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Board of Directors (Jay)
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43,454 Posts
Discussion Starter #1
This is one of the hardest measurements to determine. Because of varying valve train geometry, determining the correct length pushrod is a science unto itself.

First, let’s tackle some terminology. There’s overall length, which is the length measured from extreme end to end. This is from the very end of the ball end to the very end of the other ball end or cup end as the case may be. A couple factors affect this measurement. One being that if the pushrod being measured has oil holes in it then the measurement could be off by the amount that the machining of the oil hole subtracted from the overall length of the end. This usually doesn’t adversely affect the length depending on the diameter of the hole.

The actual measurement if there were no oil holes in the ends is called the theoretical length. Don’t let this confuse you because the difference is usually very slight. A problem of more significance is when you measure a cup and ball style pushrod. Measuring the overall length of this style can give erroneous information as the cup depth from one manufacturer to another can and does vary by as much as .060 inch. If you do know the overall length and have a caliper to measure the cup depth then this measurement will work.

The measurement from the bottom of the cup to the end of the ball is called the “effective length.” Knowing this length is more accurate as the cup depth differences won’t be factor. One way to determine effective length is by placing a steel ball (the correct diameter for the cup) into the cup and using a caliper, measure the overall length then subtract the steel ball’s diameter. This will give you the length from the bottom of the cup to the end of the ball.
 

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Stu
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21,118 Posts
Great info Jay.


Suspect the OEM 5.7 push rods to compress and shorten a little causing the "Hemi Tap". Found that the hemi tap always seems to be coming from the exhaust push rods. Replaced the exhaust push rods and the hemi tap has gone away. But, came back after just a few runs down the track. 6.1 push rods and springs have completely removed the hemi tap.

After adding Manley 6.1 push rods and springs. The tap came back. Suspect worn lifters.
The sad part is, had "like new" lifters on hand during the rebuild of the 348.
The "like new" lifter are for the 392 stroker.
 
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