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Rattling noise from engine

Posted by theseventhlegend FL (My Page) on
Fri, Jun 29, 12 at 7:11

Changed the blade 2 days ago and ran mower a little worked great. Yesterday went to mow the lawn 1 min in engine started losing power and stalled. Pulling rope to restart seemed tight, loosen blade a bit to see if helped. (didn't over tighten imo) Engine restarted 1 min in large BAM noise then sounded like a large nut was spinning around in my engine and mower quit cutting.

Any ideas?

Briggs & Stratton 4.75 hp Craftsman push mower


Follow-Up Postings:

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RE: Rattling noise from engine

Yes, you threw the connecting rod, not from changing oil but more likely from NOT changing the oil sooner OR running low before changing. Over tightening blade making it turn hard?? You need a little more mechanical understanding.

Walt Conner


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RE: Rattling noise from engine

Walt nailed it. Classic symptoms of inadequate oil in engine; first, it heats up from friction, then finally stops. I've seen them survive at that point if oil is added and the engine allowed to cool before the restart. However, your engine is now toast.
I know it seems like a chore, but check engine oil frequently during the mowing season and change it yearly.
My brother has a 1989 mower that I bought new and it still is in excellent original condition. They can last if given half a chance.


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RE: Rattling noise from engine

Thanks, this is what I was thinking and afraid of. I thought I hit a large stone and bent the crankshaft or something. Oil was changed at the begining of the season but I did mulch mow alot of leaves and turning the mower on it's side alot of dust residue dropped from the muffler so who knows.


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RE: Rattling noise from engine

IF you expect a mower engine to last, check the oil each time before using. As one who grew up on a farm running all sorts of powered equipment, that was the first lesson learned.

Walt Conner


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RE: Rattling noise from engine

Are you sure the blade didn't come off? You said you lossened the blade.


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RE: Rattling noise from engine

Please check the engine and mower out before agreeing with someone who has not even seen the mower that a rod was tossed. Lets try the simple and expensive stuff first. Lift the mower and see if the blade is attached and tight. Is there a buildup of under-deck grass holding the blade? Also check that the blade isn't hitting the frame. Finally check the crankshaft shear key.


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RE: Rattling noise from engine

Please check the engine and mower out before agreeing with someone who has not even seen the mower that a rod was tossed. Lets try the simple and expensive stuff first. Lift the mower and see if the blade is attached and tight. Is there a buildup of under-deck grass holding the blade? Also check that the blade isn't hitting the frame. Finally check the crankshaft shear key.


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RE: Rattling noise from engine

Thanks, I wasn't taking 1 persons opinion to heart and troubleshooted the best I could without ripping apart the engine. The blade became slighty loose but after retightning to be sure it still had the same issue. No deck build up. Doesn't look like blade was scraping inside deck but this happened when I replaced the blade the last time so that's why I asked. Pulling the cord the blade spins much faster now but mower isn't starting.


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RE: Rattling noise from engine

You see my theory was that I might have loosened too much and the blade wiggled while running and caught the inside of the deck and then broke something up in the engine. The bolt and key seemed secure enough when I checked after this happened but it's a different story when a motor is running at high speed. It IS the right size blade but last season when I installed a blade it was cutting into the plastic lid that covers the side grass discharge.

So when I pull the cord the blade still spins but it sounds like something is loose in the engine. And it makes a weird reving/grinding noise.

Based on my problem I was hoping someone would give me ideas to what's broken to see if it is worth fixing.


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RE: Rattling noise from engine

I reread your messages. You loosened the blade bolt somewhat and started the engine? And last time you installed a blade it hit the grass chute? And now the bolt seems secure...but who knows. This is becoming an ever unfolding story. I suggest in the strongest terms that you have a lawn mower mechanic figure out what the problem is before any more damage is done to the mower or you hurt yourself.


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RE: Rattling noise from engine

It now spins easily because the piston is no longer connected to the crankshaft, hence no compression. Piston is probably seized in the cylinder. Remove spark plug and insert a pencil or dowel rod into the cylinder until it stops, then have someone slowly pull the starter. If the piston moves, it will push the rod out and you still have a connecting rod between the piston and crankshaft. Otherwise, you don't - new engine or new mower required.


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RE: Rattling noise from engine

Saxman1 thank you for your helpful reply. I did what you said. I used a pencil and it did not move when the starter was pulled. Was only able to get the pencil about 2 1/2 inches down the cylinder. Does it sound like the piston is stuck there? Also wouldn't I just need to replace the connecting rod? Would that repair be too costly?


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RE: Rattling noise from engine

Ok I pushed the piston in and pulled the starter, the piston DID move.


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RE: Rattling noise from engine

Let me clarify on the piston moving. It pushed out only when pushed in with the pencil.


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RE: Rattling noise from engine

As I said way back, you threw the rod. Whether it is practical to repair it is something you can only determine by tearing the engine down. I doubt it.

Walt Conner


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RE: Rattling noise from engine

Generally, if you sling a rod from no/low lubrication, it ruins the crankshaft, too, and many times the camshaft, too. I would just get another mower, it would be cheaper.


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