Push Rod Legnth with Harland Sharp Rockers

[dozz302]

Hello, I built a 427 with C4AE High Riser Heads years ago. Still have it. The Harland Sharp Rockers adjusting bolts are pretty far down (almost all the way) with about a .600" solid cam. I remember reading that there should only be a couple of threads showing below the rocker bottom. Would that "Rule" apply to all rockers no matter what type?  Is that "Rule" even correct. This motor has also broken the end off a rocker shaft with hardly any miles (under 1000 miles). I'm thinking that the push rods are way too short. Thanks

[blykins]

Do you have end stands to support the rockers on the end?

An engine will run just fine with the adjuster ran down, but it can take away from the amount of lift you get to the valve.  The pushrod ends up doing a sweeping motion instead of translating motion to valve lift.  I generally like to run a thread or so down, or as high as I can go without getting the pushrod into the rocker body.

[427mach1]

Do you have the correct high-riser rocker shaft stands?  The high-riser requires a shorter stand than the low and medium riser heads.

[dozz302]

I thought that if the adjuster was all the way down that would put a lot more stress on the system? From what I described would it be worth measuring for new push
rods to place the adjusting nut all the way up as far as possible? I notice and read guys building engines talk about .010" difference in push rod length. On my engine I would be talking about at least 1/4".
Yes, proper Ford C4AE stands are being used. There are no end support stands available other than the DOVE units which would involve taking head bolts out which since the engine has been together for decades, I'm not going to get into that. The engine is sealed. I have been asking for someone make a Billett Steel simple slide on end support stand but no one wants to make it for the High Riser.

[fekbmax]

Never a bad thing having the correct length push rods.  If you're gonna take the time to measure for new, then it's a good idea to dial in your rocker to valve geometry as well.

[pbf777]

I remember reading that there should only be a couple of threads showing below the rocker bottom.

I thought that if the adjuster was all the way down that would put a lot more stress on the system?

     Your memory and your statements are correct.   

     It's basically a simple lever effect being amplified, this as the adjusting stud presents greater exposure under the rotating rocker arm body increasing the distance from where it is affixed to the pivot point juncture for pushrod; and yes perhaps some valve motion is lost due to the lateral movement invoked here, but it is greater potential for part failures that generally trump other concerns.   

     Also, particularly in this instance, remember that proper pushrod length is established only after the rocker arm positioning in the "valvetrain geometry" equation has been concluded.   

     Scott.

[dozz302]

OK, first make sure the travel over the valve stem is centered then measure push rod length. Thank you

[1968galaxie]

Make sure the sweep across the valve tip is minimized. Many times the minimum pattern is not centered.
Brent has videos I believe of rocker arm geometry set up.
With a shaft system one raises or lowers the shaft to adjust geometry.