Starter motor 'dead spot'?

[rudolph_hart]

Can starter motors - or indeed any electric motors - develop a dead spot?

My Yanmar 3GM30F (600hrs only) usually starts without problem every time, but on a couple of occasions recently the solenoid has engaged but not turned the engine (hot or cold). Usually, a jump from one of the domestics gets it going.

Engine battery (Vetus sealed 75Ah) reads 12.6v and shows the 'Green Eye' of a healthy full charge, several days after last charge, so I'm happy it's not the problem. Also, I'm reasonably confident that it's not a bad terminal post or earth connection, as I've checked them all.

Can a motor's windings degrade/break to give a dead spot at a specific point of its rotation, which would not be noticeable when it's running (because it's momentum carries it past the spot), but if it is stopped at that point, starting is prevented by no (or insuffiecient) power? If so is it common?

 

[Georgio]

this is a common Yanmar problem, I have the same on a 2GM. do a search for Yarmar starting problems for plenty to read.

One solution seems to be to run heavier wiring to the starter solinoid.

 

[charles_reed]

Clean and re-make the battery terminal clamps. It's usually the -ve being dirty that causes this problem.

 

[halcyon]

Can starter motors - or indeed any electric motors - develop a dead spot?

My Yanmar 3GM30F (600hrs only) usually starts without problem every time, but on a couple of occasions recently the solenoid has engaged but not turned the engine (hot or cold). Usually, a jump from one of the domestics gets it going.

Engine battery (Vetus sealed 75Ah) reads 12.6v and shows the 'Green Eye' of a healthy full charge, several days after last charge, so I'm happy it's not the problem. Also, I'm reasonably confident that it's not a bad terminal post or earth connection, as I've checked them all.

Can a motor's windings degrade/break to give a dead spot at a specific point of its rotation, which would not be noticeable when it's running (because it's momentum carries it past the spot), but if it is stopped at that point, starting is prevented by no (or insuffiecient) power? If so is it common?

Depending on motor type you can loose one segment on the com giving a dead spot, also the contacts burn in the solenoid, giving intermittent contact.

Brian

 

[prv]

I had the same on KS's 2GM20. I went through all the connections between battery and starter (including some unexpected ones within the engine wiring loom) and cleaned and tightened them. Worked fine thereafter.

Pete

 

[Plevier]

Can a motor's windings degrade/break to give a dead spot at a specific point of its rotation, which would not be noticeable when it's running (because it's momentum carries it past the spot), but if it is stopped at that point, starting is prevented by no (or insuffiecient) power?

Yes, for a motor with a wound rotor with a commutator.

 

[TQA]

Yes, for a motor with a wound rotor with a commutator.

But if you have a true commutator related dead spot, boosting the voltage will make no difference. The only way to get it to work again is to physically turn the armature so live spots on the commutator are engaged with the brushes. This is pretty rare. As others have said a dirty connection is much more likely.

 

[rudolph_hart]

Thanks everyone for the replies. I will go through all the connections in the starter wiring loom this weekend.

 

[ksutton]

this is a common Yanmar problem, I have the same on a 2GM. do a search for Yarmar starting problems for plenty to read.

One solution seems to be to run heavier wiring to the starter solinoid.

+ 1 Absolutely right diagnosis for sure, you can also instal a 12 volt relay near to the starter motor solenoid. Happened with my 3GM30F and also at 600 hours, I bet its worse when hot, remote relay solved the problem.

 

[ksutton]

Thanks everyone for the replies. I will go through all the connections in the starter wiring loom this weekend.

You may well not detect anything wrong, as the wiring capacity is probably slightly underrated when hot, its a well know fault.

 

[jc1]

I have a Yanmar 4JH4 with about 1000 hours. I had a problem that sounds identical. I will share my story which you may find helpful.

For many months, in Greece, I had a most frustrating problem with a starter motor that worked increasingly intermittently. Initially I didn't think much of it because it would always start after a few attempts. We even used to joke that it would only work for my wife! I checked everything: batteries, cabling, connections, voltage drop, etc. - except for the started motor because it seemed so new and I imagined it was complicated and 'off limits' for me. The uncertainty started to really worry the family and the expectation about whether the starter was going to have a good day or a bad day became a real concern.

I could hear and feel the solenoid engaging. I too started to think of 'dead spots'. Amongst many things , I tried to turn over the engine with a spanner on the main shaft to 'nudge' it like I recall doing on old land rovers. This even seemed to work once.

For a while it seemed I could always get it going by 'jumping' the house bank. So, even though the battery voltage was fine, I thought it was a battery problem. But a week after fitting a new battery the problem persisted. I had to face the fact that I had made a wrong diagnosis.

When it failed in Rethymnon, Crete on the eve of a national holiday I thought I was lucky to get an engineer to turn up within an hour. He seemed confident and jumped to the conclusion that it was the starter motor and said it had to come off. He rushed off with the starter motor to his workshop. He came back saying he had tested it and found everything was fine, leaving me not sure what to think. When he refitted it, of course, it worked perfectly and we sailed off thinking we were OK.

But I remained secretly concerned because I knew we had not really found an explanation. Sure enough a few weeks later it happened again in the middle of nowhere. In desperation I decided to check for myself the only thing that I had not personally checked and so, after studying Nigel Calder, summoned the courage to remove and strip the starter motor myself. It was quickly obvious from looking at the pristine paint on the nuts that the motor had never been stripped by the 'engineer' in Rethymnon. He had charged his fee for nothing! When I took it apart I could immediately see that all was not well. I removed masses of what I can only describe as black cotton wool (see photo), and saw evidence of serious physical damage to the bits that hold the magnets in place and to the wax like stuff around the windings. I stripped and cleaned everything, reassembled it and refitted it. As you can imagine the whole crew was amazed that it worked perfectly even in this damaged state! It kept going fine until I could get a new motor and the engine has been great ever since. Confidence in engine restored!

I would be interested to know why the starter motor failed in this way. My only theory is that, we used to have one of those large 'cork float' type key rings for the engine key. I fear the cork key ring might have once jammed in the steering wheel and yanked the ignition key, against the ignition spring, into the 'on' position for some seconds before it was noticed. I imagine that if the starter was engaged with a running engine this might be the result. If so, it was an expensive mistake. I have now got rid of this key ring and now tie the key with a short line to a SS eye a few inches from the panel in the cockpit.

Lessons for me were numerous: 1. On numerous occasions I made the mistake of thinking that if the starter worked, I had solved the problem. 2. I have always been nervous about 'engineers' that I am never likely to see again as we move on to new grounds and who come unrecommended. But we needed help and he seemed a good guy and was confident, but... 3. The engineer's positive verdict, through me off the scent and I wasted more time checking everything else. 4. I now realise that there was no need to be afraid of stripping the starter motor. All it took were 2 nuts!. If I had done it myself the first time, I would have found the problem much sooner. Knowing what I know now I should have asked the engineer to strip it in front of me on the boat so I could see for myself. 4. The engineer was never as careful as me. He unnecessarily removed raw water cooling pipes to get at the starter, spraying salt water everywhere. I didn't. 5. I got my replacement motor from www.startermotor-alternator.co.uk/ It was an identical Chinese copy and was about a quarter of the price of the Yanmar Hitachi part. At that price I will keep a spare and, of course, now I know how to change it in 15 minutes!

Good luck!