Ol' Ron
Well-known member
Bearings vs oil pressure
O.
Notice that all the clearances in a stock engine are very tight. Main and rod bearings run from .001/.002". Cam bearings even tighter, but no more than.003". An important one Rod side clearance, .006/,010. Now you know where all the pressure comes from, resistance to the oil pump output.
Now trying to shove some heavy oil through these clearances, forces the relie valve to open. The relief valve is only so big and can't reduce the pressure below #50 if the oil is too thick, thus forcing this heavy oil through the small spaces. However the pressure of the oil coming out of the small spaces is much higher that 50 or 60 lbs. More like several hundred lbs. THis is the principal of waterjeting, cutting steel with hi pressure water. This high pressure also contains small particles which blast the bearings and surrounding materials. One thing we've forgot is: why we put oil in the engine anyway? I have a hit & miss engine that doesn't have any oil in it, but a drip system for the cylinder and rod. Yes, it lubricates the bearings and most everything else. But it also cools the bearings by removing the heat generated by the force of the connecting rod being driven down by combustion pressure. To cool these bearings we need flow, the more flow the better. In fact all the bearing mods are designed to increas flow.
WE do this by increasing the bearing clearances to .oo23/0027,both crank and rods, and ncreasing the rod side clearance to .010 for hot street to.o15 fro racing and to cool the bottom of the piston
I'll end this now, Food for thought. If you're contimplating building a 276/284/294, this might be the way to go. Next: the allout compiyion, blown, nitro burning beast???? Now you know why I don't like a heavy oil in a stock engine.
ramps
O.
Notice that all the clearances in a stock engine are very tight. Main and rod bearings run from .001/.002". Cam bearings even tighter, but no more than.003". An important one Rod side clearance, .006/,010. Now you know where all the pressure comes from, resistance to the oil pump output.
Now trying to shove some heavy oil through these clearances, forces the relie valve to open. The relief valve is only so big and can't reduce the pressure below #50 if the oil is too thick, thus forcing this heavy oil through the small spaces. However the pressure of the oil coming out of the small spaces is much higher that 50 or 60 lbs. More like several hundred lbs. THis is the principal of waterjeting, cutting steel with hi pressure water. This high pressure also contains small particles which blast the bearings and surrounding materials. One thing we've forgot is: why we put oil in the engine anyway? I have a hit & miss engine that doesn't have any oil in it, but a drip system for the cylinder and rod. Yes, it lubricates the bearings and most everything else. But it also cools the bearings by removing the heat generated by the force of the connecting rod being driven down by combustion pressure. To cool these bearings we need flow, the more flow the better. In fact all the bearing mods are designed to increas flow.
WE do this by increasing the bearing clearances to .oo23/0027,both crank and rods, and ncreasing the rod side clearance to .010 for hot street to.o15 fro racing and to cool the bottom of the piston
I'll end this now, Food for thought. If you're contimplating building a 276/284/294, this might be the way to go. Next: the allout compiyion, blown, nitro burning beast???? Now you know why I don't like a heavy oil in a stock engine.
ramps
