Checking engine valve clearance

Yanmar 3YM30


A few years ago, I replaced Calypso’s trusty 1976 Sabb GSP diesel with a new Yanmar 3YM30. The new engine is smaller in every dimension: length, width, height, and weight, yet cranks out 29 HP – albeit at 3600 RPM. We’ve finally racked up enough hours that it’s time for the prescribed 50 hour maintenance, which includes:

  • Drain the fuel tank.. Humm… nuts. No, not happening.
  • Replace the lube oil and filter. Yeah, good idea. I do that every year regardless.
  • Replace the gearbox oil. OK.
  • Adjust the alternator and raw water pump belts. Check.
  • Adjust the intake and exhaust valve clearance. Humm that looks “involved“…
  • Check the remote linkages. OK.
  • Check the shaft alignment. OK.

The engine is long out of warranty, and I need to start getting familiar with this baby. So I’m not inclined to hand this off to a certified Yanmar mechanic. So time to roll up my sleeves and get dirty.

The tank draining advice is whacky. I replaced everything when I put this engine in, including the tank. Unlike the Sabb, this engine recirculates fuel back to the tank – so to some extent it is always polishing fuel through the primary filter. Skip.

The meatiest part of this list for me is adjusting the valves. Everything else is pretty straight forward. Adjusting the valves involves taking the valve cover off – and the notion of taking what is still a brand new looking engine apart… well there is some trepidation.

Anyway, here we go…

Step 1: Remove the air filter

Undo the hose clamp circled in yellow below, and remove two bolts that affix the air filter to the engine block in the vicinity of the green arrow below. Then the air filter housing can just be pulled off.


Step 2: Remove the valve cover

Remove the 9 bolts circled in red above. Then the valve cover can be lifted off.

Step 3: Remove the bell housing inspection port

On the starboard side of the flywheel bell housing, there is a rubber plug covering a view port (circled in red below) which lets you see the flywheel timing markings. The rubber plug can be pulled off by hand – no tools required.


Step 4: Rotate the crankshaft to #1 TDC

Use a 17mm socket and driver to slowly turn the crankshaft CCW as viewed from the front of the engine – while observing the valves… and the flywheel through the view port. Do what? Yeah, you might need a helper. Continue turning until both of the #1 cylinder’s valves are closed and the “1” timing mark appears in the view port (see second photo below). The #1 cylinder is the forward-most – see photo below). The valves are closed when the the valve stem is not pressed down by the rocker.

I had expected the crankshaft to be difficult to turn through the individual cylinders’ compression strokes. But you can easily relieve cylinder pressure by just pressing on the relevant rocker with your hand to push down the valve stem and open the valve. You might have to do this a few times as you slowly rotate the crankshaft.



Step 5: Adjust #1’s valve clearances

Each valve is actuated by a rod coming up from the crankshaft. The rod engages one end the rocker, and the other end of the rocker engages the top of the valve stem. When the clearance between the rocker and the top of the valve stem gets out of spec, you sometimes can actually hear more pronounced engine clatter when it is running. To adjust this clearance, back off the lock nut on the rod side of the rocker, and back off the screw which adjusts the clearance. Insert a 0.20mm feeler gauge between the valve stem and the rocker, and then close the screw until the feeler is lightly pressed by the rocker. The feeler should not be tightly bound, but it should take a little bit of hand pressure to move the feeler while it is in the gap.  Once you have the right clearance, leave the feeler in place and tighten the lock nut with a wrench while holding the screw in place with a screwdriver. Double check the pressure on the feeler. If too tight or too loose, adjust again. Do this for both #1’s valves (intake and exhaust).


Step 6: Repeat for #3 and then #2

Once done with #1, continue turning the crankshaft slowly about 240 degrees CCW until the “3” mark appears in the view port. Then adjust #3’s valves. Once done with #3, rotate he crankshaft CCW another 240 degrees until “2” appears in the view port. Then adjust #2’s valves.

Step 7: Reassemble and test run

When you are done adjusting all six valve clearances, use a socket and driver to ensure that all six lock nuts are tight.

Reassemble the valve cover reversing the steps above.

Run the engine and listen to her purr.



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