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JD 647 tiller is a brute :)

14940 Views 14 Replies 9 Participants Last post by  dmay
I was tilling a part of my yard site and encountered numerous buried rocks of various sizes. The 647 tiller would just glang bang and cough them out. Then I encountered something that temporarily bogged the engine down then returned to normal. Curious I stopped to take a look and found a 2ft piece of rebar wrapped around the shaft. Took me a while with a crowbar to bend it in an orientation that allowed me to wrestle it off the shaft. Then back to tilling.

What a brute this tiller is. :thumbup1gif:
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It's great when our equipment out performs our expectaions. :good2: You are lucky not to have broke something. Hey, you'll have to remember to shoot a pic or two for us. Pete and I like pictures if you haven't heard. :mocking:
I have the deere 673 tiller and I am thrilled also. I till over 5 acres of land a few times a year. Mine also sees large rocks and other items and just keeps going. Very, very nice tiller and worth the premium in price.
Thats a nice tiller alright, to do that to rebar says allot about the way the tiller is made.
As luck would have it, I had another opportunity to test the strength of my tiller against a piece of rebar. This time I took pics. Stopped the tractor dead in the field but after another successful removal operation we were back to tilling. I'm half way through tilling ~4.5 acres so far. I'll post pics of the tilled land when I'm done.


Hey Darrell,

You are going to have to stop planting that re-bar. :laugh: Hopefully you have found the last of it. Thanks for the update and the photos. :good2:

When I added my tool box I incorporated a spot for my crowbar just for this sort of thing. I have wedged rocks in my tiller and the only way to get them out was to use the crowbar and back the PTO shaft backwards.
I am curious, doesn't the PTO shaft have slip clutch or shear pin? The "stopped the tractor dead" comment concerns me a little.
It should have a slip clutch from the factory.

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Yes it has a slip clutch but whenever I encounter something like this it does stop me cold. I might need to loosen the clutch bolts. Honestly I'm still awaiting my dealer to supply the manual for the unit.

On this or one of the other tractor forums, there is a "how to" on slip clutches. I think it is a sticky thread.

It gives a very comprehensive description of how to set up and break in a new clutch, and how to maintain one that has set over the winter/summer without being used.

I can remember a lot of the stuff I read on the internet. Not always where to find it the second time............. :unknown:

Good luck
Dmay, heed the warnings of slip clutch maintenance. It gets costly real quick if you don't. Last year I pulled my Harley rake out after sitting for the winter. Like a fool I went right to raking. 20 min later I encounters a 6" rock and bang!. I destroyed the u joint yoke on both joints.
It ended up costing me $450 in parts and 2 weeks of down time. It would have taken less than an hr to adjust the clutch in the first place. Lesson learned the hard way.:thumbsdown:

On searching I found this on another forum,

"You should loosen it, but not right slack, and then run it in slip-mode (with light load) for 5-10 seconds (seems like a long time, but it's not), to have it seat itself, and work itself together.... You know if you accomplished it because it should get warm - to almost hot, but not burning your fingers, and definitely but don't burn the clutch up! If it doesn't heat up when you do that, tighten it up a tiny bit and re-run it... it needs to run under load, rubbing the plates together, to seat themselves properly. Once it breaks itself in, let it cool, adjust it by testing it out - if you see / hear it slip under normal load, tighten it by tightening each bolt by 1/4 turn. Run it again, and basically it should be on the border line of slipping under very heavy load (tractor engine bogs down). That way, you can till with max HP going to the ground, but as soon as the load surges above that, it will slip."

No pics to go along with the above. Does this sound like a good procedure to follow for a JD 647 tiller? Anyone got a 647 manual? Mine is on order and due to arrive next week.
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Yep, that's about right. My tiller slip clutch froze up on me after I had not used it for a few years. Had to take it all apart, clean it, and then put it together and slipped it a bit. Tighten it up, use it, it slipped a bit more than I wanted under normal load, so tighten it up some more. If I hit a big rock, it will just slip, life is good.

When I go to use it this fall, I'll loosen it up and slip it first.

I also have a slip clutch on my MX6 rotary cutter, I'll loosen it up this fall and then slip it in the spring before use.

Dmay, that is great info about the strength of the 647 tiller. Good to know when the time comes for me to get a tiller (already come close a few times).

My 413 Rotary mower has a clutch. I followed the manual for adjusting it but it was still a little stronger than I wanted my previous 2305 to have to endure so I backed the spring pressure off a tad more so that when I clobbered something solid it slipped sooner instead of shocking the 2305. I guess my point is that I don't think there is any crime in adjusting the clutch to behave the way you want it to work.

Of course, the more you slip it, the sooner it wears out. On the other hand, if it never gets slipped, it eventually becomes a coupled joint and defeats its own purpose.
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Here are pics of my tiller. Easy to adjust the 8 slip clutch nuts/bolts after you remove the cover plate. I had to remove the nuts/bolts/springs completely and one rubber mallet hit to make it come apart. Everything was lightly rusted stuck in place. Cleaned and reassembled nuts/bolts/springs hand tight. Was able to slip just by using my foot to turn a tiller blade. Tractor not running of course. Then proceeded out to the field and just did a process of incremental stop, tighten and test until I got the correct tension with tiller engaging and churning dirt.


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