28 Amp Alternator blues

[GAHellinger]

My '91 ST1100 with 57k miles is displaying charging issues. Historically my Datel voltmeter displayed about 12.6v-12.8v at idle and top out at 15.1v - 15.2v at 4000 RPM with no accessory load. A couple days ago my voltage dropped to 12.4v - 12.5v at idle and 12.8c - 12.9v at 4000 RPM with no accessory load. I checked and greased the connections at the battery, the VRR, the 2P and 3P connectors. No signs of damage were found. I installed a new battery.

How should I proceed with troubleshooting? I would like to be able to swap out my VRR (31600-MS2-601) with another unit to check its operation but do not want to purchase a part unnecessarily. If possible I would like to avoid performing a 40 amp alternator upgrade until winter. Also, the Honda schematic shows a silicon rectifier, 31700-196-000. Where does this unit reside and should I find it and inspect it?

All suggestions are appreciated.

Thanks.

George

 

[BigTom]

Tick, tick, tick...

The clock is ticking. You might make it to winter, you might not. I rode mine everyday, and when it died, it was dead. I didn't have a volt meter so I changed the battery first, then the alternator. I just have no idea how long until the low charge you mention goes until it becomes negative charge...

Edit: It's really only a good day's job, I'd make sure you have all the parts just in case...

 

[John OoSTerhuis]

Hi George,

I can lend you one of the STOC loaner, known good VRRs for your controlled substitution troubleshooting. Email me.

31700-196-000 / RECTIFIER is the clutch/neutral switch diode (part of the engine-start circuitry). It's the bulge in the wiring harness next to the air cleaner on the left side. You can do a reverse part number look-up on a couple of the online microfiche sites. Here's the direct link to the Ron Ayers page:
http://fiche.ronayers.com/Index.cfm/Module/WhereUsed

edit: do the static Alternator Inspection test in the Honda Service Manual to see if one of the 3 A/C windings in the stator is out. Also, do the dynamic A/C test that Dan Alameda (bdalameda) posted here a while back:
https://www.st-owners.com/forums/showthread.php?t=84285

edit2: is your classic 91 black or Sparkling Silver Metallic?

HTH

Regards, John :STOC: Ten Fifty-Eight

 

[GAHellinger]

Completed the 40 amp alternator upgrade along with servicing the swingarm and replacing the rear wheel bearings. Thanks to John O. for the loaner tool kits; they made the work much easier.