Cam Timing an A

jpick87 · Sep 12, 2011

What should I time cam to? Reading alot on how to degree a cam and was wondering what point should intake valve open? or is there a standard or is it an every engine is different deal?

what is the best way on a 2 cylinder to find tdc with engine assembled, a bolt into a spark plug hole or just take head off and install piston stop that way? Doesnt make a whole lot of difference to me, if I can do it with engine assembled that would be great.

Is there much advantage to scavenging on these low rpm engines or can it actually hurt? Has anyone tried running different ratio rockers on intake and exhaust?

On a leak down test how many psi drop over what amount of time would be considered normal?

north puller · Sep 12, 2011

Typically cams are not timed to valve opening. This can vary depending on valve lash. A cam is timed to the intake centerline, or the top dead center of the intake lobe. I can't say foe sure where the best place is to time it. Has the cam been ground? What RPM range are you running?

jpick87 · Sep 12, 2011

(quoted from post at 23:55:04 09/12/11) Typically cams are not timed to valve opening. This can vary depending on valve lash. A cam is timed to the intake centerline, or the top dead center of the intake lobe. I can't say foe sure where the best place is to time it. Has the cam been ground? What RPM range are you running?

Ok this is a new thing for me, I had no idea to do this when i put it together. Wish I did but im learning as I go. The cam is ground but I do not have a card on it, I want to degree this cam and dyno see how that goes. I have some plans to change some things over the winter and want to know exactly what makes the biggest difference. Since I never did degree the cam I want to do that first, then change what I am going to change and see just how the tractor likes it and what the dyno says. The guy I am getting parts from might enjoy some numbers on his stuff too. I am only running stock rpm but would like to run around 1200 I think is plenty safe.

This was/is my first build, when i tore it apart and put it back together i didnt know a lot and didnt ask enough questions. I turned wrenches first and asked questions later, hard lesson learned.

mEl · Sep 13, 2011

(quoted from post at 20:23:46 09/12/11)

(quoted from post at 23:55:04 09/12/11) Typically cams are not timed to valve opening. This can vary depending on valve lash. A cam is timed to the intake centerline, or the top dead center of the intake lobe. I can't say foe sure where the best place is to time it. Has the cam been ground? What RPM range are you running?

Click to expand...

Ok this is a new thing for me, I had no idea to do this when i put it together. Wish I did but im learning as I go. The cam is ground but I do not have a card on it, I want to degree this cam and dyno see how that goes. I have some plans to change some things over the winter and want to know exactly what makes the biggest difference. Since I never did degree the cam I want to do that first, then change what I am going to change and see just how the tractor likes it and what the dyno says. The guy I am getting parts from might enjoy some numbers on his stuff too. I am only running stock rpm but would like to run around 1200 I think is plenty safe.

This was/is my first build, when i tore it apart and put it back together i didnt know a lot and didnt ask enough questions. I turned wrenches first and asked questions later, hard lesson learned.

There are several reputable people on this subject but I would recommend jdbpuller at Extreme tractor parts for your info, he pulls amazing power out of a B and I'm sure can give you specifics. Learn how to degree a cam, I had to learn the importance the hard way by assuming that custom parts manufacturers get it all perfect. mEl

north puller · Sep 13, 2011

I agree, and I also learned the hard way. I would not ask a parts builder, nor a cam grinder, but an engine builder for his knowledge. The question is who is the top JD engine builder/tuner to give you optimum cam timing specs. If JDBpuller is doing that good with his B, then he may be the guy to talk to.

I believe that if you check out the technical articles on the Hook mag website you can read an article by Gary Baker on how to time a cam.

jpick87 · Sep 13, 2011

I have read that article along with info on the isky website. I belive I understand. I suppose the head will have to come off to find tdc? Do you guys run all the same lash for intake and exhaust or run them different?

BushogPapa · Sep 13, 2011

Fairly easy to find DTC..

You need to be able to screw a "Stop" into the sparkplug hole that will contact the piston (Gently..!!) and prevent further piston travel..Mark the Flywheel at the appropriate place for future reference..
THEN, Rotate the flywheel Back around until the Piston contacts (Gently) the "Stop" once more...
MARK the flywheel at the same reference point you used the 1st time on the crankcase..
NOW, Measure 1/2 way between the Marks and you will have TDC..

Ron..

Cam Timing an A

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