How to rotate Yanmar 4JH for valve adjustment

[CaptainFred]

I have a 4JH3 diesel that I would like to do a valve adjustment on. Prior small diesels I have rotated manually, but it is apparently not possible to rotate this engine by hand and there is apparently no decompression lever. How does one rotate the engine precisely so that the valves can be adjusted? How likely am I to need a new valve cover gasket? Thank you.

 

[Don S/V ILLusion]

Always install a new gasket. As to the method of rotation, I've only done a valve adjustment twice and removed the injectors using the opportunity for inspection and testing making it easy to turn. It's a "two-fer".

 

[anchorclanker]

I have a 4JH3 diesel that I would like to do a valve adjustment on. Prior small diesels I have rotated manually, but it is apparently not possible to rotate this engine by hand and there is apparently no decompression lever. How does one rotate the engine precisely so that the valves can be adjusted? How likely am I to need a new valve cover gasket? Thank you.

There is a bolt on the front of the crankshaft pulley you turn with a socket wrench/breaker bar. Remove the injectors to ease rotation, while your doing valves check injection timing. While injectors are out, service them. You should always replace the gasket on principle, they will almost always leak after reassembly unless they are rather fresh.

 

[navigator97]

If you are turning the engine over slowly, use a socket wrench on the nut at the center of the main shaft. BUT, release the compression levers first. The nut on mine is, I believe, 28mm.

 

[Bill Roosa]

SLOWLY rotate the engine. As the cylinder that is on the compression stroke tries to compress the air it stops you from further rotating the engine crank shaft. You have to wait till the compressed air leaks around the rings to further rotate it.

 

[CaptainFred]

Thank you all for your help!