Originally Posted by heretic' post='751118' date='Aug 22 2005, 05:41 PM

Aye.



Aluminum expands at three times the rate of iron



At engine temperatures, aluminum gets sufficiently close to its melting point to lose a lot of strength. Maybe not weak enough for it to pour out into the oil pan, but enough to get tweaked under load.



Combine these two quirks, and you get the aluminum trying to force iron pieces apart, and the hotter it gets the more it tries to expand and the weaker it gets.



Mazda engineered the tension system to hold the engine together just enough when cold, yet still permit enough give for the engine to expand when hot. Proof that they did some scary-edge engineering is that you can blow coolant seals on a very cold engine, and yet you can also run the engine too hot and crush the rotor housings, which leads to blown coolant seals after it cools down because the tension bolts lose their tension, what with the housings being smaller and all.



Trapped between fire and ice.



As before, none of this is anything new. It's why when aluminum cylinder heads first started showing up, blown head gaskets were rather common, and these problems have been solved by using very long bolts that are stretched a lot when cold, yet have plenty of stretch left in them to accomodate thermal expansion.



How many people make sure that all engine parts, including the bolts, are kept at a climate controlled 70 degrees F before assembling the engine?