COMMENTS ON MODIFIED ENGINES
It seems that almost everyone involved with rebuilding a Model A engine today has some opinion as to how to improve it in an attempt to reduce the design deficiencies listed above. Unfortunately, there is no real engineering behind the majority of these improvements, and many of them are poorly implemented.
Counterweights are added to crankshafts without any calculation as to how large they should be or where they should be located, various odd-ball bearing inserts from tractors, generators, and small foreign engines are implemented without any concern for bearing loads, tang location, and availability in the future. Crankshaft thrust is often moved from the rear main to the center main. The rear main wall of a Model A cylinder block is 5/16 inch thick and reinforced with ribs while the center main wall is 5/32 inch thick with no ribs. Moving the thrust from rear to center not only overstresses the center main wall of the cylinder block but also introduces additional bending stress in the rear half of the crankshaft from clutch release loads. Crankshafts are failing from fatigue because they have had their rear main seal area diameter increased by welding for adaptation of a seal from some other engine without concern for heat treatment or flywheel mounting flange warpage. Crankshaft flywheel flange runout in many of today’s modified engines is excessive and this only hastens fatigue failures.
Holes are drilled in various places in the cylinder block for the routing of copper lines that eventually work harden and crack. Aluminum has been selected for many aftermarket parts that interface with original cast iron or steel parts without any consideration that aluminum expands three times as much as iron or steel for the same temperature change, or that the stiffness of aluminum is one third the stiffness of steel. Camshafts are notched to clear aftermarket connecting rods and some have even been relocated outboard in the cylinder block in an effort to tighten the mesh between worn camshaft and oil pump drive gears.
Most of today’s modified engines are one of a kind, and have lost their ability to interchange parts with a stock engine. In addition, many of these "improvements" can actually cause trouble in later rebuilds if the location of original machined surfaces and datums has been altered from stock.
And sadly, many modified parts have been delegated to the scrap pile on subsequent rebuilds if the rebuilder is trying to return the engine to stock, cannot determine what was done in the past, or has a different idea of what and how modifications should be implemented.
It seems that almost everyone involved with rebuilding a Model A engine today has some opinion as to how to improve it in an attempt to reduce the design deficiencies listed above. Unfortunately, there is no real engineering behind the majority of these improvements, and many of them are poorly implemented.
Counterweights are added to crankshafts without any calculation as to how large they should be or where they should be located, various odd-ball bearing inserts from tractors, generators, and small foreign engines are implemented without any concern for bearing loads, tang location, and availability in the future. Crankshaft thrust is often moved from the rear main to the center main. The rear main wall of a Model A cylinder block is 5/16 inch thick and reinforced with ribs while the center main wall is 5/32 inch thick with no ribs. Moving the thrust from rear to center not only overstresses the center main wall of the cylinder block but also introduces additional bending stress in the rear half of the crankshaft from clutch release loads. Crankshafts are failing from fatigue because they have had their rear main seal area diameter increased by welding for adaptation of a seal from some other engine without concern for heat treatment or flywheel mounting flange warpage. Crankshaft flywheel flange runout in many of today’s modified engines is excessive and this only hastens fatigue failures.
Holes are drilled in various places in the cylinder block for the routing of copper lines that eventually work harden and crack. Aluminum has been selected for many aftermarket parts that interface with original cast iron or steel parts without any consideration that aluminum expands three times as much as iron or steel for the same temperature change, or that the stiffness of aluminum is one third the stiffness of steel. Camshafts are notched to clear aftermarket connecting rods and some have even been relocated outboard in the cylinder block in an effort to tighten the mesh between worn camshaft and oil pump drive gears.
Most of today’s modified engines are one of a kind, and have lost their ability to interchange parts with a stock engine. In addition, many of these "improvements" can actually cause trouble in later rebuilds if the location of original machined surfaces and datums has been altered from stock.
And sadly, many modified parts have been delegated to the scrap pile on subsequent rebuilds if the rebuilder is trying to return the engine to stock, cannot determine what was done in the past, or has a different idea of what and how modifications should be implemented.
