Administrator
Make sure to have a good head shop look at it but it looks like the valve just failed.. Everything else looks to good to say that it was anything else. Keep cleaning and checking though, you never know what you'll find under the carbon.
Lisa, don't worry about this, you would have major problems rather than just idling rough sometimes. This is probably a one in a million and after 161,000 miles (260000km) may just be a failure on a 3.2l engine.
Scott / moncha.com
VXer
Lisa I Agree with Moncha, your problem sounds like it is nothing to serious, maybe just a new set of plugs are needed or a coil pack is starting to fail (which is easy to fix in the US because spares are easier to get than here in the UK).
If it was a valve, you wouldn't have days where it ran well
I have had to order an exhaust valve from a Vaxhall Frontera because they don't list anything for a Vehicross because it is classed as a Gray Import.
Super VXer
You've probably already thought of it but...
Remember to get new head bolts...
http://cgi.ebay.com/99-01-3-5-L-Isuz...item3ca8d8642b
http://cgi.ebay.com/99-01-ISUZU-VEHI...item5d22df1d74
Last edited by Ldub : 03/07/2010 at 04:04 AM
VXer
Yes I had thought of doing the head bolts but am having issues finding a UK supplier, I have ordered a new head gasket set to rebuild it with but wasn't sure how important it was to change the head bolts. Its something I have never done before, do these ones stretch?
VXer
Here are some better photos of that failed valve (for all those members who are as curious as me)
Looks to me like it had been fractured for a while before it came completely off, what do you guys think?
Last edited by FuddyMucker : 03/07/2010 at 10:53 AM
VXer
Has anyone else done a head gasket before and not replaced the head bolts?
Has anyone else in the UK managed to get hold of head bolts?
Administrator
Looks like that valve had been burnt for a while, then the failure. Probably from mal-adjustment.
My brother-in-law is coming over tonight and I'll show him these. He, as well as the rest of the side of his (Ms Moncha's) family owned and operated an automotive machine shop for decades. The bro-in-law specialized in valve trains. He may have a good idea of what happened.
Always, replace the head bolts as under torque, they do stretch and you want to do it right after going through all of this.
VXer
Thanks Moncha, I would be intressted in your brother-in-laws opinion
Administrator
Me too! I wanna see if I remember what I learned
Administrator
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.
Super VXer
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
Last edited by newthings : 03/08/2010 at 11:31 AM Reason: data
VXer
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******
VXer
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?
Super VXer
Here are a couple of examples of why i recommended head bolt replacement...Originally Posted by FuddyMucker
http://www.vehicross.info/forums/sho...3&postcount=19
http://www.vehicross.info/forums/sho...9&postcount=10
The links I posted for head bolts ship world wide, though a vendor in the UK would probably be less expensive.
Last edited by Ldub : 03/08/2010 at 12:16 AM
Administrator
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........
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