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Joined: Apr 06 2020
Posts: 24

Hi all,

I'd like some opinions on my V8 situation. 2001 4.6 Thor.

1600km ago I replaced the headgaskets as they had started blowing combustion out of the side of the engine. Not unexpected as the previous owner had decided fancy headbolts were unnecessary and some threaded rod would do just fine. At the same time the heads were skimmed 10thou, valves lapped and and valvestem seals replaced.
I used Elring headgaskets and Allmakes stretch bolts. One of the bolts (rhs head, inner bolt, furthest forward) seemed to go into elastic deformation slightly earlier than the others during the 20Nm, 90deg, 90deg torque procedure. At the time it did bother me a little, but I decided to just soldier on and get the engine together.

After the headgasket job the engine ran beautifully for about 1600km until this past weekend when I felt that the top radiator hose was just a little more pressurised than it should be. I couldn't find anything else wrong and the coolant level remained constant so I chalked it up to paranoia on my part. Drove it to work on Wednesday morning and as I got to the office it had started puking some coolant out of the overflow and the top radiator hose was again pressurised. Something wrong!

Did a compression test last night:
1-->127psi; 2-->110psi; 3-->122psi; 4-->125psi; 5-->124psi; 6-->122psi; 7-->120psi; 8-->120psi

Obviously something wrong on cylinder 2.

So, I'm ordering going for Elring headgaskets again. Is this fine or should I look at something else? (Elring is available here in SA, but I can import something else if it'll be better)
I've ordered a set of ARP head studs (157-4301) this time round. I've seen conflicting info on the torque procedure for these, what did you guys do?

Anything else I need to be concerned about? Anything else to check out?

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Joined: Dec 30 2015
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and as cylinder 2 is the front right, that would allow pressure into the water passage so it looks like your diagnosis is correct.

Elring are fine and I've used ARP studs in the past rather than the stretch bolts. I was advised by V8 Developments to torque them to 80-85 Nm, which works out at just under 65 ft/lbs which I'm more used to. Going on other alloy engines this seemed about right so I do them in three stages, to 35 ft/lbs (45 Nm), then 50 ft/lbs (68 Nm), then finally to 65 ft/lbs (88 Nm).

You may find that it wasn't the bolt stretching but the thread starting to pull out of the block. If the thread has pulled out of the block, or at least it has been weakened, you may not be able to torque it properly and the block will need to be helicoiled. On one engine that had been seriously overheated, I had to do all three of the upper middle ones (the long ones). I used a couple of the ARP studs as a standoff to hold an old head gasket 3 or 4 inches above the block face, that gave me a guide to drill and tap the block so it was perpendicular to the face. Then screwed 2.5x diameter helicoils in. I had to buy a pack of 10 helicoils so still have a few spare if you can't get hold of them

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Joined: Apr 06 2020
Posts: 24

Thanks for the info Gilbert, especially the idea with using the headgaskets as a guide for drilling and tapping the holes if the threads are damaged.
The engineering shop that skimmed my heads were busy with a 4.6 rebuild and the owner of that engine insisted that they replace all the threads with helicoils as a precaution. Hopefully the shop has some extra helicoils on hand if I need them. I'll find out when I strip the engine.

I did chase the threads with the correct thread chaser when I did the headgaskets before and they felt good thereafter, but you never know until they fail.

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Joined: Jul 21 2020
Posts: 143

I wouldn't rule out a problem with the actual block itself. It may be that combustion is escaping into the water system.

I had this once on a 4.0 Disco which culminated in the top radiator hose exploding with the excessive pressure! That was some years ago, a slipped liner from memory.

The second time I had this was on my 5.5 RV8 TVR. That was a split in the aluminium block behind the liner.

I don't like the sound of your stretch bolt going elastic, (which I doubt, more likely thread started pulling as said).

I don't envy you. I'll be tempted to take the engine out, strip it down and have the block tested. If it is a long-term keeper then have it top hatted and rebuild from there.

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Joined: Apr 06 2020
Posts: 24

Yes, the porous/cracked block issue is definitely something I am concerned about!
The previous owner of the car had the bottom end rebuilt while he owned it, and had the rebuilders fit top-hat liners, so slipped liners won't be a problem. Obviously this won't solve anything if the block was cracked behind the liner, so it is still a concern.

After I redid the headgaskets the engine ran beautifully and wasn't using any coolant, or pressurising the coolant system at all, until last weekend when the problem appeared and started getting worse quite rapidly (within probably 80km of driving). If the problem is a crack behind the liner then surely it would have used coolant from the start, or at least over pressurised the coolant system from the get go?

The "stretch bolt going elastic", as you put it, is the design intent with stretch head bolts.
Quite a nice explanation here: https://www.enerpac.com/en-gb/boltingtheory
My concern is that the quality of the bolts supplied isn't consistent, so applying the same torque to the bolts might make a weaker bolt stretch more than the others and possibly go into the plastic deformation stretch range instead of remaining in the elastic range as it should. This would cause the gasket to not be clamped sufficiently in the area around the bolt causing symptoms consistent with mine (I hope!).

Should I be looking at checking and setting the tappet pre-load (http://www.v8engines.com/engine-4.htm#preload) while I wait for the head studs to arrive? Am I correct in saying I'd need to remove and bleed down the lifters before doing this?
Would a 10thou skim from standard be enough to push the tapped pre-load out of spec, or is this something worth doing anyway?

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JLImmelman wrote:

My concern is that the quality of the bolts supplied isn't consistent, so applying the same torque to the bolts might make a weaker bolt stretch more than the others and possibly go into the plastic deformation stretch range instead of remaining in the elastic range as it should. This would cause the gasket to not be clamped sufficiently in the area around the bolt causing symptoms consistent with mine (I hope!).

Should I be looking at checking and setting the tappet pre-load (http://www.v8engines.com/engine-4.htm#preload) while I wait for the head studs to arrive? Am I correct in saying I'd need to remove and bleed down the lifters before doing this?
Would a 10thou skim from standard be enough to push the tapped pre-load out of spec, or is this something worth doing anyway?

That is my concern with stretch bolts. The ones that were originally fitted 20 odd years ago would have been made to a specific specification but you've no way of knowing if the ones available these days are to the exact same spec. While the stud kit is not cheap, using them, along with top hat liners will give you a much stronger engine.

10 thou shouldn't take the preload out of limits but it's worth checking anyway. There's a much easier way of checking it here http://www.v8developments.co.uk/technical/valve_train/index.shtml.

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Joined: Apr 06 2020
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Turns out you were right Gilbert! Started torqueing down the head this evening, and the suspect bolt (nr. 10 in the sequence) wouldn't reach it's torque, damn threads pulled out. Meh.

This is definitely the spot where the headgasket was leaking though, evidence of combustion escaping into the water channel could be seen on the block so at least there is conclusive proof of that.

So while I was waiting for the ARP studs to arrive from the US I also decided to replace the camshaft and lifters, so everything to get at them has also been stripped off. The nose of the vehicle is sitting quite a bit higher what with all the weight that has been stripped off and away around the engine :D

The AC condensor was actually damn dirty and clogged with years of muck which also took a while to clean. This has turned into quite a big job!

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That's always the way, you start on one job then notice something else that needs doing while you are in there. In most cases it hasn't yet made it's presence felt yet but will do sooner or later. While changing my intermediate steering shaft recently I noticed one of the engine mount rubbers had perished and split so I've got a pair of those to fit sooner or later. I've got the new ones and it isn't a big job but it does involve dragging the engine crane out to support the engine to change them and that's down the side of the garage buried under all sorts of other rubbish.

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Joined: Apr 06 2020
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Engine is all back together and running beautifully.

Fitted a helicoil where the threads in the block was damaged, which actually went quite smoothly. I bought a kit to do it with which included the correct drill bit and a helicoil fitting tool which made it easy. Was a bit nervous torqueing that head down for the 2nd time, but it all went smoothly! Happy :)

I ended up spacing the rockers by 20thou to get the tappet preload within spec. I used stainless steel shim stock, because it is what a mate of mine had on hand in the right thickness. It was a bastard to punch, but went together beautifully. Happy with that too!

I'm not sure if it is the new cam, magnecor leads, tappet pre-load setting or the new Bosch coils, but the fuel consumption seems to have decreased by around 1.5l/100km.
Mind you I've only done around 150km so far, but there is definitely an improvement, and mid range torque also seems up. Super happy with that!

All in all a good outcome. Now I just hope the headgaskets hold!

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Joined: Dec 30 2015
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If all the nuts torqued up properly, there's no reason the gaskets shouldn't last. Sounds like you've done a good job, well done.