3YM20 starter & relay ease of replacement

[ZoeImogen]

We had our starter motor jam in the engaged position on our Yanmar 3YM20. It wasn't run for long and only at relatively low RPM (moving the boat into a new berth) but from the smoke and smell, the starter motor is toast.

I'd prefer to get a proper mechanic to look at this but the boat is in Quiberon and possibly due to language barriers, we're having some difficulty arranging this. If I DIY it, is it as simple as it looks to do with the engine still in the boat or is there something else I should be looking at? Would also be replacing the seperate relay as we suspect that was the cause of the issue.

We will also look into fitting some sort of "starter motor engaged" warning because "boat possibly on fire" was not a happy fun experience, and from what I can tell this is a common 3YM20 problem.

Thanks.

 

[michael_w]

I changed my 3gm starter motor the other day. Easy peasy job, Disconnect the electrics, undo two 13mm (IRRC) bolts and slide out, Replaced with a bog standard car starter motor from the local auto electricians.

Sounds like the Bendix on yours jammed, fingers crossed the ring gear isn't chewed up too much.

 

[jwilson]

GM and YM engines very different. At least on my 3YM30, which I think is externally physically the same as the 3YM20, the starter motor on my 3YM is in a really awkward place, under the aft end, port side, tight against a bulkhead. Mine has been changed at least 4 times in about 6,000 hours running. I have never attempted it myself: the last time it was done by a non-Yanmar engineer he ended up phoning the Yanmar engineer to ask how the **** to get at it! The answer was to remove starter motor, alternator, belts, belt covers and some heat exchanger water pipes etc. had to be ddisconnected. And to be younger and fitter than me.

Your installation may be different - it could be that you can get at it very easily.

A "starter motor engaged" warning would be nice! You are right that this is not that uncommon on these otherwise mostly excellent engines.

 

[Desmo]

I had the same stuck engaged starter on my 3ym20 as I was leaving a fueling pontoon. Just as I started to notice a high pitched whining sound the smoke appeared. Fortunately my berth was just across the river and I made in ok, by which time the smoke had ceased.
The motor was burnt out but the solenoid on top was ok. Interestingly it had only been replaced by previous owner 6 months earlier (inc relay, loom and started switch) by a boatyard at the end of the hamble. They told me it was nothing to do with them, even though they supplied and fitted all parts! Needless to say we fell out over this. The motor went back to the supplier and they wouldn't entertain a replacement. I ended up sourcing a pattern part (yanmar wanted £550) for £100 and fitted it myself. Easy job if you have access. 19mm bolts i think. Needed a long extension to get back there. Apparently these are common failures so DIYing this would be good for future failures!

 

[ZoeImogen]

No bendix on the 3YM20, it's a solenoid to engage the gear so ring gear should be OK - damage will have been the starter motor overspeed. (Why don't they put a clutch on these?) Fortunately the port side of the engine is accessible via a hatch in the heads on the Sun Odyssey 30i, worst case I might have to remove the pump on the toilet to get a bit more room.

We had the same high pitched noise, that's what initially alerting me to go and check the engine. (And discover the smoke)

Thanks for all the feedback, leaning a bit moretowards a DIY replacement now.

 

[petibonvm]

I had 2 starter problems on my 3YM30. I think the key switch was stuck. A Spanish mechanic told me that the problem was common and that he added a button switch to start. + a buzzer on the starter.

 

[trapper guy]

in my experience, changing a tarter unit is easy as jobs come, just take precautions to cut the kill switches before starting work, and also take care not to short any of the positive cables to the engine body with the tools anywhere, just in case the kill switches dont isolate like they should

 

[ZoeImogen]

Update on this for anyone who comes across it later: Starter motor successfully changed with about two hours work, including the separate relay.

A good chunk of that time was driving over to the local hardware shop to get a 19mm socket and two 250mm extension bars to get the old one off - the one on the inboard side of the motor is only accessible via the front of the engine, hence needing the extension bars!

Warning Light/Buzzer system to follow...

 

[Boater Sam]

A starter motor that stays engaged after the engine starts will be instantly ruined due to the incredible speed that the armature will reach. The centrifugal force alone will spin the windings out until it touches the field poles, instant burn out.
There can only be 2 reasons for this happening. Either a rusty stuck/faulty solenoid or a defective key switch.

 

[ZoeImogen]

The insides of the starter motor when we stripped it (not with even the slightest hope of repair, just out of curiosity) were quite ruinied, yes.

I can't figure out any way of installing a warning system for the starter-mounted solenoid being jammed, other than the obvious audible and olfactory warning which is somewhat later than ideal. I'm not sure if the second post on the starter motor itself (Which seems to spin the starter when it has power applied to it) will always have voltage if the solenoid is engaged, even if the solenoid isn't powered. Unfortunately the old motor was too far gone to experiment on. Plus it stank of burnt copper and flux so we were keen to be rid of it quickly.