Hey folks,

Lots and lots of pushrod length discussions happening of late. Good timing for me as I am at that point.
New EPS Cam, GM lifters, AFR 205's, YT rockers. When I bought the used AFR's, I also got a set of Trick flow 7.4" pushrods, so something to work from. I also bought a Trick flow adjustable rod.

Because this was a fresh build, and I had 3 different pushrods to play with, I decided to use direct measurements and go flat to flat. (Calipers) And yes, the head gasket is in place.

Prior to beginning the work I established the correct wipe pattern with the YT rockers. This required a .050" shim under the stand which rather radically alters pushrod length.

From the photo below you can see the pattern and also the fact that I used some 8mm studs to mount the rockers instead of having to bolt and unbolt them for each measurement. I also rechecked after bolting them down and found no difference in my measurements.



I started by setting my adjustable pushrod to 0 lash and measuring the length. (See Chart) I came up with 7.422"

Next added the 7.4" pushrod, and checked the lash at the valve tip. I used feeler gauges, it is a feel sort of measurement if you have ever set lash this way. Lash was .016". Divide by the rocker ratio and I got .0094" different length at the pushrod compared to the adj. one set to 0 lash.

Next added a stock pushrod and did the same process.

Here is the chart I made up to check the measurements. Note the fact that the flat to flat isn't dead on what is written on the TF 7.4" pushrod. It is off by .012".



The lash settings and math verified the measured length differences.

So, if I want .080" preload, the closest off the shelf TF pushrod is 7.5". I think it is maybe best to err on the long side. I assume flat to flat the rod will measure 7.512". But who knows until you get them in your hands?

A couple of other things I checked.
There was no difference between the original lifter and the LS7 lifter as far as cup height was concerned.
A ball type pushrod and the pressed end pushrod contact the lifter cup in exactly the same place. This I figured had to be true.

Anyway, this is where I'm at.

With all the issues with noise on these LS7 lifters, I'm tempted to reuse my originals that have 78K miles.

Ron

 

I love the way people cringe when you talk about shimming your stock rockers when your measuring for correct pushrod length, but never bother to check their wipe pattern....good write up I hope people read this.

FYI, I ended up shimming my stock ones to get the correct wipe and by shimming my old pushrods ended up being the length I needed even though I went from a total .595 lift old cam, to a .624 lift new cam

 

I'm at the same point right now with my Mamofied 215's. I also checked wipe pattern and am running 0.093" shims with my YT rockers.

I'm checking every single pushrod, all 16. Did holes 1 through 4 so far and am seeing numbers that vary by 60 thou or so. These are my zero-lash numbers so far. I'll be adding 0.040" to these numbers for preload (running comp short-travel hydraulic link bar lifters) and ordering custom length pushrods.

#1I - 7.387
#1E- 7.398
#2I - 7.382
#2E - 7.326
#3I - 7.324
#3E - 7.378
#4I - 7.387
#4E - 7.349

One thing that makes this process go much faster (although it's still a pain in the ***) is to use a pair of adjustable pushrods and do two at a time.

I'm also doing this with the rocker pair that will be used on that cylinder to eliminate any tolerance variation in the rocker itself.

 

Doesn't it seem odd to you that there is so much variation?
Are you sure you are on the base circle of each lobe?
That just seems off to me.
Although I only checked # 1 intake.

I'll go mess with a few more and see what happens.
This is too much work!

Ron

 

There is always going to be variation with hand finished parts... I'm more curious/concerned as to why 1 and 3 want a longer exhaust pushrod than intake, but 2 and 4 are the opposite... and yeah, I was at TDC of the firing stroke on every cylinder.

It's a LOT of work for sure!

 

Are all of the valve stem heights the same? Maybe that's where the variation is coming from.

Also, putting the cylinder at TDC on the compression stroke may be OK, but some people say to put the lifter on the base circle 180 deg opposite the nose of the cam lobe when checking for correct pushrod lenght.

 

Glad you guys are chiming in.
Valve tip height variation is divided by the rocker ratio. It is a variable to be considered.
Variations on the pushrod side get multiplied, so those I believe will have the greatest effect.

So, I made some errors in my original measurements.
I was using a pair of used YT rockers that I bought for spares. They are in great shape, but any wear in the pushrod cup changes things.
Also, the TF 7.4" pushrods I got with my heads are in fact not new! Again, any wear here affects the measurement. And makes flat to flat length useless as the flats don't wear.
So back to the start doinfgthe measurements with my adj pushrod and new rockers. Will be interesting to see how much it changes things.
I figured this out after Reckenbackerman mentioned his variations.
So thanks again for the posts.
Here goes the whole day!

Ron

 

I don't want to hijack Ron's thread, but in my case they are not. The exhaust valve tips all sit lower than the intakes but I don't get why the #2 and #4 intake valves want the longer pushrod...

Good info, will keep that in mind. Thanks!

 

Hijack away! This is a learning process.

I'm finding that it's a pain in the butt to hit the lifter cup with the pushrod because you just can't see down there.
Also discovered that if you miss bad enough the pushrod disappears and off comes the head to retreive it! Argh!

 

Why aren't they the same height in your case ... not running stock LSx heads?

In Ron's case I assuming he has LS heads, so all the valve stems should ideally be at the same exact height above the head. In a perfect world, if all the valve stems were at the same height, and all parts were all exactly the same, then the same pushrod length would give exactly the same pre-load on every lifter. That's why I was asking if all of the valve stems are at the same height on Ron's setup to see if that's why he's getting larger variations in his measurements.

 

Sounds like the TF pushrod length is specified as 7.400" gauge length.

If you put the adjustable pushrod down to it's baseline starting lenght, what is its flat-to-flat length?

 

My heads are AFR 205. They were used. So I had the exh valves faced (minimal cleanup) and the tips cleaned up as well. So my tip heights do vary. A difficult measurement to make. The heads were not as wonderful as the seller thought.

I agree that the TF 7.4" is gauge height. It fits with the .015" difference between gauge and flat to flat.

I have no idea what the adj pushrod I'm using has for a minimum length spec. It is made by TF as well. I am just using it to set to 0 lash then measuring flat to flat. It would be nice to have a tool that directly measures gauge length, but I do not have one.

 

So is the valve stem height supposed to be (ideally) the same for all valves in that head? It would be good to know the valve stem height for each valve to see if that correlates with the variances you're seeing with required pushrod length measurements.

If you turn the adjustable pushrod down all the way and measure flat-to-flat, what do you get? Is the adjustable pushrod stamped with any lenght info? It should have a starting length (screwed all the way down to the shortest length), then be XX thousands of an inch per turn as you lengthen it. Another thing to ponder ... how accurate is you flat-to-flat measurements?

 

My heads are AFR 215's that have been "Mamofied" with larger, lighter intake valve's and all of Tony's associated massaging... I've been doing things other than working on my car all day, but Tony's actually going to call me tonight so I'll let you guys know what I come up with.

 

In a perfect world, all the heights of the tips would be the same. My tips have been machined slightly. Makes them shorter. The exh valve faces have been machined. Makes the tips higher. So who knows? The differences will be small. I have no way of knowing what they should be or in reference to which surface.

For the length checker. 6.125 to 7.5" First problem is the lower adj lock nut is too big to fit through the pushrod hole in the head. So that is removed. I only care what it's length is at 0 lash. So I'm not getting your point. Length change per turn is .038". But I'm not counting turns.
I'm using 8" calipers for the flat to flat measurements. Digital. They aren't hard to use. I bought them yesterday.

I have 2 cylinders done. 3 lengths the same and one shorter by .010". Thus far, it is making sense.

 

Wish I could say that, lol. I've done 4 cylinders (and verified a second time) and my numbers are all over the map. Fun, huh?

 

Any time valve work is done, there's always a possibility that there will be valve stem height differences. Of course, if the machine shop is good, then the difference in stem height will be very small, and they will typically adjust the stem height to the stock specification.

My point was that if you were using a good pushrod length checker it would give you a correct and accurate answer right off the bat. Of course your method with the digital caliper will work too, but is a less direct way to get the measurement and gives you the flat-to-flat length, so if you buy pushrods or have them custom made, make sure you know how the seller specifies the length.

 

Ok. I would like to see a photo of this tool.

Cailpers with special attachments so that gauge length is actually measured?

Finished with drivers side. This is a bitch to do in the car.
Variation is .017" between all 8.

On to the other side.

 

i just installed my springs today.
and all seemed to went good.

this pushrod checking,
(1)i put the pushrod checker in and tighten the rocker to 22
(2) rotate the checker until zero lash
(3) pull the checker out
(4) read the measurement and add .070

Is this correct?

Ive been reading alot about the pushrod length and preload
and i am getting more confused

im a dummy i guess and i can be pretty dense
or overthink stuff

I appreciate the help ive read from you guys

 

I had lifters sticking before they set down on the base circle! No wonder...