pushrod length help
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pushrod length help
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?
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Re: pushrod length help
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.
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.
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Re: pushrod length help
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
https://www.youtube.com/watch?v=o5is9BsH5OU
Re: pushrod length help
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.
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Re: pushrod length help
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.smokie wrote: ↑Fri May 11, 2018 3:20 pm 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?
What heads and rockers are being used?
EDIT: oops, just noticed Jim beat me to that what rocker question.
Re: pushrod length help
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.
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
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Re: pushrod length help
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?MadBill wrote: ↑Fri May 11, 2018 8:06 pm 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.
Not trying to discredit your observation.. hoping to learn how you came about making it, is all.
Re: pushrod length help
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.groberts101 wrote: ↑Fri May 11, 2018 8:31 pmGranted 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?MadBill wrote: ↑Fri May 11, 2018 8:06 pm 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.
Not trying to discredit your observation.. hoping to learn how you came about making it, is all.
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.
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
Re: pushrod length help
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
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
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Re: pushrod length help
X2 BillMadBill wrote: ↑Fri May 11, 2018 9:03 pmBecause 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.groberts101 wrote: ↑Fri May 11, 2018 8:31 pmGranted 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?MadBill wrote: ↑Fri May 11, 2018 8:06 pm 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.
Not trying to discredit your observation.. hoping to learn how you came about making it, is all.
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.
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.
Craig.
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Re: pushrod length help
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?MadBill wrote: ↑Fri May 11, 2018 9:03 pmBecause 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.groberts101 wrote: ↑Fri May 11, 2018 8:31 pmGranted 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?MadBill wrote: ↑Fri May 11, 2018 8:06 pm 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.
Not trying to discredit your observation.. hoping to learn how you came about making it, is all.
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.
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.
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Re: pushrod length help
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.smokie wrote: ↑Fri May 11, 2018 9:16 pm 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
Craig.
Re: pushrod length help
Are you using longer valves? Longer valves can produce the sweep pattern you are getting.
Re: pushrod length help
+.100 longer than stock valves. i'll see if i can borrow another roller rocker from someone & try that as well.