the curious case of the lemans that kept shorting out rotors

[lazlokovacs]

following on from this thread... http://wildguzzi.com/forum/index.php?topic=82353.msg1300527#msg1300527

a couple of months ago my lemans 1000 wasn't charging, after checking everything, I discovered the rotor had shorted out.

replaced rotor and all was hunky dory.

for about a thousand miles...

1st warning sign, voltmeter was starting to oscilate in small movements when running

2nd warning, charge light flickering at 3k+

3rd and final warning, charge light no longer comes on when the ignition key is switched to 'on.'

so, back to the same symptoms as last time, if I bridge the slip rings on the rotor with a penny, the charge light comes on. And the bike is no longer charging itself.

what could be causing these rotors to short out...?

thoughts, WAGs and opinions all gratefully accepted.

thanks as ever

[rodekyll]

My guess?  They're not shorting out.  The winding wires are breaking where they exit the 'fingers'.  There was a run of those that had the bend too sharp and too close to the hole they exited.  Even though they are potted they still broke under normal operating vibrations and heat.  That failure may lead to a short, but the failure itself is not the short.

Also be sure you're getting the right rotor for the job.  There's an early and late one -- 73.5mm dia and 75mm, or somesuch.  Someone else can explain the amp differences by diameter.  A small rotor in a big stator doesn't do much.

[lazlokovacs]

thanks rodekyll,

so... get a new rotor and hope the windings don't break?

[rodekyll]

Oh -- I see from the previous topic that the differences have already been discussed.  nevermind.

There is an aftermarket alternator some folks have been replacing the bosch with.  It puts out more power and gets good reviews. 

ouGg&vxp=mtr" class="bbc_link" target="_blank" rel="noopener noreferrer">http://www.ebay.com/itm/BMW-R-Moto-Guzzi-Alternator-Upgrade-450-Watts-Hi-Output-EnDuraLast-EDL450-/371405681674?hash=item567980f40a:m:mssOFyRZoqMgYsCLRj1 ouGg&vxp=mtr

Me, I got tired of that nonsense and did something different:

[JoeW]

Was it a new rotor or rebuilt? I don't put much faith in rebuilt ones. Also, was the center bolt torqued to spec? If you can afford it, I recommend the Ducati style upgrade from EME.
http://www.euromotoelectrics.com/product-p/edl450-altkit105.htm

[wymple]

Me too, on a couple of our bikes...






40 amps, two wires. Total. 70 bucks on ebay.

[Chuck in Indiana]

How about a little more detail on the small block? 

[charlie b]

I thought about the external alternator 'fix' too.  Ended up with the Endurlast and am happy with it.  I got the solid state rectifier/regulator at the same time.  No more rotor windings to go bad.  No more exciter voltage to watch out for.  And I can run all the lights and heated gear I have.

[Tom]

I have Enduralast too.  Works so well that the wiring couldn't handle the extra flow.  Shorted out the ignition key switch.

[wymple]

How about a little more detail on the small block? 

Don't have much for pics. It fits in there better than it did on the big block Tonti frame.





My son took the rotor and cut off everything down to the core, then I welded a pulley to that. Fabbed bracketry just like you would on a car, one side of it swings for tensioning the belt. You can see the adjustment slot in this 1st pic. Just make sure the pulleys are square with each other, ratio of 1-1 will be good enough with motorcycle engine speeds, we are 1-1 1/2 on the small block, backed off a little on the big block.  The small block has a Garmin which shows speed, so we don't use a speedo cable at all. The tach cable was a bit on the close fit, but we didn't use that either because we didn't care about it. The tach cable is in use on the big block, tho, along with the speedo. There is no belt tensioner on the big one as it came out perfect. Loosen the alternator to take the belt off, securing the bolts gives it perfect tension, so the planned adjuster was never installed. Neither bike has stock air filtration, we use foam pods. Son made an aluminum cover plate over the ignition behind the lower pulley. It should be at Illinois unless his job interferes. It's done a 2000 mile Canada trip, and we went to Mo-Kan with it as well.