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PostPosted: Tue Dec 25, 2012 7:54 pm    Post subject: JOHN DEERE 620 Reply to specific post Reply with quote

On a JD 620 how much can I shave off the head to raise the compression without getting in to problems. The engine is .125 over and cranking compression now is around 120psi. What pressure should i shoot for and how much power will be gained.
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Joined: 21 Jan 2006
Posts: 1891

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PostPosted: Wed Dec 26, 2012 8:59 am    Post subject: Re: JOHN DEERE 620 Reply to specific post Reply with quote

JD makes hi altitude pistons in oversize but I dont" know if they made in .125 Extra or excess compression can also be a problem as your carb will have to be calibrated accordingly and your iqnition will be critical. Personally I think it will mess up your burn time on regular fuel. Now if you going exotic fuel, nitro or alcohol I don"t have a clue. I once used Hi altitude pistons in a 520 and couldn"t stand how it ran, way way too much compression and it didn"t run as good as standards that I reinstalled. Cam timing etc is also a factor. Hopping up a 2 cylinder is over my paygrade but there might be pullers that can offer you the right combination, not sure they"re on this site. Good luck.
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Tractor Guru

Joined: 26 Dec 2001
Posts: 7854

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PostPosted: Wed Dec 26, 2012 12:06 pm    Post subject: Re: JOHN DEERE 620 Reply to specific post Reply with quote

I had .030 taken off the had on my 630 Gas and it is as far as I would want to go, for actual Field-Work...
It is pretty Hot, but no problems with plain old 87 Gas...Peppy, like it had LP Pistons in it..sounds darned GOOD, actually..
Pulled 4x16 F-145 Semi a year ago in Alfalfa/Jack-Wax ground in 2nd gear...
ALL it wanted, but sure did itself Proud..
Yes, I had about 250# on the front and Loaded rears, with 3 left and 2 wts, rt..
My 720 will only do one gear higher..(3rd)..
I am partial to the Valve-Job I did on the 630..
Polished, re-shaped, port-matched and opened..

I would guess I arrive at Maximum Torque at 950..
For a higher Torque, a different Cam would be needed...

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Mike M
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Joined: 31 Mar 1998
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PostPosted: Wed Dec 26, 2012 1:10 pm    Post subject: Re: JOHN DEERE 620 Reply to specific post Reply with quote

I know what you mean by "over my pay grade" There are guys doing things to these old tractors that can really build some power ! I don't know how they ever get them to hold together ?
I got enough problems dealing with all the issues on a stock build up.
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