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  #16 (permalink)  
Old 04-25-2012, 03:30 PM
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My guess is that something made its way into the cylinder and made a funny noise for a moment until it caused the piston to fracture and the bent rod is just collateral damage.

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Old 04-25-2012, 06:11 PM
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Quote:
Originally Posted by prettyboyced
I rev it to 3k but deck clearance was .028 the pistons were speed pro hyperutetic
What exactly does this mean? To my use of the term "deck clearance" this is the amount of space from the crown (not including valve reliefs, dishes, or domes) of the piston to the block surface that the cylinder head bolts to.

If this is the case .028 is extremely tight.

The other important measure is the distance between an open valve and the approaching piston. For a street engine a good rule is the intake misses the piston crown by at least .080 inch and the exhaust by .1 inch. This is because street engines don't get torn down very often and wear in the cam drive can allow the piston and valve to meet.

For a competition engine you can run this tighter say .050 and .080 with the understanding that over a season the critical wear items will be checked if not replaced.

This is an effort on top of squish/quench clearance which pretty much requires the engine be assembled with clay on the piston and rotated to get an impression of the valve then opened up, measured, adjusted if necessary, then reassembled. Here's a link to the process http://www.carcraft.com/howto/116_07...e/viewall.html

Let me add that when you do this it must be with a solid lifter, a non running hydraulic cannot be trusted to maintain position of the plunger against the retainer (even a pumped up lifter may sink against valve spring pressure) so either use a solid for testing or take apart a hydraulic and fill it with washers just as you would for determining push rod length.

I'm surprised at the bent rod, not so much at the hyper piston gone to pieces. The valve and valve train usually gets the worst of this type collision but hypers are quite strong but brittle, they don't like to be hit. The bent rod is more like something you see with a hydraulic lock. While this is usually coolant getting into the bore it can also be the result of too much oil or fuel or other liquid being poured into the intake system prior to start up. It's possible this started with liquid in the bore and the valves got bent as the piston came apart. But your dimensions and the bent valve really point me at the clearance between pistons and valves.

Bogie
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