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Unread 11-07-2014, 05:45 PM   #1
cj7red
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Push Rods

Kind of a mechanical noob here trying to learn. Can somebody tell me why push rods spin while the engine is running? What purpose does that serve? I googled it and didn't find much.

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Unread 11-07-2014, 06:56 PM   #2
RenoF250
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To keep it concentric, if it stayed in the same place it would eventually wear oblong. Probably not critical in a pushrod but it matters for the lifters.
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Unread 11-08-2014, 09:48 AM   #3
gmakra
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If you look down the lifter gallery at the camshaft you maybe able to see that the lifters ride on about 50% of the cam lobe. The camshaft is cast iron and the lifters are hardened steel. Cast iron is pretty soft as metals go but it also has some outstanding properties for the application.

Please try to picture in your mind the lifter rides on about 50% of the camshaft, now as the camshaft rotates imagine the lifter spinning on the camshaft because the lifter is rolling on the edge of the camshaft. (almost like a ring and pinon gear)

This is done so that the lifter does not wear away (machining)the camshaft lobe.

The lifter will machine the cam lobe to the bottom profile of the lifter which has a slight rocker to it. Each lifter will wear to its corresponding lobe and when you change the location of the lifters on the camshaft or put new lifters on a old camshaft it starts the machining process again. The pushrod just happens to transfer this motion to the rocker arms.
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Unread 11-08-2014, 05:33 PM   #4
cj7red
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Quote:
Originally Posted by gmakra
If you look down the lifter gallery at the camshaft you maybe able to see that the lifters ride on about 50% of the cam lobe. The camshaft is cast iron and the lifters are hardened steel. Cast iron is pretty soft as metals go but it also has some outstanding properties for the application. Please try to picture in your mind the lifter rides on about 50% of the camshaft, now as the camshaft rotates imagine the lifter spinning on the camshaft because the lifter is rolling on the edge of the camshaft. (almost like a ring and pinon gear) This is done so that the lifter does not wear away (machining)the camshaft lobe. The lifter will machine the cam lobe to the bottom profile of the lifter which has a slight rocker to it. Each lifter will wear to its corresponding lobe and when you change the location of the lifters on the camshaft or put new lifters on a old camshaft it starts the machining process again. The pushrod just happens to transfer this motion to the rocker arms.
So if one push rod is spinning slower than the others, there's probably something wrong with the lifter or camshaft?
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Unread 11-08-2014, 08:42 PM   #5
gmakra
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No, just as long as it spins
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Unread 11-09-2014, 12:04 PM   #6
cj7red
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Quote:
Originally Posted by gmakra
No, just as long as it spins
Even if it's severely slower/barely spinning?
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Unread 11-09-2014, 01:11 PM   #7
swatson454
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Quote:
Originally Posted by cj7red View Post
Even if it's severely slower/barely spinning?
I'd be calling that lifter and lobe done. Time to plan on a cam and lifter swap, IMO.


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Unread 11-09-2014, 04:20 PM   #8
RenoF250
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Quote:
Originally Posted by cj7red View Post
Even if it's severely slower/barely spinning?
Just the pushrod or the lifter as well? I would think it would be possible for the pushrod to be slowed by the rocker and not turn as fast.
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Unread 11-09-2014, 05:20 PM   #9
cj7red
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This isn't happening with my engine (that I know of). I saw a video where a guy was trying to diagnose what was causing one of his push rods to rotate much slower than the rest, and at that point I didn't even know they were supposed to spin.

I am planning on doing a 4.0 head swap and a performance cam at some point in the future, so I'm trying to learn what I can in my free time. Thanks for the all the info.
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Unread 11-09-2014, 05:38 PM   #10
hutch1200
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Maybe the others are spinning too fast because the rocker is out of adjustment? Was it a roller rocker you saw in the vid? They are SOMETIMES, more prone to needing adjustment.
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Unread 11-09-2014, 07:14 PM   #11
cj7red
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Quote:
Originally Posted by hutch1200
Maybe the others are spinning too fast because the rocker is out of adjustment? Was it a roller rocker you saw in the vid? They are SOMETIMES, more prone to needing adjustment.
No it was a flat lifter
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