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John Deere Tractors Discussion Forum

JD 70 gas

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JohnO

08-20-2004 12:00:28

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We've got a model 70 gas that has some modifications; bored .125 over, high compression pistons, electronic ignition, lp manifold, dry air filter & the head milled .150. We are going to swap/regrind the cam. I have access to a G cam that has the specs that would complement our setup. My question is can a G cam be swapped with the 70 cam? Is there a possible serial number break that the two could have possibly been the same part number?

Thanks.

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Toot

08-20-2004 14:37:13

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Re: JD 70 gas in reply to JohnO, 08-20-2004 12:00:28

As buickanddeere stated the grinds on a late styled g are the same as 70 so youre not going to gain anything. Over the years I have owned 5 G's and 3 70's. Not to burst your bubble, but remember the 70 gas has the smaller 5 7/8" bore and the G's and 70 all-fuels had a 6 1/8" bore and you apparently have an even 6 inch bore now since you bored .125 over (duh). All the G's I owned had aluminum pistons, and they would walk all over two of my 70's which were gas. Now the third 70 I had was a all-fuel model which had the 6 1/8" big bore like the G's. That tractor had the high compression aluminum pistons, and with that duplex intake system that was one romping stomping tractor for what it was. It was the kingpin powerhouse of my collection until I sold it 7 years ago. Every head on all my G's-70's had .200-.250 milled off the head. You can take them that far.

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JohnO

08-20-2004 14:54:54

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Re: JD 70 gas in reply to Toot, 08-20-2004 14:37:13

Toot,

All good points on the G vs.70 and I appreciate your thoughts. I completely understand we're behind the eight ball. But, we've managed to slip past a few Gs in the past. The old 70 is what we ended up with and we're just trying to make it run as well as it can.

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Mike M

08-20-2004 12:28:52

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Re: JD 70 gas in reply to JohnO, 08-20-2004 12:00:28

I know I have sold 70 cams to people pulling G's these were styled G's.

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JohnO

08-20-2004 12:52:03

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Re: JD 70 gas in reply to Mike M, 08-20-2004 12:28:52

One more question.

Are the cam followers the same for the styled G and 70?

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G-MAN

08-20-2004 13:46:29

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Re: JD 70 gas in reply to JohnO, 08-20-2004 12:52:03

No, they're different part numbers. The lifters run in the front of the main case on the "70" and in a bolt-in lifter block on the "G". Believe it or not, the "70" DOES use the same lifter as the "R" (it's an "R" part number - R1354R), 620/630, 720/730, and 80/820/830/830-I. I'd definitely get the lifters resurfaced for those reground cam lobes. Robert's will do them with the cam. I can't remember if it's an additional charge or included with the cam though.

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JohnO

08-20-2004 14:29:52

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Re: JD 70 gas in reply to G-MAN, 08-20-2004 13:46:29

Gman,

Thanks for the update.

FYI. I spoke to Roberts and they're charging $9.75 each to resurface the lifters in addition to the $155 for regrinding the cam.

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JohnO

08-20-2004 12:49:42

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Re: JD 70 gas in reply to Mike M, 08-20-2004 12:28:52

MikeM,

Thanks for the info. I've got access to a freshly ground competition (by Robert's) styled G cam and in the interest of time, I'd like to swap the cams out and then send the 70 cam to Robert's some other time.

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Mike M

08-20-2004 13:00:58

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Re: JD 70 gas in reply to JohnO, 08-20-2004 12:49:42

Since it is a Robert's cam I would give him a call and double check for sure if they grind them the same for what you want to do.

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buickanddeere

08-20-2004 12:32:50

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Re: JD 70 gas in reply to Mike M, 08-20-2004 12:28:52

The stock G and stock 70 cam have identical lift and duration. Even the same part number. Send the cam & lifters to Robert's carburator for a pulling grind.

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Drew

08-21-2004 11:28:13

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Re: JD 70 gas in reply to buickanddeere, 08-20-2004 12:32:50

I was just wondering if there was anyone out there that has gotten a camshaft from Robert's and got a camcard with it or was told what the acutal grid was or where to degree the thing in at. Or is it he sends a cam and says it will work..??

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G-MAN

08-23-2004 10:18:29

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Re: JD 70 gas in reply to Drew, 08-21-2004 11:28:13

I didn't receive any specs with mine, but I'm sure that if you called Robert he'd tell you everything you need to know. I've spoken to him a few times and he was very upfront and polite. I don't know how someone would go about "degreeing in" a two-cylinder cam. It only bolts to the gear in one position with no play in the holes. I suppose someone with some machining ability could modify one with something like those "hex-adjust" setups you see on performance timing chain sets, but I doubt it would be worth the effort. How are you going to know where to start? Getting in there to play with the cam adjustment wouldn't be a lot of fun, and with a 413 cubic inch engine breathing through a single- or two-barrel carburetor at 975 rpm, cam timing isn't going to be as crucial as it is in a 6500 rpm race engine.

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G-MAN

08-20-2004 13:49:07

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Re: JD 70 gas in reply to buickanddeere, 08-20-2004 12:32:50

I wonder where this "a 620 cam is better than an "A" cam" and other swaps myth got started? Did guys just naturally assume that newer engines would have more efficient grinds? By the way buickanddeere, could you drop me another email. I screwed up and deleted the last one you sent me. Did you get your home email squared away? I've got something to ask you about.

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buickanddeere

08-20-2004 22:11:01

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Re: JD 70 gas in reply to G-MAN, 08-20-2004 13:49:07

G-man

Can you send an e-mail from Rummey"s site? I house cleaned my e-mail and lost a whole wad of addresses.

B&D

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G-MAN

08-23-2004 10:23:20

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Re: JD 70 gas in reply to buickanddeere, 08-20-2004 22:11:01

Missed it again. [email protected]

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G-MAN

08-23-2004 07:40:25

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Re: JD 70 gas in reply to buickanddeere, 08-20-2004 22:11:01

It's unhidden on this post. I always type it in, but usually forget to turn off the "hide" function.

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JohnO

08-23-2004 08:53:01

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Re: JD 70 gas in reply to G-MAN, 08-23-2004 07:40:25

Gman,

I pulled the govenor off of the tractor this weekend. Discovered the thrust bearing is falling apart and it appears that the weights have been hitting the shaft for some time. I feel confident that this helps explain some of the uneven performance we've been seeing. Repairing the govenor will be new territory for me. Any suggestions?

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G-MAN

08-23-2004 10:13:07

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Re: JD 70 gas in reply to JohnO, 08-23-2004 08:53:01

There are lots of guys on here with a ton more governor experience than me, but I guess I'd suggest just doing it by the book and making sure all the parts fit well with no slop in the weights, pins, etc.

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JohnO

08-20-2004 12:46:50

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Re: JD 70 gas in reply to buickanddeere, 08-20-2004 12:32:50

buickanddeere,

That's exactly what we're doing. In the interest of time, I've got access to a styled G cam that has a fresh competition grind from Roberts.

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