compression Test Results

[Moncha]

Ok, the pro spoke.

Burnt valve is the cause the of the valve failure. The valve burnt most likely from an overheating situation. Any over heating that you remember?

That valve burnt due to the center cylinder being hottest due to design. When it got hot, It at sometime has caused it to hang open thus allowing hot gasses to blow by the valve making the valve head get hot and "Crystalize" then snap!

You can see that the head gasket was allowing gasses blow from cylinder to cylinder (Red Circles) but, not necessarily coolant because it wasn't at the water jackets.

The yellow circle shows a or the location that may have been the hot spot for over heating. That would be on the intake side and it would have been the part that got the hottest.

Advice, Take both heads off have both redone professionally, new valves, new guides, new seats, re-surface, and new gaskets along with new head bolts. If you do that then you won't be doing this again in another 1000 or so miles if you don't.

[newthings]

As an ex-failure analysis and electron microfractographer (SEM and TEM), I can definitely say it is broken. Nice last photo.
Valves are made by hot upsetting the head shape on the end of a steel bar. Axial forging might be a good description. Several additional operations result in the finished valve. The grain of the metal spreads out from the center to the edge of the disk. The machined valve seat exposes the end grain to the hot gasses. End grain is the most susceptible to corrosion and erosion.
The applied stresses on a valve head rim are complex and not intuitive for me to understand. The erosion pits around the entire seat indicate that the valve may not have been seating in the head for a long time. The hot gasses were carving out seat material with every stroke. Some spot decides to be worse than the others. Nature finds the weak link.
The fracture can open but not fully fail for some time. During this period, the fracture face is exposed to the hot environment and becomes dark. The dark area at the seat on the right side is the most likely origin of the fracture. Microscopic fracture analysis is not possible since the fine detail is smoothed over by the hot gasses. I can make out two dark arcs as the fracture spread through the uniformly thick portion of the valve head. The thickness began to increase as the crack moved toward the center of the valve, the crack then turned back toward the rim. The angle of the fracture plane also changed to 45 degrees relative to the original plane of fracture. This often called the shear lip. This is the rapid part of the fracture.
None of this may be true, but it has been well imagined. (Arthur Clarke)
Roy

[FuddyMucker]

Wow Moncha your brother-in-law really knows his stuff, impressive!
I don't remember it running hot but can see where he means (now you have pointed it out).
So a full rebuild is in order then, sounds expensive but fun, I do like tinkering although it would be nice to get to drive it more than 50 yards before I get yet another problem.

So what you are saying I need to do is

1. remove the other head
2. remove all 4 cams
3. remove all 24 valves
4. remove all guides
5. remove all seats
6. get both heads skimmed
7. buy new valves, guides, seats and headbolts
8. rebuild both heads
9. buy complete gasket kit
10. rebuild engine


Surly if I am going to go that far it would make sense to drop the bottom off the engine and replace the piston rings and main engine bearings.
******Then I would have a new engine******

[FuddyMucker]

Roy, I actually had to read that 5 times to fully understand what your were saying (dosen’t help I’m working nights at the moment), very interesting stuff.
I guess you also think, if one valve hadn’t been seating well for a while then it is probably not the only one getting to your well described condition..
I am also guessing that its a 50/50 chance of the chip being blown out as it is falling back into the engine and destroying the cylinder lining?

[Moncha]

So what you are saying I need to do is

1. remove the other head YES
2. remove all 4 cams YES
3. remove all 24 valves YES
4. remove all guides YES
5. remove all seats YES
6. get both heads skimmed YES
7. buy new valves, guides, seats and headbolts
8. rebuild both heads YES
9. buy complete gasket kit YES
10. rebuild engine Maybe

Surly if I am going to go that far it would make sense to drop the bottom off the engine and replace the piston rings and main engine bearings.
******Then I would have a new engine******

The heads, go without question, do them all and do them right or you are headed for another failure. The weak point in the head, and block is where the center cylinder meets up with the two outer cylinders, as there is a lack of water jacket between them. The engineers are relying on convection to keep it reasonably cool but when there is an overheat, those valves will be the victims for sure. The valves, especially the exhaust, rely on contact with the seat to cool by convection, in this case, that valve, whether it was a weak spring, guide galling, or gross mal-adjustment, stuck open, causing hot gases to constantly blow by, thus overheating the valve, thus burning it (Like Roy said) then causing the tell-tale 45deg notch break.

Depending on what your low end looks like. From the pics, it is quite impressive that you still have crosshatching on the piston cylinders after that many miles/kms. If there was an overheating situation, then there would be quite a bit of crap floating in the oil (however microscopically) so the bearings, rods and mains, could have some wear or galling. You won't know unless you look. If it looks good and clearances are in range than you could get by without. But........

[lasturbo]

Did the burnt valve chunk that is missing disintigrated cuz I did not see any damage to the piston and wall in the pics?