Thought I would share what I've found while checking pushrod lengths.

First, as well all know, lifter preload is not adjustable on an otherwise stock LS1 valvetrain without buying different length pushrods.

My motor just got new valve springs and had one slightly bend pushrod. Since I had to replace that one, I wanted to measure them all and buy the correct length pushrod to put my lifter preload at .080-.100" so as to keep the motor as quiet as possible.

First I did it the right way. I set my adjustable pushrod length checker to 7.400 and put the rocker on and set it to zero lash. Then I setup my dail indicator in the pushrod oil hole on top of the back of the rocker in line with the angle of the pushrod and set it to zero. I then torqued the rocker arm to 22 ft/lbs and waited for the lifter to settle and took the dial indicator reading. If it was between .080-.100 I was done, and 7.400 was the correct length. If it was more or less, I added/subtracted length to the adjustable pushrod and re-checked until it was in spec and recorded the appropriate length.

This method is an EXTREME pain in the ***. First, since I have an RX7 with an LS1, there is very little steel to attatch the magnetic base of the dial indicator to. Then once it's setup up properly, the dial indicator is so sensitive that you have to be very careful when sneaking the torque wrench around not to hit it. Getting repeatable results was very time consuming. I only managed to do about four cylinders before finding a way to mount the dial indicator became a problem.

I decided to start over using the Zero Lash method. Basically, I'd set my adjustable pushrod to 7.250. I then put the rocker on and tighten it down just so it's snug/hand tight. If the rocker was not at zero lash, I pulled the adjustable pushrod out and added 0.025" of length (one half turn) to the rod and tried again. Once I found zero lash, i added .080" to the length of that adjustable pushrod and picked the closest available pushrod size that would put me between 0.080 - 0.100"

For example. If 9 turns of the adjustable pushrod put me right at zero lash then 9 x .050 (one turn of the rod) = 0.450 The base measurement on the pushrod (zero turns) is 6.800. 6.800 + 0.450 = 7.250"

Since pushrods only come in 0.025" increments, adding .080" to 7.250" gives me 7.330 length. In my case, I want a quieter engine and a 7.350" pushrod would put my lifter preload at 0.100" right at the tight end of the acceptable range.

FWIW, I re-did all the cylinders that I measured with the dial indicator technique, and got IDENTICLE results with the zero-lash method (which is much easier).

Is my math right??? Doing it the zero-lash way; is adding desired lifter preload length to the measured zero-lash pushrod mathmatically correct? Do I need to figure in rocker ratio to the measurement? If the rocker is hand-tight/snug when I find zero lash, torqueing the rocker down to 22ft/lbs is going to require a few more turns. Does the fact that the spring levers the rocker against the pushrod NOT ALLOW me to simply add .080-.100" to the zero lash measurement?

Do I need to multiply .080-.100 by the rocker ratio to get actual lifter preload?

If that is the case, it's odd that the dial indicator and zero-lash methods gave me identicle results.

Please, comments welcome!

Thanks!!

 

Ah... brain fart. Forget the last question... I realized that if the fulcrum of the rocker is fixed (the spring) then you can simply add desired lifter preload to the zero-lash measurement.

only if the rocker is "rocking" would you need to multiply by a ratio.

This is assuming that the lifter preload force is less than that of valvespring seat pressure.

Makes sense. There's no way there is 130lbs exerted by oil pressure in the lifter, right?

 

Math is correct although you may want to setup down to 7.325". As for rocker ratio, only need to use it when using the bolt turns to figure things out. Since you are at zero lash, everything is in the correct position so preload is measured/added directly.

 

I've searched my *** off and read that the stock LS1 lifter has about .200 of travel.

I have two cylinders that I'm iffy about... they both would use 7.350's at .10x" of preload or a 7.325 at .07x"

I've also read that more preload = quieter valvetrain. None of my preloads would reach or exceed .110". Do I run any risk of motor damage with two of the lifters slightly tighter than spec? The alterantive is to run them slightly below spec...

 

I'd run em slightly below spec just to be safe...

 

Whoever installed the heads/springs the first time monkeyed up the #7 exhaust rocker stud hole. It was tuff to get the bolt in and out... couldn't turn it by hand and the bolt took a bunch of aluminum with it.

I looked down the hole with my pen light and it has about the top half of threads remaining. The bottom half are gone.

I assume I'm going to have to helicoil

I know how and have watched it being done, but never done it myself. Luckily for me the #7 exhaust valve is in front of the firewall/windshield on my RX7. I can get a regular old drill in straight from the top with no obstruction.

Can anyone tell me the bolt size/thread pitch of the OEM rocker arm bolt?

Thanks!!

 

From memory it is 8mm X 1.25 but before you do anything verify this. I can look in the service manual tonight if you can't verify the values. You also need a long heli-coil, not the shorties they sell in Autozone.

 

I did a search on here and several thread say it's 8mm x 1.25, so I think you're right.

I found a complete helicoil kit on McMaster Carr that comes with helicoils in 8mm, 12mm, and 16mm lengths.

One 16mm should do it, right? That's ~2mm shy of 3/4" long.

 

That is 2 diameters, should be good. Measure depth to make sure you can break off the tang once the heli-coil is in place.

Is the hole blind or does it open into the port?

Whoops, exhaust should be blind.

 

Thanks for the help. I think the kit comes with a "tang break-off tool".

I have some scrap aluminum I plan to practice on before I start drilling away on the head

 

Post how you make out.