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Which Alternator?


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The alternator on my 2003 1150 RT could fail at any time. I heard a new rattle, and took it to Nick's in GB. The belt was OK. The tech listened with a stethoscope and told me the rattle was the alternator bearings. Last year at this time, the belt had slipped off partially and was prolly putting a torque on the pulley, stressing the bearings. Rode the 230 miles home without it failing, but I've been to beemerboneyard. There is a 50 amp and a 60 amp alternator. Now, the specs say 700W output. That would be 50 amps at 14 volts or 60 amps at 11.66 volts. Which is recommended for my motorcycle?

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These alternators have very easily replaced bearings. In C3 clearance, quality brand name bearings should cost less than $50. Probaby much less.


You can also have your local alternator rebuilder change them



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Either one will work just fine. The 50 amp version would be the "correct" one for your bike.


I still have my 50 amp alternator from my 1100RT sitting here if you want a less expensive option.

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Morning DrMikey


Your bike came with a 50 amp alternator.


The thing you need to watch for on the 2003 1150RT is what pulley is on the alternator.


2003 was the change over year when the BMW 1150 went to the free-wheeling front pulley on the alternator. before 7/2003 used the old fixed pulley with the hex retaining nut. After 7/2003 the alternator was equipped with a free-wheeling pulley using internal splines to fit a special wrench.


The alternator is the same but if doing the work yourself you will need a special tool to remove & install that free-wheeling pulley (doesn't use an attachment nut) so it would be best to get an alternator with the correct pulley already on it.


It's also possible that part of your alternator noise is that free-wheeling pulley so if your bike is post 7/2003 you might be ahead to get an alternator with the correct pulley already on it.


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