So here is the scene: Stock 98 LS1 (roughly a metric FT of miles), just installed TSP cam, cam gear, chain, springs. Time to check the 7.400" pushrods and make sure they will work. Using the Comp Cams adjustable PR.

When I install the rocker with the adjustable PR set to the exact length of the new PRs, the rocker can be lifted off of the valve tip. Turn the PR 1/4 turn longer, and no up and down movement from the rocker and the PR can just barely be turned by a finger, which I'm told is what you want.

So my question is, do I need 7.4125" PRs? Or is that little movement or "lash" acceptable on the engines? Every post I have found had my head spinning by the 3rd reply. This is my first time inside an LS engine so consider me retarded please.

Anybody that can dumb this down for me is greatly appreciated.

 

So with that 1/4 turn, you have zero lash. Now, the best way to be sure is this.

Get a 8" or 12" caliper to measure the pushrod.

Add .075" to the length of the adjustable pushrod

Find zero lash with the rocker bolt. I mean with almost no force, where the rocker touches the pushrod.

Put a dot on the bolt at 12:00.

Turn the bolt by wrench until it snugs, but don't torque it. Just until you've taken up the preload.

If you got the dot back to right about 12:00, it's perfect.

Measure the adjustable pushrod length. Order the pushrods to the length. Tell the vendor that is as measured with a caliper

 

No - you don't want any lash. You need to add the .075" to the zero lash measurement for correct preload. Follow Darth's directions above. He knows what he's talking about.

 

And what if the dot does not make it back to 12:00?

Also, I have my calipers today so I have some actual numbers. The new "7.400" push rods measure 7.416". The stock push rods measure 7.396". The tool extended out to achieve zero lash measures 7.432".

 

With stock rocker arms and lifters, you will want .070" preload which should be between one and one and one half turns of the wrench after you get zero lash. How close to one turn do you get? Do you have stock lifters and rocker arms? Also make sure you're checking lash with the lifter on the base circle of the cam.

 

With the tool extended out .075" I can only turn the bolt to the 3:00 position.

Yes, stock rocker arms and lifters. Also yes, the lifter is on the base circle.

 

After taking another whack at it, I got it back to 12:00. But I had to put some pressure on it.

 

I measured all 16, is that what you're doing? It took me several tries over several days to finally get the hang of it and feel confident. Some guys measure just a couple, but I couldn't handle that.

Some of my problem I think was that my lifters would stick or something once pressure was put on them while dry. So when I'd try and redo it, measurements were off. Some WD40, lots of questions, and patience from Darth and others finally took care of it. Search for his write up if you want more details of the process.

 

Yeah, I feel like there is something else going on giving me trouble.
I looked at his write up last night but it was late and I was exhausted so it wasn't making much sense. I'll have to take a look at it again.

 

Take a look at the video below. It pretty much explains it all. Sounds like you need to lengthen your pushrod by about 0.010 and try again. It sometimes helps to put some white, teflon plumbing tape on the threads of your adjustable pushrod. The tape keeps the pushrod from turning too freely and measurements are more precise. This takes a little practice but you'll get it.

 

there is a range. So for example, if you get back to 1:00, it's fine. Really I would say anything between 10:00 and 2:00 is fine. You'll get a bit more rotation if you torque all the way to 22 ft pounds. Usually an extra held rotation of the bolt.

Verify the rod is definitely in the lifter cup. I had one on the lifter body give me a weird reading.

Also, do it until you get the same result a few times. Then you'll know you've got the technique. Once it clicks for you, you'll be good.

 

Thank you so much for your help. It still seems like something just isn't quite right in my measurements. Not sure if it's a lifter or what. Maybe I'm just paranoid because I haven't messed with this before. I called TSP today and we seemed to be on track for a resolution and then their phone system took a dump so that ended that. Hopefully tomorrow we'll get it figured out. My hope is that I'm doing something wrong with my measurements and the 7.400" rods that I have are correct. But time will tell. You have helped me understand a lot in the way of hydraulic lifters though, I really appreciate it!

 

One thing that helped me was to move to another cylinder. Front driver side is where I started and couldn't get it right, so I moved to the passenger side and was able to get all 8 measured. Helped me know what I should be expecting.

 

You have to be on the base circle of the cam in order to properly measure. Have you verified that you are on the cam's base circle?

Put some teflon tape on the threads of the checker so it doesn't spin easily.

Find the base circle of the cam.
Put in the checker tool.
Torque the rocker to 22 ft/lbs.
Adjust the checker and retorque until you get to zero lash.
Pull out checker and measure with calipers.
Add desired preload to that measurement.
That is your needed pushrod length.