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Measuring Push Rod Length

cngordon

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My PRW rocker rollers included a measuring rod. After installing the hydraulic lifter, and the measuring push rod, and tightening down the rocker shaft, I adjusted the rod until the rocker quit having any movement, but did not preload the lifter. My rocker adjusting screws are showing 1/2 to 1 thread.

The rod measures 8.9 inches. Comp Cams sells rods at 9+ inches. 440 Source sells them at 8.9 and 9+ inches.

I am not sure if I should have adjusted the measuring rod to include any preload. I believe the tech guy at PRW was telling me the answer is no, that the preload is obtained by using the adjusting screw after, and that 8.9 would be the correct length.

My speed shop is telling me that they think the 9+ inch ones from comp cams are the correct ones.

Anyone with experience in measuring and ordering these push rods ?
 
Yes stop wasting your breath with PRW and call Smith Brothers push rods they will make them in one day for you and advise you how to properly measure them....
 
You need to actually check this, and it seems you do not know how to..

You need to set a length with room for adjustment, and then actually adjust the valve correctly and then make a full revolution of the valve and then see if you need to move the length one way or the other to have the right pattern at the valve...

You also need checking springs on those valves or you may bend the pr check tool depending the spring psi
 
new to this so please be patient with my ignorance.

Looking at the geometry of a shaft mounted rocker I can't see how adjusting the push rod will affect the wear pattern of the roller on the valve. It seems to me you would have to shim under the shaft to raise the entire shaft to affect the geometry/wear pattern

but on a rocker that was not shaft mounted you could adjust the rocker up and down to affect the geometry.

Does this sound correct ?

Thanks for the advice.
 
new to this so please be patient with my ignorance.

Looking at the geometry of a shaft mounted rocker I can't see how adjusting the push rod will affect the wear pattern of the roller on the valve. It seems to me you would have to shim under the shaft to raise the entire shaft to affect the geometry/wear pattern

but on a rocker that was not shaft mounted you could adjust the rocker up and down to affect the geometry.

Does this sound correct ?

Thanks for the advice.
You are correct. On a shaft system with non-adjustable rockers, you cannot change the pattern without changing the pivot location of the rocker. On a shaft system with adjustable rockers, the position of the adjuster WILL affect lift and pattern of the rocker. On a hydraulic lifter setup, you will need a solid lifter with the same cup height as the preloaded hydraulic lifter to actually check/measure any of this.
 
And you want the rocker end of the push rod to be close to the shaft center line, and that is usually a couple of threads max. Too much adjuster sticking out is trouble. Sounds like you have all the basics covered.
 
Food for thought

I drew this up quickly, so please excuse the scale....
I dont believe pushrod length will change the geometry, specificaly the point in which the rocker tip contacts the valve stem from max lift to 0 lift. It will only allow you to make correct adj to the valve lash (escpecialy solid camshaft / lifter types). This is with a fixed shaft mounted rocker configuration.....
Review the drawing and you should see why...
 

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67B-Body; Thanks for the great description and I agree. But of course, the reason we check for pattern on the valve stem is because sometimes the valve is sunken in the seat (changing the stem height) or the valve stem end is 'faced' to square it to the shaft (also changing the stem height). You pointed this out in your drawing which should make it much easier for all to understand. Good job....
 
67B-Body; Thanks for the great description and I agree. But of course, the reason we check for pattern on the valve stem is because sometimes the valve is sunken in the seat (changing the stem height) or the valve stem end is 'faced' to square it to the shaft (also changing the stem height). You pointed this out in your drawing which should make it much easier for all to understand. Good job....

Yaah,,, you can buy lash caps too.....but I'm not a fan of those however...
BTW, Welcome.. :)
I had just a little bit of time to quickly throw it together in AutoCad today at the job site, then print it out to a PDF file for posting. So that's why it's not too fancy... LOL!
:happy7:
 
new to this so please be patient with my ignorance.

Looking at the geometry of a shaft mounted rocker I can't see how adjusting the push rod will affect the wear pattern of the roller on the valve. It seems to me you would have to shim under the shaft to raise the entire shaft to affect the geometry/wear pattern

but on a rocker that was not shaft mounted you could adjust the rocker up and down to affect the geometry.

Does this sound correct ?

Thanks for the advice.

If everything is perfect, i haven't seen perfect machining on many a mopar... haven't had a block yet that hasn't needed the lifter bores fixed, amongst other issues and heads with different heights..

Check them all
 
I took SnakeOil's advice and started dealing with Smith Brothers. They were indeed super. Answered emails right away, asked good questions, gave good advice, and were helpful. I would have happily concluded by ordering through them.

I ended up dealing with my local speed shop. The owner of the shop showed up at my house, helped me verify my measurements were correct, and supplied me with a 3/8" rod to make sure there would be no clearance issues using a larger diameter rod. For a novice like myself, it was nice to have the hands on advice from an experienced engine guy.
 
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