Mower engine knocking loudly - is it toast?


Old 09-01-18, 09:49 AM
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Mower engine knocking loudly - is it toast?

22" push mower with B&S 4.0 HP - at least 13 years old.

Model: 10A902
Type: 2189B3
Code 02030455

The engine has developed a loud knocking or clacking noise - the rate of "knock" is tied to engine speed. The noise occurs at all times the engine is running.

Given the age and symptom, do we just end the conversation here and say it's trash?

Or is there a possibility that it may be worth further diagnosis?
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Old 09-01-18, 10:06 AM
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Have you checked the oil? blade not loose or warped?
Old 09-01-18, 10:14 AM
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Have you run it into anything? Have you looked at the bottom yet? Have you been changing the oil regularly and maintained the proper level? At a minimum check that the blade is tight and straight and that the deck is not damaged such that it is interfering with the blade. After that it's a matter of whether you want to tear into the engine.
Old 09-01-18, 12:38 PM
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A) Grab a disposable magnet, like the advertising magnets you get for your fridge, put it in a vise-grip pliers, drain the oil and let the oil flow over the magnet. Look for chunks of ground up bearings. Look for fine chunks of bearings.

Also siphon out the gas.

B) After the oil is drained, but before refilling, flip the mower over and check whether some section of the blade is bent and scraping something. Look for a weld in the mower deck that has rusted through, or something in the mower deck is bent, which allows metal to hit metal.

C) With the oil and gas still drained, remove the spark plug and stick your little finger into the spark plug hole. Rotate the blade to move the piston, feel how the piston moves against your finder- it should be smooth like closing a vise (and, yes, you ARE basically putting your finger into a vise in this situation.) If you feel any skip, or play, then it's likely that the bottom end bearing has gone.

D) Worth fixing?
Depends on why you're fixing it. E-bay shows used-good-condition connecting for about $6. Head gaskets at $4 to $8.

Used mowers are around $90 bucks (around me) on craigslist.
However, last week I had two nephews 6 & 10 for a day and a night, (depending on your neices-nephews/grandkids situation) and tearing down a lawnmower and replacing a connecting rod IS probably cheaper and more interesting than lunch and a despicable-me matinee at the movie theater.
Old 09-02-18, 08:44 AM
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Thank you all for your useful input and I did find the problem.

It was a loose blade. The blade was not hitting the deck. The looseness was such that it moved slightly back and forth within its plane of rotation - about 3/16" at the ends.

I didn't think that small amount of movement could cause such a racket. But realizing the damping function that the blade serves, it makes sense.

Why was the blade moving? It was NOT due to a loose bolt - the bolt was so tight I almost could not get it loose. The blade is an aftermarket part and is about .020-.025" thinner than the original - the mounting hardware could not clamp down on it enough to keep it tight.

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