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Tractor Pulling Discussion Forum

john deere a compression

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2 lunger

12-13-2007 10:30:58




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how much do i lengthen my connecting rods on a stock 52 jd a to get the compression i need to make good power for pulling.




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2 lunger

12-13-2007 15:02:08




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 Re: john deere a compression in reply to 2 lunger, 12-13-2007 10:30:58  
I am going to use stock pistons stock john deere head and stock stroke, stock cam, standard bore ,all the original 1952 parts.Thanks for the info.



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Mike n Mo

12-13-2007 20:26:22




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 Re: john deere a compression in reply to 2 lunger, 12-13-2007 15:02:08  
Here's what I figured up.
All stock parts (13.0" rod)= 5.60:1 comp ratio
Stock parts with 13.5" rod = 8.0:1 comp ratio
Stock parts with 13.6" rod = 8.86:1 comp ratio
Stock parts with 13.7" rod = 9.91:1 comp ratio

I'd shoot forthe 9.0 to 10.0:1 range. You'll have to use 105-110 octane fuel to avoid detonation problems at these ratios.
If you still have the standard bore pistons, is the bore worn? After 55 years, unless it's a very low hour tractor, or been sleeved back to standard I'd consider boring to +.045 to freshen it up if you're wanting to optimize power. Obviously if you do and use higher comp aluminum pistons, shorten the rod the same distance as the compression height differance. If you're looking for cheap, find a pair of used JD .045 pistons. Should be fairly easy to find. Mike

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Mike n Mo

12-13-2007 13:28:23




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 Re: john deere a compression in reply to 2 lunger, 12-13-2007 10:30:58  
Rod length will depend on the compression height of the pistons you're using (center of the wristpin to the top of the piston). Stock rod length is 13" center to center. Are you going to use the stock head? Changing to a Heisler or a Murphy's (Jerry's) head will increase the compression significantly without changing the rods. Let me know the variables and I can give you some figures. Mike



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