What's the problem with my starter?

T

tomcolitt

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This is weird. For years, I've noticed that my engine seemed to crank over faster at times and not so fast at others. I figured, maybe a weak ground, but it always worked in the end. During the past year, I had several occasions where the engine barely turned over despite a healthy battery. Later on, it might turn over fine as if nothing ever happened. Now, I'm at the point where the starter almost doesn't budge the engine most of the time. I had the transmission out (for another reason) and the starter turned the engine easily every time. Everything back together and the same old problem. While the starter labors, I sometimes see sparks coming up from some portion of the starter wiring harness, but I'm not sure if the sparks are the cause or the result of the high current flowing when the starter is barely moving. I can't see anywhere where the wiring is being grounded out against the engine or body. After enough tried, I've even gotten it to start the engine quite normally. I don't think that anything is binding on the engine, flywheel, clutch, etc. because how could one explain that it works fine some of the time, so my question is: Has anybody ever heard of a starter motor that has "flat" spots, or is starting to lose it's power (windings?) or maybe the brushes are not making good contact to the anchor and therefore only get full power when the starter is in just the right position? In that case, I guess the sparks are just a side effect, arcing to ground from a weak spot in the insulation?...I just thought I'd ask before I go to the trouble of swapping starters and finding out the problem is still there....

Thanks, Tom
 
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Starter Woes and a bad spot

The answer to your questions is yes to all of them.

I would first meter all the resistance of the cables from the battery to starter, switch, etc for a higher condition than normal. ( They can build up resistance internal to the cable) Also the starter case to solenoid connections. If that proves to be a non issue, it's internal to the starter.

Bearings or bushes, bad or dirty segments, bad partial windings, brushes, short or sticking, etc. can cause the symtoms you describe.
 
I've had two sort of related experiences:

I had to run an extra ground cable from the battery terminal to the block near the starter on one of my coupes. Tried this after I swapped a known good starter and it had exactly the same symptoms as the original. At a minimum, make sure you have the ground strap that goes from the firewall to the engine. Hmm, this doesn't show up in the parts books?

Not on a coupe, but my Dodge van starter suddenly seemed to be very sensitive to the position of the auto trans shifter before it would start. I tried several things, but when I finally replaced the starter I had no more problems. (I was very reluctant to replace the the original starter as it seemed to be working normally when it would start.)
 
Slow starter

I had similar symptoms on my 74 3.0 csi. It turned out that the positive battery cable (that also connects to the starter) was causing it. From the outside, the cable looked fine. I replaced the cable with a new one from BMW and the problem was solved.
--John
 
Ok. I'm an idiot. I was playing around with different intake manifolds on my Motronic 1.0 (d-jet log and later 1.3 manifold) and I didn't have the ground strap to the engine because there was no place to put it. I still don't get why it worked sometimes.

Anyway, thanks to and for all your posts, I finally decided to check the wire resistance and then connect the ground strap.

It looks like the Bosch starter that originally came on my 1984 735i engine is still going strong despite all the spark and voltage spikes I tortured it with... :)

Now, on to tinkering some more to get the thing to run better with my re-worked b35 head...

Thanks, Tom
 
there is another possible cause

my first 1970 2002a had a bad bushing in the starter motor. It acted like it had a weak battery and would make a grinding noise sometimes. I replaced the bushing with a nylon unit from a 320i, but had to mod slightly to fit.
 
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