fzmax
Well-Known Member
This is probably not a very common combination as most people wouldn't consider RHS heads for a 318 in the first place, but that's a story for a different thread. The question is whether or not the domed Keith Black pistons will work with the as-cast RHS X-Heads. The answer is kinda.
There may be another thread about this, but I was unable to find any definitive answer before I started ordering parts and even Brian at IMM didn't think there would be a problem. Unfortunately when I had my block here to check the deck heights the heads had not yet arrived.
Long story short, the outside edge of the dome contacts the edge of the combustion chamber while it's still .062 in the hole. The actual running clearance will be less once the head gasket is fully compressed.
Using a piece of paper and a razor I made a template of the combustion chamber and laid that over the piston to find the point of contact. I'm not about to pull the pistons, cut them and re-balance the assembly, so I am thinking of putting a chamfer on that edge of the combustion chamber.
If my geometry skills are correct I will need to break that edge about .100 in each direction for about an inch wide, then blend the edges to remove the sharp corners. This would give me .040 clearance, shouldn't add more than a single CC and losing the sharp edge in the combustion chamber won't hurt anything.
I've attached some pics so you can see what I'm talking about. Anyone see anything I'm missing?
Paper Template:
Contact point on piston highlighted by Sharpie:
Actual Mark on Piston:
Thanks in advance for your input.
There may be another thread about this, but I was unable to find any definitive answer before I started ordering parts and even Brian at IMM didn't think there would be a problem. Unfortunately when I had my block here to check the deck heights the heads had not yet arrived.
Long story short, the outside edge of the dome contacts the edge of the combustion chamber while it's still .062 in the hole. The actual running clearance will be less once the head gasket is fully compressed.
Using a piece of paper and a razor I made a template of the combustion chamber and laid that over the piston to find the point of contact. I'm not about to pull the pistons, cut them and re-balance the assembly, so I am thinking of putting a chamfer on that edge of the combustion chamber.
If my geometry skills are correct I will need to break that edge about .100 in each direction for about an inch wide, then blend the edges to remove the sharp corners. This would give me .040 clearance, shouldn't add more than a single CC and losing the sharp edge in the combustion chamber won't hurt anything.
I've attached some pics so you can see what I'm talking about. Anyone see anything I'm missing?
Paper Template:
Contact point on piston highlighted by Sharpie:
Actual Mark on Piston:
Thanks in advance for your input.
I actually like a high winding 318! 
