Lawn boy knocking.

[Warlord]

I just picked up a 2 smoke lawn boy and after a carb cleaning and some tinkering got it running like a champ! Try as I might I couldn't stall it even in the thickest grass I could find. Problem is I skimmed the corner of a raised patio slab and now the mower makes a knocking when it runs. I didn't hit the slab hard enough to stall it and the blade is still tight. So what could this new knocking be? I hope I havent already wrecked something.

 

[tommygunn]

Sounds like you bent the crankshaft.

If thats the case, its screwed.

 

[TFB1]

Hitting something unmovable is never good, check for a bent blade and/or crankshaft...

 

[demarpaint]

Originally Posted By: tommygunn
Sounds like you bent the crankshaft.

If thats the case, its screwed.


That's my bet, a bend crankshaft.

 

[TFB1]

Bent cranks can be straightened, I've had good success using a dial indicator to find the "high" spot and then whacking it a couple good licks with a 4 Lb hammer... Recheck after each couple hits, anything less than .005 runout is OK...

 

[Warlord]

Even if it didn't stall? I just skimmed the blade across the top. Just my luck to ruin it on its first run.

 

[Hokiefyd]

Are you sure the blade isn't contacting part of the mower deck? Maybe that sounds like a knock.

 

[demarpaint]

Originally Posted By: Hokiefyd
Are you sure the blade isn't contacting part of the mower deck? Maybe that sounds like a knock.


Good point! I'd flip the mower and make sure the deck didn't crack, causing a slight wobble in the blade when the engine is running. Just enough to make contact with something. I've seen that happen too.

Obviously- Don't attempt to run the mower while checking.

 

[MichiganMadMan]

I had a similar situation with my Lawn-Boy, mine was a piece of 3/4 pipe some clown partially buried in my yard. I hit it at the worst possible angle and it sucked the mower down to the ground and scared me half to death. This sparked a complete teardown and inspection on my part(the lower seal was on it's way out anyway, it was starting to surge). Bottom line, blade was bent. Everything else was fine. I'd bet yours is the same. They are tougher than you think!

 

[Bluestream]

Pull the crankshaft and put in in some V Blocks and measure the run-out with a dial indicator...

 

[Trav]

Remove the spark plug so the engine spins freely, flip it on its side and pull the cord slowly.
You should be able to see a wobble or where its making contact with something.

 

[Warlord]

Well I tore it all down and everything seemed in great condition. Put it all back together and now no knocking. Something must have come loose and now is tight again. Purrs like a kitty!

 

[Warlord]

I do notice that I can flex the entire engine on the deck though. Just a bit but this will need further attention soon I believe.

 

[demarpaint]

Originally Posted By: Warlord
I do notice that I can flex the entire engine on the deck though. Just a bit but this will need further attention soon I believe.


Are there any cracks on the deck? Sometimes they are hard to find, unless you clean the machine real well.

 

[Warlord]

I'll have to clean it up and inspect for cracks. It's a steel deck so hopefully it's still solid.

 

[MolaKule]

Maybe the Lawn Boy is wanting to get out?

I had an older mower in which the four block-to-deck bolts got loose and enlarged the mounting holes.

Fender washers and some retorqing did the trick.

 

[Warlord]

Yep could be that it wants to find an aluminum deck to sit on. I'm not convinced aluminum is always best though. I have an old toro super recycler that is terribly rotted and patched with lots of jb weld. The aluminum deteriorated quick.

 

[Hokiefyd]

The alloy decks from Toro/Lawn-Boy are generally pretty good. They are sometimes hard to find used, as even a bare deck will sometimes fetch 50 bucks. I also have an 11 year old Honda Masters with alloy deck and it's very solid still. I would anticipate no issues with the alloy material.

 

[Warlord]

I love this thing! Mowed up a storm today and even smoked out the area bugs with my 24:1 castrol super outboard mix. Before it was running 32:1 Amsoil HP injector and smoked about the same but stank.

I'm trying to get the muffler off but the blade adaptor plate is seized in place. Looks like I'll have to find a puller to get it off.

 

[Cornbread]

Get some PB Blaster or Aerokroil and let `er soak.