How to reduce valve tip sweep pattern. Help?

[vincenelson]

Randy the larger the lift is the more sweep you will have even when you have every thing correct with push rod length. I like to be in the middle of the of the valve as possible when at the higher lifts. There is a point where you will be pulling your hair out with sweep values and pushrod lengths.

[Walter R. Malik]

Randy, I have three different sets of 1.73 roller rockers. The best steel Crowers and Comp Cams made and a set of aluminum Scorpions. The geometry appears near identical between the Scorpions and the Crowers. The Comps. are way off. What would you use on the intake side compared to the exhaust?

Thanks.

Honestly ... with the Big Block Ford there is no easy way, it depends upon which head is being used and the length of the valves and valve tip location in them.
Even they are all different from one brand to another.

[wyrmrider]

Walter worte
"I have roller rocker arms here for a big block Ford from 11 different companies and they have 6 different geometries among them."
I wrote earlier
"the rocker maker understands valve train geometry
some have some very interesting theories of what works"
Abbottracingheads post- re-read it
Do you understand it and Mad Bill's fine post?
Note that several rocker vendors do the opposite and and make the tangent point low to give a "quick lift" effect at the expense of max lift.
looking forward to the video
The little plastic checker thingies (comp) are fraught with peril BVVC
Reread Walter Malik's posts
you personally have to understand the theory and tradeoffs
a wrote method can get you into trouble if you can't write the protocol yourself- takes awhile but you'll get there
" The Comps. are way off."

[Paul Kane]

I've tried many different lengths of pushrods but still can't get the sweep pattern on the valve tip below .085 on the exhaust. Intake is over .100. This is a stud setup on a BBF. I also tried three different 1.73 ratio rockers. That didn't help. The Comps made it worse and moved the pattern away from center.

Any ideas on how to narrow the pattern?

Thanks,

Frank

When one focuses only on the roller tip side of the rocker arm when setting up valve train geometry, he is dismissing the more important side of a rocker arm's activity, which is the pushrod side of the rocker arm. This is because it is the pushrod side of the rocker arm that receives the cam's information and then sends it to the roller tip side. Most of the common stud rocker arms have a pushrod cup that is too high in their body relative to the roller tip side, and so when overlooking the pushrod side and referring only to the "minimal sweep" on the roller side, you neglect evaluating any over-arcing, effected valve opening and closing velocities, resulting area under the curve, general valve timing events relative to crankshaft rotation and position, valve train loading, stability, and harmonics, pushrod flex, etc.

For this reason, the pushrod side should also be considered so that it may be optimized to send as much of the cam's information as possible over to the roller tip side. True Mid-Lift geometry looks at the entire valve train, not just where the roller tip sits. (Incidentally, where the roller tip rides atop the valve stem has nothing to do with valve train geometry and should be the last factor to consider, if at all [only if its rolling off the tip of the valve stem]).

This "minimal sweep" crap is "sweeping" the internet forums, and while it may be simple for the average joe to comprehend, the fact is the "minimal sweep" method overlooks the more critical side (the pushrod side) of the rocker arm and can thereby compromise the cam grinder's intended valve timing events for every degree of crankshaft rotation (not just peak lift). The minimal sweep method is akin to dashing out and buying a set of 18-inch tires for your car and then going home only to find out you have 16-inch rims on the car. Instead, one should start at the source (ie, the cam lobe) and then work his way toward the other end (ie, the valve) without skipping over anything along the way.

By excercising this approach with several different rocker arm brands, it will become dramatically apparent how all these different manufactures design their rocker arms so differently from one another, and also help you determine which particular rocker arm best suits a given valve train setup. As Randy has noted, you may even decide that for your 385 Series you will opt for different rocker arms for the intake than the exhaust.

One last thought based on your camshaft specs: If you are using a solid roller cam then I strongly suggest you stay away from the scoprion rocker arms, as they are the most likely to fail on your particular engine (of the three rocker arms you mentioned having).

[tsanchez]

[quoteThis "minimal sweep" crap is "sweeping" the internet forums, and while it may be simple for the average joe to comprehend, the fact is the "minimal sweep" method overlooks the more critical side (the pushrod side) of the rocker arm and can thereby compromise the cam grinder's intended valve timing events for every degree of crankshaft rotation (not just peak lift). The minimal sweep method is akin to dashing out and buying a set of 18-inch tires for your car and then going home only to find out you have 16-inch rims on the car. Instead, one should start at the source (ie, the cam lobe) and then work his way toward the other end (ie, the valve) without skipping over anything along the way.
][/quote]

I agree but if at min sweep the pushrod side is that bad you need to look for better rockers and not run it, all of it needs to be checked and evaluated and compromises made. Some rockers will be fine at .550 lift and completely horrible at .800

[wyrmrider]

some rocker designs (sic) are just plane horrible
some rocker mfg have no idea what they are doing geometry idea
and
some have funny geometry ideas
you will find out when you check both sides of the trunnion
tangent to the pushrod side should point to the lifter at half lift if you are using half lift on the valve side
and not contact the pushrod at either open or closed

[Walter R. Malik]

"mid lift", "quick lift", "max lift", "spring pressure balanced", "minimal sweep", ALL incorporate different geometries on BOTH sides of a rocker arm and trying to condense them all into one small grouping of what is correct and what is not, is just wishful thinking; especially on a big block Ford.
Being totally correct for one aspect usually makes it incorrect in another place or others. Getting to the best compromise of everything on BOTH sides of the rocker arm, (with a bit more emphasis placed upon the pushrod side), will usually present the least amount of total stress from everywhere.