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ATTENTION : Mike Aylward re:JD Cams

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Ohio G Puller

03-12-2005 06:31:57

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You said you have the specs for the G and the 720 gas cams.Would appreciate it if you could share that information with me.
Is this the correct number for the 720 gas cams
F2551R? Would like to install in an unstyled G.
Thanks in advance!
Dave

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Lynard

03-13-2005 07:33:33

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Re: ATTENTION : Mike Aylward re:JD Cams in reply to Ohio G Puller, 03-12-2005 06:31:57

Dave I posted the specs for a stock cam below and the one we bought is: Intake 106.6 degrees ATDC and exhaust 71.2 degrees ABDC lobe centers. Duration at .050 is 220 degrees. This gives around 108 degrees lobe sepreation. He ground the lift to be .415 inch. This gives a lot more opening and actually closes the intake a little sooner. I think it would work better with 210 degree duration on both profiles from the work I have done to A,s. Lynn

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CASEPOWER

03-12-2005 07:17:44

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Re: ATTENTION : Mike Aylward re:JD Cams in reply to Ohio G Puller, 03-12-2005 06:31:57

Yes that is a 720 gas cam.

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Mike Aylward

03-12-2005 15:50:38

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Re: ATTENTION : Mike Aylward re:JD Cams in reply to CASEPOWER, 03-12-2005 07:17:44

OhioGPuller, here are the specs of each cam:

Late G and 70:

Intake Open 5* ATDC Intake Closed 55* ABDC
Exhaust Open 45* BTDC Exhaust Closed 10* ATDC

The early G specifications are the same as above with the exception that the intake open is at 5* BEFORE TDC. This retarding of the intake valve was also done with the late A's and 60's.

720 & 730 (G):

Intake Open 6* BTDC
Intake Closed 26* ABDC
Exhaust Open 20* BBDC
Exhaust Closed 4* ATDC

As you can tell, there is quite a difference in the timing events of the two camshafts. I have a reground F900R that Robert's did. The lobe circle is smaller, gaining lift for the lobe. I will have to degree it when I install it to know how much, if any, the timing events have changed. I am assuming the above events are calculated in full lift, not the now standard .050" specification. Hope this helps. Mike

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JDGnut

03-12-2005 17:31:03

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Re: ATTENTION : Mike Aylward re:JD Cams in reply to Mike Aylward, 03-12-2005 15:50:38

Mike, do you know the lope seperation of the stock cam?? I know Roberts are 106*.... Did you find those specs.. or did you actually measure them??? Just curious, because I need to degree the cam in my G to get a comparison.. (I have no idea on the grind on my cam...) One last thing.. do you know the lift on the cams?? Thanks
JDGnut

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Lynard

03-13-2005 07:15:51

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Re: ATTENTION : Mike Aylward re:JD Cams in reply to JDGnut, 03-12-2005 17:31:03

JDGnut I haven't measured the G cam but we bought a reground cam in 91 from a guy named Smith in Indiana. He sent the specs from a stock cam and from his. He said the stock cam was 200 degrees at .050 for both the intake and exhaust. Lobe center on intake was 122.3 degrees and exhaust was 75 degrees. This figures out to 113.5 lobe centers as Mike N said below. He said cam lift was .375 times 1.47 ratio minus tappet clearance gives .551 inch. Lynn

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Lynard

03-13-2005 07:25:32

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Re: ATTENTION : Mike Aylward re:JD Cams in reply to Lynard, 03-13-2005 07:15:51

I should have said 122.3 degrees ATDC and 75 degrees ABDC. Lynn

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Mike Aylward

03-12-2005 18:45:42

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Re: ATTENTION : Mike Aylward re:JD Cams in reply to JDGnut, 03-12-2005 17:31:03

JDGnut, these specifications came from John Deere Service Bulletin no. 259 dated November, 1957 (20 series specifications). I do not have the lift of the early cam but I believe it to be very near or exactly like the late cam, which is .5658 (valve lift). This probably allows for the .020" lash setting, and going through the stock 1.5 ratio rocker arms yields a lobe lift of .3972", if my calculations are right (.3972", less.020" lash, x 1.5 ratio = .5658" at valve). Hope this helps. Mike

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Mike N Mo

03-12-2005 18:35:02

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Re: ATTENTION : Mike Aylward re:JD Cams in reply to JDGnut, 03-12-2005 17:31:03

JDGnut, IF (I've been up a long time) I did the math right, th G/70 cam hasthe intake lobe centered at 120* atdc, and the exhaust centered at 107*BTDC, giving a lobe seperation of 114*. The 720/730 cam has the intake centered at 112* ATDC, and the exhaust centered at 262*, yeilding 105* lobe seperation. Mike

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JDGnut

03-13-2005 11:32:28

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Re: ATTENTION : Mike Aylward re:JD Cams in reply to Mike N Mo, 03-12-2005 18:35:02

Thanks for all the info guys... about 4yrs ago, I had a local shop grind a cam for me.. I thought the cam was going to Crane, or Comp Cams.. (since that is usually who they use.) but I found out later that they just pulled some numbers out of the air... I think it might be a good cam... at 5000rpms... because the duration seems to be way too long.. Next time I have the valve cover off, I'll do some checking... Thanks Again..
JDGnut

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