Ghibli de Hongrie [ENG]

[alpa]

Yes, I've read about it since then. What's special about the heads' cooling? I'm starting to understand why this engine is said to be well designed, contemporary and ahead of the others.

There is a collecting galery on the top (intake) side of the head and two outputs from the galery: front and rear. This is good to balance the water flow and make water go up to the rear of the head before returning to the pump. The traditional way to balance the flow is by increasing block-to-head passages (or even blocking them) in the head gasket, but this does not work well at low RPM. And it can not be modified once the head on.m not saying it's perfectly used in the engine, but at least it's potentially perfect.
In fact these engines (18v and 24v) run very lean for turbo engines, they stay at 1 richness even WOT. Most of engines would melt pistons down, these ones are just fine. The only explanation with this hp/L ratio: excellent cooling.

As we know the rings are not available from Maserati anymore, but did someone maybe sources custom rings from any manufacturer?

No grooving used pistons is a waste of money. Additionally your pistons are forget and quit good, using them with antic 1.5 rings would be a bad choice.
There are many ring manufacterers custom or not, in Europe and US. Check their catalogues.
Carrillo (italian, first choice), Arrow, King Pistons, Total Seal, Wiseco, Goetze.
Don't forget japaneese NPR.
There is a story about which kind of ring material you should use with 2L liners, but I'm not sure there is any difference with iron liners. Liners are Nigusil coated (not Nikasil as many say), if you query a company you may want to specify this. I made a thread about that 2-3 years ago.

[spacecadet]

Thanks for the interesting information regarding cooling.

Definitely don't want to re-groove the pistons with those thick rings. Will ask around the ring manufacturers mentioned.

[spacecadet]

I found rings at Wahl Pistons (they were originally with Mable, still using their blanks) in Germany. They kindly even offered to swap my 1.5 set with a 1.2 set. But to be completely sure I've sent them the pistons and the pins. In the pistons they cut contact reduction grooves above the first ring and an accumulator groove between the first and second ring. Also measured the grooves and turned out the axial clearance was too big so they did cut 1.5 grooves. Besides on the second ring they cut a Napier groove. With all the modifications the changing to 1.5 won't be such a big issue. The pins were also reconditioned, they used a method which is even finer than honing. All of the above on a very reasonable 25 EUR / piston price.

[Konimino2]

I found rings at Wahl Pistons (they were originally with Mable, still using their blanks) in Germany. They kindly even offered to swap my 1.5 set with a 1.2 set. But to be completely sure I've sent them the pistons and the pins. In the pistons they cut contact reduction grooves above the first ring and an accumulator groove between the first and second ring. Also measured the grooves and turned out the axial clearance was too big so they did cut 1.5 grooves. Besides on the second ring they cut a Napier groove. With all the modifications the changing to 1.5 won't be such a big issue. The pins were also reconditioned, they used a method which is even finer than honing. All of the above on a very reasonable 25 EUR / piston price.

Interesting to know. Who in Germany?

[spacecadet]

https://wahl-spezialkolben.de/fr/

[alpa]

With all the modifications the changing to 1.5 won't be such a big issue. The pins were also reconditioned, they used a method which is even finer than honing. All of the above on a very reasonable 25 EUR / piston price.

It's cheap for sure.
And for sure the engine will work with thicker rings. They are just heavier and higher tension, I understand they seal less on partial engine loads and they may vibrate at high RPM.
They all add everywhere these decompression grooves, I understand they are needed only when the volume above the ring is low like on modern pistons. Otherwise they lower sealing even more on partial loads. It's good for high boost engines, 1 bar is not high, race engines run 1.5-2 bars boost. I don't remember how are Ghilbli pistons but I believe the crown is quite high so it's already "decompressed". Well I'm not an expert.

[spacecadet]

I'm especially not an expert so I accepted their advice after explaining the parameters the engine. But your points do make sense as well. Since there is no turning back now (don't want to buy new pistons), I put together the block.





I also put back the valves into the heads earlier, but found some left-over dirt hiding in the oil galleys Finally today was engine build day, so took apart the heads again, and clean, clean, clean. It's pretty much spotless now. Then measured the combustion chambers. 38.5 cm3 on one head, 40 cm3 on the other. Damn machine shop Calculating with 38.5 cm3 the compression ratio changes from 7.6:1 (that's with the factory 41.5 cm3) to 8:1. I hope it's acceptable. Probably will take down a bit more from the other head too, to get identical numbers. Hopefully won't consume both in the end

Feels like 1 step forward, 2 steps backwards, but I'm telling to myself, it's better to discover these things before assemby and getting a badly running / short living engine.

[Froggie]

It's a bit scaring to discover all the required adjustments that appear sound on paper, but then the (small) departures from expectations when making your way.
To me however (a no-expert ) you are taking the right decisions and you seem to work with a lot of care.
Wish you good success!

[alpa]

I also put back the valves into the heads earlier, but found some left-over dirt hiding in the oil galleys Finally today was engine build day, so took apart the heads again, and clean, clean, clean. It's pretty much spotless now. Then measured the combustion chambers. 38.5 cm3 on one head, 40 cm3 on the other. Damn machine shop Calculating with 38.5 cm3 the compression ratio changes from 7.6:1 (that's with the factory 41.5 cm3) to 8:1. I hope it's acceptable. Probably will take down a bit more from the other head too, to get identical numbers. Hopefully won't consume both in the end

Please don't touch the heads !

Yea it's difficult to find competent people. I wonder if they still exist. I prefer doing machining by a general mechanic machine shop: they don't pretend to understand engines, they just properly do whatever I ask them to do.

Check again chamber cc. If they are that different then check piston crown thickness. If you have let's say 5mm of thickness then remove some material from the top to increase the cc. You don't care about pistons, at the next rebuild they'll be worn. Ghibli (like all our biturbo engines) run lean (stoichio in boost), increasing CR that much is dangerous.
The other valid solution would be to use a thicker head gasket but they don't exist, you would need a custom made one. I wonder if we'll end up with this solution anyway, after having surfaced the heads 2-3 times.

[spacecadet]

That's exactly what I was afraid of, you already wrote above that these engines run lean (wonder why though).

If I change the pistons on only one side, won't that cause imbalance because of the different weights on the two sides?

I though the lack of competent people is only a local problem for me, but seems like it happens globally, which sounds quite bad.

[Froggie]

Check again chamber cc. If they are that different then check piston crown thickness. If you have let's say 5mm of thickness then remove some material from the top to increase the cc. You don't care about pistons, at the next rebuild they'll be worn.

How is it possible to have such a 5 mm difference on new pistons' dimensions?
It seems huge to me...

If I change the pistons on only one side, won't that cause imbalance because of the different weights on the two sides?

Not a specialist but that will certainly substantially impact the weight of each piston and hence the overall balance.
Might require a rebalancing of all the pistons/rods system...

[alpa]

That's exactly what I was afraid of, you already wrote above that these engines run lean (wonder why though).

If I change the pistons on only one side, won't that cause imbalance because of the different weights on the two sides?

I though the lack of competent people is only a local problem for me, but seems like it happens globally, which sounds quite bad.

Already explained: they run lean for turbo engines, they run stoichio in boost, because extra-enrichment is mainly for the charge cooling. These engines have excellent cooling system so they don't need extra-cooling.

In theory you'll have an imbalance. In practice you'll remove few grams but will get back combustion balance. While now the balance is (should be) good but combustion is imbalanced which is not good. A v6 engine is never fully balanced and especially an odd-firing one, it's all about compromises.

[alpa]

Check again chamber cc. If they are that different then check piston crown thickness. If you have let's say 5mm of thickness then remove some material from the top to increase the cc. You don't care about pistons, at the next rebuild they'll be worn.

How is it possible to have such a 5 mm difference on new pistons' dimensions?
It seems huge to me...

That's not what I said.

[Froggie]

Check again chamber cc. If they are that different then check piston crown thickness. If you have let's say 5mm of thickness then remove some material from the top to increase the cc. You don't care about pistons, at the next rebuild they'll be worn.

How is it possible to have such a 5 mm difference on new pistons' dimensions?
It seems huge to me...

That's not what I said.

I understood we were talking of a 3 cc discrepancy (38.5 compared to factory 41.5), so a thickness to be erased from the top of the piston of close to 5 mm and about 10 g (if in aluminum alloy).
I would not be happy to machine off the piston(s) such a thickness of material by trial and error and play with the overall balance of the mobile train.
But if this is the only option left...

[alpa]

82mm Bore -> 4.1x4.1x3.1415 / 10 = 5.28cc/mm
3cc -> 0.57mm off
If the crown is 5mm thick then removing 0.6mm in average does not hurt. If it's 2mm then it's a problem.

[Froggie]

Sorry, my mistake, 0.5 mm.
Still need to find a good machining shop

[alpa]

No need for shop, a Dremel is far enough.

[spacecadet]

Already explained: they run lean for turbo engines, they run stoichio in boost, because extra-enrichment is mainly for the charge cooling. These engines have excellent cooling system so they don't need extra-cooling.

Ok, understood now

In theory you'll have an imbalance. In practice you'll remove few grams but will get back combustion balance. While now the balance is (should be) good but combustion is imbalanced which is not good. A v6 engine is never fully balanced and especially an odd-firing one, it's all about compromises.

What about slightly reshaping the combustion chamber. It's much harder to do consistently and measure precisely, so not a good option in practice, but would it work in theory?

Custom head gasket would also only work by using two different thicknesses on the two sides, 2 cc difference -> ~0.4mm which also doesn't sound like a good option.

I really don't understand how could they make such a mistake... Looks like I have to learn machining (and bodywork) too. Last time it was painting, at least preparation, sanding, primer, the most important what they usually are lazy to do properly.

But I'm thinking about getting a different used pair of heads. Which means I loose the newly installed valve guides. But would like to have a stable engine, which can run at least another 150k kms.

[spacecadet]

No need for shop, a Dremel is far enough.

That I have

[alpa]

What about slightly reshaping the combustion chamber. It's much harder to do consistently and measure precisely, so not a good option in practice, but would it work in theory?

I think these heads are much more valuable than pistons that can be easily custom made.

Custom head gasket would also only work by using two different thicknesses on the two sides, 2 cc difference -> ~0.4mm which also doesn't sound like a good option.

0.4mm is nothing. People use two composite heads gaskets with a copper gasket in the middle and then run 2bar boost or even more.