JD A stock cam specs

[Fredsjdb]

Hi all, I am rebuilding my 50 A for farm stock pulling. I"m trying to found out what the specs are on the late styled A cam. Several companies offer regrinds on your cam for pulling but I need the stock specs to compare with new grind. I"m reluctant to have mine reground if the specs are similar. Any help would be greatly appreciated. Thanks, Fred

 

[Lynerd]

Fred Bought cam 19 years ago from fella in Indiana and he had paper that showed stock lobe center 115 degrees ATDC and 70 ABDC exhaust. Cam displacement was .292. This is at .050 inches. His was 220 degrees duration and107 degrees ATDC intake center. Exhaust 76 ABDC center. I have measured an A cam at 21 ATDC intake open and 23 ABDC intake close. Roughly 113 CL. Exhaust open at 35.5 BBDC and closes at 12 BTDC. About 67 ABDC CL. And .300 cam lift. I suggest as I have used this grind you get 205 degrees on both and 108 degrees lobe center and .380 to .390 cam lift. Should do this with out welding up cam. This will add 20 degrees to intake duration and not change exhaust. Set intake center to 107 108 and should work. Lynn

 

[Mike N Mo]

The specs from the JD service manual are as follows:

Intake open 10* ATDC
close 220* ATDC (40* ABDC)
exhaust open 135* ATDC
close 5* ATDC
Lobe lift 0.300" (Both)
This results in an intake lobe centerline at 115* ATDC
This will be somewhat close to the modern "Total Duration" spec. There was no "at 0.050" spec in the service manual. An approximate @0.050 duration would be 192^ in / 203* ex.

In my opinion, the exhaust lobe is ok as is. For a close to stock displacement and stock head, don't go crazy on the intake lobe. I put a longer duration cam in my 60 before I put in the powerblock, and it turned it into a dog. Sluggish throttle response, and lost 3 hp on the dyno. I put the powerblock in it, and it really came alive. HP per CU IN was then better than with the stock cam. This one had about 20* more duration than a stock cam with a lot more lift.I would add about 10-12* duration (intake) for a stock type engine, advance the intake centerline to 109-110*, but change the LSA to 109* to keep the exhaust lobe timing the same.

My $0.02 worth. Mike

 

[Fredsjdb]

Thanks Mike and lyn, this is exactly what I was looking for. All I"ve done is a .125 bore and installed aluminum M&W style pistons. The head is stock as well as everything else. They only run around 1175 rpm so a great deal of duration wouldn"t help that much. If anybody else has any other advice please give it. I want to get the best bang for the buck within the realm of reality. I know this is just a stock motor. Thanks aqgain. Fred

 

[Lynerd]

Fred Years ago did 2 A's for a friend. 44 models. One had .125 over and the other had .090 over. Different manifolds both cold. He shaved a lot off block and head on both. One with .090 over I put the grind I mentioned and it run 46 HP. The .125 over had stock cam and made 45 HP. Not a lot of difference. I agree with Mike on the cam for a stock motor. I think you could take the money you would use on a cam and a lot of work degreeing it in could make more HP on something else. Lynn

 

[jd b puller]

(quoted from post at 18:58:33 11/04/10) Hi all, I am rebuilding my 50 A for farm stock pulling. I"m trying to found out what the specs are on the late styled A cam. Several companies offer regrinds on your cam for pulling but I need the stock specs to compare with new grind. I"m reluctant to have mine reground if the specs are similar. Any help would be greatly appreciated. Thanks, Fred

Fred, until you do something with the rest of the motor, I'd leave the cam alone. Yes, when we regrind the cams, centerlines and lobe lifts are changed, but if you're still a stock motor, you won't see a big difference. There's a lot of variables in the engine, and efficiency is the easiest to change. Efficiency as in -- compression ratio, breathing, lightening the reciprocating mass, etc.