Pushrod Length

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Thomas792
Posts: 54
Joined: Fri Oct 05, 2012 6:02 am

Pushrod Length

Post by Thomas792 »

So 25 years ago I had a 401 rebuilt and then got deployed overseas for 9 years (Hawaii, Korea, Okinawa). Got married and my J10 sat at my parent's barn with a nearly complete engine since then. I was convinced that I needed roller rocker arms so I had the heads worked during the rebuild for Crane gold roller rocker arms - screw in 3/8 studs and two piece guide plates (that's all I remember). In the age before the widespread use of the internet I didn't know that this valvetrain setup required different length pushrods so I was stumped why it would not push the valves down when I turned the engine over by hand.

On previous trips to see my parents I didn't have time to spend on the Jeep seeing how the wife and kids wanted to do things other than get greasy.

I might be going to see my mom soon and I'd like to get one step closer to finishing the engine. I've watched some videos on measuring the correct length of pushrod but I have some questions.

1. What length adjustable pushrod gauge should I get? I've seen 6.88 to 7.88 and 7.88 to 8.88 on a powerpoint presentation someone did a while back. I'm sure even if I bought both neither would be the correct length for my setup with non-stock parts so any suggestion to gauge would be great.

2. When I check the length I want the lifter to be full of oil? If not, how does the lifter top not compress into the lifter when the valve spring pressure is stronger than the lifter spring?

3. Can this all be done with the intake installed?

Beyond that it all seems fairly simple having looked at the presentation and watched youtube videos. Any reason that procedures on a Chevy from the videos would be different from an AMC?
1974 J10 - 401, TH400, QT, D44, 28" tires - Sold under duress
1988 GW - "Mrs Tickety" - 360, 727, NP228, D44, 32" tires
Retired Marine

chevelleguy
Posts: 379
Joined: Mon Oct 08, 2012 10:11 am
Location: Hughes Springs, TX

Re: Pushrod Length

Post by chevelleguy »

When measuring for custom pushrods, you are supposed to use light weight valve springs so that they don’t compress the lifter. If you aren’t getting any movement with the stock pushrod, you’re going to need something longer than 8”, so get the longer adjustable push rods.


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Topic author
Thomas792
Posts: 54
Joined: Fri Oct 05, 2012 6:02 am

Re: Pushrod Length

Post by Thomas792 »

Thanks. I was searching extensively the pas few days and found this as a near complete answer
https://theamcforum.com/forum/401-push- ... 61111.html

I have watched the video referenced several times and it looks like the light weight springs are only needed for checking pushrod length once the custom ones arrive.

It looks like the 7.88 to 8.88 are the ones I need as they say something similar to my setup will need 8.14 to 8.16 pushrods. Chevelleguy confirmed this and that I need the longer checker tool.

Last thing remaining is whether or not the intake needs to come off? I put it on to seal up the engine for what I thought was temporary storage.
1974 J10 - 401, TH400, QT, D44, 28" tires - Sold under duress
1988 GW - "Mrs Tickety" - 360, 727, NP228, D44, 32" tires
Retired Marine
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Stuka
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Re: Pushrod Length

Post by Stuka »

Thomas792 wrote: Sat Oct 16, 2021 9:16 am Last thing remaining is whether or not the intake needs to come off? I put it on to seal up the engine for what I thought was temporary storage.
With it sitting that long, its probably worth pulling it off just to check things over. And then you can visually inspect the lifters as you rotate the assembly.
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Pevious Jeeps: 1981 J10, 1975 Cherokee, 2008 JK, 2005 KJ, 1989 XJ
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1978J10REDWHITE
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Re: Pushrod Length

Post by 1978J10REDWHITE »

There is a good set of YT videos on VLV train geometry, the best one I saw was this YT name, 'pushrod geometry for engines" dated Sept 11 2014. Very simple and thorough explained.
You will need an adjustable pushrod and a set of those skinny little vlv springs to swap out , measure and then have a set made. I know of one place that can cut you a set once you get your length correct.
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