Posted by Gordon on Saturday, April 27, 2002 at 2:20PM :
In Reply to: Re: didn't realize............. posted by KenWeza on Saturday, April 27, 2002 at 11:11AM :
It's not really a case of them penetrating the water jacket, merely that it's not good casting practice to make it ( the block casting) thick enough so such a hole wouldn't penentrate the casting section.
It's difficult to make any engine casting, particularly a flathead when so much detail in the valve area is included. If you broke an engine block you might find 3/32" more thickness on one side of the engine just depending on how the internal profiles were formed by the sand cores. Normal practice is to make a trial and break it to measure section thickness all over, and then grind material off the mould patterns that form the inside of the engine block to thicken up the actual casting at whatever point you find to be thin.
Normal practice with studs is to have a dual thread, with UNC on the end that goes in the casting and UNF on the end that is exposed. that way the coarse thread can be locked permanently into the casting, and more torque can be applied to the nuts that go on the fine thread. It all falls apart on manifolds (literally)because the exposed UNF threads that are on the stud nuts rust a lot more than the ends inside the casting, which means when you turn the nuts it tends to turn the stud out of the block.
A related problem is cylinder head bolts, particularly on the MB / GPW jeep or any flathead. People re-finish the block and head, thereby losing hole depth in the block, and then try to tighten the jeep head bolts down enough to stop blowing gaskets --- and just strip the head bolt threads in the block instead. Proper solution on such an engine is to use cylinder head studs instead with UNF / UNC ends, then just drop nuts onto the UNF end. If you have really lost section thickness you can put a washer under each nut.
Gordon
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