R65 (1981) altenator

[MR.E]

Now then

Can anyone tell me where the alternator is on the bike please?
I ain't looked yet, to be honest, but are they easy to repair or should I just buy a new one??

Thanks

[Bob_Roller]

The alternator is located under the front cover.

The cover is held on by two allen head type fasteners .

There a 'hot' connections under the cover, by that I mean they always have battery power available to them, regardless if the key is in the ignition or not .

Remove one of the battery cables and secure it out of the way .

The cables are old and have taken a shape over the years, that will allow them to move back if they aren't secured by a ty rap or  something similar .

The alternator is easily replaced, you can replace the rotor, stator, diode board rectifier, or regulator itself, not a 'package' like on a car or truck .

[Lucky_Lou]

Yes listen to Bob, you dont want to fry the board disconnect the battery first. Underneath the alternator you will see the "Bean can" 81 should be electronic ignition but could be a points unit.Did you sort the carbs out?
Lou

[Bob_Roller]

But , I have to admit, I had my '81 R65 over 20 years before I learned this !!!!!!!!

[MR.E]

now then

cheers for the advice, i'll be heading down in 5 mins to strip it off.
If it's not charging what might i need to replace?

it's an electric start 81 model, but it's not charging on ride outs & by the end of the day i usually have to bump it off down the road.

Lou, think the carbs are ok, not had much chance to test em, been buying the mrs a house for when pip's born!!
looks like with the decent weather this week i'm gonna get some time to finish it off.

thanks

[montmil]

... If it's not charging what might i need to replace?

... it's not charging on ride outs & by the end of the day i usually have to bump it off down the road.

Check the carbon brushes - confirm they are not worn down so far that they no longer are making contact with the rotor. If the "pigtail" springs are contacting the brush holder, that may be a clue of excessive wear. You might try lifting the springs, insert a small plastic or wood spacer, replace the springs and see if you get a charge.

Brushes are in two positions. The stator ring must be removed to service the rear brush.

Check all wiring terminals for security. Be sure negative battery cable is disconnected prior to messing wit' da 'lectics.

Also, confirm GEN lamp is not burned out.

Monte

[Bob_Roller]

Probably a bit too late for this, but before you take anything apart, you need to do a bit of troubleshooting .

First, when you turn the key to the 'ON' position, does the red "GEN" light come on.

If it does, attach the leads of a multimeter to the battery, start the bike and bring the rpm's up to 3500-4000 rpm, voltage should be in the 14 volt range, it should be higher than the battery voltage before you started the engine . .

[MR.E]

now then

got sidetracked so haven't started yet!

the bike no longer has the rev counter fitted BUT the red gen light used to come on when i turned the key, then went out whilst i was riding.
I've not tested the battery with a meter, whilst it's running, so will do that tonight.

Thanks

[tvrla]

Well, there's your problem!

The alternator needs the electricity from that light bulb in the tachometer to function. Without it, no voltage is generated!

[MR.E]

Well, there's your problem!

The alternator needs the electricity from that light bulb in the tachometer to function. Without it, no voltage is generated!

you pulling my leg??

[Bob_Roller]

No he isn't !!!!!!!!!!!!

Look around the connector that went on the tachometer, there should be a light blue wire, connect that blue wire to a solid brown wire, solid brown wires are grounds or earths on BMW motorcycles .

Once you do that, you should have a functioning charging system.

The "GEN" light has an important function on these 'farm implements', it completes the circuit from the voltage regulator to the alternator rotor !!!!!!

[MR.E]

well bugger me!
thats crazy stuff!

& it saves me loads of trouble.

Thanks lads, once again!

[tvrla]

The "GEN" light has an important function on these 'farm implements', it completes the circuit from the voltage regulator to the alternator rotor !!!!!!

Once you know how to 'read' the charge light, you can pretty well tell what's going on with the alternator. It's really a misnomer to call it an idiot light - probably named that by one.  

[MR.E]

The "GEN" light has an important function on these 'farm implements', it completes the circuit from the voltage regulator to the alternator rotor !!!!!!

Once you know how to 'read' the charge light, you can pretty well tell what's going on with the alternator. It's really a misnomer to call it an idiot light - probably named that by one.  

will it be worth me fitting a light to it, so i can 'read' it??

[tvrla]

I think so. I like to know what's going on with the charging system so have either the bulb or gauge, or both. Not sure if there's any other negative impact running a hot lead straight to the alternator, rather than through the bulb. I think the bulb does limit the current to the alternator, which limits overall output.