Alternator pulley failure

[Thezz]

2005 BMW R1200RT with 44,000 miles

Last week I was running into town to fill the RT with gas when at the stop sign ½ mile from my house the craziest racket started coming from my engine.  Sounded like a piece of barb wire was caught on something in the engine and was slapping the inside randomly.    

I immediately returned to my drive way and killed the engine.  Took off my helmet so I could hear properly and restarted the engine.   The noise was coming from VERY high on the engine – just under the gas tank.   It then lasted for about 5 seconds and just quit!!

I couldn’t make it repeat the noise and so I decided to take a ride, which occurred without any additional excitement.

The next morning, I started the bike cold again to see what would happen.   It really wasn’t making the same crazy noise but there was some noise and I noticed that the alternator symbol was on the display.  I then killed it and restarted the bike to see if it would be persistent -- the alternator symbol disappeared. 

This made me believe that something strange was going on with my alternator drive.    Today I put the bike on my lift and removed the belt cover so I could see the motion of the belt and the alternator.   Also put a voltmeter on the battery so I could determine if and when the alternator was charging the battery.   Before pushing the starter button, the battery showed 12.8 volts (fully charged).   I started the engine and the voltage dropped to 12.5 volts.    I immediately looked at the face of the alternator with a flashlight (so you could see the internal fan on the front) and it was just barely turning.   Every once and a while there would be a clicking noise and the alternator would spin up to speed for a short while.  

I had found my problem, the decoupler pulley on the alternator is failing.  Which brings me to my question.   Has anyone ever replace the pulley on their alternator without pulling the alternator.   Looks like it can be done, but I will have to remove the front shock to gain access to the front of the pulley to use the pulling tools which I now own.

[dirtrider]

37 minutes ago, Thezz said:

2005 BMW R1200RT with 44,000 miles

 

Last week I was running into town to fill the RT with gas when at the stop sign ½ mile from my house the craziest racket started coming from my engine.  Sounded like a piece of barb wire was caught on something in the engine and was slapping the inside randomly.    

 

I immediately returned to my drive way and killed the engine.  Took off my helmet so I could hear properly and restarted the engine.   The noise was coming from VERY high on the engine – just under the gas tank.   It then lasted for about 5 seconds and just quit!!

 

I couldn’t make it repeat the noise and so I decided to take a ride, which occurred without any additional excitement.

 

The next morning, I started the bike cold again to see what would happen.   It really wasn’t making the same crazy noise but there was some noise and I noticed that the alternator symbol was on the display.  I then killed it and restarted the bike to see if it would be persistent -- the alternator symbol disappeared. 

 

This made me believe that something strange was going on with my alternator drive.    Today I put the bike on my lift and removed the belt cover so I could see the motion of the belt and the alternator.   Also put a voltmeter on the battery so I could determine if and when the alternator was charging the battery.   Before pushing the starter button, the battery showed 12.8 volts (fully charged).   I started the engine and the voltage dropped to 12.5 volts.    I immediately looked at the face of the alternator with a flashlight (so you could see the internal fan on the front) and it was just barely turning.   Every once and a while there would be a clicking noise and the alternator would spin up to speed for a short while.  

 

I had found my problem, the decoupler pulley on the alternator is failing.  Which brings me to my question.   Has anyone ever replace the pulley on their alternator without pulling the alternator.   Looks like it can be done, but I will have to remove the front shock to gain access to the front of the pulley to use the pulling tools which I now own.

 

Evening  Thezz

 

Removing the front strut (alternator in place) is how the BMW service manual calls out the pulley replacemnet.

 

As long as you have access to the correct tools to hold the pulley then turn the alternator shaft then it is a fairly easy job. Without the correct tools then it is usually easier to remove the  alternator & take it to an alternator (auto electric) shop for pulley swap-over.   (that over-running pulley isn't cheap from BMW so sometimes a used alternator from E-Bay is cheaper).

 

 

[Thezz]

Thanks for your reply Dirtrider.   I value your advice.    I have the tools to remove the pulley.   I will pull the strut (Just two bolts) which should give me room to get the tools on the pulley for removal.     Has anyone ever replaced their over-running pulley with a solid one?  Just wondering if this is one of those ideas that lost it's shine when used in the real world.

[dirtrider]

10 hours ago, Thezz said:

Thanks for your reply Dirtrider.   I value your advice.    I have the tools to remove the pulley.   I will pull the strut (Just two bolts) which should give me room to get the tools on the pulley for removal.     Has anyone ever replaced their over-running pulley with a solid one?  Just wondering if this is one of those ideas that lost it's shine when used in the real world.

Morning  Thezz

 

To answer your question, yes, to answer your question on the 1200 hexhead possibly but no-one that I know of has done it.

 

The over-running alternator belt pulley on the BMW 1150 is no longer available so those are being replaced with the standard (non over-running) pulley by BMW dealers when they fail.   

 

On the BMW 1200 hexhead the alternator is not adjustable like on the 1150  so the replacement pulley would need to be the same size as the removed over-running pulley (or elastic belt length compensation would need to be figured out then sourced in the correct size).