I have a murray riding mower with B&S engine that lately , everytime I start or or stop (low speed revolutions), it makes a knocking noise.

When it's running full speed and mowing I don't notice it.

It's as it is going slower just before stop or faster from a stop on crank.

 

This may sound really strange,, But make sure the bolts that hold the engine to the mower are tight.... If they come loose,, they make lotsa knocking noises @ times... Good Luck,,, Roger

 

I think hopkinsr2 has you on the right track, the engine mounting bolts are probably loose.

 

Ok I'll check it out but when i checked last the engine didn't wobble when i put my hand on it.

7 years
210 hours btw.

 

The engine may not ""Wobble"" when you put you're hand on it,, but when the flywheel & pistons & stuff come to a sudden halt,, anything that is even a bit loose will move... Just telling you what may be a simple fix, 'cus I really don't want to see you tear into the engine for what may be a couple loose bolts.... I see lots of tractors each year with loose mounting bolts... But you may have something deeper???/ Roger...

 

Yea I would appreciate a quick fix.
At this point I'm thinking of taking it in.
I used it some yesterday. The motor sounds great, but a lot of vibration when in drive without blade engaged. And when hitting some deep grass with carriage low it is very rough.
pushing clutch in and it sounds smooth. It seems maybe drive related but even out of gear when turning off or on I get that knocking sound.

It seemed to have started when I used a jack to jack up front end to bang out a dent in undercarriage. Is it possible I bent something under engine jacking it up?

 

Yes, if you bent the main pulley underneath it would jerk and vibrate badly.

 

Ok looks like hopkinsr2 was right.

When my brother came up to look at it he saw the motor jump when i cranked it. For some reason I never noticed it. Then he pushed on it and it did slide. I was expecting something really loose and didn't push it as hard.

So it looks like the motor came loose.

Thanks again.

 

Glad to hear you have it fixed & thanks for the feedback on a successful repair... Glad to be of help..Happy Mowing..... Roger