04-11-2020, 09:56 PM
Hi Terry.
You are correct about the pistons. The shotest piston was used in saws with 1.375 stroke and the Mc-5 Kart engines, also 1.375 stroke. The longer piston was used in saws with 1.50 stroke and 1st year Mc-10 kart engines (all had thick rings) also 1.50 stroke. The skirt legnth of the piston was increased so the exhaust did not free-port. ALL Mc-6 pistons had THIN rings, but the piston was the same except for being thin ringed, as the one you showed. Late model Mc-10s had the thin ring piston used in Mc-6s. ALL Mc-10 stroker (1.625 stroke) pistons had thin rings. The Mc-10 stroker pistons had a longer skirt legnth than the longest piston you show (being 0.080 longer than the pistons used in saws with a 1.50 stroke or in Mc-6s/Mc-10s) again so the exhaust did not free-port. The piston on the Mc-9 rod that Kirk showed was, in fact a stroker piston for 1.625 stroked Mc-6/Mc-10 engines. The top ring is also 0.0625 lower so it doesn't come out of the cylinder at TDC. 1.625 stroke mc-6s/Mc-10s have the piston pop out of the cylinder at TDC
between 0.0625 and 0.065 thou. A THICK head gasket is used so the piston does not hit the head. The longest skirt piston creates no problem for clearence on the bottom of the stroke. And YES the scolloped piston top changer the intake port timing by opening the intakes sooner. It is probably a Moss Piston.
Best Regards TORQUE
You are correct about the pistons. The shotest piston was used in saws with 1.375 stroke and the Mc-5 Kart engines, also 1.375 stroke. The longer piston was used in saws with 1.50 stroke and 1st year Mc-10 kart engines (all had thick rings) also 1.50 stroke. The skirt legnth of the piston was increased so the exhaust did not free-port. ALL Mc-6 pistons had THIN rings, but the piston was the same except for being thin ringed, as the one you showed. Late model Mc-10s had the thin ring piston used in Mc-6s. ALL Mc-10 stroker (1.625 stroke) pistons had thin rings. The Mc-10 stroker pistons had a longer skirt legnth than the longest piston you show (being 0.080 longer than the pistons used in saws with a 1.50 stroke or in Mc-6s/Mc-10s) again so the exhaust did not free-port. The piston on the Mc-9 rod that Kirk showed was, in fact a stroker piston for 1.625 stroked Mc-6/Mc-10 engines. The top ring is also 0.0625 lower so it doesn't come out of the cylinder at TDC. 1.625 stroke mc-6s/Mc-10s have the piston pop out of the cylinder at TDC
between 0.0625 and 0.065 thou. A THICK head gasket is used so the piston does not hit the head. The longest skirt piston creates no problem for clearence on the bottom of the stroke. And YES the scolloped piston top changer the intake port timing by opening the intakes sooner. It is probably a Moss Piston.
Best Regards TORQUE