Testing the charging system question 74 /6

[mfp4073]

On the way home tonight my charge light came on bright and wouldnt go off. Tested the battery and has 12.2 charge. When testing the charging with engine running it still tests about the same. So I turned to the clymers manual and am a little confused about the testing they say to do. Its first test is between the diode board and the alternator. B+ terminal and D+/- terminal at the alternator. Instructions say to remove the connector plug (seems to mean the outer one as there are two) from the diode board then start the bike. When I remove this wire, the bike is dead, no power to starter, lights or anything. Am I missing something here or does that tell me something?




Not my pic, but the F tab on the right is where it says is the B+ terminal and the outer wire is what is supposed to be removed. I also tried removing the inner wire and then both wires to the same results. What am I missing here?

thanks in advance.

[Wirespokes]

The 74 is wired different than the ones that followed. You've got two wires at that terminal, all the rest have only one. That's why those instruction don't make sense.

The fact of the matter is your alternator isn't charging. And the first suspect is normally the rotor. In this case the brushes are obviously making contact and there is a flow through the rotor to ground. Normally the rotors fail open, but they can short circuit as well, and that's what I suspect in your case.

What you need to do is measure the resistance between the slip rings with a good ohm meter. insulate the brushes from the slip rings with something nonconductive, like a bit of cardboard. The rotor should measure 3 ohms - something in that range. If it's zero, that's the culprit!

[mfp4073]

Originally Posted by Wirespokes

The 74 is wired different than the ones that followed. You've got two wires at that terminal, all the rest have only one. That's why those instruction don't make sense.

The fact of the matter is your alternator isn't charging. And the first suspect is normally the rotor. In this case the brushes are obviously making contact and there is a flow through the rotor to ground. Normally the rotors fail open, but they can short circuit as well, and that's what I suspect in your case.

What you need to do is measure the resistance between the slip rings with a good ohm meter. insulate the brushes from the slip rings with something nonconductive, like a bit of cardboard. The rotor should measure 3 ohms - something in that range. If it's zero, that's the culprit!

First to respond always and with the right info out of the box. Let me see what if I can follow your directions and figure it out.

[mfp4073]

Originally Posted by mfp4073

First to respond always and with the right info out of the box. Let me see what if I can follow your directions and figure it out.

Ok, lets pretend I am kinda dumb here and dont know all of what you are trying to tell me to do! (its not much of a stretch to pretend).



This is not mine, but an online pic. I see the brush, and the slip ring is where the brush rubs on? And from there where I am I measuring to and from?

[mfp4073]

Ok, maybe I got this. Put cardboard between the rings and brushes (where the brushes contact) and measured from one ring to the other. That sound right? If so I got nothing there. Sound like what you were thinking? And if tested right, is it just a question of replacing? Prices are EXPENSIVE for new. Are they rebuild-able or am I looking at a used one?

[crazydrummerdude]

Yup. Had that (open rotor) happen on both my 1974 R90/6 and 1974 R75/6.

http://www.motoelekt.com/charging.htm for $90 rebuilt ones.

You'll need a special bolt to pop it off the shaft.

[mfp4073]

Originally Posted by crazydrummerdude

Yup. Had that (open rotor) happen on both my 1974 R90/6 and 1974 R75/6.

http://www.motoelekt.com/charging.htm for $90 rebuilt ones.

You'll need a special bolt to pop it off the shaft.

Two things, first think there is any chance of getting them to charge me a core charge and send it out right away? I wont have the time to pull and post it to them for a few days....every day I dont have the bike costs me big money in gas. 2, in reading the clymers, I am seeing the part about the "special bolt" being used as a way to pull the rotor out, but not really understanding how it works.


Edit, looks like the no core charge new units are $125. So that might be the way to go for me.

Are used ones a risk? As in a $65+ risk? I am seeing them on ebay for that price or less

[boxerboy81]

Motobins
Part No.71810A
UKP49.50

[ignatz72]

Motoelekt.com was out of them a few weeks ago but Eurouromotoelectrics.com has them Stateside also... Shipping might be quicker and cheaper than Motobins.

[craydds]

Originally Posted by mfp4073

I am seeing the part about the "special bolt" being used as a way to pull the rotor out, but not really understanding how it works.

Call Jeff Trapp at Northwoods, http://www.northwoodsairheads.com/Tools.html . He has the tool you MUST have, with instructions.

[bmweuro]

For testing and understanding the charging system everyone needs a copy of this book http://www.motoelekt.com/goodstuff.htm. If you need a new rotor the guy in Colorado that sells the hi output systems sells and Italian made rotor really cheap and the quality is very good as a had sold 1000's of them in the past trouble free.

[mfp4073]

Originally Posted by crazydrummerdude

Yup. Had that (open rotor) happen on both my 1974 R90/6 and 1974 R75/6.

http://www.motoelekt.com/charging.htm for $90 rebuilt ones.

You'll need a special bolt to pop it off the shaft.

He doesnt have any of the rebuilt ones in, he said he is having a harder and harder time getting them rebuilt because the guy he has doing them is older and having a lot of health issues. The new versions are out too, but expects them monday. Hopefully they come in and he can get them in the mail. :(

[Wirespokes]

One easy way of checking the rotor is to take an ohm reading through the brushes. Remove the wire from one of the brushes spade terminals and touch your ohm meter leads directly to them. You will, however, be getting a reading of the resistance of the brush/slip ring connections also, so keep that in mind. But is a quick way of finding out if you're in the ball park.

I think everyone who depends on their airhead should have a spare rotor on hand for times such as this. It's a whole lot less stressful, and usually cheaper watching for a deal, and no over-night shipping. I've gotten them for twenty or twenty five bucks before.

The rotor won't come off while the stator is in place. So that must come off first. It looks like a simple thing to unbolt the stator and yank it out of there, but there can be problems. First off, the steel of the stator can corrode to the aluminum of the case and won't want to come out. Trying to pry it out can possibly break something, so be careful! It may take a bit of penetrating oil and heat gun to remove it. Also, the stator is just sort of pressed into its aluminum housing and if it wiggles around much, can damage the wires attached to its face or their connections.

Then when installing the stator, be absolutely certain it is lined up with the case and seating properly. If it's not, and the screws are tightened enough, one of the screw tabs can shear off. Don't go there! Take it easy, tighten a little at a time, and if it's not going in evenly, don't expect it'll pop in with a little more force. No. Back it off, get it aligned properly and tighten the three screws each a little at a time. You definitely don't want one side all the way in and then tighten the next...

The rotor has threads in it and there are also threads in the crankshaft where it mounts. The rotor fits on a tapered shaft, and the normal rotor hold-down bolt has threads from the end to half way up its length. Where there are no threads, the bolt has been thinned down to fit inside the threads in the rotor. So when the bolt is tightened, it draws the rotor onto the crankshaft.

The rotor removing tool is just the opposite - it has threads from the head to half way, and then it's skinny to the end. When the bolt is threaded into the rotor, the skinny end pushes on the end of the blind hole in the crank (with the threads) and pushes the rotor off the taper.

These rotors often jump when they break free and fall to the ground. You don't want this to happen! If it hits on the slip ring, it'll mash it and that's not a good thing! Even though it's broken, try to keep from damaging it. Place a box with rags under it, have some way to soften its fall or catch it. I've held onto these things fully expecting I'd be able to hang onto them, and still have them jump off and fall. They're pretty heavy for their size!

[mfp4073]

To Wire, et all,

Thanks for your help. FINALLY got a new rotor in and bike is running again. Need to do a once over for valve set, carb sync, and timing/points set and will get into that sat.

I cant imagine fixing this bike without this boards help. Hopefully down the road I can pay it back to those I meet over the years in person and online....its the only real way i can ever pay yall back!!!!


A few final questions. Do rotors go out a bit at a time...meaning do they get LESS efficient and then finally stop working or are they one day they work and next day they fail? Next, when I got my new brushes in, they didnt have any insulation on the leads. My old brushes did, so I put some shrink wrap on them because it looked like they needed to be insulation from the housing. Thoughts?

[_cy_]

Originally Posted by mfp4073

To Wire, et all,

Thanks for your help. FINALLY got a new rotor in and bike is running again. Need to do a once over for valve set, carb sync, and timing/points set and will get into that sat.

I cant imagine fixing this bike without this boards help. Hopefully down the road I can pay it back to those I meet over the years in person and online....its the only real way i can ever pay yall back!!!!


A few final questions. Do rotors go out a bit at a time...meaning do they get LESS efficient and then finally stop working or are they one day they work and next day they fail? Next, when I got my new brushes in, they didnt have any insulation on the leads. My old brushes did, so I put some shrink wrap on them because it looked like they needed to be insulation from the housing. Thoughts?

wirespokes was on the money for prior instructions!

rotors can go out all sorts of ways ... best is total failure so isolating problem is easier. intermittent problems are always the worst. for instance rotors can work fine when being tested, then fail after heating up.

generally rotors has highest failure rates. spare diode boards are worth having around too. voltage regulators are easily tested by full fielding. a spare charging indicator bulb is good to have around too. bulb is part of charging circuit.

after bike is running .. if your system is charging, voltage will be 13.4 to 14.2v with engine rev'd into mid range. when running if your volts reads slightly lower than battery resting voltage. then it's not charging.

from resting overnight ... assuming you have a lead acid battery... if your battery reads 12.85v .. then your battery has a full charge.

your bike runs off your battery, then alternator charges battery back up. sounds basic and it is... but some folks don't grasp why after putting a new fully charged battery... bike runs perfect for a short while then goes dead again. battery gets blamed, when charging system is at fault, not battery.