Pushrod Length & Rocker Arm GeometrySTOP! Before you order custom length pushrods for your new camshaft, please read this important information.
A large number of variables are involved in determining the correct length pushrod for your application. Pushrod length is affected by any one or all of the following:
• block deck height
• head deck height
• head stud boss height
• rocker arm brand/design
• cam base circle size
• lifter design/brand/pushrod seat height
• valve stem length
Don’t assume anything in determining the right pushrod for your new engine. A pushrod that fits one engine may not necessarily work in another. Any number of items can be different on your engine, requiring you to use a different pushrod length. Following the steps below will streamline the pushrod selection process, ensuring that you get the right parts the first time.


1. Buy a checking pushrod
Do not buy pushrods when you buy the cam, lifters, and the rest of the valve train components.

2. Determine correct valve train geometry
What is the correct length pushrod for your application? The one that produces correct valve train geometry. What is correct valve train geometry? When the rocker arm roller tip rolls from the intake side of the valve tip, across the center of the tip (at approximately mid-lift), to the exhaust side of the valve tip (at full lift) and back. See Diagram A.



3. Measure the resulting pushrod
Measuring the length of a pushrod is really rather simple, but it can be confusing at times. The most important thing to remember is that different manufacturers measure pushrods differently. So not all pushrods of a stated length will measure exactly the same. The three most common pushrod measurements are shown in Diagram B on the next page. Theoretical Length: This assumes that the pushrod has no oil hole in the end of it. Therefore, the radius at either end is complete, which lengthens the pushrod approximately .017" in the case of a 5/16" pushrod with .100" diameter oil holes, minimally chamfered. Actual Length: This is what you would measure if you had a set of calipers large enough to measure over the oil holes at each end of the pushrod. This is the measurement that most people can relate to. Unfortunately, this measurement is affected not only by the diameter of the oil holes, but also by the entrance chamfer for each oil hole. Gauge Length: Although the most difficult to measure (it requires a special length checking gauge), this measurement is the most reliable. This is because the oil holes and their chamfers are eliminated from the measurement. The only problem is that not all companies use the same gauge diameter. COMP Cams® uses a .140" gauge diameter. All of the Magnum and Hi-Tech custom length pushrods are measured using this technique. See Diagram B on the following page.


4. Simple measurement techniques
The above was not meant to confuse you needlessly. We know that most people don’t have access to the special gauge required for these measurements or even to a dial caliper large enough for most pushrods. We’ve developed three techniques to help you determine exactly how long the pushrod is that you so diligently played with until the perfect valve train geometry was achieved in your engine. [hr] Pushrod Geometry
Technique #1: This technique assumes that you have purchased one of our Hi-Tech pushrod length checkers. These are marked with a standard length stamped in them. This number represents the gauge length of the part (.140" gauge diameter) with the two halves screwed completely together. Extending the pushrod one rotation lengthens the gauge length .050". For example, a pushrod stamped 7.800 screwed apart one rotation would be 7.800" + .050" = 7.850" gauge length. Therefore you would order the part number from the catalog that matches this gauge length, since gauge length is how they are listed.



Technique #2: This technique assumes you have purchased one of our less expensive pushrod length checkers. Once fixed, you don’t need to have an expensive gauge or a pair of calipers to measure it. You just need a pushrod of a known length to compare it to (a standard). Then use a pair of common 6" calipers to measure the difference between the standard and yours. [font="arial, helvetica, sans-serif"][size="2"]


Technique #3: In addition, these can act as a standard for future pushrod measuring jobs that you may have.
A few final hints about pushrods in general. It is always a good idea to buy a few spares when purchasing a set of custom length pushrods, and stick them in yo

 

how about you site the source of your plagarism

 

didnt say it was his own, not plagarism.

 

http://www.compcams.com/information/Products/Pushrods/



http://www.mustangcentral.net/tech/geometry.html

this is the site adder used, it has better pictures


Remember that proper valvetrain setup builds horsepower!

 

If it were plagiarism then everyone on these forums would be guilty in some way or another of that[sm=chairshot.gif].......anyway good info to post ...that's what I've always done...it kinda sucks to wait the few extra days for the custom push rods to come but sure beats trashing a new motor

 

learn how to spell

Plagiarism

and no, its public information meant to be shared from the original author and intended of such. And me claiming no credit of being the Original Author, but sharing it, so when a newbie hits search, he finds
reference and infromation from a reputable public source.

ie, im only trying to help

 

6.125-7.500 stock 6.200

http://store.summitracing.com/partdetail.asp?part=TFS%2D9000&autoview=sku

$11.95

 

just found out , my rockers are not centering on the valves, in fact, they need to be of a shorter length, so Im ordering the pushrod checker soon to get it right when installing the 351w.

My heads were milled .030, and thin compression gaskets installed on the 347 for more power.

this is where im at using the 6.200 347/302 pushrods,with 1.6 roller rockers.



with my 351w, this is where I will need to be

 

this should be a sticky

 

it does not seems to me that he is taking others info and saying that he wrote it. just FYI. its a good piece of info. this is the kind of stuff everyone that does a cam or head swap otta know.

good info thanks