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Tractor Pulling Discussion Forum

JD G cam

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Dougie

10-24-2004 20:31:40




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What kind of cam do I need for a 1948 John Deere G w/ 430 ci, .125 HC pistons, jerry"s manifold, head work, little carb work, and getting a distributor w/ electronic ignition? Also, how much horsepower will I have w/ and w/o it the cam? I think I have around 60-65 hp. Thanks

Dougie




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Gwiz

10-26-2004 10:58:51




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 Re: JD G cam in reply to Dougie, 10-24-2004 20:31:40  
I need your sn# off the tractor to tell for sure.I dont have my parts book handy but I think the cam change was around sn# 34000.



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Dougie

10-26-2004 18:35:58




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 Re: JD G cam in reply to Gwiz, 10-26-2004 10:58:51  
The sn # is 34522. I doubt the tractor has had the cam replaced in it because the tractor when I got it, had the cheapest parts to fix it. The head had 22 cracks in it and a unstyled a carb on it. There was so many unstock things on it, I tried to forget it.



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Gwiz

10-25-2004 12:12:34




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 Re: JD G cam in reply to Dougie, 10-24-2004 20:31:40  
Dougie, I just put a roberts pulling cam in my G that is basiclly set up as yours with a flathead. I checked on dyno at 540 pto rpm 75 horse power.I have not pulled it yet to try it out but it really barks.



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buickanddeere

10-24-2004 22:12:53




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 Re: JD G cam in reply to Dougie, 10-24-2004 20:31:40  
A cam from Robert's Carburator and a fresh set of followers are as good as any. Estimating HP from "a far" is risky business. Tuning and a hundred minor but important tweeks will make of break an engine. As for lift and duration. The later G cams were identical to 70,720 & 730 cams.



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not true

10-26-2004 11:35:52




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 Re: JD G cam in reply to buickanddeere, 10-24-2004 22:12:53  
the timing points on these cams is not the same



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G-MAN

10-26-2004 13:53:49




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 Re: JD G cam in reply to not true, 10-26-2004 11:35:52  
I'm afraid you're incorrect. The earlier "G" cam for tractors serial #34689 and up subs up to the F900R cam that was used in the later "G" AND the "70". The difference between those cams and the 720/730 cam is that those tractors drove the distributor off the end of the cam, which required a different shaft. The specs are the same.



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Mike Aylward

10-26-2004 15:53:50




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 Re: JD G cam in reply to G-MAN, 10-26-2004 13:53:49  
Glen and G-MAN, I"m afraid "not true" is right. The late A"s and 60 through 630 had the same timing events even though they had different part number cams. The late G"s and 70s also shared timing specs because they used the same number cam. The later 720-730 tractors used a different number cam which did drive the distributor but the timing events were altogether different than the earlier F900R cam. Just wanted to clear up things. Mike

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Earl S

10-26-2004 19:36:50




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 Re: JD G cam in reply to Mike Aylward, 10-26-2004 15:53:50  
Mike are cam followers same diameter in the 70 & the 720,730? I don't have any specs in my records on the 720,730 followers. Earl



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G-MAN

10-26-2004 17:39:34




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 Re: JD G cam in reply to Mike Aylward, 10-26-2004 15:53:50  
So everybody was at least partially right. Buickanddeere was right that the lift and duration were the same. I was right that the 70 and late "G" cams were the same, and "not true" is right that the 720/730 cams were different, but would have been incorrect in throwing the 70 cam in with them, correct? BTW, where do you find the actual lobe timing specs?



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Mike Aylward

10-27-2004 18:26:00




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 Re: JD G cam in reply to G-MAN, 10-26-2004 17:39:34  
The lift may be the same with the F900R and 720 cam but the duration is different. I can post the specs if needed. Earl, I imagine the followers are different diameters in that the 70 followers are cylindrical and the later ones are mushroom type. Mike



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Will P

10-28-2004 20:22:43




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 Re: JD G cam in reply to Mike Aylward, 10-27-2004 18:26:00  
What is the cam spec difference in the "old" G cam to the F900R cam. I have a 49 with the old cam. Motor is open now and thinking of upgrading.

Will P



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Mike Aylward

10-29-2004 14:44:43




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 Re: JD G cam in reply to Will P, 10-28-2004 20:22:43  
Will, I don't have the specs in front of me right now but I am thinking the only difference is the intake valve opens at 5 degrees after TDC instead of 5 degrees before. Otherwise the rest of the specs are the same. This same change was made in early '49 for the A's. Mike



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Earl S.

10-28-2004 07:23:43




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 Re: JD G cam in reply to Mike Aylward, 10-27-2004 18:26:00  
Good discussion Mike. Same cam profile???? Different diam. followers??Cam timing??What happens when you narrow lobe for stroking no longer strikes in the middle of follower?? Earl



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Dougie

10-25-2004 16:47:23




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 Re: JD G cam in reply to buickanddeere, 10-24-2004 22:12:53  
Since mine is a 48 model, what cam do I have? The F900 or the older cam?



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G-MAN

10-26-2004 13:55:44




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 Re: JD G cam in reply to Dougie, 10-25-2004 16:47:23  
I forget where the '48 serial numbers stop, but if your tractor is number 34690 or newer, it will have the later cam in it. Or, if the cam was replaced at some point, it could still have the newer cam in it as the old number subbed up to the newer number.



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Will P

10-27-2004 16:15:36




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 Re: JD G cam in reply to G-MAN, 10-26-2004 13:55:44  
G-man, I have my 49 (31,???) stock G apart right now. It still has the older cam in it. I read the PN on it. What is the difference in the specs. of the cam??? Looking into pulling it out for the rebuild.

Thanks,

Will P



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Dougie

10-25-2004 16:44:26




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 Re: JD G cam in reply to buickanddeere, 10-24-2004 22:12:53  
Since mine is a 48 model, what cam do I have? The F900 or the older cam?



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buickanddeere

10-26-2004 22:20:24




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 Re: JD G cam in reply to Dougie, 10-25-2004 16:44:26  
I should explain myself better when posting. As G-Man cleared up, the later G,70 and 720/730 shared the same duration & lift. As did the late B,50 & 520/530. Along with the late A,60 & 620/630. The old trick of slipping a 720 cam into a G wasn't so trick. The things I do in the middle of the night for people with money to pull but can't purchase the parts book/CD. The A/AR & AO was upgraded for the 1936 model year at #424025 & 270616. Intake 10 ATDC &40ABDC. Exhaust 45 BBDC & 5 ATDC. The B was upgraded at 201000 in mid 1947. Intake 0TDC & 50 ABDC. Exhaust 55BBDC & 5 ATDC. The G was upgraded at 34690 in mid 1949. Intake 5 ATDC & 55ATDC. Exhaust 45 BBDC & 10 ATDC

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