Roller Rocker Install, Push Rod Lenth Check Question # 1531

FoxMustangLvr

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Oct 14, 2012
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I am installing pedestal RR's on a 306 w/ Edelbrock alum heads, 2.02 int, 1.6 ex, TFS 2 cam, edelbrock RPM intake blah blah. I'm installing Scorpion roller rockers and my push rods seem short. I wait for intake to open and then as soon as it closes I install the RR on the exhaust side. MOTOR HAS BEEN ON A STAND FOR A YEAR AT LEAST AND NOT STARTED. So it's obvious the lifters are bled down.

My question, WHAT IS THE BEST WAY TO DETERMINE PUSH ROD LENGTH when lifter are bled down. I do not want to have to pump them up.

Does this method work below?

The pushrod length on a non-adjustable rocker is for lifter preload only and you're shooting for approx. .030 to .080 preload with a standard type lifter. The best way to check with an adjustable pushrod is to make the pushrod shorter than needed. Put the lifter on the low part of the cam lobe (valve closed), put the pushrod in, install the rocker with all hardware and tighten the attaching screw. Lengthen the pushrod (lightly) until you've just taken the up and down movement out (zero lash without depressing the lifter). If the intake manifold is off you can see if you start to depress the lifter. Remove the pushrod measure it and then add the amount of desired preload to the the pushrod length and you're done.

I would suggest checking more than one cylinder as machining variances with heads, cam, block etc. may vary this. If this is not an all out, high rpm race engine you don't have to get carried away as the engine basicily will not perform any different if the preloads vary. As long as you keep it out of valve float the engine only knows it's running with no lash. No you can't use a solid lifter as the pushrod seat height may not be the same as your preloaded hydraulic lifter.

If the valves are close to stock length then you would not have to worry about the rocker to valve contact as it is fixed with the pedestal height.
 
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Dave2000GT

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Oct 3, 2005
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That seems to more or less make sense. But keep in mind the following:

- You will of course be getting a whole set of push rods the same length, so you have to base the length off of the longest possible case, then add some to that since hydraulic lifters require preload. Remember, you can shim up the rockers to effectively 'shorten' the length of the pushrods with respect to the lifter but you can't drop the rockers without modifying the pedestal which I'd highly recommend not to do for many reasons. I'm not sure of the exact amount to add after measuring, but I would measure a few of them, take the longest case, then add say 0.050 preload (so you have long enough pushrods! - see next thing below though).

- The actual preload you want to run, for performance purposes is not 0.30 to 0.080 but more like 0.010-0.020. Most experienced engine builders particularly with 5.0s will tell you this, minimizing preload is key to maximizing performance. Ford designs them with the preload at that spec because it eliminates the need to custom fit every single rocker. But you as the performance enthusiast should do just that, and custom fit each one to the smallest amount of preload, like 1/8 to 1/4 turn after zero lash will give you the 0.010 to 0.020 preload you want to run.