Pushrod Clearance RPM Heads
#3143537
05/09/23 10:27 PM
05/09/23 10:27 PM
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Joined: Mar 2008
Posts: 554 Kentucky
clovis
OP
mopar
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OP
mopar
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Kentucky
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Did a couple of measurements on my RPM heads and I got about .300 thickness between pushrod and port, does that sound about right? I am using a 3/8"-7/16" tapered pushrod and am getting just a little contact. I also measured the side to side width of the pushrod hole and got .500. Is increasing the hole .050 considered reasonable? Actually, it appears I am just making the hole round instead of oblong. How much clearance is actually necessary?
'75 Plymouth Duster Phase I 451 906/590/2-660 10.75/126 Phase II 451 Stage VI/590/1050 9.82/135 Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Pushrod Clearance RPM Heads
[Re: clovis]
#3143551
05/09/23 11:55 PM
05/09/23 11:55 PM
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Joined: May 2019
Posts: 713 Lake Villa Il
INTMD8
super stock
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super stock
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Lake Villa Il
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Do you mean .030 between pushrod and port? Can't imagine contact with .300 clearance unless your pushrods are made of rubber.
Opinions vary but for myself run clearance tight. Once I can slide a piece of paper between the pushrod and (everything) I consider it done.
69 Charger. 438ci Gen2 hemi. Flex fuel. Holley HP efi. 650rwhp @7250 510rwtq @5700
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Re: Pushrod Clearance RPM Heads
[Re: Cab_Burge]
#3143597
05/10/23 09:49 AM
05/10/23 09:49 AM
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Joined: Mar 2008
Posts: 554 Kentucky
clovis
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mopar
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OP
mopar
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Kentucky
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The .300 is the thickness of the head between the pushrod hole and the intake port, thus is the amount of meat I have to work with to cut. I wanted to open the pushrod hole up to the point where I have .020 clearance. Since the pushrods are tapered the higher they go, the bigger they are. When I was checking the scrub on the rocker arms, I noticed I got to a point in rolling the engine over by hand that it stopped. I have over .250 of piston to valve clearance, so checked the push rods and it appears I had a couple that were touching.
'75 Plymouth Duster Phase I 451 906/590/2-660 10.75/126 Phase II 451 Stage VI/590/1050 9.82/135 Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Pushrod Clearance RPM Heads
[Re: clovis]
#3143602
05/10/23 10:14 AM
05/10/23 10:14 AM
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Joined: Feb 2005
Posts: 20,195 PA.
pittsburghracer
"Little"John
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"Little"John
Joined: Feb 2005
Posts: 20,195
PA.
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Man you must be running some crazy spring pressure to need those pushrods.
1970 Duster Edelbrock headed 408 5.984@112.52 422 Indy headed small block 5.982@112.56 mph 9.42@138.27
Livin and lovin life one day at a time
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Re: Pushrod Clearance RPM Heads
[Re: pittsburghracer]
#3143658
05/10/23 01:54 PM
05/10/23 01:54 PM
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Joined: Mar 2008
Posts: 554 Kentucky
clovis
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mopar
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Kentucky
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Actually no, pretty mild Isky 8005A. After trying a couple different pushrods and comparing lift numbers, I was surprised to see the amount of deflection, so my theory is to run as big as I can, plus these large pushrods are actually super cheap as NASCAR leftovers and you can usually find them in .025 variables, so no need for custom pushrods. When you move over to ball on ball pushrods you also eliminate the "kick out" from ball adjuster and can actually run longer pushrods. Jack your shafts up along with thicker, longer ball to ball pushrods and you going to get the most out of your cam, as you have eliminated deflection, kick out and scrub loss.
'75 Plymouth Duster Phase I 451 906/590/2-660 10.75/126 Phase II 451 Stage VI/590/1050 9.82/135 Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Pushrod Clearance RPM Heads
[Re: clovis]
#3143677
05/10/23 02:38 PM
05/10/23 02:38 PM
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Joined: Jan 2003
Posts: 5,486 SoCal
Brian Hafliger
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master
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SoCal
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If your seeing deflection with a 3/8 rod, something is wrong. With those springs, you shouldn't. It's possible the larger rod is binding a bit on the head, causing the lift to be better at the valve, but it won't like it once it's running!
Brian Hafliger
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Re: Pushrod Clearance RPM Heads
[Re: Brian Hafliger]
#3143750
05/10/23 07:50 PM
05/10/23 07:50 PM
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Joined: Mar 2008
Posts: 554 Kentucky
clovis
OP
mopar
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OP
mopar
Joined: Mar 2008
Posts: 554
Kentucky
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I'm not following the binding causing a higher lift at the valve-can you explain?
The deflection was from a 5/16 pushrod.
'75 Plymouth Duster Phase I 451 906/590/2-660 10.75/126 Phase II 451 Stage VI/590/1050 9.82/135 Phase III 383 906/Victor-Pump gas 11.30/119
"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"
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Re: Pushrod Clearance RPM Heads
[Re: clovis]
#3143879
05/11/23 10:37 AM
05/11/23 10:37 AM
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Joined: May 2019
Posts: 713 Lake Villa Il
INTMD8
super stock
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super stock
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Lake Villa Il
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my theory is to run as big as I can Agree 100%
69 Charger. 438ci Gen2 hemi. Flex fuel. Holley HP efi. 650rwhp @7250 510rwtq @5700
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Re: Pushrod Clearance RPM Heads
[Re: clovis]
#3143893
05/11/23 11:59 AM
05/11/23 11:59 AM
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Joined: Aug 2003
Posts: 43,257 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,257
Bend,OR USA
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I had a set of custom made Smith Bros. 3/8 pushrods that were supposed to be .120 wall 3/8 diameter, one of them broke in my test mule motor on the local Studka engine dyno at 5200 RPM. That pushrod broke into two pieces (it had a metal flaw in it where it boke) and bent the one next to it and falling out allowing that pair of roller lifters to pop out of the lifter bores allowing the broken one to get into the bore and gauge the cam lobe When I took those two bad ones back to them they told me that those pushrods were .083 wall, not the .120 wall I had ordered and paid for They replace the two broken ones for no charge. I ordered a set of identical Manton .120 wall x 3/8 diameter and made five more pulls on the dyno with the Smith Bros. pushrods and them swap in the Manton's with no other changes and they made 8 HP more at peak RPM (6700 or maybe 6800 RPM, CRS now , they gained more power from the start to the finish of all pulls after that My last Hi Po bracket motor had Manton7/16x.145 wall pushrods on the exhaust valves and 3/8 to 7/16 single tapered pushrods on the intake valves to help add some more clearances on them to the head up high near the valve cover gasket surface
Last edited by Cab_Burge; 05/11/23 12:03 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Pushrod Clearance RPM Heads
[Re: Cab_Burge]
#3143897
05/11/23 12:08 PM
05/11/23 12:08 PM
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Joined: Apr 2006
Posts: 4,220 West Plains, MO
DrCharles
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West Plains, MO
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When I took those two bad ones back to them they told me that those pushrods were .083 wall, not the .120 wall I had ordered and paid for They replace the two broken ones for no charge. Well, that was generous of them /s They didn't replace the entire set with .120 that you paid for?? I got my last set of pushrods from Manton, guess I will continue buying them there!
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Re: Pushrod Clearance RPM Heads
[Re: DrCharles]
#3143899
05/11/23 12:15 PM
05/11/23 12:15 PM
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Joined: Aug 2003
Posts: 43,257 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,257
Bend,OR USA
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When I took those two bad ones back to them they told me that those pushrods were .083 wall, not the .120 wall I had ordered and paid for They replace the two broken ones for no charge. Well, that was generous of them /s They didn't replace the entire set with .120 that you paid for?? I got my last set of pushrods from Manton, guess I will continue buying them there! They didn't offer to replace all of them probably because they didn't have any 3/8x.120 wall stock I didn't think to ask what the price differences were between those two walls sizes That was the last pushrods I bought from them My revenge is to tell anyone who ask about Smith Bros. pushrods to tell them Mantons are a lot better at a better price I was told several years back that Manton doesn't keep any shelf stock, they custom make each set
Last edited by Cab_Burge; 05/12/23 12:59 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Pushrod Clearance RPM Heads
[Re: clovis]
#3143938
05/11/23 02:42 PM
05/11/23 02:42 PM
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Joined: Jan 2003
Posts: 5,486 SoCal
Brian Hafliger
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master
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SoCal
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As the rocker gets pushed up, if the rod binds on the head it CAN come out of the PR socket in the rocker arm and actually push the rocker further open than normal because it's sliding out of the socket and therefore gaining lift as it does so. Not saying that it is doing that, but it's worth a look.
Brian Hafliger
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