[Slewis]

Yes, I believe I have all the perpendicular bisector aspects down, but the offset throws a third angle into the mix that cannot be overcome by adjustment. It being dependent on head casting and valve placement. I suppose without the shaft rocker system or offset rocker cup it can only be slightly improved upon if at all.

[gtotomm]

I set up a pair of Dart pro 1s w/ mid lift geometry on my 502 BBC, When it was all said and done, i had to use adjustable guideplates, longer rocker studs, longer push rods, and Crane gold rockers to keep the roller tip on the valve stem. With the midlift geometry in place, the radial motion of my rockers leaves me w/a .030 contact patch on top of the stem. Neither are exactly centered, but real close, and i have the least amount of wasted motion across the top of the stem. The guide plates that came w/ the heads were not usable, so adjustable plates are the way to go.

[Slewis]

Originally Posted by gtotomm

I set up a pair of Dart pro 1s w/ mid lift geometry on my 502 BBC, When it was all said and done, i had to use adjustable guideplates, longer rocker studs, longer push rods, and Crane gold rockers to keep the roller tip on the valve stem. With the midlift geometry in place, the radial motion of my rockers leaves me w/a .030 contact patch on top of the stem. Neither are exactly centered, but real close, and i have the least amount of wasted motion across the top of the stem. The guide plates that came w/ the heads were not usable, so adjustable plates are the way to go.

Thanks abunch, thats the answer I was looking for! I have a set of 200cc E-Techs, and if the roller is set to ride equidistance on the stem horizontal, it puts the cup and pushrod trajectory nowhere near the guideplate slots that Edelbrock sells with these heads.

Also, the pushrod through holes are huge, but if set up equidistance, it appears they might rub right at the top. Might have to whittle me .050 clearnce right there after getting the adjustable plates set. Wich leads me to another question. Did your plates come with the slots cut at an angle, or did they have enough clearance that the pushrod did not bind??

[ap72]

Originally Posted by gtotomm

Slewis, Its not the guide plates you need to focus on. At mid lift, half way through the lift cycle(of your cam), your rocker trunnion center, straight line through to the roller tip center, should be at 90* to the valve and or retainer. Its really very easy to accomplish. Adjusting the rocker is as simple as adjusting the pushrod up or down. you can use a adjustable pushrod checker and checker springs on one set of valves to set this all up.

Not the cnter of the roller on the tip but where the tip and valve meet.

[gtotomm]

AP72, no, your 180* line is drawn from the folcrum center through the roller tip center, or the axle or pin that holds the roller tip on. From there you should be 90* to your valve stem at mid lift. This will give you the narrowest contact across the stem tip. look up jim millers mid lift theroy, he has the diagram that im refering to.

[beertracker]

8.900" is the push rod length I need to order. Factory length was 9.125"

bt

[gtotomm]

I have never seen mid lift corrected w/ shorter pushrod, are you sure?

[ap72]

Originally Posted by gtotomm

AP72, no, your 180* line is drawn from the folcrum center through the roller tip center, or the axle or pin that holds the roller tip on. From there you should be 90* to your valve stem at mid lift. This will give you the narrowest contact across the stem tip. look up jim millers mid lift theroy, he has the diagram that im refering to.

that's incorrect. Its as I stated. The point I referred to and the center of the smaller roller do not travel in the same arc.

[gtotomm]

of coarse not. The mid lift theroy is based on a 180* line drawn the folcrum center throught the roller tip center. Thats the way i set mine up and it works perfectly. i have the least amount of movement across the stem. my witness marks are .030 wide. Further more, at mid lift my pushrod is at 90* to the rocker as well.(are yours). Im as efficient as i can possibly be.

[41pu]

My engine chassis dynoed better with out vac advance hooked, so I decided to run with out for now. I installed the vac advance eliminator that came with the MSD dizzy. Afterward just for kicks I put the timing light on it. It use to be set 22 static with 14 mech. all in 36. Is it normal for the eliminator to change the timing cause now I have 32 static and 40 something at all in at 2500 or so. I know in order to set the elminator in you have to move the rod hooked to the reluctor to set it down in place but i didn't think about it advancing the timing. Does this sound right?

[cobalt327]

Originally Posted by 41pu

My engine chassis dynoed better with out vac advance hooked, so I decided to run with out for now. I installed the vac advance eliminator that came with the MSD dizzy. Afterward just for kicks I put the timing light on it. It use to be set 22 static with 14 mech. all in 36. Is it normal for the eliminator to change the timing cause now I have 32 static and 40 something at all in at 2500 or so. I know in order to set the elminator in you have to move the rod hooked to the reluctor to set it down in place but i didn't think about it advancing the timing. Does this sound right?

Absolutely that sounds right. Unless the vacuum advance eliminator piece were to position the advance plate/pick up coil-reluctor in exactly the same place as the vacuum can did at rest, the initial (aka static) timing has to change.

I would question why the engine ran better on the dyno w/o a vacuum advance- especially at peak, where the vac. adv. is supposed to be out of the picture.

[Slewis]

Here is what happened to me using a dissasembled/cleaned of oil/reassembled/and cup travel measured stock lifter, and the running valve springs.

With the lifter bottomed out and all clearance removed, I started with the roller tip contact patch well on the inboard side of the stem, approximate to where CompCams says to put it. Upon rotating through two complete crank cycles measured max lift was nowhere near the cams measured .328 x 1.6 , but closer to .515. Each time I extended the pushrod length and recycled the crank, the lift increased and the roller tips location moved outward. I finally arrived at .525 lift and found the 90* locations right where Miller says they should be. I am however uncomfortable with where the roller tip ended up, wich leaves the witness marks outboard at approx .060 from the stems edge, and not much stud threads for the lock nuts. Now I only have one piston/one pushrod in right now so I doubt my needle torque wrench will show small ft.lb differences, but I could definitely "feel" the crank requiring less effort to turn this method vs. old method.

Now I'm still trying to figure out the lesser of two evils, pushrod to valvestem parrallelism, or roller tip to valvestem equidistance. Feel free to laugh at my artistic skills!

[Cobra720]

I have 17* KC Brodix heads and Scorpion 1.6 rockers with a 8mm valve tip. I tried the Mid Lift method. As I increased the pushrod length toward proper Mid lift dimensions the roller tip moved further outboard on the valve tip. When I arrived at the proper dimensions my sweep decreased but I was at the outboard 1/3 of the valve. This did not look good in my opinion. when I used the middle valve tip method the pushrod was much shorter, sat better on the stud shank was dead center on the valve but I'll admit had a larger sweep.
I believe the problem is the relationship between the stud axis and the valve stem axis (or the length between the roller tip centerline and the fulcrum centerline). If I had either of these distances changed, the former increased or the latter decreased, I would be able to make Mid Lift work.
I also checked my lift at the valve, and I showed full movement.
For my application of .550 lift hydraulic flat tappet, I should be good. I'll let you know how it wears over time.

[ap72]

Originally Posted by Slewis

Here is what happened to me using a dissasembled/cleaned of oil/reassembled/and cup travel measured stock lifter, and the running valve springs.

With the lifter bottomed out and all clearance removed, I started with the roller tip contact patch well on the inboard side of the stem, approximate to where CompCams says to put it. Upon rotating through two complete crank cycles measured max lift was nowhere near the cams measured .328 x 1.6 , but closer to .515. Each time I extended the pushrod length and recycled the crank, the lift increased and the roller tips location moved outward. I finally arrived at .525 lift and found the 90* locations right where Miller says they should be. I am however uncomfortable with where the roller tip ended up, wich leaves the witness marks outboard at approx .060 from the stems edge, and not much stud threads for the lock nuts. Now I only have one piston/one pushrod in right now so I doubt my needle torque wrench will show small ft.lb differences, but I could definitely "feel" the crank requiring less effort to turn this method vs. old method.

Now I'm still trying to figure out the lesser of two evils, pushrod to valvestem parrallelism, or roller tip to valvestem equidistance. Feel free to laugh at my artistic skills!

Put a thin lash cap on your valve stem tip and set your pushrod length the proper way. Exessive scrub will kill your guides. Btw you can call it whatever method you want but you're just minimizing scrub and that's nothing new.

[Cobra720]

Quote: AP72 "Exessive scrub will kill your guides."
This is where I'm understanding it now. I am better off being off center and pushing straight on the axis of the valve stem, or close to it, then to have +.100 scrub on the center.
I'll have to order longer push rods than I expected.
Lou