Briggs & Stratton Opposed Twin Knocking?

it's normal to hear the knocking noise at too low an rpm.. I have a 1972 opposed twin B&S and a 1973 Kohler opposed twin, if I lower the rpms below 1500 it banks like a bi...h.. keeping up over 1500 and it runs nie and smooth and proper like.. Running so low in rpms will mess with the lubrication, while sounding cool sure everyone likes an idling harley, it will dmge the engine nd is not worth the effect..

run up the rpms to the recomended spec. you'll be fine..
 
Wondering if it was one of those non OEM mufflers making the ticking sound? They both are different. Or an exhaust leak from the home made plumbing parts for the exhaust??

Take a small hose, one end to your ear and the other end on the suspect part. Listen for a tick. The redneck doctor trick.

slomo
 
slomo said:
Sounds like lack of lube from low revs. Not recommended to idle down a splash lube engine. Keep her at 3200-3600 revs at all times, if possible.

slomo
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1750 rs is its factory idle. Torque curve for flathead is pretty low...1800 to 2800. Torque curve for OHV engines is 2400 to 3400+. With fresh oil warmed up I wud think the splash lube does well enuf but ppl can't...check the oil before each run of day or change oil every 50 hrs n clean or new oiled air filter, depending on dust, every 50 hrs. Mi refurbished 18 hp Oppy knocks bad... It was WORN!! I put .010" oversize rings on stock pistons as it had BIG LIP AT TOP OF CYL that had to be dremelled out to get piston out without beating them to death. Honed cyls with 3 shoe hone. Cleaned, oiled it, reassembled it, started, broke in 5 hrs on test stand (plywood on stacked old mower tires) n hv screamed it to 4500...n survived. Flywheel didn't xplode n kill me.. Yet. 6" motor pulley to 4 inch transaxle pulley, that I Gilles transaxle wit STP OIL TREATMENT, N it she go...once I put motor on n figure belt length n guard to keep belt on. 7" pulley too big, clutch pulley ran into 7" motor pulley. With double od it she do 35 mph that is faster than brakes n steering can deal with. Anyway it KNOCKS even with 20 50 oil n 20% STP OIL TREATMENT in it? 12 hrs on test stand so far. Compression.. 60 psi per cylinder. Not 100 psi per cylinder it she have. Oh well it will be down on power some but we'll see what it will do. I put a .015" feeler gauge tween piston n cylinder skirt so it needed .020" over bore for .020" piston I have but machine shop time $$$$ wud cost more than I want to put into motor that was free with the no hood craftsman GT with 6 speed 820 transaxle...now FULL of STP OIL TREATMENT (liquid grease). Got 44 x 25 x 7 mm double lip e bay seals for 1" axles and greased them good with green grease before sliding them on sanded axles so the seals didn't get torn up bmsliding down rusty non greased axle shafts
 
Knocking Oppy said:
1750 rs is its factory idle. Torque curve for flathead is pretty low...1800 to 2800. Torque curve for OHV engines is 2400 to 3400+. With fresh oil warmed up I wud think the splash lube does well enuf but ppl can't...check the oil before each run of day or change oil every 50 hrs n clean or new oiled air filter, depending on dust, every 50 hrs. Mi refurbished 18 hp Oppy knocks bad... It was WORN!! I put .010" oversize rings on stock pistons as it had BIG LIP AT TOP OF CYL that had to be dremelled out to get piston out without beating them to death. Honed cyls with 3 shoe hone. Cleaned, oiled it, reassembled it, started, broke in 5 hrs on test stand (plywood on stacked old mower tires) n hv screamed it to 4500...n survived. Flywheel didn't xplode n kill me.. Yet. 6" motor pulley to 4 inch transaxle pulley, that I Gilles transaxle wit STP OIL TREATMENT, N it she go...once I put motor on n figure belt length n guard to keep belt on. 7" pulley too big, clutch pulley ran into 7" motor pulley. With double od it she do 35 mph that is faster than brakes n steering can deal with. Anyway it KNOCKS even with 20 50 oil n 20% STP OIL TREATMENT in it? 12 hrs on test stand so far. Compression.. 60 psi per cylinder. Not 100 psi per cylinder it she have. Oh well it will be down on power some but we'll see what it will do. I put a .015" feeler gauge tween piston n cylinder skirt so it needed .020" over bore for .020" piston I have but machine shop time $$$$ wud cost more than I want to put into motor that was free with the no hood craftsman GT with 6 speed 820 transaxle...now FULL of STP OIL TREATMENT (liquid grease). Got 44 x 25 x 7 mm double lip e bay seals for 1" axles and greased them good with green grease before sliding them on sanded axles so the seals didn't get torn up bmsliding down rusty non greased axle shafts
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I've also read Briggs stating low idle speed is 1750rpm. Still Briggs says to run at full revs for max durability. I'm not into idling a mower like a car engine. Give her the beans.... Top of the engine will appreciate it.

slomo
 
Knocking Oppy said:
Mine KNOCKS after rebuild...cyl WORN BIG TIME so put .010 rings on good piston n new top rod n put back together
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Was it bored and honed to 0.010" over? Did the bore have a ridge? Did you do the boring or a machine shop? Was the piston 0.010" over?

Cylinder worn big time might need a more aggressive boring to clean it up proper.

Did you check ring gaps with the piston in the bore?

slomo
 
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
 
Most all of them sound like that never seen one blow up though. Have heard that it could be carbon build up on top of piston but you cleaned up good when you built it so probably not that. I would run it and not worry about it if it is too bad you could buy some ear muffs. LOL
 
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