Re: Fuel pump?
Posted: Sat Sep 21, 2019 2:39 pm
Firstly, the gasket surface on top of that cylinder looks as though it's been grooved and filled with something-maybe epoxy? Not a good situation at all. I have yet to see a head gasket survive with that little area to prevent blowout. My Pop once had a big bore saw Mac that Russell Karting cut the head off from for Pop. There was about the same amount of area left as your block exhibits. We couldn't keep a head gasket in it for love nor money. I hope you'll be luckier.
Secondly, I'd still suggest disassembling that engine and installing new crank seals and gaskets. While you're at it, invert the piston and rod in a can filled up well past the wrist pin with solvent, and let the assembly sit in there for a day or two. Empty the solvent out and blow out the wrist pin bearing. Put the rod and piston back in the can and fill it past the wrist pin with thin oil-maybe 3-In-One or 10 weight. Let the bearings soak for a day. Mac wrist pin needle bearings are a weak point, and a good clean and soak won't cost much time or money. Reassemble the engine using NEW rod screws, and follow the torque requirements for all the screws carefully.
Thirdly, if it were my motor, I'd find a Tillotson HR carb, throw away the BDC Mac carb and mod the reed cage to pulse the Tillotson. It requires filling the four pulse holes in the big Mac reed with four No. 8-32 socket head screws, drilling a new pulse hole for the Tilly and using the proper gasket for the Tilly. Somewhere, there's a picture tutorial on the procedure. The cage has to be tapped for the No. 8-32 screws, and they need to NOT protrude thru past the gasket surface on the reed cage. The heads of No. 8 socket heads will clear the flange and gasket on the HR Tilly. The HR is far easier to service and tune, and EC Carbs in Tennessee has all the gaskets and diaphragms to rebuild the HR Tilly. Ted
Secondly, I'd still suggest disassembling that engine and installing new crank seals and gaskets. While you're at it, invert the piston and rod in a can filled up well past the wrist pin with solvent, and let the assembly sit in there for a day or two. Empty the solvent out and blow out the wrist pin bearing. Put the rod and piston back in the can and fill it past the wrist pin with thin oil-maybe 3-In-One or 10 weight. Let the bearings soak for a day. Mac wrist pin needle bearings are a weak point, and a good clean and soak won't cost much time or money. Reassemble the engine using NEW rod screws, and follow the torque requirements for all the screws carefully.
Thirdly, if it were my motor, I'd find a Tillotson HR carb, throw away the BDC Mac carb and mod the reed cage to pulse the Tillotson. It requires filling the four pulse holes in the big Mac reed with four No. 8-32 socket head screws, drilling a new pulse hole for the Tilly and using the proper gasket for the Tilly. Somewhere, there's a picture tutorial on the procedure. The cage has to be tapped for the No. 8-32 screws, and they need to NOT protrude thru past the gasket surface on the reed cage. The heads of No. 8 socket heads will clear the flange and gasket on the HR Tilly. The HR is far easier to service and tune, and EC Carbs in Tennessee has all the gaskets and diaphragms to rebuild the HR Tilly. Ted