520-h knock (I think)

[Ike 75]

I have a slight knock when one of my 520’s is at idle.  It appears almost centered around the fly wheel.  When I raise the throttle, the knock goes away.  The motor just purrs around 25-3k rpm.

 

The tractor is a low hour machine at 290 hours.  Any feedback would be appreciated!

[Ike 75]

Also, the motor does not smoke or burn any oil. 

[lynnmor 7,354]

Rotate the engine by hand, easier done with spark plugs removed.  Rotate it a small amount and then rotate just a small amount each direction.  Keep doing it advancing a small amount each time till you are around two turns.  If there is a problem, you should be able to detect it this way and get a better idea where it is coming from.  Note that there is an expected small noise near the top and bottom of the stroke.

[JoeM 7,874]

18 hours ago, lynnmor said:

Rotate the engine by hand, easier done with spark plugs removed

and the PTO and drive belts removed, start it with the belts off too. 

[Ike 75]

Rotated engine by hand.  No abnormal noise.  Also, ran without drive belt and slight knock only at idle.  Changed plugs, oil and soon will rip apart care to see if I can smooth out the idle a bit.  Thanks for the reply’s!

[bc.gold 3,403]

A loose flywheel key, the knock disappears as engine rpm's increase.

 

Engine would sometimes be hard start.

 

Possible cause, if the mower blade struck something hard embedded into the ground or the pto had taken a sudden shock, the key is made from soft material which is meant to shear but often only as shown in image below.

 

[Ike 75]

I just finished cleaning the carb and idle jets and the knock has strangely quieted down.  I am replacing the drive belt then using the machine and see if the noise is worth digging deeper.  will check flywheel.  The machine starts instantaneously.  No difficulty at all.  

[chex313 123]

Glad you smoothed it out, I am still trying to get over the fact that your 520H only has 290 hours.

[Ike 75]

She is pretty clean too!

 

Edited May 17, 2020 by Ike
Photos are blurry when I upload them.