Yanmar - Tapping Noise

[newburyporter]

We have a tapping noise in our engine.

An engine expert I know said it could be that the valves need adjusting.

Question:
Does Yanmar have hydraulic self adjusting valves or do they need to have "lash" ajdusted manually? We have a 4JH5E engine...

The boat yard said they should do a compression test. A valve may not be seating properly in their mind...

What is the most likely cause?
The tapping noise is audible at low RPM in idle. It does not go away when in gear (either forward or reverse) and increases in frequency when the throttle is raised...

Thanks in advance for your thoughts!

Brent

 

[Patronus322]

Engine noise

You are describing what sounds like valve train noise. My 2 cyl Yanmar 2gm20F uses manually-adjusted valves, so they need to be adjusted on occasion. The clattering noise could be caused by the gap opening up to an out-of-spec condition. I don't believe this would be picked up with a compression test as the valves are seating ok, just staying seated a bit longer than they should since they are not being pushed open enough. This nibbles away at the performance a bit... The adjusting process is very simple, and it is nice to get a good look at how the engine looks while it is opened up.

 

[kloudie1]

Patronus is right on.. the valves need manual lash adjustment and the valves should be checked regularly. On my 3GMF, the recommendation from Yanmar is every 500 hours.. (after an initiall 50 hour check when new) I feel like 200 is more appropriate, and it is a straightforward process, but ya have to be exact in the procedure. While you are there, re-torque the head before you set the valves. If it is running fine and evenly, I would not do a compression check ..

 

[Charles Erwin]

The manual shows setting the rocker arm clearances and says to remove the starter so as to be able to see the reference marks on the flywheel. Strikes me as a whole lot of work for such simple maintenance.

How do you check/set these clearances without taking the starter off?

Charles

 

[Bill Roosa]

You can do the valve lash adjustment without pulling the starter but you need to understand 4 cycle valve operation. At the top of the compression stroke/beginging of the power stroke the valves are both closed. that is almost 360 degrees of crankshaft rotation without those valves on that cylinder moving. then the exhaust opens for 180 degrees and then the intake for 180. Set the valve lash at the top of the compression stroke. I believe you set them when the engine is cold but have not read the manual

 

[Don S/V ILLusion]

Always eliminate the easy stuff first. Not that doing a valve adjustment is difficult but it takes more time than some other possibilities which can produce similar tapping sounds.

I'd suggest you first check the belt tensioner pulley, the water pump bearing and the alternator for worn bearings particularly on engines with lots of hours under their "belt"

 

[RichH]

Once you reconcile that its NOT your valve train (lash), then check out the cam and follower on your high pressure fuel injection pump ... they sometimes need to be 're-shimed' to stop the annoying loud (hollow sounding) 'tap' heard when the engine is at idle.