[C320-list] Engine knock

[Mitchell Berenson, MPH]

It does have the rocker arms on top of the head. To take the valve cover off, you take the engine covers on the front and the back of the motor and then the valve cover bolts are on top. I had to use a small handsaw to make enough room to take the valve cover off of the motor. All in all, it was a very simple activity.   My rocker arm failed at 300 hours. 

Good luck. 

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> On Jul 22, 2017, at 10:00 PM, Dan Kolean <dkolean60 at gmail.com> wrote:
> 
> 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.....
>>> 
>>> Sent from my iPhone