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720 pistons to raise CR

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jonathan

04-30-2000 00:13:09




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Can I use 720 or 730 diesel pistons in a gas 720, mill about 0.050 off the tops, and get somewhere around 9.5 compression? Are the pins in the same place? Does someone make pistons for the 720 that give more than the normal 6 to 1 or so compression? Mine needs a rebuild. It is an AllFuel so I definately needs MORE compression. Good gas is not that pricey.

Thanks
Jonathan




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Bob

04-30-2000 21:57:58




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 Re: 720 pistons to raise CR in reply to jonathan, 04-30-2000 00:13:09  
Get your self a set of aluminum power seal pistons they will give you the compression to burn gas in your all fuel. You also might want to put a gas manifold on it. That will help alot.



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Gman

04-30-2000 20:41:03




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 Re: 720 pistons to raise CR in reply to jonathan, 04-30-2000 00:13:09  
Jonathon---I think a allfuel 720 has a 6 1/8 bore and 7 in. stroke,I'm not positive but a 70 allfuel is the same as a "G" 6 1/8x7 Funderburk has the pistons and so does Hinerich in Ind. I'v got a set of .90 MW high compression piston,but now you want to be careful,are you fimiliar with Kinetic energy,you get that iron a spinning and the energy stored in that big heavy flywheel is kinetic energy,you raise that compression to high and that will take away the stored energy,takes more energy to squeeze the gasses. First thing I would do is check and see how many 720 allfuels were made before you modifiy it,lot of the allfuels command a premium,If you plan on pulling get some trousers with deep pockets,there's no end to the spending. Later Gman

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Jonathan

04-30-2000 21:19:20




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 Re: Re: 720 pistons to raise CR in reply to Gman, 04-30-2000 20:41:03  
The AllFuel I have is fairly rare. I want to at least put gas pistons in the tractor to get it to 60 HP where it belongs. I have no interest in buring distilant in the tractor. Other than getting the HP up some, we plan to keep it original. I will keep the original pistons in the event someone wants the tractor more than I do.

Thanks for the info.
Jonathan



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G Taylor

04-30-2000 21:44:56




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 Re: Re: Re: 720 pistons to raise CR in reply to Jonathan, 04-30-2000 21:19:20  
All 720 spark ignition egines shared the 6.00 bore & 6.375 stroke. The all fuel used 4.60 to 1 pistons,gas 6.11 to 1 and propane 8.00 to 1. With proper air fuel mixture,timing, 94 octane fuel and gasoline parts installed in the allfuel carb no problems. Lots more power and efficiency due to utilizing more of the combustion chamber presure before the exhaust valve opens with the greater expansion ratio.Part throttle & idle improvements as well. In fact parade only tractors that idle & putt around foul the plugs less and burn the fuel better with more compression as well.

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Chuck

04-30-2000 19:29:53




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 Re: 720 pistons to raise CR in reply to jonathan, 04-30-2000 00:13:09  
I used lp pistons rebuilding a 520. They are flat tops and came to the end of the block. The compression was 150#s and I had all sorts of problems. The carb was not calibrated to that much compression. Didn't want to alter went to the standard pistons, back to 125# and I ran like a top. I believe the high compression did not help at all.



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clooney

04-30-2000 07:47:19




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 Re: 720 pistons to raise CR in reply to jonathan, 04-30-2000 00:13:09  
Jonathan, the 720 (LP) has around 8 to 1 compression, a little higher with an oversized piston. If you can find the LP pistons someplace that would be the way to go.



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cut rate

04-30-2000 00:42:31




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 Re: 720 pistons to raise CR in reply to jonathan, 04-30-2000 00:13:09  
Jonathan, I may be wrong on this, but think that the 70-720-730 gas versions had a smaller bore than the 720-730 diesels did. always heard that the propane versions had higher comp. pistons, maby somone with the real story can assist.



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al

04-30-2000 06:33:23




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 Re: Re: 720 pistons to raise CR in reply to cut rate, 04-30-2000 00:42:31  
You can have a set made by Funderburk in NC. Turn down a set of G Pistons an 1/8 if the pins are the same.Build up the tops of yours with weld on alum.,Stroke it and you get it automatically with the stock set.Lenghten the rods like alot of pullers do..... etc...

al



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jr

05-01-2000 19:30:15




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 Re: Re: Re: 720 pistons to raise CR in reply to al, 04-30-2000 06:33:23  

i have 720 gas with 45 over size pistons and does very well . it gives 4020's hard time in 9500 lb class.



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