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The piston line up. When Mercury came out with the Direct Charge it did not have a boost port. The piston did not have a hole. Then the boost port was created and the hole was added. Later they decided to add the eyebrow clip on the piston crown. So, on the left you have a service piston with the dome clip for non boost ported. The test piston I cut down which is the full blown piston with boost hole and eyebrow clip, which is the piston supplied for service today. Then the early version of the boost port piston without eyebrow clip. Next is the piston supplied by Wiseco as requested, my re-machined Wiseco piston and a Quincy Looper 60 inch piston.
The following are pictures of the machine work on the piston to create the loop piston. The changes that Wiseco made were, eliminate the boost hole which would have allowed cross flow between the transfers and the exhaust ports, elimination of the dome eyebrow cut which would have changed transfer timing, the piston is .100 longer on the skirt length below wrist pin for better exhaust port coverage a top dead center which would have been .063 and now .162. The notches for wrist pin keeper removed and the chamfering of the pin hole was eliminated. The wrist pin diameter is large and spans the web between the upper transfer ports and the web between the exhaust ports. Elimination of those operations keeps that width at the wrist pin diameter and to stop the cross contamination thru the wrist pin I will press a .75 long aluminum plug into the mid point of the wrist pin.
With the now known final piston height, I installed a .062 walled sleeve into number 5 hole and bored to size. Set up the block with crank installed and checked the deck to piston to verify port positions and the the final deck height. I had planned for a total remaining removable of .250 from the three faces, case to block, block to case and the head surface. The number came to .260. Removed .085 from case face, .080 from block to case face and .080 from head surface, leaving .015 on head to clean up after sleeve placement and final porting. Will have .015 piston to head running clearance. A guessed at number. The Quincys ran piston flush with the block and the head gasket gave .010 running clearance. Pistons ran so close to the head that there would be a distinct combustion color change on the top of the piston.
The reed blocks are on the crank only as holding fixtures, they split easily, bearings do not need to be loaded and they snap tight into the half case.
Originally Posted by Fastjeff57
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