Old Briggs/Stratton

21" Yard Machines push mower with 4.5 hp Briggs/Stratton Quattro, about 12 years old.
Yesterday I pulled/sharpened the blade, cleaned the air filter, and changed the oil. Old oil looked about the same as always after 1 full season.
Today I start it up, I get a CLANK-CLANK-CLANK proportional to rpm, and kinda like a rod knockin'. Gets lots worse as I try to mow, so I stop and test. The motor will turn over and start with the rip-cord, but it feels t-i-g-h-t. Oil is clean and up-to-level.
Definitely a candidate for the junkyard, but ... what happened? Key sheared off the flywheel??
P
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Puddin' Man wrote:

I'll bet the problem is centered on the blade you removed/replaced.
Is is balanced? On upside down? Hitting something?
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Mea Culpa!
I hadda lock washer on the blade bolt. Torqued the hull outa it. Checked it when the problem first arose. Looked OK.
But it weren't. Blade rattled loose again. Sounded damned funny for a loose blade, too.
Thanks, P
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On Mon, 18 Oct 2010 18:07:27 -0500, Puddin' Man

That sure will cause the "CLANK-CLANK-CLANK proportional to rpm..." <grin>
Glad you found it and the blade stayed on the shaft, saving a foot.
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Thanks for the follow up.
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On Sat, 16 Oct 2010 17:49:58 -0500, Puddin' Man

If the engine runs with any reasonable expectation -- my guess it is not a shear pin/key that has broken.
If this started after you worked on the blade, go back and look. Follow the problem backwards.
Got any barbed wire/string caught around the shaft?
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Well, a couple things come to mind.
Blade may be loose -- the engine relies on the "flywheel effect" of the blade to keep the crankshaft turning.
Please double check that you added the correct ammount of oil. Probably about 20 ounces.
As others have written, please check to see if something is tangled in, or hitting the blade.
If the mower has a "safety handle", please check to see if the safety brake is fully releasing. Could explain the tight feel.
Might not be an issue. But, pull the spark plug out. Then yank the rip cord a couple times. Sometimes oil gets in the cylinder. With the plug out, the oil will spray out when you pull the starter cord. I've seen oil or gasoline in the cylinder, after a mower is tipped on its side.
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Stormin Mormon wrote:

How long would you expect that oil to stay in the cylinder when he had the engine RUNNING?
Jeff
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Oh, it varies. Depending on how much oil.
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This is probably not related to your problem but does your lawn mower have a fuel filter? I also have a Briggs and Stratton and didnt know it didn't have a fuel filter until I had to take it apart recently. I had to buy an in line fuel filter an put it in the fuel line because the gas tank seal and fuel hose were disintegrating.
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On Sat, 16 Oct 2010 19:37:27 -0700 (PDT), Molly Brown

Right. The OP has a "CLANK-CLANK-CLANK proportional to rpm..."
Nuttin to do with fuel.
Now if he ran over a cow bell, I could be wrong.
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wrote:

Sounds like more than likely when you installed the blade, it wasn't properly centered and is hitting the underside of the deck.
Bob-tx
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Puddin' Man wrote:

Look out, the rod is ready to come out the bottom of the crank case.
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If it is a vertical shaft lawnmower, the rod, assuming you mean the connecting rod, will come out the side of the engine, not the bottom. You are exposing your lack of knowledge of lawnmower engines.
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hr(bob) snipped-for-privacy@att.net wrote:

The bottom is usually facing the rear on a single cylinder vertical. You just don't know what the bottom is, your ignorance.
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On Mon, 18 Oct 2010 18:16:38 -0400, LSMFT wrote:

Isn't that an end, rather than a bottom? :-)
I've just been soak-testing my spare vertical-shaft B+S engine after patching up its damaged cylinder bore - the darn thing made me rather nervous, particularly when tuning the carb, as I wasn't 100% confident that it was going to hold together.
Give me a horizontal-shaft engine any day, as at least it's generally possible to stand close to it somewhere where you aren't going to get hit in the shins if it goes bang :-)
cheers
Jules
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And it is MUCH more likely to come out the side than the bottom or back, regardless which way the shaft is oriented.
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Rods throw out the thin sides of an engine, not a bottom of an engine block.
If the rod journal stays attached on the crank, breaks, a portion of the rod is slung to the side.
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On Sat, 16 Oct 2010 17:49:58 -0500, Puddin' Man wrote:

I'm not sure if that's sound logic... :-)

Others have mentioned a blade issue, but also is there a chance you've broken or bent something at the top of the engine while you were working on the underside? Maybe an engine cowl or something like that?
(anyone know if these smaller B+S engines have a vane governor, or do they have a mechanical governor in the sump and driven off the cam, like the larger B+S engines do?)
cheers
Jules
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