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Mine are 27 years old, do they deteriorate much, and would new oem cables make a difference?
I know there are those super whiz-bang cables available from E-Bay, but new cables from Motobins only cost 1/2 as much. Can there be that much difference?
(I know they can be made, but I imagine finding the correct terminals would be a pain.)

The biggest problem I have found is corrosion on the positive cable, usually at the battery end, up underneath the insulation.
Pull that back a ways and see what you have. If it is clean, I'd say keep using it. Look at the starter end if you are really worried.

Are you experiencing sluggish starting? Or is it just too cold to ride?

justoneoftheguys wrote:Are you experiencing sluggish starting? Or is it just too cold to ride?

It is getting cold, but I still think it should spin more quickly.
I will check for that corrosion tomorrow.

Surely it goes without saying that you should clean the contacts with emery cloth and apply some dielectric grease whenever the opportunity arises.

The corrosion will be that nasty white powder.

Do a voltage drop test. You should only drop about .2 of a volt between the battery and starter.

+1 on the positive terminal tending to fail just under the insulation at the battery end. I've seen this a couple of times.

justoneoftheguys wrote:Surely it goes without saying that you should clean the contacts with emery cloth and apply some dielectric grease whenever the opportunity arises.

Actually I am quite obsessive about preventative maintenance on all electrical terminals.

Garnet wrote:Do a voltage drop test. You should only drop about .2 of a volt between the battery and starter.

Interesting... Uhm, could I overstate the obvious with regard to starters and the only way I know to isolate them in testing all too well, is to see how much current it draws under load. Yes, yes, Ohm's Law you say will tell us, but voltage really? Could work, but I've never seen it used in practice because it is not very precise; easier to read a 20 Amp difference than a 0.2 volt one and much more reliable IMHO...

The battery condition, cables, solenoid, etc. etc. are all in question here. Connect in series with either cable, be prepared for a decent draw. Don't recall what these tiny Bosch BMW starters draw now, but suffice it to say, common sense should be your guide. I can get you a figure if no one else has it readily available.

As for starters, your ear-drums should tell you all about the more common "old and used" starter failure mode, that is the sintered bearings on either end of the armature have worn to the point of dragging it (the armature) against the field windings' steel. Brushes go bad, but usually (naturally, sadly not always...) a more noticeable, catastrophic failure ---> no starter when they quit, or they are so worn, they jump on the commutator. ---> Look for lots of sparks through the holes in the back for this... Solenoid contact issues as well are far more common to exhibit something more than a "slow-crank" condition, but again not unheard of at all by any means.

Finally, the least common failure is the business end(s) themselves; armature or windings' have a partial short. The lacquer on old starter's windings can eventually break down and then you need either a re-wind, or replacement of the failed part, armature, or field...

Here are the steps I use.

1) With charged battery, crank over engine, use your ears - if one pays attention, you can usually hear a dragging armature.

2) Check and test battery - make sure it is not "sulfided" too badly and accepts a full charge; batteries can lose 1% charge in a week when unused.

3) (This really should be #1, but... we are taking your word as far as maintaining the electrical system) Inspect cables for visible wear and abuse. If either end is in question, use an Ohmmeter to check the resistance of the cable by measuring from both holes. Be certain the connections are clean and ALWAYS coat with dielectric grease (or any grease...) the connections upon re-assembly. If you are following this flow chart for a reason (IE something is not right, like in your case, see #4 before reassembling, leave either cable disconnected from the battery...)

4) Place meter that will handle the current draw of said starter in series with either cable and crank the engine. Observe how much current is drawn and compare to known reasonable figure for your model starter. They make all manner of cheap meters just for this purpose, one can be had for a low investment --> automotive is all you'll likely find and matters little as the difference between good and bad is generally a big stretch. Personally, for a motorcycle, I'd just use any old meter that can take it, like one of my antique Simpson's. BTW, they now make cheap clamp on meters (DMM's) that would not require one to put your DMM in series with the circuit; meaning you don't have to disconnect anything. (DC, yes ---> now in DC form; I've never had one!!!)

5) You now should know with little doubt where to go from here, battery, cables, or starter/solenoid issue (assuming it cranks at all, but yours does... )

6) If it is not 1-3, than it is in the starter. Since these have the solenoid built in, fixing the issue will be a matter of removal and working the standard rational flow-chart for any starter. If you want sources for how to service them and BMW sources are not readily available, look for how to rebuild any old DELCO(-REMY) starter, 6 or 12 volt even; it was their (GM division's) design...

Good luck. Feel free to PM me if you end up finding your issue(s) to be starter related and would like guidance. Old starter and generator shops, for the most part are all gone now, so getting someone to run a growler on the field and armature "gratis" as one could in the days of old may be difficult. I always run the commutator through a lathe as well when rebuilding them; it makes certain one does not wear out the brush-holders, particularly on starters with pivoting style tensioners, can't recall what's in these off hand... I have a special little lathe for this easily twice my age... Then a touch up with Crocus (sic?) cloth.

As Duane is fond of saying, Ask me how I know this? OK, I learned the hard way and made all of the mistakes once, many, many starters ago... Post if you want the nominal current and cannot find it listed in all of the usual places...

Regards,
Douglas

I've just added two extra earth cables to Brunhilde - gearbox to frame and frame to diode board - as recommended by GSPD* and others. The starter spins significantly faster, the alternator light goes out at lower revs, the horn is actually audible (instead of going 'beee erp' it goes 'BEEEEP' - first time I heard it I nearly fell off the bike). Everything is happier; even my cat is purring more often. The cable I used is not huge, it's rated at 20A. I'll be replacing the battery to starter cable next.

* Where the bloody hell is GSPD?

We found failing battery cables within 3 years of new. The OEM cables are not of quality and BMW really should have done better.

When we found a starter issue, our first action was to reach down on each side and grab a battery cable. Try to rotate it on the battery post. If it rotates, then the action of rotation is often enough to correct to some degree the high resistance. That is no fix, just a fast way to get the bike on the road, or for our shop purposes, to test it. If things improve, then we know that some error exists. If there is no change, then it doesn't mean that all is well, it just means that this quick and dirty test didn't show it.

As far as the cables are concerned, here is what we found commonly. The crimping of the terminal on the wire was done without any grease, or sealing. The result is that moisture could wick up the wire just past the terminal and corrode the copper. If the wire were soaked in grease and then sealed up from moisture laden air, the wire up under the first inch or so would not corrode.

The usual symptom is that the wire is flexible to some extent. If it is less flexible in the last inch just next to the terminal, wala, you have found it. One more symptom usually exists too. That is that the corrosion expands the contents under the insulation. The insulation can be seen to be slightly swolen, but not a lot. So if the wire is stiffer near the terminal, you have a problem. Strip it down, warm it up, soak it in grease so that it wicks up into the individual strands of copper and crimp on another terminal. Use shrink to seal it up.

As an inspector of just this type of copper cable crimping, the technician must also clean off the terminal. Depending upon the specific metal plating on the terminal, it can slightly discolor. That is oxidation, clean it off so that it is bright and shiny. The battery terminal must also be cleaned off well. Coat both with grease and connect.

Bad connections can be the bane of the mechanic. Just a bit of prevention can save so much headache later.

I won't go into the various ways of testing, but all require some knowledge of Ohm's law to make use of them. It is easy to make voltage measurements and have them mean nothing at all. That is a whole nother conversation.

I do some work in cellular telephone site inspections. Commonly we have a ton of batteries for storage. The cables are as thick as your finger and carry hundreds of amps of current. Our tyypical battery string is capable of 10 times the capacity of a large electric welder. That can be really exciting when someone flashes the terminals by carelessness.

Any error in crimping and connecting can be costly and hard to find. Using strict standards on your motorcycle will pay in greatly increased reliability of the wiring. It isn't difficult, but at first seems obsessive/compulsive.

Please indulge me for a war story. Our rubber insulated cables are so heavy that a 50 foot piece laid out on a linoleum floor will stick to the floor so well that it is impossible to pull it along the floor. However, a simple trick will allow it. Just whip it so that a loop runs down the length of the wire, all the while pulling on it. The "whip" unsticks it from the floor and allows it to be pulled. Just don't stop until you get where you are going with the cable.

It is almost impossible for one person to run this sticky cable through the overhead racks that we call "cable tray". The dirty trick is before even taking the cable into the shelter, lay it in the dirt. Toss dirt/dust on the outside rubber insulation and shake off any extra. With it unrolled, clean off the excess with a rag. However, some dust stays on and is not noticeable, but allows it to glide on a smooth surface. Now the cable will be much easier to thread up, over, around and through the cable trays. Now that I am not doing the installing of the cable and now doing the inspections, I can tell which installers know how to handle the cables. We aren't supposed to pass it, but it actually gives a better job. The dust also allows the cables to not get so kinked up due to a twist. shhh, don't tell.