Ford 1210 engine slap/knock when running 48" rototiller

[DMoneyAllstar]

Running my old Ford 1210 4wd with a 48" tiller attachment. I only use tiller attachment to till my garden in spring and to till up my grass clippings / compost pile a few times in the summer.

When running it and it starts to work a little bit, it sounds like the drivetrain or the engine is slightly "slapping" at every rotation of the PTO. When it starts to knock/slap, I'll raise the 5pt up a bit to lighten the workload and it goes away. Only makes the noise when it's having to work a bit.

When tilling, I'll throttle the engine up to full RPM and then back it down like 10% before letting her till.

Is this play in the drive-train? Crank bearings? Piston slap? Normal/abnormal?

It has oil, fuel with additive, and has always smoked a little bit. It's a ~1984 with right around 1050hrs.

 

[TractorTech]

Do you have any other PTO implements to see if it will make a similar noise? Or, when pushing a heavy load with the loader does it make noise?
Without isolaing an area for the noise, I would guess that it is probably in the rear PTO drivetrain like a bearing.
Could it also be possible it is the tiller driveline?

 

[DMoneyAllstar]

Thanks for the quick response!

Nope, don't have any other PTO implements to test.

Doesn't make "the noise" when driving nor when using the loader bulldozing/lifting with the bucket. And doesn't make "the noise" when there's nothing on the PTO (just running freely without any load).

It's definitely coming from the rear of the engine or front of the drivetrain, not the tiller itself.