TAMD41A strange starter issue??

[petrolhead63]

we have twice experienced a bizaar starting issue with our port engine, both times after dropping anchor and restarting after an hour or two.
The port engine refuses to turn over,,,starter motor whirs a bit. Then start the starboard engine and the port one goes.
Things checked.
Three batteries seem good...one starter battery, two domestic which also start engine via a diode set up protecting the starter battery from domestic use. I have checked all cells with hydrometer after 1st time it happened, all good. Also a load test and all seem fine. Both engines start well from cold having been left a week no charger on and also when we moored up after the day out they stop and start fine.
Checked issue from both helm stations to rule out an upper helm problem on the key etc.... port did not start off either station. Both engines start off same battery/s.
To sum up, port engine fails to spin over twice, both times after dropping anchor and sitting an hour or two.
All other times it starts just fine...so far!
Any ideas gratefully received. All I can think of is a poor starter motor when sat hot which given the extra boost of voltage with the starboard engine started then works?

 

[gordmac]

Swap the starters over and see if the problem follows?

 

[petrolhead63]

well yes, I had thought I may do that, did it with other things in the past to pin point problems! it is most strange though.

 

[DavidJ]

Of course the reason the port engine will start successfully after the starboard engine starts is because of the extra voltage that is now available. Cracking torque brings the voltage way down maybe as low as 7 volts. (from 12V) The starboard alternator will be helping to retain a high voltage while port cranking.
Do you have a link switch/button to join all batteries temporarily together?
Be interesting to compare on the volt meters the voltage drop port v starboard while cranking.
I’m just trying to do a bit of diagnostics before the laborious job of swapping motors over.
My hypothesis at the moment is weak port side battery despite the tests you have done
Maybe swap batteries over?????

 

[Mr Googler]

I’d start with checking and cleaning battery cables.

 

[petrolhead63]

Of course the reason the port engine will start successfully after the starboard engine starts is because of the extra voltage that is now available. Cracking torque brings the voltage way down maybe as low as 7 volts. (from 12V) The starboard alternator will be helping to retain a high voltage while port cranking.
Do you have a link switch/button to join all batteries temporarily together?
Be interesting to compare on the volt meters the voltage drop port v starboard while cranking.
I’m just trying to do a bit of diagnostics before the laborious job of swapping motors over.
My hypothesis at the moment is weak port side battery despite the tests you have done
Maybe swap batteries over?????

the boat is a 1989 Storebro. It does not have a link switch.....the two domestic batteries are isolated from drawing off the starter battery by a big diode set up.
What mystifies me is why does the starboard engine spin and start just fine but the port does not without the extra grunt from the other engine running. Both engines are cabled and start off the same batteries.
It has only done it twice...left warm at anchor, it starts from cold having had no charger left running after a week or more.
Cabling battery wend is all good, I took them all off. cleaned etc when I tested the 3 batteries with hydrometer after a week OFF charge and also put a load test on them.

 

[DavidJ]

Hypothesis 2
Starter motor brushes worn to just an extent that poor contact is compromising performance.
I think I’d get it off and take it to a back street repairer. Don’t mess with swap-over.

 

[petrolhead63]

Hypothesis 2
Starter motor brushes worn to just an extent that poor contact is compromising performance.
I think I’d get it off and take it to a back street repairer. Don’t mess with swap-over.

yes, thanks. I too was feeling starter tired or even just needing a good clean inside! 35 year old marine environment. Maybe when warm expansion of something makes it worse. I have concerns about batteries even though they test ok....I know how long ago I fitted them haha. However, the Starboard engine has not had the symptom.

 

[Mr Googler]

Have you got longer battery cable runs to the port engine

 

[petrolhead63]

Have you got longer battery cable runs to the port engine

Hi, I thought of that and yes you are correct.....not much but will be seeing as batteries are in port stern, switches/isolators are further forward starboard and then the cable must go back over to port starter which is also on port side of engine.
As an aside...I wonder if the diode arrangement is working? perhaps I only have one battery in use starting?

 

[DavidJ]

As an aside...I wonder if the diode arrangement is working? perhaps I only have one battery in use starting?

Good point
The diode is to stop your fully charged ‘cranking’ battery draining into your auxiliary battery when it’s a bit low. My guess is that you only have one cranking battery for both engines and that your diode is probably working OK

 

[Momac]

I had an intermittent starting issue which proved to be a corroded electrical connection to a starter relay in the black box on top of the engine.

 

[Mr Googler]

It certainly sounds like resistance somewhere as once the other is running…you have a boost of amps to overcome the issue.

Battery cable can degrade over time for sure. I bought a boat with poor cranking and found the cable runs were crazy long to put the isolators in a convenient place. OEM I might add.

I replaced with solenoid isolators and literally 1/4 the cable runs and used thicker cabling. Span over like mad after that!

 

[petrolhead63]

thanks people, I will investigate and also look at the cable diagram I have.....Lucky being a storebro we have it all! a full book with every cable, its size, its length, its fused rating! I will look at how the diode bit works on the diagram.

 

[petrolhead63]

my understanding of the diodes is that they do indeed protect the starter battery from doing anything but current to starter motors. This means the domestic pair can supply the starters, meaning in effect there are three batteries can start the engines but one is protected from domestic drain?? is that correct then?

 

[DavidJ]

I pulled this off Google. I’m thinking your system is something like this. The writing is blurred on the middle block but it looks like a diode pack. This implies only one battery pack for starting both engines.

 

[Mr Googler]

my understanding of the diodes is that they do indeed protect the starter battery from doing anything but current to starter motors. This means the domestic pair can supply the starters, meaning in effect there are three batteries can start the engines but one is protected from domestic drain?? is that correct then?

In a word….no

The Diode only allows current to flow one way. From the alternator to the battery or batteries so one alternator can charge multiple batteries . When starting…the diode would stop current being drawn from the domestic batteries in the same way it stops current being drawn from the starter battery to domestic systems

Sometimes there is a joining switch to tie all batteries together for emergency starting which by passes the diode in effect

 

[DavidJ]

The port engine refuses to turn over,,,starter motor whirs a bit.

Can you explain this a bit more. Is it turning the engine or just spinning without engaging

 

[DavidJ]

Assuming it’s a pre-engaged starter motor ie the solenoid piggy backs on the motor. I don’t understand the whirl you experience. The solenoid will only activate the motor when the pinion is fully in mesh with the flywheel so it will either turn the engine or stop dead
Hmmmmm?