I wouldn't say it is that rare with small engine. Yanmar engines have a 
weakness to this regard.
The fuel pump is a rubber diaphragm activated by one of the engine cam. Over 
the year, the rubber membrane can start leaking through a crack in the rubber. 
When it starts leaking, the diesel goes in the pan, where it start mixing with 
the engine oil (not a good thing). A small leak will go unnoticed until it 
develop to a substantial leak. The leak start filling up the pan until such a 
point when the pressure coming from the piston initiate self burning in the 
pan. The engine then goes wild and pulling down the throttle does not do much. 
I happened to me once and this when I discovered this weakness. When checking 
the engine oil, beware if the level seems to increase or remain stable where 
there should be a slight decrease. Look  also if oil gets darker  with lower 
viscosity. If the engine is getting old, I suggest preventive replacement of 
the pump membrane. Not a big deal to replace.

Antoine (C&C 30 Cousin)

Le 2013-05-26 à 00:03, Martin DeYoung a écrit :

> Back in my Merchant Marine school days, during a diesel engine maintenance 
> class a video was shown detailing what happens when a large displacement 
> diesel engine runs away, uncontrolled by the governor as it fed on lube oil 
> through the supercharger seals.  Just before it failed (exploded) you could 
> see fire shooting out between the block and head.  
>  
> When attempting to stop a runaway diesel do not place your hand over the air 
> intake.  Use foulweather gear or similar sacrificial air blocking material 
> that will conform around the air intake.  If you have a Halon (Calypso’s 
> engine space has a 7.5lb auto-deploy Halon system in place) or a larger CO2 
> extinguisher on board they may be used to slow the engine slightly to make 
> the stopping easier.
>  
> This sort of failure is rare in small auxillary diesel engines, but more 
> likely with turbocharged engines.  If a pleasure boater (power and sail) does 
> basic maintenance (do not over fill the lube oil) and every few years calls 
> in an expert to check the more complicated systems (especially the injection 
> pump, head bolt torque, and turbo seals) the risk of runaway should continue 
> to be small.
>  
> Martin
> Calypso
> 1970 C&C 43
> Seattle
> From: CnC-List [cnc-list-boun...@cnc-list.com] on behalf of Josh Muckley 
> [muckl...@gmail.com]
> Sent: Saturday, May 25, 2013 7:16 PM
> To: cnc-list@cnc-list.com
> Subject: Re: Stus-List Fwd: Stopping a diesel
> 
> So let me get this straight:
> Run away engine - gonna blow.  Decompress - gonna blow
> Sounds like a dammed if you do dammed if you don't.
> So don't decompress.  Good to know for the normal "non-emergency" shutdowns.  
> I'm still gonna do it when shutting of the fuel and air don't kill the engine.
> Thanks for checking me and the books,
> Josh
> --
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