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jd 70 lp pistons and what psi should i go for


 
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70 jd puller
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PostPosted: Mon Mar 28, 2011 6:07 pm    Post subject: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

i am rebuilding my 70 lp and want the most hp i can get while boring .125, what is the ideal compression or psi i want to be at and keep good low end power when tractor pulling.
 
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north puller
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PostPosted: Tue Mar 29, 2011 1:57 am    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

I don't know first hand, but I have heard that 10:1 is not a problem for LP. 11:1 is borderline. The cam will effect cranking pressure, but that should be in the 220 psi range.
 
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70 jd puller
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PostPosted: Tue Mar 29, 2011 4:32 am    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

Do i shoot for 11 or just under? What ratio would 220 psi be? Do you know anyone i can go over this with so i dont waste alot of time and money? Thanks
 
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north puller
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PostPosted: Tue Mar 29, 2011 4:43 am    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

I have said before (because I learned the hard way) that you should spend a lot of time, as much as it takes, on the phone to sort out your project before you spend any money. So I think that you are on the right track.

Call Jeff at Murphy"s Motor Service, or Ray at Extreme Tractor Parts. Both of these guys know John Deere"s and both can build you pistons. I have no experience in LP, but one of them might. I have had better luck personally doing business with Murphy"s, but that is just me. Both are VERY helpful on the phone.

You can google both of them to get their numbers. Good luck.
 
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buickanddeere
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PostPosted: Tue Mar 29, 2011 7:54 am    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

Bore it only 45 if that cleans up the bores. You won't be able to find the difference in HP on a dyno between 45 and 125 over. The difference in air temp and humidity between two days will have more effect.
You can't figure combustion pressure until your cam grinder and piston builder knows what each other is doing.
I do hope you are getting that 55+ year old cam and followers re-ground. How can you expect the engine to make power while loosing lift and duration? Eye-balling the cam & followers isn't an inspection either.
 
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north puller
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PostPosted: Tue Mar 29, 2011 8:30 am    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

I agree with buick that after 55 years the cam won't be perfect. However you realize that the cam only turns 600 rpm and it is big. In the words of Sonny at Bullet cams, "this ain't no chevy, it's big stuff". It will be worn, but not that bad. A set of ratio rockers will give you more lift than stock regardless of cam wear.

I have been down this road. You WILL have the crank out of a 70 before you can get the cam out. The lifter bores are cast into the case. You can't get the cam gear off without dropping the crank out of the way. So if you want to inspect the cam, be prepared to have the crank in your hands. That opens up a whole new discussion of what to do with it.
 
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PostPosted: Tue Mar 29, 2011 10:06 am    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

I've heard people say the 1st part of the two cylinder Deeres to make it's way down the production line was the camshaft. Then everything else is built around it.
 
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north puller
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PostPosted: Tue Mar 29, 2011 12:46 pm    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

When you try to drive the cam out of the cam gear, there is a flat spot on the flange that will clear the top of the case. When this is lined up, the front side of the flange hits the lifter bore casting. On a 60 for example, the lifter bore casting is a separate piece you can unbolt and remove. On the 70 it is cast into the case. To get the required clearance you remove the crank and then drop the cam down. Then remove the 2 oil lines that go from the pump to the gov housing and then you can fish out the cam through the top.

This procedure requires dropping a few f bombs.
 
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PostPosted: Wed Mar 30, 2011 2:34 am    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

I was going to get a cam and followers from dengler's and custom pistons. What cranking psi do i want to be at or static compression as some refer it to. I will be in 3-4 mph stock class of coarse. what kind of hp should i be hoping for??
 
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PostPosted: Wed Mar 30, 2011 4:40 am    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

With a 70LP making a 6500lb class will be tough. A 70 in 2nd gear pulling the 8000lb class? Just a cam and high compression won't do it unless the track is sand.
1st gear in the 8000lb class on a clay power track will lugg a high compression & cammed 70LP.
 
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PostPosted: Wed Mar 30, 2011 4:49 am    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

was planning on 7000 in 1st gear. what compression would be best? 9 or 10:1 or 11:1 or 12:1? Cranking psi 150/160/180 or go into the 200-220? Which one would make the best all around power and lug. Cam will be a torque cam not for high rpm.
 
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PostPosted: Wed Mar 30, 2011 7:09 am    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

This is where you send the cam to the grinder and tell him what the application is. The cam grinder takes care of the cam and he tells you what compression ratio to run.
 
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2-banger
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PostPosted: Wed Mar 30, 2011 4:33 pm    Post subject: Re: jd 70 lp pistons and what psi should i go for Reply to specific post Reply with quote

get a hold of josh blackburn on here he could get u a cam and pistons. bob at triple g also does a good job on cams.
 
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