What is causing the knocking sound in my lawnmower engine?

Answer by  champaign9497 (11977)

The oil is probably low pull the dip stick and see what it says but do it when the engine is cold that way you will get a true reading then add the amount the stick tells you.

Answer by  mrsmyers (474)

In my experiance most engines are built to run pretty much the same way so think about your car engine in this case. The only time I have ever heard a knocking sound come from a car engine is when the oil was low so you should check to make sure there is enough in your lawn mower.

Answer by  wingdog987 (154)

If it's a loud knock like someone hitting a hammer against steel it is most likely a rod knocking. If you're lucky it could be a bent deck hitting your blade, which can be easily fixed. If it's a rod knock get a new mower.

Answer by  Lordschild (1398)

The most likely cause is that the piston connecting rod is coming loose or the rod bearing is going bad. It could also be a problem with the valves.

Answer by  ceannidghe (9)

I had a knocking noise also and, as I suspected, it turned out to be a loose engine mounting bolt. If the engine moves, that may be the source of the problem.

Answer by  LeheckaG (1826)

Lawnmower "knocking" can be: - bent/loose blade striking the deck, - piston-connecting-rod hitting cylinder-casing, - bad muffler, - ignition issues: (low oil, bad gasoline, dirty spark-plug, bad-wire, carburetor-misadjustment, dirty air-filter)

Answer by  ladybud (1069)

Could be a few things. first check the oil to ensure its not a valve push rod.could also be a piston push rod and bad bearings and c-clip check to make sure your using the correct spark plug this will cause knocking,change the oil and look for metal shavings and piece's of metal could be rings are bad.

Answer by  amtcura66 (1340)

Your lawnmower is making that knocking noise because there is something really wrong with it. You could try and check the engine. You could also check the blades. You might of mowed your lawn too hard growth the lawn mower and it is angry at you. Consider visiting a therapist.

Answer by  jughead (4)

i have a troy built riding mower. The oil was low in it and then it started to knock then it started turning free hand on the fly wheel

Answer by  ceannidghe (9)

Could be a loose engine mount bolt.

Answer by  Anonymous

it's a ghost hoping that by knocking, someone will let it out!!!!!!!

Answer by  Anonymous

check your flywheel keyway if its bent it sets timing off and results in knocking, had the same problem