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Would pushrod length make this much difference? #2448178
02/07/18 08:28 PM
02/07/18 08:28 PM
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BradH Offline OP
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A couple of diagrams I did trying to get a sense for how much difference might result from running the shortest possible pushrod vs. one at the max exposed adjuster length.

Seems like -- on paper, at least -- there's a significant ratio difference... and not something I'd given much thought to before.

Oh, the reason why the tip of the adjuster ball in the first picture isn't the actual point of measurement is that I was trying to account for my using that same style of rocker with a brand of adjuster screw that's noticeably shorter than what's pictured.

Rocker geo 1.jpgRocker geo 2.jpg
Re: Would pushrod length make this much difference? [Re: BradH] #2448191
02/07/18 09:01 PM
02/07/18 09:01 PM
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Yep, using a pushrod that is as long as possible will give you more valve lift. But you have to watch out for the gotchas. For example, with Harland rocker arms on my 470 I toasted the pushrod ends since the long pushrod puts the cup out of reach of the oil squirt. Pushrod oiling solved that problem. With T&D rocker arms you have to have the adjuster in the correct location or else they won't oil. So you can't screw the adjuster all the way in or all the way out, it has to be in the middle of the range or else you'll kill the rocker arms.

This trick is also dependent on the design of the rocker arm. If you get a bunch of different Mopar rocker arms and put them on the same shaft you'll see that everyone designs their rocker arm differently. So the angle of the backside of the rocker arm is different. The pushrod to rocker arm angle can vary a lot between different rocker arms so the long pushrod trick may or may not work.

Re: Would pushrod length make this much difference? [Re: BradH] #2448199
02/07/18 09:13 PM
02/07/18 09:13 PM
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Great Neck,LI,new york
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Pushrod oiling is the answer to anything that has an issue with burnt cups.


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My condition is fully BLOWN!!
Re: Would pushrod length make this much difference? [Re: AndyF] #2448274
02/07/18 11:55 PM
02/07/18 11:55 PM
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Mt Morris Michigan
mopar dave Offline
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Yep, turn your adjuster all the way up, then 1 turn down. From there you only have 1 turn either way. The closer you get to 1 full turn either way the less oil you get.

Re: Would pushrod length make this much difference? [Re: BradH] #2448280
02/08/18 12:35 AM
02/08/18 12:35 AM
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Sport440 Offline
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Your pics don't give the minute differences justice.

Longer pushrod equals more max lift while a shorter pushrod gives quicker more mid lift but with less max lift.


Significant difference??, in the scheme of the whole overall lift event, either way, long/short pushrod, doesn't make any significant difference in performance on the engine involved. The valve train, does like the longer pushrod though, less stress on the rocker arm because of the lesser angles involved. IMO

Re: Would pushrod length make this much difference? [Re: BradH] #2448310
02/08/18 01:47 AM
02/08/18 01:47 AM
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The minimum adjuster length isn't a specific number of turns. What matters:
1. no contact throughout the range of travel
2. enough adjustment to get lash


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Re: Would pushrod length make this much difference? [Re: BradH] #2448348
02/08/18 04:37 AM
02/08/18 04:37 AM
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I've seen adjusters and pushrod cups broken off due to using to short of pushrods, way to short work
To long can and may beat up the bottom of the rockers also so my choice is to see between 1/8 of a thread to three complete threads max exposed under the rocker arms up
As already mention on the single shaft T&D system they like 1 1/2 turns out to three turns out max on their adjusters for oiling the push rods properly shruggy
I think I have 1 1/2 threads exposed on my 440-1 with the Jesel pair shaft system with pushrod and spray bar oiling up


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Would pushrod length make this much difference? [Re: Cab_Burge] #2448496
02/08/18 01:50 PM
02/08/18 01:50 PM
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BradH Offline OP
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I've read where both Jesel and T&D say to set their cup adjusters to one turn out from seated in order to limit the exposed (unsupported) amount of the adjuster, and to keep the oiling passages aligned.

Seems like part of the cup-style pushrod-to-rocker clearance concerns could be addressed by converting to cup-style adjusters. Is going from ball-type to cup-type adjusters as simple as changing to hollow pushrods, as long as the lifters support pushrod oiling?

Re: Would pushrod length make this much difference? [Re: polyspheric] #2448499
02/08/18 01:56 PM
02/08/18 01:56 PM
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Mt Morris Michigan
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My point on the on the 1 turn from seated up was to get enough oil to the pr tip. With TD rockers i always seat lash from that 1 turn down from seated position. I latter added spray bars and it didnt matter.

Re: Would pushrod length make this much difference? [Re: BradH] #2448543
02/08/18 03:27 PM
02/08/18 03:27 PM
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Brad, the Jesel adjusters are hollow and don't have any provisions for oiling the axles or valve tips shock shruggy
I called them about this and they said that splash oiling was good enough confused
So I added the spray bar valve covers luck


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Would pushrod length make this much difference? [Re: BradH] #2448623
02/08/18 06:03 PM
02/08/18 06:03 PM
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I'm curious as to why pushrod length affected the lobe lift.

Re: Would pushrod length make this much difference? [Re: Stanton] #2448629
02/08/18 06:13 PM
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BradH Offline OP
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The lobe lift only changed because I reversed-engineered the lobe lift for the same valve lift to account for the ratio change. If I'd left the lobe lift the same, then I'd have had to increase the lift curve on the valve side. It was simpler to leave the rest of the rocker diagram the same and only tweak the pushrod adjuster arc to match the ratio difference.

Last edited by BradH; 02/08/18 06:16 PM.
Re: Would pushrod length make this much difference? [Re: Stanton] #2448661
02/08/18 07:42 PM
02/08/18 07:42 PM
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Be a good excercise with the rocker on the head, an adjustable pushrod, a checking spring, and a dial indicator.


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Re: Would pushrod length make this much difference? [Re: fast68plymouth] #2448664
02/08/18 07:53 PM
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BradH Offline OP
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Originally Posted By fast68plymouth
Be a good excercise with the rocker on the head, an adjustable pushrod, a checking spring, and a dial indicator.

Yep. scope

Re: Would pushrod length make this much difference? [Re: BradH] #2448675
02/08/18 08:21 PM
02/08/18 08:21 PM
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Sport440 Offline
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Originally Posted By BradH
Originally Posted By fast68plymouth
Be a good excercise with the rocker on the head, an adjustable pushrod, a checking spring, and a dial indicator.

Yep. scope



Yep, and Your just the right kind of guy to do it. Put the car on hold for just a little bit longer. laugh2 up

Re: Would pushrod length make this much difference? [Re: BradH] #2449055
02/09/18 12:51 PM
02/09/18 12:51 PM
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BradH Offline OP
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More "stuff" to think about... the location of the pushrod contact point w/ respect to the rocker arm fulcrum also affects whether the lift curve translated by the rocker arm from the cam lobe is linear or regressive. The diagram below came from an old Crane Cams presentation that shows an example of how the leverage ratio actually decreases across the lift curve as the valve is opened.


Regressive ratio diagram.jpg
Re: Would pushrod length make this much difference? [Re: BradH] #2449070
02/09/18 01:08 PM
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Re: Would pushrod length make this much difference? [Re: BradH] #2449119
02/09/18 03:29 PM
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I wonder if these instructions apply to stud mounted rockers only? shruggy


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Would pushrod length make this much difference? [Re: Cab_Burge] #2449182
02/09/18 06:41 PM
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Originally Posted By Cab_Burge
I wonder if these instructions apply to stud mounted rockers only? shruggy


Nope. Adjuster position affects geometry on stud and shaft rockers.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Would pushrod length make this much difference? [Re: BradH] #2449197
02/09/18 07:28 PM
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Interesting info posted.

Folks mention the cup oiling window of setting, so when also taking into account possible rubbing issues, scrub pattern at the end of the day what, say does .050 off give or take just for an example in terms of usable power/rpm amount to?

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