Posted by Bob on April 14, 1998 at 16:30:25:
Here's the problem: My '53 Super M has a pronounced engine knock at idle and low speeds. The knock goes away above about 800 RPM - then the engine runs smooth and quiet. The engine has plenty of power, uses no oil, and otherwise runs great.
The knock occurs exactly twice per crank revolution - it can be clearly heard while cranking with the starter. Oil pressure is fine - 20 psi at idle and rising to 50 at full speed. The oil gage has been tested off the tractor and reads correctly.
This tractor is equipped with an engine-driven hydraulic pump. With the engine at slow idle, the knock disappears if a load is put the hydraulic pump, either by slowly turning the steering wheel (tractor has power steering driven from the hyd pump) or by operating the remote hydraulic valve. But if I load the engine by slowly engaging the clutch with the tractor in road gear, the knock persists right until it stalls.
This leads me to believe the knock is somehow related to the hydraulic pump or it's drive gear. But the hydraulic system works fine - plenty of flow and pressure, and the fluid is clean. So I doubt the problem is in the pump itself.
I figure there's two possible sources of the knocking:
1 - Excessive backlash in the crank/cam/hydraulic pump gear train, or
2 - Excessive end play in the camshaft - thrust developed by the helical drive gear and the variable torque of the camshaft is causing the camshaft to move in and out with each 1/2 turn of the crank.
Before I remove the front bolster, radiator, etc. and take off the front cover off the engine, does this make sense? Can something else be causing the knock that I am missing?
Any ideas are appreciated!
Bob