High Riser push rod legnth question

[dozz302]

Hello, On a High Riser engine (all factory castings with no serious milling to block or heads)) with Harland Sharp rockers & stock stands I currently only have 2 threads above the adjusting nut on top of the rocker. All of the threads are mostly below the rocker. Are my push rods too short? Thanks

[gt350hr]

 Yes! The "cup" of the pushrod ( well IMHO) should be as close to the rocker as possible BUT still have clearance. What you have now changes the angularity and is the biggest cause of failure in that area. I welcome other opinions / experience.
  Randy

[dozz302]

I already broke the end off shaft once. Motor has less that 1000 miles. Just running a 600" lift cam > nothing crazy.

[blykins]

Agree with Randy.  Choke that pushrod up tighter to the rocker arm. 

[pbf777]

     The first thing to do would be to establish that the rocker arms are positioned properly in height in relation to the valve stem tips, aka. proper rocker arm geometry as H.S. rockers are not O.E. production pieces and therefor may not present the same relationships meaning that some changes maybe necessary to correct; and this being accomplished regardless of the pushrod length.       

      After this, then as Randy said.       

      Breaking the end off the rocker shaft thru the shaft bolt hole is probably not relevant to the pushrod to rocker arm relationship.       
 
      Scott.

[gt350hr]

   Many think the "strap" or thin bottom of the rocker fails because it is simply too thin. If  you look at the change in "actual" leverage as the adjuster ball extends away from the rockerat full lift., you can see what I mean. As the rocker gets to full lift , the pushrod is putting a tremendous "rear load" on the threaded portion of the rocker and the load ( read load induced FLEX) goes to the weakest point an begins to work harden and eventually crack the "strap" of the rocker. Aluminum or ductile iron it still does it . reducing the "backwards load" by keeping the majority of the adjuster in the rocker itself reduces the load significantly. A slight inward angle on the adjuster could help "IF" it didn't cause the relief in the rocker body to be deeper. Going to a "cup adjuster" and ball ball pushrod helps with that issue as the cupped adjuster doesn't move the same as a cupped pushrod end does. This is why Jessel , T&D and POP , have gone that way. I helped FPP figure that out  about 35 years ago during their transition from the Harland Sharps to their own ( now POP).
    Randy

[Nightmist66]

From what I've seen playing with the Harland Sharps once or twice, the adjuster usually ends up with 1-2 full threads showing on the bottom. This gets the best ratio out of it, but still keeps the adjuster up in the rocker like Randy was talking about.

[dozz302]

Great info here. How do you figure out if the rocker stands are at the correct height (Factory Stands with Harland Sharp Rockers) before ordering the correct length push rods? I think this where it gets confusing. Thanks for the help guys.

[blykins]

Great info here. How do you figure out if the rocker stands are at the correct height (Factory Stands with Harland Sharp Rockers) before ordering the correct length push rods? I think this where it gets confusing. Thanks for the help guys.

The stand height affects the geometry on a shaft rocker, so you check the geometry or contact pattern.   When you get the geometry nailed, and the adjuster in the correct spot, then you can measure and order for pushrods. 

A roller rocker should put a narrow pattern on the valve tip close to or on the center of it.  If it's too far to the intake side, then the stands need to be shimmed up.  If it's too far to the exhaust side, then the stands need to be cut down.  When you get the geometry nailed, you should have a .040-.060" wide pattern. 

[gt350hr]

  +1 great advice!!!!

[pbf777]

A roller rocker should put a narrow pattern on the valve tip close to or on the center of it.  If it's too far to the intake side, then the stands need to be shimmed up.  If it's too far to the exhaust side, then the stands need to be cut down.  When you get the geometry nailed, you should have a .040-.060" wide pattern.

     Generally, agree on the "narrow pattern" and width statements (if adopting the "Mid-Lift" theory), but this may prove to be in conflict with position on the valve stem tip issue!         

     Remember, the world isn't a perfect place, and the internal combustion engine often consists of less than idea execution!           

     Scott.

[blykins]

A roller rocker should put a narrow pattern on the valve tip close to or on the center of it.  If it's too far to the intake side, then the stands need to be shimmed up.  If it's too far to the exhaust side, then the stands need to be cut down.  When you get the geometry nailed, you should have a .040-.060" wide pattern.

     Generally, agree on the "narrow pattern" and width statements (if adopting the "Mid-Lift" theory), but this may prove to be in conflict with position on the valve stem tip issue!         

     Remember, the world isn't a perfect place, and the internal combustion engine often consists of less than idea execution!           

     Scott.

I don't really subscribe to the mid-lift theory, but I also don't fret if the pattern isn't centered. 

[gt350hr]

   +1   "I" try for minimal "sweep" and keep it off the edges. I DO look carefully at the motion on the pushrod side. On many occasions I have found a bind between the rocker and pushrod because of angularity issues. The bind was minimal but over time the "self clearancing" caused abnormal wear issues between the two.