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Discussion Starter · #1 ·
I am getting close to finishing the engine for my '75 F150, but I have some questions regarding pushrod length.
I spent hours last night reading about pushrod length and valvetrain geometry but I'm still a bit confused.

This 460 has iron heads with the oem non-adjustable rockers, oem pushrods, aftermarket hydraulic lifters, and a Melling MTF-3 cam. This cam has lift of .485/.511 with the factory rocker arms. I also put in the springs that Melling spec'd for this cam.

I did the test where permanent marker is applied to the tip of the valve stem, rocker arm assembled, and the engine turned over 2 or 3 times to see the wear pattern. On the 4 or 5 that I tested the pattern was in the center-ish of the valve tip.

What else can I do to assure the stock length pushrods will work alright with my set up? Help is greatly appreciated!
 

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You are going to have to assemble engine and check to see what length push rod is needed.

The bolt down rockers on your D3 heads have a radiused contact tip. The pattern starts on the center inboard of the valve stem tip, moves toward center as motion progresses and then back toward center inboard.

Bolt down rocker geometry is set and only adjustable with shims under the bolt down fulcrums.

Cam base circle
Deck height
Cylinder head deck cut
Valve stem tip height

All of the above are variables which effect needed PR length.

Start with your OEM push rod which should be about 8.620 long.
Snug the rocker until play is taken out from between rocker and lifter cup.
3/8 to 3/4 turn to seat rocker in slotted pedestal is ok. Best at 1/2 turn BEFORE torque is set.

Less than 1/4 and the push rod is too short
More than 3/4 and it is too long.

Buy better push rods with a .080" wall.








Scotty J. "AKA" The "Mad Porter"
"EMC 2006" 3rd place finisher
Ported BBF iron head specialist & Aluminum heads from all sources.
Custom ground cams
See our products in the Vendor for sale section
Customized crate engines
ParklandAutoMachine.com
R-H-P.biz
"Parkland Performance Auto Machine" Formerly RHP
(253)-988-6648
Parkland Auto Machine
 

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Discussion Starter · #3 ·
You are going to have to assemble engine and check to see what length push rod is needed.

The bolt down rockers on your D3 heads have a radiused contact tip. The pattern starts on the center inboard of the valve stem tip, moves toward center as motion progresses and then back toward center inboard.

Bolt down rocker geometry is set and only adjustable with shims under the bolt down fulcrums.

Cam base circle
Deck height
Cylinder head deck cut
Valve stem tip height

All of the above are variables which effect needed PR length.

Start with your OEM push rod which should be about 8.620 long.
Snug the rocker until play is taken out from between rocker and lifter cup.
3/8 to 3/4 turn to seat rocker in slotted pedestal is ok. Best at 1/2 turn BEFORE torque is set.

Less than 1/4 and the push rod is too short
More than 3/4 and it is too long.

Buy better push rods with a .080" wall.








Scotty J. "AKA" The "Mad Porter"
"EMC 2006" 3rd place finisher
Ported BBF iron head specialist & Aluminum heads from all sources.
Custom ground cams
See our products in the Vendor for sale section
Customized crate engines
ParklandAutoMachine.com
R-H-P.biz
"Parkland Performance Auto Machine" Formerly RHP
(253)-988-6648
Parkland Auto Machine
In the part I bolded, do you mean vertical play of the pushrod?

Also, does play count as the movement of the lifter plunger? As in tighten down until I can no longer depress the plunger at all? (By pushing down on the rocker arm right above where the pushrod sits)
 

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In the part I bolded, do you mean vertical play of the pushrod?

Also, does play count as the movement of the lifter plunger? As in tighten down until I can no longer depress the plunger at all? (By pushing down on the rocker arm right above where the pushrod sits)
Yes.
Plunger need only be preloaded .050" as you seat the rocker in the pedestal.





Scotty J. "AKA" The "Mad Porter"
"EMC 2006" 3rd place finisher
Ported BBF iron head specialist & Aluminum heads from all sources.
Custom ground cams
See our products in the Vendor for sale section
Customized crate engines
ParklandAutoMachine.com
R-H-P.biz
"Parkland Performance Auto Machine" Formerly RHP
(253)-988-6648
Parkland Auto Machine
 

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Discussion Starter · #5 · (Edited)
Alright well further tinkering has revealed that on any valve that is closed, if I push on the end of the rocker arm that holds the pushrod tip, the lifter plunger will move further down. Not a whole lot of pressure is required to get the plunger to move.

This is with all rocker arms fully torqued down to their pedestals. Is this normal?
 

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Alright well further tinkering has revealed that on any valve that is closed, if I push on the end of the rocker arm that holds the pushrod tip, the lifter plunger will move further down. Not a whole lot of pressure is required to get the plunger to move.

This is with all rocker arms fully torqued down to their pedestals. Is this normal?
The lifter plunger has about .100:+ of travel available.
When there is no oil in the galleys and the engine hasn't been pre-lubed being able to compress the lifter plunger is normal.

With oil pressure the plungers will pump up.







Scotty J. "AKA" The "Mad Porter"
"EMC 2006" 3rd place finisher
Ported BBF iron head specialist & Aluminum heads from all sources.
Custom ground cams
See our products in the Vendor for sale section
Customized crate engines
ParklandAutoMachine.com
R-H-P.biz
"Parkland Performance Auto Machine" Formerly RHP
(253)-988-6648
Parkland Auto Machine
 

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Discussion Starter · #7 · (Edited)
Now I am even more confused lol!

I have been attempting to measure the preload on some of the lifter plungers by loosening the rocker bolts until I can spin the pushrod with my thumb and middle finger. Then I scribe a line on the pushrod with a straight edge resting on the valve cover gasket surface. Then I tighten down the rocker bolts and scribe again.

However on a number of them I can still spin the pushrod with my thumb/finger even after tightening/torquing down. I don't know if this is normal or what. On one exhaust valve I was able to measure preload at between .035 and .040. On that accompanying intake valve I couldn't get much of if any preload. My technique may be off though.

This is a dual pattern cam. Would that automatically make the int/exh pushrod lengths different?

In addition, all of the exhaust valve seats were recut, but none of the intake seats.
 

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With new lifters you can in many cases still spin the push rod with the empty lifter and plunger properly preloaded.
Detecting the difference between spinning with preload and before slack is taken up is a pain in the ***.

Dual pattern cams do not AUTOMATICALLY require a longer exhaust push rod but the BBF sometimes needs a longer exhaust side push rod.

It appears you've installed new springs and now the OEM retainers are ill fitting. Revisit that choice.
OEM push rods with heavier spring pressures invite bent push rods.

The method you show is close enough provided that the dial indicator probe is perpendicular to the tab as it is depressed.

In your case buy longer push rods to accommodate the intake side and then utilize rocker shims to fine tune the exhaust side preload.





Scotty J. "AKA" The "Mad Porter"
"EMC 2006" 3rd place finisher
Ported BBF iron head specialist & Aluminum heads from all sources.
Custom ground cams
See our products in the Vendor for sale section
Customized crate engines
ParklandAutoMachine.com
R-H-P.biz
"Parkland Performance Auto Machine" Formerly RHP
(253)-988-6648
Parkland Auto Machine
 

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Discussion Starter · #10 ·
With new lifters you can in many cases still spin the push rod with the empty lifter and plunger properly preloaded.
Detecting the difference between spinning with preload and before slack is taken up is a pain in the ***.

Dual pattern cams do not AUTOMATICALLY require a longer exhaust push rod but the BBF sometimes needs a longer exhaust side push rod.

It appears you've installed new springs and now the OEM retainers are ill fitting. Revisit that choice.
OEM push rods with heavier spring pressures invite bent push rods.

The method you show is close enough provided that the dial indicator probe is perpendicular to the tab as it is depressed.

In your case buy longer push rods to accommodate the intake side and then utilize rocker shims to fine tune the exhaust side preload.





Scotty J. "AKA" The "Mad Porter"
"EMC 2006" 3rd place finisher
Ported BBF iron head specialist & Aluminum heads from all sources.
Custom ground cams
See our products in the Vendor for sale section
Customized crate engines
ParklandAutoMachine.com
R-H-P.biz
"Parkland Performance Auto Machine" Formerly RHP
(253)-988-6648
Parkland Auto Machine

Thanks for your help, I appreciate it.

I'm understanding this whole deal better now, I was overthinking it, as usual lol.

Using the dial indicator method on 2 cylinders,with the valves closed, the preload on both the intake/exhaust lifters are at .100-.105 intake and .090-.095 exhaust.
I am going to check more of them to make sure this measurement is consistent.

This would require shorter pushrods to get to the .020-.060 preload spec, yes?

Stronger pushrods are on the list for sure.

As for the retainers, do you think the diameter is too small? They assembled with the springs and keepers with no problems.

Thank you again!
 
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