Got the block back from the machine shop. I’ve had this Benson sleeved block machined 4 or 5 times and every time they tell me the sleeves walk. It’s never been an issue but it has to be a result of the open deck, unsupported sleeve design. However this time they told me the sleeves tilted about .002” but grew about .010” above the deck! He squared them up to the crank and had to mill off about .009 ~ .010” before the sleeves matched the aluminum. Oddly the 2 outer sleeves didn’t stand as proud. It’s almost like it was a stepped deck, but it wasn’t.
I don’t understand how that’s possible but the deck had to be made flat. What sucks is that we had agreed on milling .005" off the deck so I had built the custom pistons with .005” lower compression height to compensate and keep my piston to head clearance the same as last year. To compensate I will need to get a thicker head gasket now.
The cylinders are bored and honed to 3.3445" or 84.95mm with .0040 ~ .0045" piston to wall clearance. I ran .0035" p2w last year without issue for those of you who are keeping track.
The O-ring groove was a b!tch to cut. 85mm bore didn’t leave a lot of room and I told them I didn’t want to rings to overlap if possible. The cutter they had would not fit a bore smaller than 3.5”. He ended up cutting it manually with a square carbide tooth cutter in a Criterion boring head in a Bridgeport mill. The groove is .040" wide and 0.028" deep. The copper wire I will be using is 18 gauge or .0403”.
There is a tiny chip or tooling mark on cylinder #4 intake side. But its on the inside of the ring. I dont think it will be an issue.