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Old 02-23-2009, 12:07 PM
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Originally Posted by BIGWISEXY
they are 194 and 202 i believe. every thing is clearing, there is no shouting and the pistons are not hitting the heads valves. The 202 valve on cly 8 intake side is hung open. I have takin the head off already. but this is the only one having the problem,, we had it up to about 3500 rpm then we heard the valve hit the piston. but like i said no other cly is doing this.. I believe my machine work was bad,,
A 1.94 inch valve is right on the edge of what can be stuffed on top of a 283 bore, care must be taken to insure that all the valves will clear the cylinder walls. A 2.02 is guaranteed to hit the wall.

Normal manufacturing tolerances are more than enough to create a situation where some heads will have problems and others won,t.

Any Hot Rod parts store will have a selection of off set locating pins that are used to align the head such that once the valves are known to clear, the head will return to that position.

Testing is done with the engine disassembled. The heads are installed and located for proper position to the cylinder from the bottom of the engine so you can see up the bores. Minimum clearance to the cylinder wall is our commonly seen .050 inch.

Baring that, the wall needs to be relieved to provide sufficient clearance. This is the technique of last resort in my book, try to get the head lined up first.

Keep in mind you're dealing with tolerances with the bore center position, the valve pocket, port, seat and guide positions. All this can add up to problems. As previously stated aligning the head position can be used to overcome these issues as can relieving the top of the bore where the valve interferes, or the guide position can be moved which of course also moves the seat and possibly the spring pocket. Unfortunately if you're running a 1.94 and certainly a 2.02, the chamber may be out of space in which to machine a new and relocated seat.

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