[C320-list] Engine knock

[Dan Kolean]

Great suggestion, does the motor have a cam that pushes a rod to a rocker arm on top of the head and the other end of the arm opens and closes the exhaust or intake valve?  How hard is it to look at the rocker arm? Is it under a valve cover that you can get at with  the engine in the boat?  Do you have to pull anything else off to get at the valve cover? Like the heat/water exchanger on the starboard side of the motor?  Do you know if the valves can get hit by the piston if the rocker arm breaks and they are down or open?  I know a bit about this but not everything, my experience is with gas engines.  Thanks for the help
Dan Kolean
Holland, Michigan
Hull 489
Mary Kate

Sent from my iPad

> On Jul 22, 2017, at 10:41 PM, Mitchell Berenson, MPH <mitchell at communityiv.com> wrote:
> 
> Could it be a rocker arm. My motor broke a rocker arm on the center piston.  Easy diagnosis and resolution.  
> 
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> 
>> On Jul 22, 2017, at 1:54 PM, Daniel Kolean <dkolean60 at gmail.com> wrote:
>> 
>> As we were motoring yesterday the engine started to knock. Quickly shut it down, got a tow off the lake. Ran at idle and decompressed one cylinder at a time. Determined the knock is in center cylinder (Yanmar 3gm30f). Rod bearing, wrist pin, cracked piston or ring? Anyone ever experience such a sad event with their Yanmar? 1170 hours, ran great, no smoke, oil actually stays real clean after a change. I searched our forum and couldn't find anyone who had problems like this. Engine is getting pulled Monday and we'll drop the oil pan and look at the bottom end, then the head and see how the top looks. To be continued.....
>> 
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