Well yes, it is bent. The real question maybe if it is bent improperly! :) Anyways, you'll need to put the blade back on and mark a spot in the housing and turn the blade a 180 and see how close it is end to end. Or, buy a new blade and lay one on the other. BTW these almost always will shear the 2 little nubs that match the small holes if something was hit. Best to do the above test w/ the spark plug wire disconnected and tip the mower w/ the airfilter facing up.

At the same time, look at the end of the crank and see if it's in an elliptical orbit while you are turning the blade. A bent crankshaft might be more likely.

Both good advice.

Walt Conner

Okay I will try that! Also on the crankshaft above the blade I noticed a part that looks like there is supposed to be a key that fits into it but I don't have anything in it.

The keyway was made for another application that you don't have. Don't worry about it.

This has happened to me ( a bent crankshaft ).
I used a dial indicator - it was then obvious - a heavy to to a 90% repair - a fair amount of pounding and measuring.
Now, with the present Lawn-Boy oil burner, it seems as if the lower engine bearing is worn excessively.
So, I too have a vibration and noise.
And, I do see why Lawn-Boy has a following - its a very good mower,IMO.

It is not possible to determine if the blade is bent from the information provided. You have to mount the blade on the mower, scribe a mark where one end passes a certain point on the inside of the deck, then observe to see if the other end meets the same mark. If not, you then have to determine if the blade or the crankshaft is bent.

Eathworm: let me guess - you have a 10201 with 'V' engine?

If it was me I would just treat your mower to a new blade and eliminate one cause of vibration immediately. You can then check for a bent crank.

Mr Roadbike sir.Never buy a part until the problem is identified. A bad crankshaft is too expensive to fix. Engines are cheaper. A crankshaft would only be done if you had a thing for the mower. A dedicated LB guy would replace the crank f'rinstance. Me, a hacker, would just find and fix up a good replacement mower. They are everywhere. Some better than others. I have rescued 3 mowers from Craigslist free stuff. I'm into my 5th season with a C'list free stuff 2 stroke LawnBoy. It is my favorite mower. I use a Toro 3 speed with a 4 stroke Suzuki for keeping back the under brush. All that one needed was a 5/16 shoulder bolt on a height adjuster. 2nd summer for it. Waiting on the shelf is a personal pace Lawngirl with a Tec OHV. I fixed that with 2 3/8 bolts I had in a can on the shelf. I got it running on the 1st pull. It mows fine and I stored it for the future.I haven't bought a mower in 20 yrs. I am doing better and better since I found this and a few other small engine sites. I sorta like fixing stuff and keeping it going, and I am spending more time mowing than I do fixing mowers. So I figure I'm ahead or at least even. When I see the stuff being sold for car money, my cars anyway, I 'm glad I can tinker my old stuff.

Saxman, I think this was a Snapper mower from 15 years ago. It was a POS.
Andyma,
Lawngirl ? What is that ?
My Lawn-Boy of today is the best yet - by far...Offhand I do not know the model, but it has the great drive system, just push and go...
I applaud those who buy for $0.0 or less and DIY.

Lawngirl is the name LB cultists give the green Toro currently being sold as a Lawnboy. If it doesnt have an offset RF wheel, its a Lawngirl. I was spending more time fixing my 5yr old ,bought new Craftsman, than I was mowing with it. I started with a freebie Murray and have gotten more and more selective with each succeeding mower. I have had my freebie rider, a 77 IH Cadet 80 for 10yrs. It is an ugly old wreck, but it gets the job done.

Dear Andy: The original poster does not appear to have the tools or experience to determine whether one or both problems are indicated. So an inexpensive way to rule out or fix the very common problem of a bent blade is to simply replace it.