What's going on with my heads?
Discussion
Pulled the heads off today. Suspected they weren't holding compression. Valley gasket and oil filler always stink like petrol when opened and performance is off.
Lo and behold looks like I have issues with the even bank - cylinders 4 & 6
Can anyone with more expertise pinpoint where the issue lies? To my eye looks like issue with number 1 stud which would match the black marks on the heads themselves.
Heads were skimmed 4 thousand miles ago and refitted with fresh gaskets.
Steve_D said:
You will not know a way forward until you have had the heads and the block inspected.
Even though the heads were skimmed does not mean they are not distorted again.
Steve
Good call. The heads will get inspected. I have a new 4.8 block that has just been skimmed with fresh liners so block *shouldn't be a problemEven though the heads were skimmed does not mean they are not distorted again.
Steve
carsy said:
Did you check tighten those studs after a few hundred miles. Ive found they do need a nip up.
This ^ I also found the same they compress after a fair few heat cycles 
lets not forget Elring HG's are designed to be used with yield/stretch bolts so constant pre-load is certain unlike ARP fasteners I use both, I indexed each ARP before loosening one at a time and found each and every nut tightened further on re-torquing confirmed by index marks , just a warning 
not surprising really 
Oh and this was on a freshly decked block and square head faces and bob on running temps Edited by Sardonicus on Wednesday 30th May 23:02
Sardonicus said:
This ^ I also found the same they compress after a fair few heat cycles lets not forget Elring HG's are designed to be used with yield/stretch bolts so constant pre-load is certain unlike ARP fasteners I use both, I indexed each ARP before loosening one at a time and found each and every nut tightened further on re-torquing confirmed by index marks , just a warning not surprising really Oh and this was on a freshly decked block and square head faces and bob on running temps Edited by Sardonicus on Wednesday 30th May 23:02
I've heard the high-power V8 guys in the US pop a small ball bearing down the hole first so stud bottoms out completely....Might be the way to go debaron said:
I've heard the high-power V8 guys in the US pop a small ball bearing down the hole first so stud bottoms out completely....Might be the way to go
So actually looked into this a bit more. Turns out that installing studs isn't *that* simple a process.With ARP's at least it's *imperative* that the shoulder of the stud doesn't come into contact the deck, by screwing the stud all the way down. This is probably why a ball bearing is used - to allow the stud to bottom out and be able to be torqued up (very lightly) but keeping the shoulder above the deck.
Also it's also imperative that the head stud bores are countersunk. As I understand, when the heads get hot and expand, it can create high spots around the studs on the block if there isn't a little room for expansion there.
On inspection on my block, the bores are countersunk but the threads in stud bore 1 are knackered...Not sure why yet!
debaron said:
So actually looked into this a bit more. Turns out that installing studs isn't *that* simple a process.
With ARP's at least it's *imperative* that the shoulder of the stud doesn't come into contact the deck, by screwing the stud all the way down. This is probably why a ball bearing is used - to allow the stud to bottom out and be able to be torqued up (very lightly) but keeping the shoulder above the deck.
Also it's also imperative that the head stud bores are countersunk. As I understand, when the heads get hot and expand, it can create high spots around the studs on the block if there isn't a little room for expansion there.
On inspection on my block, the bores are countersunk but the threads in stud bore 1 are knackered...Not sure why yet!
I'm not an engine builder so I'm not disputing this, but surely if there was any mushrooming of the head surface when the studs are torqued up that would equally apply to the original bolts being torqued up too, and even them would only be an issue if the mushrooming occured later on and released some clamp load. If the mushrooming was an issue during the torquing up process it would only have an effect once the bulging part exceeded the gasket thickness? And that's only likely if the block had been overheated and the properties of the aluminium changed to significantly soften it ..With ARP's at least it's *imperative* that the shoulder of the stud doesn't come into contact the deck, by screwing the stud all the way down. This is probably why a ball bearing is used - to allow the stud to bottom out and be able to be torqued up (very lightly) but keeping the shoulder above the deck.
Also it's also imperative that the head stud bores are countersunk. As I understand, when the heads get hot and expand, it can create high spots around the studs on the block if there isn't a little room for expansion there.
On inspection on my block, the bores are countersunk but the threads in stud bore 1 are knackered...Not sure why yet!
It's difficult to tell from the pictures of the head faces, but from the markings on the gaskets it looks like your heads have had a very coarse fly cut skim. The carbon is tracking through these grooves in the fire rings. You might want to just investigate what surface prep you need for the gaskets you are using.
It's also difficult to tell because of picture quality but in your very first picture, top right on the edge of the fire ring adjacent the top right stud .. is that pitting evidence of detonation damage?
Pictures need to be better to really get a handle on what's going on .. you also need to run them past pumaracing in the engines section. He's as blunt as anything but it always pays to listen if he throws a titbit of info your way! He's good.
It's also difficult to tell because of picture quality but in your very first picture, top right on the edge of the fire ring adjacent the top right stud .. is that pitting evidence of detonation damage?
Pictures need to be better to really get a handle on what's going on .. you also need to run them past pumaracing in the engines section. He's as blunt as anything but it always pays to listen if he throws a titbit of info your way! He's good.
Edited by spitfire4v8 on Friday 1st June 09:13
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