Why did the oil pump fail?

As you might have read last night in my previous question I am rebuilding a 8N engine.

When I purchased the tractor the motor was stuck and stuck bad. Oil pump had failed compleatly and she spun up two connecting rod bearings and one of the mains. Well she finaly threw a rod and realy made a mess. Yes sounds bad, but I got her for a GREAT price because of it.

Now the Question. Why did the oil pump Fail? When I say fail, I mean the large gear that runs off the timing gears, sheered off of the shaft. The large gear was spinning but the pump gears were not. I expected to see a chunk of spare mettle or something wedged in the gears, causing them to lock up. But there was none. By the way the screen on the oil drain plug was missing.

So now I am ordering parts to put this mess back together, and I am fearfull that if I can't figure out what happend, it might happen again to my new motor!

Any Ideas?

Thanks in advance for the help.

8N-Dan.

Having said all of the above, I still find it hard to believe the pump failed in the way you stated. I might even suggest another more likely story. ---- The oil pick up tube developed a leak or the weld holding in on to the pump is cracked - this caused a loss of prime in the pump, then when you ran the engine - not only did the rod and main bearing fail, but also the oil pump with no lube also got hot and seized up and then broke.

An important lessen here ($$$$$) - IF the oil pressure guage reads "ZERO - NO PRESSURE" immediately stop the engine, find the problem, fix it before the entire engine fails.

Good Luck with the rebuild, let us know what you find out about the pump, Jim