Yanmar 2GM20F stalling at idle after prop loss?

[pickpaul]

Hi,

I'm wondering if anyone has any thoughts on my recent experience that may be helpful.

After a 3 hour downwind sail with genoa only, I furled it, started the engine and settled in for the ride back straight into wind and against current.

After about 15 mins the engine revs climbed rapidly and noisily to max and I lost all power. After checking that the prop shaft was spinning at the stuffing box, I came to the conclusion that I had lost my prob. It seems probable as the installation by the previous owners left no room for the slim 1" zinc and so I had to cut it down to half it's size and I live in a hot marina. A diver recently told me there was shaft erosion where the zink was but it didn't look structurally weak. I guess he was wrong. So I tacked back and made it back to my slip safely.

Here is the mystery. The engine now dies at idle. It seemed to happen at the same time (I don't remember having the problem before) as the prop falling off (assumed until put on the hard in spring) but I can't fathom a connection. Two separate problems?

Anything spring to mind?

Thanks, Paul.

P.S. I guess it's engineless sailing for me for now, good experience I guess. Docked like a boss under full main in this incident :-D

[a64pilot]

Should have hurt nothing, your shaft got eaten through? I have heard of props being eaten, but not shafts.
Anyway engine is governed so it can't over rev. Does it die in neutral too or just in gear?

[fstbttms]

Jeezus, have someone dive the boat to find out what's going on.

[pickpaul]

The revs just went to the governor speed when the load went away is what it sounded like to me.

I just checked it again tonight and it wasn't stalling at idle until the very last time which was in neutral. I dropped to idle quickly and it just stopped.

The diver was just down there a month or so ago, said the prob was fine but shaft was corroded ahead of it where the zinc used to be. I don't think a diver could repair it, it's being put on the hard in 2 months, it can wait. Just curious if dying at idle when closing throttle quickly is just a coincidence. What normally causes that?

[lockie]

My money is on a very small air leak in the fuel system. Is your fuel tank outlet above or below the lift pump on the starboard side of the engine block?


Cheers, Graeme

[Jim Cate]

The revs just went to the governor speed when the load went away is what it sounded like to me.

Not an expert dieseler, but this sounds a bit strange to me. When you removed the load, the revs should have continued to be governed at the same speed... that's what a governor does. So, perhaps there is a fault in the governor's functioning and when you drop the throttle back to idle it is overdoing the drop (so to speak) and it dies.

No idea if this is related to your putative prop loss. I'd sure be looking for a friend with a go-pro on a stick and having a look at what's down there... if anything!

Jim

[seasick]

I recommend putting your boat in gear at the dock and look to see if you're pushing water out the back.

When you say "I lost all power" do you mean that you lost forward thrust? You may have sheared off your shaft key as well your transmission may be slipping.

I suspect that your fuel filters need replacing which would account for the stalling at idle and would make sense with the fact that this occurred 15-minutes after turning around and bouncing into waves. Power loss could also be attributed to dirty filters but the climbing revs sounds more like you dropped the prop. A GoPro on a pike pole will show you what's going on with the prop.

[Sputnik]

If the valves had a load of carbon on the back of them then when the rpm went to the limiter it may have shaken the carbon off of the backs of the valves, this then gets jammed between the valve seats and the valve and reduces the compression......turn the engine over by hand using a socket on the crankshaft pulley to see if you have a compression leak past the inlet valves. If you do then revving the engine to the governor limit (make sure its up to running temp' before) may displace the carbon..if not its a top end overhaul to de-coke the valves and head.

Does it still start from cold as quickly as it did before the prop' loss? If not it supports this theory.

The other possibility is that the governor may not have settled correctly and you will just have to re-set the idle speed.

Neil