Valve lash (clearance)

[Dubo]

Hi,
I am adjusting the valve clearance on my 2GM20f Yanmar since it probably hasn't been done in years. Overall this is a fairly simple task once you know how to do it. I am following the Selco instructions and not being a mechanic I am puzzled about a few things. As I rotate the crankcase shaft clockwise (facing aft) to find TDC, I notice on the flywheel there are 2 pairs of notches for each cylinder. In the pic I have attached you can see the flywheel and the span between the two notches(red area). My question is, is TDC on the notch with the number and what is the area between the notches telling me? It seems like a fairly broad area. Does the unnumbered notch mean anything?
Also, I notice that the gap on the rocker is closed when on TDC. Does it take 2 rotations for the gap to open up and can I adjust the #1 and #3 rocker arm on the same stroke, assuming they are off the lobe?

TIA

 

[Barnacle Bill]

First of all your TDC has to be on the compression stroke and the engine cold. Your matching mark will be at the line next to the "2" in your graphic. Set to the position at which the valve rocker arm shaft does not move even when the crackshft is turned to the left or right, centered around the matching mark. Now you check and adjust the intake and exhaust valves of the #1 piston. With the 2GM you adjust the valve head clearance of the #2 cylinder in the same manner after turning the crankshaft 180 degrees. The clearance for your engine is 0.2 mm (0.0079 in). If you adjust the valve head clearance of the #2 cylinder first, turn the crankshaft 540 degrees. Adjust the clearance of the #1 cylinder in the same manner on a two cylinder engine.

 

[Benny17441]

I do not normally concern myself with the markings on the flywheel. I will rotate the engine by hand until both the intake and exaust valves on each cylinder are both closed with maximum clearance showing. When turning the engine by hand you can feel when one of the cylinders is on the compression stroke. (Make sure the fuel stop is pulled) Ill use a flathead screw driver and a closed box wrench. I'll loosen the locknut and insert the feeler gauge and tighten the screw until the gauge slips in and out with little pressure but with full contact and then while holding the screw in place securely I 'll tighten the locknut. After tightening test again to make sure the gap remains as intended. I'll verify the gap on both cylinders once again before replacing the valve cover back.

 

[kloudie1]

As you rotate the crank clockwise looking aft, the first mark is the fuel injection timing mark. It is about 15 degrees before the other mark. The next mark is TDC for the cylinder marked.. 2 or 1 .. you can be one turn of the crank off, but both valves should be marginally loose when at TDC on compression, at that time, the other piston will be at bottom dead center and its intake valve will be tight

 

[Dubo]

Compression stroke

There is a point when turning the crankshaft that a lot of effort is needed. Is that the start of the compression stroke?

I didnt realize the injector timing mark was the unlabeled mark.

Thanks for the helpful points.

 

[finding41]

Yes, if you are turning it in the right direction.

 

[sailaway78]

The for sure way

If you have any doubts, try this. Takes a little longer, but is positive. Just turn the engine over till you have a valve fully open, The other valve on that cylinder can now be adjusted.

 

[Joe23455]

I have the same engine, I know the valves have never been adjusted.
My question is: What is the indicator that the engine valves need to be adjusted?
Thanks,
Joe s/v trinity

 

[Dubo]

Feeler gauge

I have the same engine, I know the valves have never been adjusted.
My question is: What is the indicator that the engine valves need to be adjusted?
Thanks,
Joe s/v trinity

Sound may be an indicator???

The best test though is to put a feeler gauge to it. Two of the rocker arms were > .25 mm. Spec is .20 mm. Be aware if you remove the cover you will need a new gasket (10.00) probably. Also something to help the gasket adhere to the groove in the cover is a must or you can turn the engine upside down so gravity doesn't misalign the gasket.