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Tractor Pulling Discussion Forum

G-motor build question

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730-LP

08-17-2003 18:57:38




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I am building a John Deere G to pull in a 6000&6500 lb. 4 mile per hr. class stock stroke, styled block with .125 over alum m&w style pistons ,unstyled flat head and a cam with a 580 lift.my question is?Is the compression going to be to high for the tractor to lug good at the end of the pull or will it be fighting against its self? Thanks




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luke

02-21-2004 16:43:26




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 Re: G-motor build question in reply to 730-LP, 08-17-2003 18:57:38  
i tore down a g took out the cam took it off the gear had it done does any bodey know where it goes back on the gear a real dummy in ohio



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Bus Man

08-20-2003 18:14:23




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 Re: G-motor build question in reply to 730-LP, 08-17-2003 18:57:38  
I'm running about the same thing that you are asking about. Bored .125 over, no stroke, high compression pistons, and a flat head. It has 265 psi compression, cold. I run 110 octane fuel and have 14.9x38 cut tires. It makes good power wide open but after the rpm's drop out of the power range I start to get spark knock and detonation and the power drops off. I can't lug it down very far when that starts to happen because I don't like the noises that I start hearing. It really starts to work against itself. I pull 2nd gear in 5500 and 6500 and 1st gear in 7500 and have very seldom ran out of power. It's when I pull in the next gear up that I can run out of power depending on the track, sled, etc.

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Chads

08-23-2003 05:37:56




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 Re: Re: G-motor build question in reply to Bus Man, 08-20-2003 18:14:23  
Have you done any cam work, other cyl head modifications? I would start with the timing, You could adavance the distrbutor, a few degrees, it may help with the knock, It also could be hammering the crankshaft too, what was the rod bearing clearence?, or does it use shims?
I know that diesils have a distinctive knock it them I would say that the high compression ratio has something to do with it, If timing, or octane does not cure the knock, check your clearences on the crank/rods, they may be a few thousandths too loose. Just my opinion. Chads

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buickanddeere

08-20-2003 19:55:24




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 Re: Re: G-motor build question in reply to Bus Man, 08-20-2003 18:14:23  
Running a mag or distributor? That combo properly set up, should lug to the last putt without detonation.



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ChadS

08-20-2003 18:45:48




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 Re: Re: G-motor build question in reply to Bus Man, 08-20-2003 18:14:23  
You need to go through the carb, the air fuel mix is off, Have you ever dyno the tractor? Chads



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Bus Man

08-22-2003 01:25:23




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 Re: Re: Re: G-motor build question in reply to ChadS, 08-20-2003 18:45:48  
I'm running a distributor. I also seem to be getting plenty of fuel. Do you think that I need a hotter spark, different advance curve, more/less fuel? I always thought that with that much compression that spark knock at the low to mid end would be hard to get away from. I've never had it on a dyno. When I put it on a diet to loose weight the pto shaft went into the shed when I made a cover for the diff.

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a puller

08-18-2003 11:40:22




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 Re: G-motor build question in reply to 730-LP, 08-17-2003 18:57:38  
throw it together and put it on a compression tester...you don't want over 9:1...I don't think it would be too much, what would the diff. be in a G w/flat head and .090 and a good port and polish job...its about as close as we have come to perfect compression wise..



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JDGnut

08-18-2003 14:54:44




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 Re: Re: G-motor build question in reply to a puller, 08-18-2003 11:40:22  
Compression is up to you.. everyone has a different Idea what they want.. (I'll stay out of the compression discussions..) You should be happy with that for the $$$$ you should have in it.. On the head.. put it together and run it... The flat head I use has been pinned... which means it has a piece of round stock in the water jacket to support the upper part of the head in the combustion area.. to help keep it from flexing.. but I know lots of those heads running in the same comb without the pins and are running good.. With that set up I could run in 2nd on most sorry tracks at 5500, 6000.. but at 6500 was usually pushing it... but I have also been on some really good tracks that choked it out at 6500 in low gear... Just depends on where and what U are pulling on... JDGnut

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