404 Utility...time for a rebuild!

Hey guys! Slowly working in my 404 utility. Compression was 150, 150, 130, 150psi. Engine smoked and quickly oil fowled plugs 2 and 3.

Was hoping to get away with a valve job and rings, but from the looks of these pistons I don't think that's a possibility now. Agree?

Worst looking to cylinders are shown. What causes the top of pistons to look like this? Guessing maybe carbon deposits falling off the valves?

Thanks for the input!
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definitly need valve job , as those are really recessed. almost looks like was running without air cleaner. how much ridge is there?
 
Not sure about air cleaner...I just bought the tractor this summer as non-running. Was told it needed a clutch and was using oil.



Can catch your fingernail on 2 cylinders but not the others. Haven't torn it down further yet or measured the sleeves.
 
My vote is spark knock. Which would be exacerbated by the oil consumption lowering octane. Would be accentuated by high loads and high rpms. Could also be affected by poor cooling system performance. Bottom line is my free opinion is that it's heat damage.

The top ring land is the weakest area of the piston and also one of the hardest areas to remove heat from the piston.

A spark knock analogy is that it's akin to sandblasting your index finger for a millisecond. It hurts and gets "hot" but the "heat" passes. One single knock doesn't do anything except cause a localized heat. But, line up a bunch of combustion events in a row with a spark knock (again the high rpms is the main factor) then the piston can get damaged by a much more concentrated flow of heat.

Any piston (not these) that have sharp edges due to valve relief pockets (typically in 4 valve heads) are also susceptible to heat concentration, and typically are driven into overfueling/rich operation to protect the piston well ahead of a 2 valve head with a relatively smooth piston.
 
Would say detonation over time. Notice quite a few fire carter pistons with those signs. Sometimes antifreeze seeping in to cylinders over time will also look something like that sometimes. Don't know about a 404 but some fire crater sets came with parts to richen fuel mixture when used and parts to limit max ignition time. One with damage on spark plug side maybe saw pre ignition. Also with instructions to make sure cooling system was in top condition.
 
I don't know what is causing the damage to pistons and head, but what in the world is going on between the liners and the block? In the images, it almost appears that the counterbores are not concentric to the liner flanges, and there appears to be enough of a shadow line that I would definitely look at liner protrusion. Maybe all of this is just an illusion created by the lighting in when you took the images,....
Good luck! jeff
 
Jim, Right you are, and thanks for the correction. Well, the gasket is on the block, but I stand corrected all the same. I must rather sheepishly admit that my eyesight is woefully inadequate to the task. Mr. Magoo has nothing on me!

Jt
 

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