3YM30 starter motor failed to disengage

[bdh198]

We had a bit of an issue with the starter motor of our Yanmar 3YM30 at the weekend. The engine started several times without incident and probably ran for a couple of hours in total throughout the day. However, on the last start of the day the starter motor failed to disengage from the engine. We didn’t notice for about six or seven minutes until the cabin filled with smoke - the over heated starter motor had fried some wires. The starter motor is now jammed and needs to be replaced.

We have been trying to establish the cause of the starter motor failing to disengage and can’t see anything obvious having taken it off, although we are far from being engine experts! We are looking to get it refurbished as a backup and that might help to establish what happened. However, one suggestion has been whether the key has got stuck in the ignition and kept the starter motor engaged. Is this something that could have happened (is it even possible on this engine?), and if so is there any quick check we can make when the new starter motor is installed to see if this was the cause and if so to stop it happening again?

Any advice and suggestions gratefully received!

 

[RichardS]

There have been several reports of this over the years on here, not just Yanmars. In my experience, it's an extremely rare occurrence with car engines but I wonder whether boats are more susceptible because the ignition switch is outdoors and therefore more liable to corrosion and sticking.

I'd be surprised if it's the solenoid as that would presumably also affect car engines, and once the power is cut-off I would have thought that the cog is bound to disengage as it's on a strong spring.

I would squirt WD40 into the starter switch and make sure that everything is turning very freely and then keep it regularly lubricated and keep a close eye on it.

Richard

 

[andyc352]

It may be of interest that UK registered light aircraft were fitted with a warning light to indicate if the starter motor was still engaged following engine start. I think this was introduced following an engine fire. It was a UK only CAA requirement in the distant past. Not sure if it still is and I’m not suggesting you go to the trouble of getting a warning light fitted, but it is a possibility if you’re really concerned about a recurrence.

 

[lw395]

If the key was stuck, I'd expect the motor to disengage at least partially as it fired and revved faster than the motor is trying to drive it?
You'd notice some grinding noise
I'd suspect the solenoid or pinion mechanism was stuck.
However it would be prudent to check the switch, maybe fit that warning light temporarily?

 

[matt1]

This,or a similar issue, appears to be widely reported on another forum I’m on. In that case all pretty new Yanmars. One theory on that forum is the start switch gets engaged by people’s legs leaning against the switch. Not something I subscribe to. My boat is still under warranty and when I asked about it a mod was applied - essentially a bigger connector terminal on the starter motor (as I understand it). Not sure if that is helpful or not. Other issues reported on the forum seem to suggest wiring looms may be an issue