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Author Topic:   simple question on push rods
hughes
Member
posted February 27, 2002 08:57 PM
I was wondering about the different lengths, such as - .100 or +.100/ +.150 and so on. Does this serve the same purpose as a 1.6 rocker arm, or a larger cam. If say I had a .500 lift cam and put a -.100 intake and +.100 on the exhaust, would this be like having split pattern cam. Basically what can I accomplish by playing with push rod lengths. How much does a +.100 add to my cam lift (if this is how it works).


chickasaw kid
Member
posted February 27, 2002 09:07 PM
i'm not an engine builder but i think different pushrod length is to correct geometry of rocker arm to valve.i dont see how that could affect lift or duration of cam



sdhnc29
Member
posted February 27, 2002 10:05 PM
The only affect that push rod length has , is strictly rocker geometry .

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


ryan
Member
posted February 28, 2002 12:11 AM
Steve are there any set rules of when to use longer push rods and when to use shorter. I am going to buy a pushrod lenghth checker but how will I know when its the right length. thanks


sdhnc29
Member
posted February 28, 2002 12:34 AM
Generally speaking , you want the tip of your rocker to set just off of center toward the intake side with the valve closed . As you open the valve , you want to see the tip of the rocker move across the valve stem toward the exhaust side , and stop just past center at full lift . If the rocker set's too far toward the intake , and only travel's to the center of the valve , then you will need a longer push rod , and vise-versa for needing a shorter push rod .

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


Chad
Member
posted February 28, 2002 12:33 PM
when the pushrod begins to push up and start to open the valve, this begins the process of rotating the rocker arm around the fulcrum; if the pushrod is pushing up on the rocker and it rotates around the fulcrum, how can the roller tip of the rocker move from the intake side (closest to rocker stud) outward across the head of the valve to the exhause side??? Wouldn't the rocker tip start on the exhaust side of the valve tip and move toward the intake side as it pivots on the fulcrum of the rockers??? Maybe I'm not thinking about this correctly, but it's a good question about how the rocker should be set. I've wondered this too.


RangeRover
Member
posted February 28, 2002 01:13 PM
RangeRover is correct .

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


hughes
Member
posted March 01, 2002 07:09 AM
Thanks guys, I was just thinking that since the cam pushes the lifter and the lifter pushes the rod in theory you could accomplish the same effect as say a 1.6 rocker arm. I appreciate the replies.


RangeRover
Member
posted March 01, 2002 02:19 PM
Hughes, that theory is incorrect. You are talking about two completely independent things in pushrod length and rocker ratio. No matter if you shorten or lengthen the pushrod, the point in which it contacts the rocker will be the same point. It is the fixed location of that contact point and the point that pushes down on the valve tip in relation to the rocker's fixed fulcrum point which give you the rocker ratio. There are roller rockers that are adjustable between 1.5 and 1.6 ratios. The change is accomplished by rotating the little socket that the pushrod seats on. The rotation positions that socket in an offset which locates it a little bit closer (going from 1.5 to 1.6) to the fulcrum and presto, new rocker ratio.


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