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Old 19-09-2015, 14:12   #1
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yanmar 3gm30 issue

I have installed two rebuilt Yanmar engines in my boat 2 yearsago. they have approximately 100 hours each on them. one of the engines has developed an occasional taping noise. Took off valve cover for visual inspection all seems to be in good order however a couple of the rocker arms seem very marginally loose. could this be a simple valve adjustment or something else. again the rapping noiese is intermittent and not consistent.any input much appreciated thank you
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Old 19-09-2015, 16:30   #2
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Re: yanmar 3gm30 issue

Intermittent light tapping could be lifters if they are hydraulic, I don't know if they are, or loose valve adjustment although valves usually wear tight. Valve clearance is very easy to check and adjust though, so check it.

My bet would be dirty fuel injectors that can cause a rattling sound as the spray pattern is bad and fuel isn't being atomized as well.


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Old 19-09-2015, 16:48   #3
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Re: yanmar 3gm30 issue

some rockers will be "loose" if you are not rotating the engine to the proper place to test them.
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Old 19-09-2015, 17:02   #4
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Re: yanmar 3gm30 issue

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Originally Posted by Cheechako View Post
some rockers will be "loose" if you are not rotating the engine to the proper place to test them.
Interesting satement. In my opinion the position to perform adjustment (on the heel or base of the lobe) coresponds to the position where clearance would always be the greatest.

If a rocker appears too loose, it needs adjustment. Performed at or near TDC on the compression stroke for that cylinder of course.

To the OP, a valve adjustment after 100 hours of break in on rebuilt engines seems reasonable to me. The first service intervals are usually short on most engines. And loose tappets can produce intermitant taps.
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Old 19-09-2015, 18:56   #5
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Re: yanmar 3gm30 issue

Only real wear on the valve train should be between the valve and it's seat, which reduces valve clearance. I say should be, but should bees don't make honey do they.
Either way a valve clearance check is so easy that it should be done just to eliminate the possibility. Always start with the easy and or inexpensive stuff first when trouble shooting, you never know you might get lucky, Been a long time ago, But I heard an engine that I was certain was the bottom end worn, you know the hollow knock. Turned out it was a torque convertor flex plate that was cracked and nothing wrong with the engine at all.


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Old 19-09-2015, 19:13   #6
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Re: yanmar 3gm30 issue

Agree a64pilot. However on rebuilt engines some components get replaced and some not. So a new valve stem head or rocker can experience break in wear. Or reused lock nuts can be an issue. Or a new valve guide can have a slightly different angle if not carefully installed leading to a new wear pattern.

Not every builder puts the rockers back in the same spot as well. So lots of variables on a rebuild not there on an all new engine.

I usually add 10% to the lash clearance on a rebuild to compensate for the freshly faced seats. The lash spec is a range anyway.

BTW, good call on the damper plate. Random and similar light ticking sound.
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Old 19-09-2015, 19:29   #7
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Re: yanmar 3gm30 issue

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Interesting satement. In my opinion the position to perform adjustment (on the heel or base of the lobe) coresponds to the position where clearance would always be the greatest.

If a rocker appears too loose, it needs adjustment. Performed at or near TDC on the compression stroke for that cylinder of course.

To the OP, a valve adjustment after 100 hours of break in on rebuilt engines seems reasonable to me. The first service intervals are usually short on most engines. And loose tappets can produce intermitant taps.
and what if it appears "very marginally loose" to quote the OP? Apparently you are the expert I guess, so from your statement "If a rocker appears too loose" is that .009 or .013"?
:>)... it depends on your assessment of the OP's statement "seem marginally loose".... My thought was that simply looking under the rocker cover, "yes some will appear loose and some will appear tight". I have no idea of his experience with engines. I assume little if he's asking here.
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Old 19-09-2015, 19:51   #8
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Re: yanmar 3gm30 issue

In doubt a novice would consider 9 or 13 either one to be "loose", unless they considered that there should be no play at all.

Probably should have said if a lash appears loose it should be checked, not necessarily adjusted.

Not an expert. Just a guy that's rebuilt most every engine that I've owned.
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Old 20-09-2015, 18:59   #9
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Re: yanmar 3gm30 issue

Thank you everyone for the input. I agree, a valve adjustment is in order. Will get back and let you know how it works out.
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Old 20-09-2015, 20:08   #10
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Re: yanmar 3gm30 issue

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Thank you everyone for the input. I agree, a valve adjustment is in order. Will get back and let you know how it works out.
Not so fast. If the engine has solid lifters, there would be no such thing as intermittent. If it has hyd lifters and you felt a loose rocker, then that lifter has collapsed.
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Old 20-09-2015, 20:17   #11
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Re: yanmar 3gm30 issue

They are solid lifters and very capable of noise as described.
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Old 20-09-2015, 20:22   #12
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Re: yanmar 3gm30 issue

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They are solid lifters and very capable of noise as described.
Correct. As the uncontrolled position of an excessively loose rocker will vary at the moment the stem contacts it.
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Old 20-09-2015, 20:30   #13
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Re: yanmar 3gm30 issue

Maybe a lock nut backed off.

Though could be an injector or cracked damper plate as a64pilot mentioned.

Could even be a fresh water pump bearing. All these are very similar noises.
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Old 20-09-2015, 20:38   #14
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Re: yanmar 3gm30 issue

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Originally Posted by shakey doug View Post
They are solid lifters and very capable of noise as described.
He said, "Intermittently". Stuck solid lifter, I don't think so. Maybe something else.
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