Alternator Size - '86 K75C

[2000rsv]

Did a quicky search for this but did not come up with good answers.

Have an '86 K75C.  Stock everything that I can tell.  What is the available power from the alternator/stator?  Is there a higher output alternator/stator available?

I intend to add some HID auxiliary lights and add the capability to hook up heated gear.  Would like to know if the stock power system could handle this or not.

Martin Fabrication lights - about 40W each (x 2)

Warm and Safe heated jacket liner (gen 2 or 3 - not microwire) - about 90W

Warm and Safe heated gloves (gen 2 or 3 - not microwire) - approx 50W

Would also like to upgrade the headlight bulb.  Not sure on that.

[cheetah]

Running all three (Martin lights, jacket and gloves) at the same time, your current draw is 18A.

Google is saying your alternator output is 33A.

This is a 50A model http://catalogue.alternatorstarter.com/Partdetails.aspx?Part=220-5569

If you upgrade the headlight bulb, you may want to upgrade the stock wiring to something heavier or add relays.

[mac]

I run 40W total of LED aux lights (dimmed down to <20W most of the time), plus 1157 running lights in the rear turn signals, plus the jacket and gloves you describe (modulated down to <50% most of the time) on my '86 with the factory 32A alternator and I haven't had any issues.

If I turned everything up to the max, I'd probably out strip the charging capacity. I had planned on the 50A upgrade, but haven't needed it in practice.

[JamesInCA]

You can swap in the 50A alternator used on the later bricks and the R-bikes from mid-90s to 2000s. It's this: http://www.bmwmcchattanooga.com/showAssembly.aspx?ukey_assembly=189562&ukey_make=398&ukey_model=7529&modelYear=1995&ukey_category=15886&ukey_driveLine=132

For whatever reason, if you find one of these on eBay for a K-bike, it will be much more expensive than one you find for an R-bike. It's the same part.

If you get the R-bike alternator, which is belt-driven, you need the following additional parts to fit it onto your brick (items 2, 3, 4 & 8 from the diagram linked above):
12312305329 Clutch housing
07119933155 Spring washer
12311459814 Hex nut
12311464877 ; 12311460306 Monkey nuts ... er ... Rubber mounting (need 3)

You already have the monkey nuts on your bike, but unless you've replaced them, they need replacing.

The clutch housing from your alternator is not interchangeable with this one. Different shaft.

You'll also need to snip the alternator plug off your wiring harness and crimp on a ring terminal or two.

This is a very easy afternoon project.

[2000rsv]

James,  Thanks for the great info.  You are right.  On Fleabay, 50A K bike generator $175.  R bike $55.

Will see where this goes.

[JamesInCA]

Yup, I picked up a 2001 R-bike alternator for my '87 K75 at some ridiculously low price, and the conversion parts from BMW are surprisingly inexpensive.  (It was the newest part on my bike until recently, when I discovered that the K1200 water pump up through 2009 is also the same as mine. Those are also stupid cheap when listed "for" a K1200, vs for a K75.)

The hardest part of the installation was getting that nut tight, holding the cup ("clutch housing") onto the alternator shaft. It's imperative that the nut not stick out any further than its design height, within the cup, or it can rattle against the drive unit on the bike. The alternator itself bolts right up.