4tnv98 questions about internals and head damage

[franka02809]

Mechanically I am not very well versed. This is my first time opening a motor but I am interested and driven to learn about what I am seeing. The reason I started on this journey of removing the head is that I was getting compression out the radiator expansion tank. It would blow the coolant out the tank. I could see what looked like the combining of oil and coolant. I had a head gasket test tool but that thing would also bubble up and overflow almost immediately after starting. So the machine could be cold but it would still blow bubbles like crazy. In looking this up the general consensus was that it had to be a head or gasket issue. The pictures I am posting here are of the piston walls and the head before cleaning in more detail so I can get some help identifying what the problem was. In addition just before all of this the machine was running to hot. I ended up replacing the sensors inside the coolant housing attached to the head. Sorry I do not know the names of things just yet so I may make some mistakes here as I learn. It may be hard to detect what I see in this image that shows the head and one of the cylinders with visible damage to the head itself (missing metal)

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This is the inside of the cylinders and I can make out numbers etched in the top of each one so I think someone has already been inside here.
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I am wondering if the cylinder walls seem normal to have a black ring at the top. I am wondering if the build up I see in the cylinders and pistons is normal for these. I am trying to make sure I identify the issue before I clean more and check the block is flat with a square. There is marks on the block I can see from what looks like someone trying to separate the head from the block with a screwdriver. Another thing I find odd is one of the push rods seems smaller than the others and does not have the same marking the others do (the yellow ring) Once removed it looks like its a bit rusty on the bottom like it may be from another motor. Its the one on the far right of this image View attachment 20251126_161040796_iOS.jpg

 

[bmaverick]

Looking at the head images, has this engine ever used starting fluid? It has some telling signs starting fluid has been used before. This is why the pitting is seen.

For diesel engines, never use starting fluid or ether fluid. This does extreme damage to the metals in the head and pistons in diesel engines.

Clean all of this up per the Service Manual. Then re-assemble with a new head gasket per the Service Manual.

YANMAR YANMAR 3TNV82A 3TNV84 3TNV84T 3TNV88 4TNV84 4TNV84T 4TNV88 4TNV94L 4TNV98 4TNV98T 4TNV106 4TNV106T SERVICE MANUAL 0BTNV0-U0000.pdf

Found on the YTOG for free.

 

[bmaverick]

All of the carbon soot build up relates to,

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How to keep the soot away and ways to prevent having the head warp and crack on these Yanmar engines.

- Do not let the engine idle below 1200rpms for longer than 10mins max at a time. And the time is with 20mins between.
- Do use 10W30 summer and 5W30 winter for engine oil. Do not use the heavy thicker 15W40 as it will hold the heat longer in the engine. Yanmar makes engines to JIS standards, not SAE. So the cooling oil passages are narrower in metric.
- Do keep the air intake filter clean. A clogged filter makes the engine work harder and heat builds up within the engine.
- Do keep the radiator and the screen clean.
- Do check the coolant. Do not use extended life coolants in these vintage machines.
- Do start the tractor slightly above idle.
- Do not race the engine from slow to fast and fast to slow.
- Do slow the engine speed down gradually, idle for 15 seconds then turn the engine off.
- When parking and doing the engine shut-off, be on level ground, take and place the gear in neutral and if equipped, the PowerShift in neutral.
- Diesel engines, especially the 2-clyliner types will cause a lurch-back on the last 2 piston firings. To prevent the energy going to the drivetrain, be in neutral.

Some of these tips are from Deere, some are in the Yanmar USA bulletins and some came from the Yanmar JP website before 2018.
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[bmaverick]

Here is a 2TNV90 head damaged and with a crack due to starting fluid.

I didn't see a crack in yours.

 

[mrmikey]

.....visible damage to the head itself (missing metal)

Probably cause by pre-ignition or more than likely as was said starting fluid. It's odd tho, usually it's the piston that'll melt.
Definitely a head gasket fail. You can see where the cylinders are connected and it looks as if the water jacket and oil passages are connected too. Got a pic of the head gasket?

I am wondering if the cylinder walls seem normal to have a black ring at the top.

Yup, totally normal. That's the distance from the top of the block, head surface, to the top of the first combustion ring on the piston. Basically it's as far as the combustion gasses get to before they hit the first ring.

Cylinders look good, it would have been better if there was a bit of cross hatch left but there's no gouges or marks. Purpose of the cross hatch is pretty much to hold oil to lube the rings as the piston moves up and down.

As for the head your best bet would be to get the head surfaced, I'd bet money you're going to find it needs it. That pitted cylinder may give you a problem as far as retaining the valve seats especially around that intake valve, it looks as if there's nothing left.

If you're thinking someone else has been in there, any chance the previous owner slapped a head gasket in it to get rid of it? Or even stuck another ahhhh...less than perfect head on it as it's odd there's no piston damage on that same cylinder.