I'm a little new to looking up parts for my '93 K75. Generally, I just go to realOEM and fumble around there until I find what I'm looking for. The shop manual doesn't seem to have part numbers (or they're not where I would expect to find them?)

At the moment, I'm trying to find some parts for the alternator. RealOEM has the diagram , but where it should list the parts, it just says "No parts found matching your car".

So does anyone know the obvious thing I'm overlooking, and where to find the part numbers for the parts in this diagram?



EDIT: Well, I found a diagram *with* part numbers under a different model. I guess I'll cross my fingers and hope they're the same?

What do you need? That's the 50amp Police version of the alternator - yours should be the 33amp version.

https://www.realoem.com/bmw/enUS/showparts?id=0501-EUR-11-1983-K589-BMW-K_100_83_0501,0511_&diagId=12_1631

I use the MaxBMW parts fiche when I need to find a part. It will have current availability and prices. I figure that if it works for the parts counter guys, it will work for me.

https://shop.maxbmw.com/fiche/DiagramsMain.aspx?vid=51739&rnd=09082020

Bonus is that you can buy the part just by clicking on the shopping cart.

Max does free shipping and doesn't add sales tax either, not to mention the M&M's that come with each order.

If when searching in ETK (from a dealer's site or realoem) if you type in your VIN then search you will often find that parts which aren't listed for your bike from the factory will not appear, or be 'greyed out'. This is an indication BMW didn't put them into your specific model. A dealer's site will be more specific. www.realoem.com doesn't know the difference. When I wish to see the range of available part numbers I do a generic search of that model type.

Part personnel at authorised BMW dealers are not always using the catalogue that we see when we go to their website to look parts up in the consumer version of ETK. BMW has a new system called AIR and it is dealer only and clearer on specifics. I can't provide a link for you to it here.

Point-Seven-five wrote:I use the MaxBMW parts fiche when I need to find a part.  It will have current availability and prices.  I figure that if it works for the parts counter guys, it will work for me.

https://shop.maxbmw.com/fiche/DiagramsMain.aspx?vid=51739&rnd=09082020

Bonus is that you can buy the part just by clicking on the shopping cart.

Max does free shipping and doesn't add sales tax either, not to mention the M&M's that come with each order.

Thanks! I'll definitely use this from now on!

Dai wrote:What do you need? That's the 50amp Police version of the alternator - yours should be the 33amp version.

https://www.realoem.com/bmw/enUS/showparts?id=0501-EUR-11-1983-K589-BMW-K_100_83_0501,0511_&diagId=12_1631

Thanks! Is there any disadvantage to using the 50A version? (like will it kill my fuel economy or something?)

50 amp won't hurt anything. Alternators only put out what the electrical system needs to run everything and charge the battery. With the 50 amp you can add an additional 200 watts of load to what the 33 amp alternator can run.

Unless you are running a bunch of halogen lights and all sorts of heated gear with a big stereo chances are the 33 amp alternator will do the job. Police bikes have lots of lights and sirens and a radio transmitter to power so they need the big alternator.

Point-Seven-five wrote:50 amp won't hurt anything.  Alternators only put out what the electrical system needs to run everything and charge the battery.  With the 50 amp you can add an additional 200 watts of load to what the 33 amp alternator can run.  

Right, but it gets that power from somewhere (additional magnetic resistance to the shaft turning in the alternator, powered by the engine I'm guessing). I guess I was wondering where that extra 17A comes from, and what it costs.

EDIT: Looks like the 33A version is hard to come by, but a 50A version is pretty readily available.

Be absolutely sure you're not looking at the 60amp R-series alternator with the pulley drive taken off. Although they are the same diameter as the 33A/50A ones, the mounting flange is a lot bigger and the holes don't line up with the K's engine. 50A ones are (relatively) rare.

In bikes with more sporting intentions, a lighter alternator with lower output is often used to reduce drag on the engine as it spools up. I don't believe this to be an issue of consequence in our beloved Bricks.

As an aside, my 2013 R1200RT-P (K26) with Authorities package doesn't use an alternator with any higher output than the standard model, which is 720 watts or 60 amps, despite the potential for added draw from oil cooling fan, siren, radio and lights, but it does have a secondary battery the same size as the original, and charged from said alternator like the original. I have to frequently use a Battery Tender, alternating the charge ports between the two, if not riding it for two or more week stints. The newer (K52) water-boxers allow one port to charge both onboard batteries. Interestingly, those new water-boxers also share an alternator between authorities and civilian bikes, and have a higher failure rate than civilian bikes as a result. 

BMW traded a difficult to access clutch of the Oilheads/Hexheads for an easy to access alternator when they decided to move the wet clutch to the front of the engine and the alternator to the back internally on the new (since 2013) water-boxers - the engine has to come out, and when it karks it it spits fragments all through the interior of the engine. What a racket it makes. I've seen three fail in the past four months. Doh!

The additional power is only drawn from the prime mover(the engine) when the electrical load requires it.  

If you are running a 50 amp alternator on a bike with a 20 amp load, the alternator is only going to make 20 amps and draw approximately 250 watts(plus efficiency losses) which equates to about 1/3 hp.  This is exactly the same as what a 33 amp alternator would draw in the same situation.

At a full 50 amp output it will be drawing about 650 watts(plus efficiency losses) or a bit less than 0.9 hp.  

Since a 50 amp alternator puts out a bit more power at each engine speed(especially at idle) it was probably originally spec'd for police bikes that might be required to run their lights and radio transmitters for extended time when not moving or moving very slowly(city traffic). 

I suspect they were added as standard to RT and LT bricks in the 90's when riders were adding electrical doodads like halogen driving lights and wearing more heated gear when touring(Goldwing syndrome), thus adding more load to the bike's electrical system.