pushrod length help

[smokie]

i'm building a 383 sbc with a comp cams retro fit hydraulic roller cam & lifters. i checked my geometry & i get that i need a 7.650" pushrod, but is the sweep to close to the edge of the valve stem? the pattern is about .035"-.040" wide. should i be checking with a solid roller lifter?

[BOOT]

I prefer it narrow as I can get it and somewhat in the middle 1/3. Use weak test springs, you can get some at the hardware store that may fit over your valve seals, the comps ones I tried long ago didn't.

edit: Noticed your guideplates are twisted out of the way. If the knurl is catching I just carefully grind/sand it down till the tool slides in. I prefer to put the adjusted side down into the lifter still so it won't catch any on the guideplate.

[mdla]

I ran across this video the other day from Straub Technologies. It does a good job of explaining how to correct your problem, I think. I hope it helps!


https://www.youtube.com/watch?v=o5is9BsH5OU

[smokie]

actually, that video is where i learned to figure out pushrod geometry. i'm just not crazy about where the sweep is on the valve tip.

[77cruiser]

What kind of rockers?

[groberts101]

i'm building a 383 sbc with a comp cams retro fit hydraulic roller cam & lifters. i checked my geometry & i get that i need a 7.650" pushrod, but is the sweep to close to the edge of the valve stem? the pattern is about .035"-.040" wide. should i be checking with a solid roller lifter?

Looks like too long a pushrod to me. Using a solid lifter will only make matters worse.. IF.. the current hydro lifter is already collapsed when producing that pattern location.

What heads and rockers are being used?

EDIT: oops, just noticed Jim beat me to that what rocker question.

[MadBill]

Since the pattern seems about as narrow as the trigonometry of rocker arm length and valve lift would permit, the pushrod length must be close (for mid-lift geometry), so only a shorter arm or an offset trunnion will move the outer edge of the contact patch closer to the valve centerline.

[groberts101]

Since the pattern seems about as narrow as the trigonometry of rocker arm length and valve lift would permit, the pushrod length must be close (for mid-lift geometry), so only a shorter arm or an offset trunnion will move the outer edge of the contact patch closer to the valve centerline.

Granted that sweep pattern is pretty narrow.. but how did you interpret that it's been set for optimum mid-lift geometry without the posted ratio and lobe lift spec's, Bill?

Not trying to discredit your observation.. hoping to learn how you came about making it, is all.

[MadBill]

Since the pattern seems about as narrow as the trigonometry of rocker arm length and valve lift would permit, the pushrod length must be close (for mid-lift geometry), so only a shorter arm or an offset trunnion will move the outer edge of the contact patch closer to the valve centerline.

Granted that sweep pattern is pretty narrow.. but how did you interpret that it's been set for optimum mid-lift geometry without the posted ratio and lobe lift spec's, Bill?

Not trying to discredit your observation.. hoping to learn how you came about making it, is all.

Because the only way to get a pattern that narrow is to have a near-perfect (for mid lift) pushrod length. If you visualize the rocker to valve contact, per the Straub video a few post back, the furthest out across the stem that the roller can reach is when the arm centerline is at 90°to the stem.

Relative to how much the valve lifts, the arm swings up or down and either way the roller contact moves back towards the trunnion side. The least travel will occur with the least arm angle change, which happens when the starting point is 90°. For example, if the PR was chosen to give 90° at full lift, the roller would be moving away from its furthest out contact point for the entire valve closing cycle, instead of just half, making for a much wider pattern.

[smokie]

the heads are assualt/proheader,nkb200 dart copies. the rockers are scorpion 1.5 roller rockers. the block has been decked to 9.005". the cam is XR294HR-10. Duration @ 0.006": 294° / 300°, Duration @ 0.050": 242° / 248°. Max Lift w/ 1.5RR: .540" / .562".

using the mid lift method, it calls for a 7.65"pushrod. a 7.200" (factory vortec) centered the sweep, but it was about an 1/8th inch wide.

how can i make sure the lifters are pumped up? i guess i need to use checker springs as well.

thanks everyone

[cjperformance]

Since the pattern seems about as narrow as the trigonometry of rocker arm length and valve lift would permit, the pushrod length must be close (for mid-lift geometry), so only a shorter arm or an offset trunnion will move the outer edge of the contact patch closer to the valve centerline.

Granted that sweep pattern is pretty narrow.. but how did you interpret that it's been set for optimum mid-lift geometry without the posted ratio and lobe lift spec's, Bill?

Not trying to discredit your observation.. hoping to learn how you came about making it, is all.

Because the only way to get a pattern that narrow is to have a near-perfect (for mid lift) pushrod length. If you visualize the rocker to valve contact, per the Straub video a few post back, the furthest out across the stem that the roller can reach is when the arm centerline is at 90°to the stem.

Relative to how much the valve lifts, the arm swings up or down and either way the roller contact moves back towards the trunnion side. The least travel will occur with the least arm angle change, which happens when the starting point is 90°. For example, if the PR was chosen to give 90° at full lift, the roller would be moving away from its furthest out contact point for the entire valve closing cycle, instead of just half, making for a much wider pattern.

X2 Bill
Obviously pushrod length is pretty daen close for the lift he is seeing,,
Also note that if using a hydro lifter that is not allowing us to see full valve lift then that pattern would not be telling us the full story.

[groberts101]

Since the pattern seems about as narrow as the trigonometry of rocker arm length and valve lift would permit, the pushrod length must be close (for mid-lift geometry), so only a shorter arm or an offset trunnion will move the outer edge of the contact patch closer to the valve centerline.

Granted that sweep pattern is pretty narrow.. but how did you interpret that it's been set for optimum mid-lift geometry without the posted ratio and lobe lift spec's, Bill?

Not trying to discredit your observation.. hoping to learn how you came about making it, is all.

Because the only way to get a pattern that narrow is to have a near-perfect (for mid lift) pushrod length. If you visualize the rocker to valve contact, per the Straub video a few post back, the furthest out across the stem that the roller can reach is when the arm centerline is at 90°to the stem.

Relative to how much the valve lifts, the arm swings up or down and either way the roller contact moves back towards the trunnion side. The least travel will occur with the least arm angle change, which happens when the starting point is 90°. For example, if the PR was chosen to give 90° at full lift, the roller would be moving away from its furthest out contact point for the entire valve closing cycle, instead of just half, making for a much wider pattern.

Right.. I get that but unless the op wants to hunt for an idealized pivot length(and there are many available) to centralize the sweep pattern it may be best to just shorten up the pushrod for an improvement over what he currently has. So if 7.65" is ideal for midlift and 7.2" is ideal for a centralized pattern then maybe call a 7.4x length pushrod a middle of the road compromise?

Otherwise just move towards a shaft setup which often offsets the fulcrum location beyond what a stud mount allows and adjusts pivot length to a more advantageous location to reduce and better centralize the sweep pattern.

[cjperformance]

the heads are assualt/proheader,nkb200 dart copies. the rockers are scorpion 1.5 roller rockers. the block has been decked to 9.005". the cam is XR294HR-10. Duration @ 0.006": 294° / 300°, Duration @ 0.050": 242° / 248°. Max Lift w/ 1.5RR: .540" / .562".

using the mid lift method, it calls for a 7.65"pushrod. a 7.200" (factory vortec) centered the sweep, but it was about an 1/8th inch wide.

how can i make sure the lifters are pumped up? i guess i need to use checker springs as well.

thanks everyone

IF you know the rocker is set at correct height for mid lift AND the hydro lifter gives that sweep pattern as it collapses you are missing some of the LAST section of the sweep pattern which will be coming in toward the intake and in reality making the sweep a little wider and make the pattern look on average closer to the center of the tip. It would take a much shorter pushrod to bring the whole pattern in board which would mess rocker geometry badly. I would take a good midlift setting over sweep placement so long as the tip in not going over the edge of the valve!! Can you borrow a different brand rocker to test? That said, I have run the sweep pretty close to the edge on flat tappet and hydro roller stuff when options for change were not available and have not had any problems doing so. Good geometry rules over sweep placement any day.

[Geoff2]

Are you using longer valves? Longer valves can produce the sweep pattern you are getting.

[smokie]

Are you using longer valves? Longer valves can produce the sweep pattern you are getting.

+.100 longer than stock valves. i'll see if i can borrow another roller rocker from someone & try that as well.