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A engine rebild, BIG time

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A-man

11-07-2001 18:04:24




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After pulling my '51 JD hard this summer at the tractor pulls, I am beginning to think that I don't have enough power to keep up with the pack. My "A" has 84 psi In the nuber one cylinder and has 85 psi in the number two cylinder. I am thinking about boring out the motor, and installing model "G" or "70" pistons as well as shaving the head as much as is needed to reach a compression of 9.5:1 . Do any of you seen any conflicts with the plans I have here? Will the new "G" or "70" pistons fit my stock rods. What about the block? will the oversize bores be to big for the "A" block? How much will I have to shave the head to accomplish a 9.5:1 compression ratio? Is there anything wrong with this high a ratio? Will the stock crankshaft be able to take the increased hp? Any other reccomendations? Thank-you!

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Todd

11-07-2001 19:11:06




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 Re: A engine rebild, BIG time in reply to A-man, 11-07-2001 18:04:24  
If you have a 51 model, you should have the low low first gear, which already gives you a power advantage over the fast gear two speed models. 70 gas pistons which are 5 7/8" bore will work, G's will not. You do not need that high of a compression ratio for low gear pulling. By installing a .045 - .125 over bore aluninum piston kit mde for that tractor, and cutting off .125 off the head you shoul bump up to 120 - 140 psi. Yes the crank will hold up. You will get several opinions about this, but depending on tire size, weight classes, you pull in, and what gear, its hard to give opinions. If you are wanting to pull above first gear, you will need 70 gas pistons and a stroker crank. The sky is the limit on what you want to spend.

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A-man

11-07-2001 20:08:21




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 Re: Re: A engine rebild, BIG time in reply to Todd, 11-07-2001 19:11:06  
Thanks for the comments so far! It is true that I have the VERY low firt gear which I have used for pulling all season... I have NEVER even came close to running out of power in that gear, but I would like to pull in second gear... It will pull really well in second up until the end of the track and then it just flat runs out of power. so I was hoping by doing a complete engine overhaul I would be able to have the power to pull in second gear. Since the compression is fairly equal in both cylinders right now, would it be reasonable to bring up the compression buy just shaving the heads .125 like you said? Is there much to be gained by adding the .045-.125 over bore and the "70" pistons? I figured the only reason I would change pistons is to increase my cubic inches, and by only that much overbore, it doesn't look like there is very much to be gained. You are correct when you say I don't need that high of compression to pull in low gear. BUT, why not have it? The engine will be more efficient, and may possibly give me the needed power to pull in second gear. My "A" runs on gas and is not an "all fuel", I pull in weight classes between 6,000 and 7,500 lbs. and I plan on using a 15.5 size tire in the following year. When you said model "G" pistons won't fit, is that becuase the bores would have to be honed out to excessivly, or is it because the block is simply not big enough? Thanks for the help so far. A-man

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G Taylor

11-09-2001 04:39:16




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 Re: Re: Re: A engine rebild, BIG time in reply to A-man, 11-07-2001 20:08:21  
To paraphrase the "Old Puller" some time ago on the pulling page.The three most important factors to win while pulling are tire traction,tire traction & tire traction. Then weight distribution & everything else. Before going into the engine try an old hard set of Firestone 23 degree "Traction Field & Road" 15.5x38 or larger if you class allows. A set of 18.4x38 with most of the tread worn off from being driven on pavement are ideal. No grinder scuff marks either from pavement/concrete spun tires. There is cheap HP in a Roberts cam/carb, 60LP pistons, cold gasoline intake,dry airfilter conversion, oversize valves, port/valve bowl cleanup (not porting) & the straight exhaust stack. May need it even in 1st gear if good traction is found with taller/faster tires.

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