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John Deere Tractors Discussion Forum
Show Parts for Model:

620 rebuild questions??

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dflippin08

08-05-2014 08:49:47
70.192.212.17



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I have had issues with blow by and oil leaks as most of you know. I finally decided to put it down and overhaul it. It has gas pistons in it now. My question is does anyone know how much i can take off the head to put the compression were it would be with lp pistons?




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dflippin08

08-06-2014 18:30:36
174.236.227.140



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 Re: 620 rebuild questions?? in reply to dflippin08, 08-05-2014 08:49:47  
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Well I pulled her down this pm. The pistons that are in it are standards. They are worn down to 5.465.... The block has had a crack that I welded up. I bought a replacement block that is bored to .045 over. I'm going to bore it to .090 over and buy aftermarket pistons.



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BushogPapa

08-05-2014 20:19:41
173.88.50.145



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 Re: 620 rebuild questions?? in reply to dflippin08, 08-05-2014 08:49:47  
I took .030" off my 630 head, cleaned the ports/valve pockets, opened and re-worked the seat areas and re-shaped and polished the valves.. Blocked the "Heater Cavity" in the intake/exhaust area too keep heat and carbon debris out..

I can tell you, if you intend to use 87 Gas, you should be at about the limit, with your Gas pistons (for actual Farming)... Mine has been on my 4x16" semi-mount F-145 plow and handles it well, but IS a full load.. Needed 250# on the front, loaded rears, with 3 wts on each rear wheel..that is with new 15.5x38 rears.. 2nd gear all day... The power the 620/630 should put out is very impressive, without changing much. Ron.

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BushogPapa

08-05-2014 20:30:45
173.88.50.145



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 Re: 620 rebuild questions?? in reply to BushogPapa, 08-05-2014 20:19:41  
I advise you to add a short threaded extension tube where the oil feed line exits the block on each Main Quill.. They only need to extend out enough to insure that the O-ring JD calls a "Gasket" cannot swell or migrate into and Block the oil passage. The threaded Brass top tube from a very OLD house lamp was the correct size.. there are plenty threads open in the fitting at the oil feed to thread them in and they do not need to protrude more than 1/8th inch.. I also found that my driven PTO gear (at the bottom and inside the 1st reduction) was over-traveling and I replaced one bolt with one that stops the engagement at the correct place (it would engage too far and rub on the casting behind the gear..

Ron.

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dflippin08

08-06-2014 07:37:17
70.192.199.64



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 Re: 620 rebuild questions?? in reply to BushogPapa, 08-05-2014 20:30:45  
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I have added a stop for the PTO lever as mine was doing the same thing. I think that I will stay with gas pistons. Its Still a working tractor and I dont want any issues down the road while plowing or bush hogging. I am going to do the things you mentioned except I found a LP manifold set that I am going to use. I think its down on power at the moment but I dont have anything to compare it to. I have a F125 that is 3-14's and thats all it wants.

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Gtx1967jewison

08-05-2014 13:08:15
70.197.201.21



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 Re: 620 rebuild questions?? in reply to dflippin08, 08-05-2014 08:49:47  
You could take it all the way to the water jacket & not gain enough to notice. Get some aftermarket pistons.



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teddy52food

08-05-2014 10:29:33
184.94.175.179



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 Re: 620 rebuild questions?? in reply to dflippin08, 08-05-2014 08:49:47  
Leave the head alone as you won"t gain much & put lp pistons in it.



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dflippin08

08-05-2014 10:55:48
68.142.177.151



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 Re: 620 rebuild questions?? in reply to teddy52food, 08-05-2014 10:29:33  
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I can't seem to find any for .090 over.



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teddy52food

08-05-2014 19:15:10
184.94.175.179



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 Re: 620 rebuild questions?? in reply to dflippin08, 08-05-2014 10:55:48  
You may have to get it sleeved & bored to the size you can find. $$$$$$$$$$$$$$$$$$



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