Yanmar engine 4HJ3-E 1997 8600 hours is blocked

[Fletcher7]

Hello Pete, when I install new exchanger, engine has been cleared of cooling water and sea water. The exhaust elbow really lower than cylinder head. A leak through new exchanger porous casting or crack is always possible, but complicate to get it test.A drop of carbon buildup into cylinder if also possible, for sure.
I will remove cylinder head this morning. Thank you, Paul.

[Patrick of M]

I won't bother with my 2 cents about cause, because basically all possibilities have been covered. Unfortunately forum advice usually jumps to worst case scenarios first so if you are trouble shooting this, I would suggest start with the simplest easiest check first and proceed in like manner. That way if it's something simple you don't have to discover it after you have already torn the block apart.

[Rumrace]

Around 5,000 hours it’s a great idea to check valve guides oil seals. I suspect someone did not.
If it’s a dropped valve and had hit the piston a few times when you add up crank, wrist pin, piston, cracked head the sound of $4,700.00 for a new Yanmar 40hp sounds fun. New engine mounts too.

[Rumrace]

Disconnect all electrical disconnect fuel and cap. Drain oil. Place two 2x6 in front of engine. Place towels to protect companion way 3 2x6 cross beam with winch. Unbolt drive engine mounts lift up the nose 2” and drag on to 2X 6. Have the yard crane switch out motors and slid back in place. Then go buy expensive tools to line the engine up or call a mechanic who will be delighted to work on a new motor. Estimated damage $6,800.00. Trouble free and a new Hitachi 80 amp Alternator you wish was bigger.
So you buy a Bosch Liquid cooled 150 and Aftermarket serpentine anodized blue billet aluminum serpentine pulleys and have dodged a future Yanmar problem.

[Boatyarddog]

Originally Posted by Patrick of M

I won't bother with my 2 cents about cause, because basically all possibilities have been covered. Unfortunately forum advice usually jumps to worst case scenarios first so if you are trouble shooting this, I would suggest start with the simplest easiest check first and proceed in like manner. That way if it's something simple you don't have to discover it after you have already torn the block apart.

This forum is rife with worst case senerios

Always best to ferret out the simple causes, first.
What has the OP found wrong, anything?
I've not seen any post about actual cause.
Boatyarddog