Thought I'd offer this up to the mechanic gurus to see what your thoughts are. I have my theory but want to hear yours, please. Two sets of valves, adjacent cylinders. One Intake valve is pitted - the other cylinder's valve is clean. I'm not even sure when the last time cyl #5 even had a combustion. :16suspect Just more puzzling evidence. ref: AFR 185 Heads PN #1422 appr 11.2:1 CR 93 Octane Cyl 5 had 180 psi of static compression Cyl 6 had zero as the gasket was extruded between 6 and 7.
I've never seen that on one cylinder, so I did a quick search and found this: Burning and pitting are caused by the valve failing to seat tightly, permitting exhaust blow-by. This condition is often caused by hard carbon particles on the valve seat. It may also be due to weak valve springs, insufficient tappet clearance, warpage and misalignment. Warpage occurs chiefly in the upper valve stem due to its exposure to intense heat. Out-of-round wear follows when the seat is pounded by a valve whose head is not in line with the stem and guide. Oil and air are sucked past worn intake valve stems and guides into the combustion chamber, causing excessive oil consumption, forming carbon and diluting carburized fuel. Who knows if any of this will help?? I doubt you have any carbon build up. But may have been caused by the head gasket failure?
1-3-7-2-6-5-4-8 (1990 Mustang 5.0 Donor) Thanks, Dave. Interesting. I'll know more when the machine shop pulls them. FWIW, I did the "gasoline" test. Faced the heads with the valves up and poured gas into the valve chambers. No leaks. But that's under static condition. That all goes away when the engine is running.
Intresting...would have liked to seen #7 as you mention it also. Are those actual pits or carbon? Hard to make out on here on my end.
I'm going to offer a opinion or two.. I think the cylinder 6 valve is either bent or the guides are shot the pitting is detonation debris (caused by the shot guide letting oil in the cylinder and lowering the fuels octane ) it detonated blew out the head gasket violently into the next cylinder where you found the firing ring in the exhaust port.. possiblity 2 is a to hot of a spark plug and detonation blowing the gasket (check the top of your rod bearings for pounding damage) either way that cylinder was hot hot hot.. and it had debris in it hot enough to burn pits in stainless steel.. IMHO see what your engine builder comes up with
to bad you cleaned the heads I remember seeing oil tracks into your chambers on a uncleaned picture I think your valve guides are toast.. are your pushrods the right length.. are the tops of your valves mushroomed or the wear off center..maybe a couple of pictures of the valve stem tops the rollers on your rockers and the uncleaned pictures to your heads.. another possibility is your intake doesn't align correctly.. wished I knew if the oil was from the intake or exhaust side.. either way you have struck oil and that not good.. if your wondering how I know that cylinder was hot look at the discoloration of the intake valve it's brown like hot stainless headers get intakes are cooled by the incoming air charge look at the unpitted valve it's clean and shiny no deep discoloration the exhaust valve laquer buildup is normal and in 1 direction (coming from the intake heading across the chamber) the cylinder 6 valve is brown and laquered across the face my guess is that valve guides oil leakage cooking to the valve..also look at the discoloration of the head itself.. sucker was hot
I have a question now that I looked at the pictures a couple of times.. are those heads cut for o-ring seals and are you running o-ringed head gaskets ?
i think it is called... "the weakest wink"...fix it and move on to the next "weakest wink"... that's "racing" not that i would know anything about "racing" Ricks' friend,Effies' friend Frank.
Lets see. I'll try to answer all the questions in one post. * Blugene - most all the other intake and exhaust valves look the same as #6 (pitted). I chose to just show a close up of the worst one. Yes, these are PITS, the pictures don't really make it that evident. All the pistons are fine (no material loss) or witness marks of "bad" things happening. * Scooter - I'm 99% sure the pushrods are correct length. There's nothing super special about the cam, rockers, valve springs, etc. * I've attached a picture showing where cyls #6 & #7 were joined in holey matrimony by the extruded gasket. The appearance of the piston is typical of all the rest. (The debris you see at the bottom of the cyl is non-related "stuff" left there after the heads were pulled.) * The tops of all the valve stems look great. * The theory of the leaking valve guides makes sense - I just wouldn't have thought that this would happen in relatively new heads from AFR's factory. Never know though. * I also agree with you that "something" got hot - but the other head-scratcher is that NONE of the pistons indicate that. I would think the aluminum would melt under super hot conditions. * Niether the block nor the heads are o-ringed (yet, at least - that might change). * I looked but couldn't find any pictures of this head before clean-up. Maybe it was of the gasket itself showing the blowout? * RE: Intake aligment. Hmmm... I'll have to check that. Note: Going today to get new feeler gages. The old rusty set I have shows #6 piston to have +.007" standoff (extends beyond the deck). The adjacent pistons don't appear to have nearly that much. I'll measure and record before I tear it down. BTW, the block was "zero decked". I realize the gasket would compensate for standoff too. But it's just more data to collect in my search of "why". Frank - a very good point - I just don't want to have this latest 'weakest wink' happen again. I'd much rather the next link be a split block - that way, I'd know all my crap was working right. I'll post the machine shop's conclusion for future reference.
brand spanking new edelbrock preformer rpm heads (1.90/1.60) undecked factory nov 72 date coded block required .060 longer pushrods.. to align correctly thats why it came to mind no harm in posing a idea for the group intellect >
What do you mean by this? I have a wild theory, but I'm no mechanic or guru so don't laugh. Maybe #6 was too far out of the hole and caused the blown head gasket. It would blow from #6 to #7 because #7 was probably opening for its exhaust cycle and would have low pressure whereas #5 would be closed and have some pressure. Path of least resistance from one cyl to next would be #6 to #7. Then when #6 had no compression it put a lot more load on the #5 cyl, which fires right after 6. Extra load caused detonation in #5.
Note: Going today to get new feeler gages. The old rusty set I have shows #6 piston to have +.007" standoff (extends beyond the deck). The adjacent pistons don't appear to have nearly that much. I'll measure and record before I tear it down. BTW, the block was "zero decked". I realize the gasket would compensate for standoff too. But it's just more data to collect in my search of "why". detonation compressed the top bearing shells and they bottoms are beaten out because of it leaving the piston out of the hole.. (another posing the idea to the collective borg/peanut gallery) waiting for you to pull the bullet and have a look in the bottom end.. should prove to be most intresting
