[C320-list] Engine knock

[Graeme Clark]

Broken rocket arm would mean the valve remained closed so the piston would either be compressing when it should be pushing out exhaust or not taking in air when it should be
In second case injector would still squirt in fuel which would be blown into exhaust and produce lots of white smoke 
In first case I'm not sure what the symptoms would be
I once had an exhaust valve stick open which gave me smoke and power loss but no knocking
I also had an injector issue which produced rough running causing vibration and a lot of knocking but that was the engine vibrating not a true knock from within!
Traditionally a knock indicates a big end bearing. 
Hope this helps
Graeme

Sent from mobile: please excuse typos etc.!


> On 23 Jul 2017, at 04:00, 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.  
>> 
>>> NOTICE: This email and its attachments, if any, may contain confidential or proprietary information and are intended solely for authorized use by the intended recipient(s) only. Any other use of this email is prohibited. If you have received this email in error, you are hereby notified that any retention, disclosure, copying, forwarding, distribution (in whole or in part and whether electronically, written and/or orally) and/or taking of any action in reliance on this email, its contents and/or any attachments thereto is strictly prohibited. If you received this email in error, please notify the sender by replying to this message and permanently delete this email, and any attachments thereto, from your system immediately.
>> 
>> 
>>> 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