Small Engines (Lawn Mowers, etc.): Push mower blade replacement, lawn mower blade, crankshaft seal

Question
Can I replace my 21-inch lawn mower blade with a 20-inch blade?

I hit something in the yard and the blade nicks the side of the metal "cover" now. It still starts, but makes a horrible metal-on-metal sound.

I thought the blade might be bent, so I replaced it but it still hits the side.

I figured maybe I could just use a smaller blade and solve the problem.

This is a brand new mower too!

Thanks for your help.  

Answer
Hello Matt:

From your Description it Sounds like the Crankshaft is Bent. If you have the Proper Length Blade and there is Nothing Bent Under the Mower Deck, then the Crankshaft  is Bent and this Allow the Blade to Swing too Close to the Deck Causing the Blade to Hit the Deck. Remove the Spark Plug. Tilt the Mower so the Spark Plug Hole is Point Up. Turn the engine and Watch the Center Blade Bolt. If the Bolt is Not Turning True and Wobbles, the the Crankshaft is Bent and will Require Straightening or Replacing. Some Service Centers will Straighten the Crankshaft for $50.00us to $75.00us if the Engine is Removed from the Mower Deck. If the Crankshaft Requires Replacing, then  the Cost for this Repair will be $175.00us to $225.00us. All these Prices are Depending on the Shop Labor Rates and the Part Cost. If this is One of the $100.00us to $125.00us Mowers, then it will be Cheaper to Replace the Mower. You can Use a 20" Blade, but you will have Problems with the Lower Crankshaft Seal Leaking Oil and Even Replacing the Lower Seal will be a Waste of Time. The Seal will Start Leaking Usually within 1 Cutting, Depending on How Bad the Crankshaft is Bent. Also, you will have a Vibration when the Engine is Running. If you Hit a Snag or this Does Not Correct the Problem,  I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Thanks.

Respectfully

John