmeter at 2000 rpm and above. I do have a LED taillight, but also have front and rear running lights in my turn signals, using the stock twin filament incandescent bulbs. Before adding the rear running lights, I showed 14.1-14.2 VDC, but accept the slight loss in return for (hopefully) better rear visibility.
 
aldo5468 said:
I had the same issue with the keyway in the Racetech rotor I bought being too narrow - some hand filing on the key itself, then dressing it smooth with emery paper, required for proper fit. I use a band-type oil filter wrench on the rotor circumference to hold it while loosening or tightening the locknut - the band is wide enough to span both halves of the rotor assembly evenly, so no risk of damaging the rotor in this process. With clean slip rings and good brushes and battery, I get 13.8-13.9 VDC showing on my analog voltmeter at 2000 rpm and above. I do have a LED taillight, but also have front and rear running lights in my turn signals, using the stock twin filament incandescent bulbs. Before adding the rear running lights, I showed 14.1-14.2 VDC, but accept the slight loss in return for (hopefully) better rear visibility.
Click to expand...

For sure, those running lights are keeping the voltage below the preferred 14.1 volt area.
Seems like everything in life is a trade off.:)

You could use LED running/turn signals. Another easy way to save amps is to use a 40 watt headlight instead of the 55 watt.
 
I also used a racetech and filed the keyway in the rotor to fit the key. I also sanded the face with some fine wet n dry paper there was a bit of flash left over from machining. Some acetone to remove the varnish from the taper and slip rings is probably a smart precaution. On the 82 it's showing 5.6 ohms and over 14 volts @ 3K RPM with all stock bulbs and lead acid battery in good charge.
 

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