5.0 horsepower briggs and stratton makes a loud knocking sound

**chevyman984** · 06-24-2012, 09:54 PM

My mtd 22" cut makes a loud knocking sound when I put the engine under strain(cutting high grass)it shouldn't be a rod knock because I just Bought it 2 years ago and I have always changed the oil in it with pennzoil SAE 10W-30 platinum synthetic ( high quality oil) the blade is not loose so I have no clue what it is. It sounds like someone beating on metal with a hammer really fast. To be honest it sounds like a rod knock but I just wanted to see what y'all had to say :)

**LawnWorld**

**Lawnranger** · 06-24-2012, 10:55 PM

Sometimes the blade adapter (if equipped) cracks and will knock even though the bolt is tight. If your mower has a blade adapter, disconnect the spark plug wire, tip the mower with the carburetor up, remove the blade & adapter and inspect carefully. Replace parts as necessary. Also, check the engine mounting bolts for proper torque. Hopefully for you, one of these tips will fix your mower.

**chevyman984** · 06-25-2012, 12:07 AM

Originally Posted by Lawnranger

Sometimes the blade adapter (if equipped) cracks and will knock even though the bolt is tight. If your mower has a blade adapter, disconnect the spark plug wire, tip the mower with the carburetor up, remove the blade & adapter and inspect carefully. Replace parts as necessary. Also, check the engine mounting bolts for proper torque. Hopefully for you, one of these tips will fix your mower.

Thanks a lot for the tips. I will try it and get back on here with the results

**chevyman984** · 06-25-2012, 09:44 PM

Ok I checks all of that and its all good, still knocks.

**chevyman984** · 06-25-2012, 09:46 PM

Ok I check all of that and still knocks :(

**Lawnranger** · 06-26-2012, 08:00 AM

Sounds like it's time to open the engine and find out where the excess clearance is. Rod to crank or wrist pin to piston/rod perhaps? Something else coming apart in the engine? Without the ability to hear the knock it's difficult to diagnose through email.

**chevyman984** · 06-26-2012, 06:16 PM

This is something that might help you lawnranger, when its. Cold, and I first start it, it knocks six times, it starts, and knocks 6 times. Not five or seven...six. its weird

**Lawnranger** · 06-26-2012, 07:12 PM

Originally Posted by chevyman984

This is something that might help you lawnranger, when its. Cold, and I first start it, it knocks six times, it starts, and knocks 6 times. Not five or seven...six. its weird

Live with it or tear into it.

**chevyman984** · 06-26-2012, 09:57 PM

Well then! I was just telling you!

**Lawnranger** · 06-26-2012, 11:01 PM

Originally Posted by chevyman984

Well then! I was just telling you!

I appreciate you telling me. No offense meant, I was just saying that from here you have two choices and I guess I didn't choose the best way of saying it. Sometimes I use the least amount of words to express my meaning and it can be taken the wrong way. I'll rephrase what I meant: Since the blade, blade adapter and engine mounting bolts are all in proper order you can use the mower as it is and see how long it will last or you can disassemble the engine to look for the possible cause. I've not heard of something causing a knock other than a loose blade/adapter, loose engine mounting bolts or excessive clearance in the connecting rod to crank or wrist pin to rod/piston. I'm not saying that there isn't or couldn't be another possible cause, just that I haven't heard of anything other than the items I mentioned. I'd sure like to be aware of another reason for a knocking sound such as you describe if there is another reason. Please post the cause if/when you find it as we all can learn from this situation.

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