alternator

malcolmkaty

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Just been away to the black forest in Germany great ride down in the rain just as we pulled into the BB car park I had the front blub warning light come on and the battery light and red triangle come then after about 5 seconds the battery light went off. I checked the dip beam and it had blown so I change it that night .next day no more than about 5 mins of running the front blub light came on blown again another dip beam blown. On and off that day as we headed back into France at slow speed the red triangle and battery light would come on a quick raise the revs and off it would go for an hour or 2 .Anyway the bike made it home ,I check the charge at the battery with a volt meter about 14.3 running and I checked the belt which I thought might have been slipping but nothing .quick check with a torch and a nice crack under on the bottom of the alternator so it looks like this was causing the alternator to fail .would this also cause the alternator to over charge and blow the dip beam as the battery should level the charge out or was it just by chance both stopped working plus there was more vibration than normal which I hope was because the alternator was running rough .Just looked at my options and BMW dealer £570 plus vat or motorworks 2nd hand £255. Makes you wonder why these are so dear compared to a car one ,I have looked on ebay and seen 2 in the states but does not seems many options
 
Been there, cracked casing, found a replacement on eBay in USA for £70 IIRC including taxes and air freight. It came from a 40,000 mile GSA in Arizona and was mint.

A cracked casing wont cause overcharging, a failed regulator will (built in to the alternator). 14.3v is about right to charge a 12v cell.
 
My 2005 1200 GS alternator also cracked its casing and sounded like a washing machine on full spin with the bearings gone!
Got a used one on eBay for £40 and fitted myself. So far so good.
I'm no expert but from my experience there seem to be 2 possible types, bosch or nippon denso, and the loom plug is different for both but I think can be changed to fit somehow.
The output of later alternator was increased and if you have the earlier spec its worth looking at a later one to replace it with.
Oh, and I think there might be different pulley sizes, but not sure of the details.

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I have seen some rough looking ones on ebay just over 100 pounds i am thinking get one but can you get them reconditioned and how much


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Sgt.Cupid said:
My 2005 1200 GS alternator also cracked its casing and sounded like a washing machine on full spin with the bearings gone!
Got a used one on eBay for £40 and fitted myself. So far so good.
I'm no expert but from my experience there seem to be 2 possible types, bosch or nippon denso, and the loom plug is different for both but I think can be changed to fit somehow.
The output of later alternator was increased and if you have the earlier spec its worth looking at a later one to replace it with.
Oh, and I think there might be different pulley sizes, but not sure of the details.

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Click to expand...

I might be wrong but the one used on a GSA has a higher output hence the different types. But I'm sure someone will be along to correct me if I'm wrong


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Initially the GSA had a higher output alternator due to foglights, then the GS was fitted with the same uprated item as owners were known to be fitting more farkles.
 
If i fit a denso one from a gsa is the pulley size different do i need just need to get a longer or shorter belt


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My GSA now has a lower output Denso that replaced the cracked high output Denso. It works fine. How much electrical power does a bike need?
The lower power version needs a longer belt as its got a bigger pulley.
It's fortunate because I never did manage to get my old pulley removed.
It cost me £50 including delivery from Germany plus the cost of a longer drive belt.

I hear the Bosch gennys have a gap in the casing so they don't hold moisture so don't distort like the Denso type. The Bosch has a different electrical connector.
 
Did mine earlier this year that was a Bosch item which i managed to get from a breakers and taken from a 4000 mile RnineT as they run the same unit.
Not a pleasant job but not too hard to do,just strip everything off the front end and get the front shock out to make it easier to wangle the alternator out the near side.
 
Has anyone done the change from a denso to bosch and what is needed is it just changing the plug over as there seems to be many more bosch ones about


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The Bosch one will fit,but as stated the connector is different,
A repair loom is available from the dealer,so that the old one can be cut off and replaced with one suitable for a Bosch unit.
A bit of searching on the forum will find a few threads on the subject ,along with the part no for the loom
 
I changed my denso alternator to a Bosch when the denso corroded and seized the Bosch came from motorworks for £175 including the new single pin wireing loom plug required the denso uses a four pin plug with two wires blue and green I cut off the denso plug then I soldered the Bosch plug to the blue wire and taped up the green wire this has worked fine for the last year if you use the Bosch they are a better design and do not corrode and seize the Bosch alternator came from a 1200 RT with 3,000 miles on it.
 
The Denso can be fitted by removing the front steering head LHS brace strut.

I believe the Bosch is slightly bigger which would need to have both struts taken off.
Removing the suspension shock would not help.

All of the electronic boxes have to come off. You will spend ages putting the wiring back correctly.
 
FMy like new alternator from the states should be with me soon,what can I do to stop this one from splitting the case ,would a good coating of ACf50 stop any internal corroison
 
I slathered mine in ACF50 then allowed the excess to drip out before fitting.
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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