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Tractor Pulling Discussion Forum

G CAM GRIND?

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G thing

12-21-2003 18:00:54




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Any one running a roberts pulling grind cam in a stock stroke G? I am running stock stroke ,.125 over high comp. pistons with flat head BIG intake valves manifold and carb opened up match ported and polished . Tractor runs really strong but just does not lug down and carry like it should at the end.Will his cam help me out,or is the grind to much with out a stroke? I STILL HAVE STOCK CAM IN THE TRACTOR.

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Gthing

12-24-2003 05:29:18




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 Re: G CAM GRIND? in reply to G thing, 12-21-2003 18:00:54  
Thanks for all the in put. I am running 16.9x38 tires. I think i will try the cam.



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tractorboy

12-23-2003 18:13:43




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 Re: G CAM GRIND? in reply to G thing, 12-21-2003 18:00:54  
I talked to several engine builders about designing an engine for an A and they told me that the best cam you could get was a 630 cam. Maybe this would be same for G. I put 60 cam in early A once and it really done a good job.



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buickanddeere

12-23-2003 21:38:49




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 Re: Re: G CAM GRIND? in reply to tractorboy, 12-23-2003 18:13:43  
valve lift ,duration and timing is identical from a 47 and maybe earlier "A" right though the 60,620 and 630. I'll check my parts CD tomorrow for the serial number break on the "A" when the cam was improved.



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tractorboy

12-23-2003 21:11:07




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 Re: Re: G CAM GRIND? in reply to tractorboy, 12-23-2003 18:13:43  
You know I was talking about a 70 720 730 didn't you?



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buickanddeere

12-24-2003 07:58:30




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 Re: Re: Re: G CAM GRIND? in reply to tractorboy, 12-23-2003 21:11:07  
I was talking about Tractor Boy looking for a 630 cam. I'll dig out the parts CD and find if there is any mixing and matching of the G/70 into the 720/730. I would rather have a fresh reground cam than chance a used cam anyways.



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tractorboy

12-24-2003 09:03:38




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 Re: Re: Re: Re: G CAM GRIND? in reply to buickanddeere, 12-24-2003 07:58:30  
don't get too rough, it was just a thought



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buickanddeere

12-24-2003 19:25:22




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 Re: Re: Re: Re: Re: G CAM GRIND? in reply to tractorboy, 12-24-2003 09:03:38  
G's from 1938 to early 1949 used the F120R cam. The G's from then to 1953 and all 70 spark ignition tractors used the F900R cam. The F900R is a factory replacememt cam for pre 49 tractors with the associated parts. The 720/730 spark ignition tractors used the F2551R cam. I'm 99% certain it had the same specs as the F900R, just a gear added to drive the distributor at 1/2 crank speed. Instead of crank speed off the governor. I can't find some of my data after moving this year.

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Bus Man

12-23-2003 15:47:39




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 Re: G CAM GRIND? in reply to G thing, 12-21-2003 18:00:54  
Just curious, what gear(s) do you pull in and what weight classes? What size tires are you running?



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Jonathan

12-22-2003 09:49:16




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 Re: G CAM GRIND? in reply to G thing, 12-21-2003 18:00:54  
I have a JD G with roberts carb,his cam grind,.125 over pistons with 6.5 to 1,2.0 ratio rockers it will lug down very good, 260pto rpm and 400lb of torque at that speed.



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520-LP

12-21-2003 19:25:02




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 Re: G CAM GRIND? in reply to G thing, 12-21-2003 18:00:54  
We have been pulling one with the same set up that has had the cam done {not Roberts}it will not lug either I think the compression ratio is to high for a stock stroke



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buickanddeere

12-21-2003 22:48:01




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 Re: Re: G CAM GRIND? in reply to 520-LP, 12-21-2003 19:25:02  
Large ports and valves are for high rpm HP. Too large ports/valves or serious area of turbulance or caused by porting jobs done without a flow bench will cause port velocity to drop. Less air/fuel mixture will be rammed into the combustion chamber. And/or fuel droplets will drop out of suspension in the airflow or be slung to one side of the port.



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G-MAN

12-22-2003 13:29:27




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 Re: Re: Re: G CAM GRIND? in reply to buickanddeere, 12-21-2003 22:48:01  
Exactly. Those large heads and/or drastically oversize valves will HURT performance in a near-stock "G", not improve it.



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buickanddeere

12-22-2003 17:47:02




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 Re: Re: Re: Re: G CAM GRIND? in reply to G-MAN, 12-22-2003 13:29:27  
It might be worth trying a bone stock carb from a A or G tractor before tearing it apart? Doesn't even have to be a big nut 51 on that application.



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