Yanmar 2GM20F knocking sound

Sep 11, 2015
147
Hunter 31 Marina del Rey
Could someone help me diagnose this knocking sound coming from my 2GM20F engine> Halfway through the recording I am playing with the decompression levers to see if the sound changes.

1) When I lift the the decompression lever for cylinder 1, I get a pulsating feedback on my finger.
2) When I turn the crankshaft by hand, slowly, at a certain position, I can hear a spring sound, such as tsk-tsk-tsk, once per revolution.

Thank you,
SV Pizzazz
 

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Feb 27, 2004
172
Hunter 335 North East, MD
I must not be hearing it but it really sounds like a normal 2 cylinder diesel to me- sorry:(
 
Jan 8, 2015
360
MacGregor 26S, Goman Express 30 Kerr Reservoir
Yep, sounds just like my engine.
That tsk-tsk-tsk sound could mean your valve lash could use some adjusting.
 
Nov 6, 2006
9,885
Hunter 34 Mandeville Louisiana
I don't hear a problem either except as Cowpoke says, check the valve clearances..
Sometimes a phone recording will not catch some low freq transients.. could be you are hearing a tired motor mount that is not coming through on the recording?
 
Dec 14, 2003
1,393
Hunter 34 Lake of Two Mountains, QC, Can
Was engine warm or was the recording done just after start-up. My engine (3GM30F) sounds like yours until it has reached normal operating temp.
 
Mar 29, 2017
576
Hunter 30t 9805 littlecreek
Owners Manuel requires adjusting valve lash every 100 hr. Because there are no hydraulic lifters solid pushrods require maintained clearance.
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Kinda hard to tell which sound is which without some narrative on when things are happening. with that said, if the engine was warm I'd check the valve lash, if the engine was cold then warm it up and see if the noise gets less loud. Just as a diagnostic tool the valve noises are at half the frequency of the piston noises so if you have a view of the crank you can tell which system is causing the noise. 600 RPM is 10 revs per second on the crank and 5 / sec on the valve train. You can actually count that with some practice BTW.
 

pateco

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Aug 12, 2014
2,207
Hunter 31 (1983) Pompano Beach FL
It sounds just like my 1983 2GM.

Owners Manuel requires adjusting valve lash every 100 hr. Because there are no hydraulic lifters solid pushrods require maintained clearance.
How hard is this to do?
 
Mar 29, 2017
576
Hunter 30t 9805 littlecreek
Adjusting the valves is easy especially if you can get good access to top engine. There's. you tube videos on it and lots info on line
 
Feb 1, 2010
210
Hunter 33.5 El Dorado Lake, Kansas
I’m no mechanic I did it to my 2QM15. It made a big difference on how it ran. I also changed the injectors at that time.
 
Jan 22, 2008
1,654
Hunter 34 Alameda CA
Best to purchase a new valve cover gasket and the O-rings for the hold down knobs as well.
It's an easy task and if it hasn't been done in a long time you will hear a noticeable change in the rattle these engines make.

When you peek through the hole in the back on the clutch cover and locate the timing mark, use a magic marker on the crank shaft pulley to make a reference mark. Then when you rotate to the next cylinder position make another mark. It makes locating the top dead centers easier the next time. I think I got that idea from Ralph. It was a picture he posted.

If the rockers (both exhaust and intake) for the appropriate cylinder are still tight you have to rotate the engine one more revolution to get that piston to top dead center. Then proceed with the adjustment.

I used a 1-1/16" socket on a breaker bar to rotate the engine. I can't remember if once the valve cover is off if that releases the compression. Maybe. It makes it easier to turn.
 

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