Quote Roy.
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However, there may be another cause that I am still trying to evaluate as a possibility.
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Some things that pass my mind.
Vacume?
The engines I took apart showed huge diferencences in the amount of coal in the chambers.
Sometimes cilinders had a realy lean burn.
Yes, that is one possibility Herman, and a good one in some respects. As I said previously, in all my own cars I have not had a head cracked, but I have seen it with many others cars. So this raises a question why? Now it may be that as I attend to any faults quickly, such as a leak on the headlamp vacuum system which would cause lean running and high cylinder temperatures; or a loss of coolant; both which could lead to cracking, are eliminated. So good maintenance will be a factor here.
Did the Turbo engine had this trouble to when mounted in a Peugeot?
It was hanging freely in the front of 505 getting more air to cool down where the Murena engine is locked away in the mid section.
Whilst the mid-engined location probably means higher engine bay temperatures, if the cooling system is in good condition I know it can cope as my cars have run fine without problems over many years. However, going back to the fact of high cylinder temperatures - another reason for this can be people using non-standard air intake systems. You often see people who have dispensed with the original air filter and intake, especially if they have converted to twin side-draught carbs. such as Weber DCOE or Dell'Orto DHLA but with 'pancake' air filters. The original 'S' used the same type of air filter as the standard car, and the air pick up is low down to get cool air. Using pancake filters on the carbs. or none at all, means drawing hot air from the top of the engine bay and that will not be good for the engine - it will mean higher cylinder temperatures and less power as the hot air is less condense with consequently lower oxygen.
As I can recall the oil pump also generated problems in fast corners.
Whilst the oil pressure does drop slightly in long fast right hand corners, this has never caused a problem with mine, and should affect the things that are oiled, first, such as main and big-end bearings, and should have almost no effect on the cylinder head. Plus, as I have always said, use a really good oil - at least semi-synthetic - I have always used fully synthetic, and even the lower pressure in those corners is still over 2.5 bar and that is plenty for an engine to keep it lubricated well.
There are too much cracked head from Murena's.
Thre must be a cause to that.
Yes I agree, but I think in a large number of cases it is down to those things I have already mentioned: poor maintenance, letting the coolant drop, running with leaks in the headlamp vacuum system, using pancake air filters breathing at the very hot top of the engine bay, etc. Other factors may be running too much anti-freeze or not enough, having a slack vee-belt that slips so the water pump does not pump correctly, or allowing the radiator to become too silted, not changing the thermostat and coolant often enough...
Pictures of various Murena cylinder heads...
I am also curieus why this happen so often.
There must be something structural wrong with this heads or secundairy circumstances that cause it.
Herman
Again I agree, the heads always crack in the same areas, which makes it easy to check them as you always know where to look first!
However, whilst a lot may be down to poor maintenance, I also think there might be a contributing factor in the head casting design. If there are 'shapes' in the internal design that cause 'hot pockets', i.e. small steam bubbles, to form; these will cause local overheating even though the overall coolant level may be fine. The heat can only transfer to the coolant as long as it stays in contact with the metal. If you get a steam bubble form in a pocket, the heat transfer immediately stops or drops drastically, and this can lead to stress cracking in those areas. This is why I am going to investigate using waterless coolant. Even if the local pockets still run slightly hotter, the waterless coolant will not form a gas pocket as it does not boil until it reaches 180 degrees, and any engine that hot would have seized anyway! So the liquid will remain in contact and heat transfer will still take place.
Roy