Hello everyone! I have a question about checking pushrod length that's been brought on by one of my rocker arms coming off the stud.

I've researched this a lot and can only really find one way to check the pushrod length: wet erase marker on the valve stem, set rocker arm on stud, tighten to zero lash, turn the crank so that the engine rotates 2-3 times. Is this the only way to do this?

The reason I'm asking is because I kind of half-assed checking the pushrod length in my build (I didn't know about checking pushrod length until after the engine was in the car and running last November). I put dry erase marker on the stem, tightened down the rocker stud a bit, turned the key in the ignition but stopped before the engine started, and then checked the wear pattern and it looked dead-center. I didn't question it because I didn't want to go through the hassle of pulling everything apart with Winter coming. These were stock-length pushrods with the LT4 hot cam, matching rocker arms, and Howard's valve springs. But my heads were milled .015" and I used the .026 Mr. Gasket/Victor Reinz head gasket, so I'm pretty sure that I actually need shorter rods since the rocker arm was theoretically brought closer to the lifter.

I guess my question is: is there any way for me to measure the pushrod length that doesn't involve removing the spark plugs and turning the crank by hand? I also use the engine running method to set zero lash, so I'm not sure what to do about that either. Is there a mathematical way for me to figure out what length pushrod I need?

Thanks in advance.

 

That's how I checked my pushrod length. Instead of removing the spark plug and cranking by hand which sounds like a huge pain in the ***, just remove your fuel injector fuses from the under-hood fuse box. Then you can crank the engine all day and it will never start.

 

Yeah, that's what I thought too. But then I realized that I wasn't at zero lash so it probably wasn't actually helpful. I'm using the poly locks with the 1.6rr.

In order to get it to zero lash, I would have to crank the engine as you described and hope to catch it on top dead center or take the spark plugs out and manually turn the crank until I was at TDC and then do the spinning or up-and-down method for setting zero lash. THEN I would be able to crank the engine over a few times using the key.

Or am I overthinking this whole thing? It's also worth noting that the lifters I used are the OEM replacement (not LS7) units that I picked up from Skip White Performance.

 

You want to initially lash the valve at zero when that particular valves lifter is on the base circle of the cam. Mark the top of the valve stem with a Sharpie first. Then you can either crank the motor over a few revolutions or rotate it by hand using a 5/8" socket on the damper bolt. I do the later and I don't remove any plugs. Just turn motor slowly using a socket & ratchet.

Remove RR and look at witness mark. You want the narrowest sweep that is centered or "slightly" towards the exhaust side of the motor

Assuming the PR being used is stock length (7.200") and the witness mark is favoring the exhaust side to much you would want to use a adjustable PR tool then set at 7.150" and repeat process. If still to far towards exhaust side try 7.100"

In OP's case given heads were decked and thiner head gasket he "may" need a 7.150 but you need to measure to confirm

Another way is to use the Proform (pic) tool which is very simple to use and requires a feeler gauge to measure whether you +/- PR length. There are youtube videos how to use them. No instructions come with the tool. You still need to rotate engine so whatever valve you are working on has the lifter on base circle of cam.

The Proform tool comes in 3/8" or 7/16" for whatever RR stud size you have

Video (guy is not right about some stuff but you get the idea on how to use it)
https://www.bing.com/videos/search?q=profirm+push+rod+check+tool+video&view=de tail&mid=2CB17978FC4FD9DA3EB82CB17978FC4FD9DA3EB8& FORM=VIRE

 

You can also pull the PCM fuse in the inside fuse box and it kills fuel and ignition.

 

Thank you all for replying. So, to be clear, from my understanding the base circle is essentially any point on the cam that isn't the ramp or nose?

When I was first setting the lash, I tried rotating the crank with a socket and ratchet but it was really difficult. I don't think that I was trying to do it with the belt on, so I'm not sure what was going on--knowing me, I might have left the car in gear. I'll see if I can try it again tonight and report back. I might be able to borrow a pushrod length checker, but at least I can check the stock length tonight with the materials I have.

 

you want to be on the heel "bottom" of the base circle of cam

 

There are uppity ups who will say they can tell just by eyeballing a lifter when it's "dead nuts center" of the base circle, but yes, base circle is anywhere other than when the lobe starts to ramp.

 

Perfect, thanks for this! I feel like trying to find where it would be at the opposite of the peak of the lobe would be really difficult for me.

 

Using the picture as reference...the center of "heel" of the base of the cam is at 6 o'clock. Basically anything between 4-8 o'clock would be fine on a hydraulic roller with 1 turn of pre-load

 

I just watched a video on how to use this tool. Holy crow--looks easy! Can one substitute an adjustable pushrod for the feeler gauge when using this tool? It seems like that would work alright.

 

Okay, thanks! That's the same picture that I was looking at!

So you recommend a full turn of preload? I had done 1/2 turn when I set it with the engine running.

 

yeah you could use a adj PR....but the tool is easily used with feeler gauge. You just add or subtract whatever the feeler gauge distance is as shown in video to the PR you are using for the test.

I have compared this tool to regular adjustable PR method and get the exact same results. The proform tool requires no lash, turn motor over, etc. Just have whatever valve you are checking on the base circle of cam

stock pre-load is 1 1/2 turns. 1 turn is fine unless you are using "short travel" lifters

 

Alright, so the Proform tool came in today. I used it with the stock length pushrod and had quite the gap between the blue tool and the valve stem:



It's tough to see because I had to have the lens very close to the stem since this was on one of the valves a bit further back on the passenger side. But you can see the gap between the stem and the tool on the foreground.

Then, I broke out the adjustable pushrod (decided that would be easier instead of feeler gauges) and started at 6.800 and worked my way up until the tool sat flush on the valve stem and made consistent contact with the pushrod. I measured the pushrod length at that point to be 7.000" even. Does this sound right? I'm going to run it again, but I think it's reasonable given that the heads were milled .015" and I used the .026" Impala gasket.

Anyway, thanks again everyone for the assistance!

 

You have cut about .038 with head deck and thinner head gasket assuming you had a .049 head gasket before. By math that would take you to a (approx.) 7.150 (stock is 7.200)

7.00 is shorter than a typical swap

Just use a feeler gauge with the stock PR. Likely .050-.100 gap max

 

Thank you. This might be a dumb question, but how do I use a feeler gauge with the stock pushrod? Slide it in the gap between the valve stem and the blue tool?

 

yes..

 

Thanks, I guess that I couldn't wrap my head around that being a 1:1 approximation of the extra length of the pushrod. Also, the pictures that I saw of feeler gauges being used were of people using them on the pushrod side which wouldn't work if the pushrod was too long, only if it was too short. Sorry for my confusion.

Thanks again! I'll update with results.

 

So it looks like I'm going with 7.150", but I'm sort of at a loss. The cheapest set of 16 that I can find is the Trick Flow TFS-21407150.

https://www.summitracing.com/parts/tfs-21407150

It looks like they're chromoly and I don't think I want that because I still want the pushrods to be able to give out (instead of a cam lobe, etc) if there's something wrong. They also say "for guideplates" which I don't think means anything other than that they CAN be used with guideplates, not that they have to, but I want to check. I would prefer a set of just hardened pushrods at a lower price point if anyone can point me in that direction.

Thanks for checking my work and helping me along.

 

7.150 is what I would expect. Nothing wrong with the TF ones, I use them. For a quality PR the $99 is a good price. Comp Cams are more.You don't have to use them with guide plates if you are running SA RR

The thicker wall PR will not flex like the stock ones can

There may be cheap off shore made ones....you typically get what you pay for.