Small Engines (Lawn Mowers, etc.): craftsman 6.25 hp self-propel lawmower, bolt torque, rod bolts

Question
This is my dad's mower. Last summer we knew it was about to go, so we decided to use it til it quit. It lasted all summer. The problem is when the mower gets under a load it begins to knock, like it is going to throw a rod. It blows oil and smoke out of the exhaust and by the time we get through mowing the deck as evidence of oil. I have begun to tear down the mower and found that the key for the blade adapter and the blade adapter key way are in pretty bad shape. Could this be my problem? I have another 6.0 hp engine that may fit the deck, both are craftsman. But if changing out the adapter would solve this, It would save me from swapping the engines. The 6.25 runs fine if in low grass and no load. No repairs to this mower as of yet. Model #917.377210, year 1997

Answer
Those Tecumseh engine rod bolts are know to come loose...I have found a lot of busted connecting rods because a rod bolt came loose.

I highly doubt the blade adapter key would cause the oil consumption, but it will definitely cause the knock.  A loose blade bolt or defective blade washer can cause the adapter to loosen which causes the knock.

I would also check the flywheel key.  Aluminum flywheel keys shear pretty easy, especially if the blade adapter bolt loosens.

I would install a new blade adapter/key, check the flywheel key and change the oil.  This may solve your problem.  You can also check the rod bolt torque by removing the oil vent cup located under the flywheel.  The cup is either rubber and pushed in the block or held in place by 2 screws.  Once it is removed you can see inside the engine to check the rod bolts...you will have to rotate the crankshaft in order to see the connecting rod bolts.  The bolts are torqued to 200 inch pounds.

Let me know what you find.
Eric