19-09-2019, 09:24 AM
(This post was last modified: 19-09-2019, 10:04 AM by Bob Culver.)
I have not worked on 3 brg engines and questions about them are not rhetorical. Did they retain the rod drillings? Were the original shells provided drilled? Did the original shells have trenches?
Incidentally modern shells for all cars may not have obvious relieved areas but the clearance adjacent the parting line is generous. A quite generous minimum side clearance is usually specified.
Edge apparently cribbed the Seven engine from the FN motor bike with the same arrangement bearings and lubrication. Did early FN versions have the conrod drillings?
If Woodrow suggests up to .060 side clearance that seems excessive. Any factor which caused the rod to move back and forth could cause an elusive knock
Local pressure distribution varies with the film which is influenced by oil supply. The leading edge of the trench often shows slight distress, evidence of either close contact with the crank before film builds, or the effect of entry dirt on a thin film. Film pressure on the trailling side must be higher than in a flooded bearing without trench
Many grapple with the concept of very different de/accelerations at top and bottom of stroke. Most easily understood if you imagine a 3 inch stroke Seven with a conrod just say 1 5/8 inches long. For the crank turning 90 to 270 deg the piston would barely move, but from 270 through 360/0 to 90 again the piston would execute near the whole 3 inch stroke. The de/accel involved going over the top obviously hugely increased. With the 6 inch conrod of Seven more than half as much again as at bottom. Hence the high upward load on rods and crank. (And the vibration of a four because the down pistons do not counter the up)
Incidentally modern shells for all cars may not have obvious relieved areas but the clearance adjacent the parting line is generous. A quite generous minimum side clearance is usually specified.
Edge apparently cribbed the Seven engine from the FN motor bike with the same arrangement bearings and lubrication. Did early FN versions have the conrod drillings?
If Woodrow suggests up to .060 side clearance that seems excessive. Any factor which caused the rod to move back and forth could cause an elusive knock
Local pressure distribution varies with the film which is influenced by oil supply. The leading edge of the trench often shows slight distress, evidence of either close contact with the crank before film builds, or the effect of entry dirt on a thin film. Film pressure on the trailling side must be higher than in a flooded bearing without trench
Many grapple with the concept of very different de/accelerations at top and bottom of stroke. Most easily understood if you imagine a 3 inch stroke Seven with a conrod just say 1 5/8 inches long. For the crank turning 90 to 270 deg the piston would barely move, but from 270 through 360/0 to 90 again the piston would execute near the whole 3 inch stroke. The de/accel involved going over the top obviously hugely increased. With the 6 inch conrod of Seven more than half as much again as at bottom. Hence the high upward load on rods and crank. (And the vibration of a four because the down pistons do not counter the up)