Range EFI 3,9 cylinder head diagnostic

Good morning,
following my disassembly for my range with lower engine redone 12 years ago (very little driven since) but which notably lacked power, I took the compressions on my right cylinder head, 12 to 12.5 bars which is rather fine, except on the 1st where I couldn't take any compression because the spark plug threads were messed up. as I had one or more leaky injectors, that was one more reason to remove the cylinder head.
Diagnosis from my side:
- the gasket is metal, I expected a composite, thicker because the cylinder heads were resurfaced during the 2008 repair. In any case the gasket is in good condition, apart from a little corrosion on the 1st water passage.
- The cylinder head plane also looks good to me, very slight corrosion and no visible cracks
- The inlet valves are not badly carbonized although few km since the restoration (or the cylinder head had not been cleaned?) and the exhaust valves are light brown. 1st question, is it worth it to remove the valves, or just to check the tightness of the combustion chambers.
- the pistons are carbonized except on their periphery...maybe a more recent leak from the injectors?
- the cylinders are scratched, and this is my biggest source of concern and questioning: very little marked horizontal scratches, and a few more pronounced vertical scratches, which can be felt when passing your fingernails...signs of the repair of 2008 which would have been badly done? origin of the loss of power of my beautiful V8?

Thank you for your feedback and your answers to my questions.

Having got that far, it would make sense to remove, clean & re-lap the valves for a better seal. There will probably be carbon build up at least on exhaust valve shafts as well. Also this way you can clean the inlet & exhaust ports properly.

Another trick is to install the old spark plugs & pour in some carb cleaner to soften the carbon. That will also show if any valves are leaking !!

Definitely check the head & block for flatness with a steel rule. Also clean the threads & all oil passages.

I used ARP studs on my P38 heads, but definitely check if you have 10 or 14 bolt heads.

pwood999 said:

Having got that far, it would make sense to remove, clean & re-lap the valves for a better seal. There will probably be carbon build up at least on exhaust valve shafts as well. Also this way you can clean the inlet & exhaust ports properly.

Another trick is to install the old spark plugs & pour in some carb cleaner to soften the carbon. That will also show if any valves are leaking !!

Definitely check the head & block for flatness with a steel rule. Also clean the threads & all oil passages.

I used ARP studs on my P38 heads, but definitely check if you have 10 or 14 bolt heads.

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I'm surprised you can see head distortion with a steel rule. I used to use plate glass and engineers blue.

The horizontal scratches look to have been caused by debris, usually loose carbon deposits or foreign dirt got in there when it was being built, swarf from when the heads were skimmed for example.

Being its a pre serp engine you have standard headbolts not TTY so tin gaskets are a standard fit.

Composite gaskets are slightly more forgiving but your compression ratio does drop slightly.

pwood999 said:

Arrivé aussi loin, il serait logique de retirer, de nettoyer et de roder les soupapes pour une meilleure étanchéité. Il y aura probablement une accumulation de carbone au moins sur les arbres des soupapes d'échappement également. De cette façon, vous pouvez également nettoyer correctement les orifices d'admission et d'échappement.

Une autre astuce consiste à installer les anciennes bougies d'allumage et à verser un peu de nettoyant pour carburateur pour ramollir le carbone. Cela montrera également si des vannes fuient !!

Vérifiez définitivement la planéité de la tête et du bloc avec une règle en acier. Nettoyez également les filetages et tous les passages d'huile.

J'ai utilisé des goujons ARP sur mes têtes P38, mais vérifiez bien si vous avez 10 ou 14 têtes de boulons.

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Merci pour les conseils.
Je vais vérifier mes 14 boulons : taille, endommagement... avant de les remonter...

Henry_b said:

Les rayures horizontales semblent avoir été causées par des débris, généralement des dépôts de carbone lâches ou des saletés étrangères qui s'y sont introduites lors de sa construction, des copeaux provenant du rasage des têtes par exemple.

Étant donné qu'il s'agit d'un moteur pré-serp, vous avez des boulons de culasse standard et non des TTY, de sorte que les joints en étain sont un ajustement standard.

Les joints composites sont légèrement plus indulgents, mais votre taux de compression baisse légèrement.

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Je pense que je vais reprendre un joint en étain...

Datatek said:

Je suis surpris que vous puissiez voir une distorsion de la tête avec une règle en acier. J'avais l'habitude d'utiliser du verre plat et du bleu ingénieur.

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Je vais prendre une règle en acier et un jeu de cales.