It bored itself...over the years with few oil changes, run low low on oil. Just dremelled the big ridge put of top of cyls to get piston put without destroying them when rings ran into that BIG LIP AT top of cyl. Just honed it smooth top to bottom n put .010" oversize rings on stock piston that seemed fine. New top rod that spun freely on rod journal where old rod wud hang up on one spot on crank...egg shaped rod big end? File fit new .010 rings to get .016" ring clearance...
Later reading u tube Oppy rebuild by guy that really was meticulous abt the rebuild surface sanding block n heads on flat piece of... Tabletop granite? With sandpaper to make sure head n block were flat. He said .010 is enuf ring gap.
Took that wonky gov mechanism out of motor n that wonky gov linkage off front that flutters up the motor n can fail n lbs junk in the motor when it goes.
E bay digital tach n hour meter works fine for $10 to keep eye on revs. Put 15-40 n 20-50 oil in it with 20% STP OIL TREATMENT to THICKEN OIL BIG TIME...still knocks bad like the almost worst of the ones on posted videos??? Piston slap or rod knock? ???? I don't know, 14 hrs on test stand running banging away. Seems to run fine. No choke needed to start so it must run rich at this altitude 3666'.
Supposed to go to smaller jet over 3000 and lose 3.5% for each 1000' of higher elevation cuz less air pressure. 13 psi here... Not 14.7 psi at sea level. Less air, no matter how much gas dump in it, = less power.
Oh well they r torque down low engines...1800 to 2800RPMs. OHV engines torque is from 2400-3600rpms. Better flow thru OHV head.
656 cc briggs intek v twin is 20 hp...the 656cc briggs Oppy 16 hp is 656cc also, so down 4 hp from same size engine. ANYWAY I will keep it FULL OF OIL, run it, be ez on it with yard donkey /street cruiser occasionally n it might last...???
I shut off fuel every time n let carb run out of gas so fuel won't go bad in carb. Stabil gas treatment in all tanks of gas, MMOIL in gas? To lubricate the rings n valve's? Snake oil but for $4 bottle. Not that much to try to make motor last...50 hrs? 14 hrs so far per e bay digital tach/hour meter.
Open up square access port on back n check RODS/torque? Retorque RODS? Plastigauge them? Nothing I can do if crank journal is worn, but looked fine to me. No imperfections on it??..
Read somewhere "briggs flathead like more rod clearance than the factory states (.002-.003"). More like .005" rod clearance...for oil to get to rod journals on splash lubricated engines???
Did the oil mod to the crankshaft n ground off the big lips over the top of rod journals. The big overhang acts like eaves of house, to keep rain off side of house, n out of Windows. Great idea for house, not so good for splash lubricated engine that needs oil falling into the groove tween the rod big end n crank journal...on the crankshaft throws that stick out in the oil rain
