how to accurately measure push rods on 350

I now have the pushrod length checker [per Larry, aka the wizard!] and the long digital caliper to measure with .......... so exactly how do I go about determining the appropriate length for new pushrods? As a refresher from my previous posts I had put in new factory length pushrods [9.65"] during the rebuild and realized they were 'way tight.' And didn't know to do this with the length checker until I learned from our forum my mistake. Obviously the resurfaced heads changed things. All wisdom and/or advice will be enthusiastically received ....

lane

 

Once you have the measurements, using the data is important! Here is a spreadsheet that I made when I did this a few weeks ago as an example:

https://docs.google.com/spreadsheets/d/1ki_6Je8wGaCrz57Xuo27HI66sCKjeYS8FUIIDgm2WRg/edit?usp=sharing

Here you see the rows listed by cylinder. Under the blue columns that say "Intake" and "Exhaust" are the measurements I took off the checking pushrod once I had adjusted it to zero lash in each of the 16 places (note that I did not add any preload in the checking pushrod, I add it later as you will see below). I would lock the nuts carefully by hand, remove the rocker shaft, and carefully take out the checking pushrod. Then I would measure the checking pushrod with my calipers and record the measurement. Then repeat as mentioned above (I had my intake off and could see when a lifter was on the base circle easily, so I didn't necessarily go in the above order).

Then what I did is make separate columns for different pushrods that I could buy. You'll see one that says 9.800" (Stock). This is the length of the pushrods that I removed from the engine when I first got it (stock length is actually supposed to be 9.650", who knows why mine were longer!). I used a simple spreadsheet formula to subtract the length of this theoretical pushrod from each of the "Intake" and "Exhaust" columns. The result is the amount of preload that you would get on each lifter given that pushrod.

I've heard of people taking the average of all 16 measurements but this way you can see all of the preloads that you will have and pick the pushrod length that gives you the closest to your ideal preload number. For example you can see that for my engine, 9.800" was way too long, giving me preloads above 0.100"! Also if your valve heights are different at all (like mine are) then it's a good idea to measure it all.

I also tried 9.600" and 9.625", but I ended up choosing 9.650" (that's why it's gold colored!) because it gave me preload numbers that were closest to my ideal 0.020" - 0.80" range (this according to the instructions that came with my lifters) with #3 and #8 exhaust being a bit on the high side but not too bad. Ironically 9.650" is the supposedly the stock 350 length!

Feel free to use my sheet and ask any questions about how to input your own numbers into it! I am by no means a spreadsheet expert but I found it useful in this situation!

 

Thanks millions Patrick and Larry ........... glad I bought the checker and the digital caliper Patrick recommended on amazon. This will be more involved than I thought but sure don't want to mess up. And yes I saved in print form the forum about finding TDC on number one cylinder. If there are problems I will call again. I will use the spreadsheet as it is a really graphic way to follow the measurements.

 

Those are good articles!

I've been lead to believe that in our non-adjustable shaft rocker system, we're not able to alter valvetrain geometry at all, and pushrod length only affects lifter preload. This is where I'm reading this:

 

I found the articles Larry listed as good background. I often learn more by reading multiple opinions or facts than by any other means. And Patrick's later post of excerpts is equally informative. My original rebuild DVD [which isn't working] talked about some of the techniques - marking with a marker and looking later at how and where the pushrod etches the mark ........ I have forgotten much of what he demonstrated on it but somehow the position was important to determine before final lockdown/torque of the rockers and it is beyond me why the DVD didn't even mention geometry changes which affect pushrod length. Thanks guys .............. now I am literally scared to death of messing up [just kidding!] ........ there's so much to know [I hadn't even considered how to change lifter preload until now and mine were definitely too tight]

 

Just to make sure I'm not missing something. After loosening the rocker arm and placing the length checker into the opening of the pushrod being checked the rocker is put back into place and the turning of the checker begins until tight against the spot where it fits nicely plus one half turn for preload ......... then rocker is removed and the new length measured? And this is done for every pushrod on both sides? ....... i.e., the rockers come on and off and tightened each time? Should I tighten the rockers to factory recommended torque for each measurement or just snug? Will it hurt anything if I move the crankshaft a small amount counterclockwise to find the sweet spot? Engine, transmission, and driveshaft are all hooked up - could going backward [counterclockwise for just a smidgin'] harm anything? Forgive my ignorance here
lane

 

This is the way I did it:

-Make sure the lifter you are checking is on the cam base circle
-Remove rocker shaft/rockers
-Insert checking pushrod (shortened most of the way)
-Reinstall and torque rockers/shafts to 25 Ft. Lbs. (factory spec)
-Expand checking pushrod to zero lash (I didn't add turns for preload because I wanted to use my spreadsheet)
-Remove rockers/shafts
-Remove and measure checking pushrod

 

Thanks ........... I'm gonna' do this too .......... that way I know the differences between each pushrod. How did you ascertain that the lifter was on the cam base circle? By sight? And with the rocker shaft off? Or on? The list seems to indicate that it was determined with rockers in place. Did you use the starter to move things or with a wrench on the crankshaft bolt?

 

Larry, wouldn't adjustable pushrods actually solve everything? Maybe that's a less labor intense option. I just looked in the TA catalog and they are only about 55 dollars more than non-adjustable. Going back to stock isn't important for my purposes anyway. I won't be able to see the cam as the intake is in place and I figured getting the sweet spot was by looking at the top of the valve stem. After looking at Patrick's spreadsheet numbers his were off a little too. Thanks for this feedback ............ would you like to buy a set of new 9.65 length pushrods [I'm just joking]?

 

I came so close to going adjustables but decided on one piece pushrods due to durability concerns. If you search the internet you'll find many opinions on both sides of the fence . . . I didn't want to have any more unknown factors in my engine than necessary haha.

My worst valve tip was low by 0.017", not enough for me to worry about it affecting the preload a ton (IMHO).

 

Thank you both very much - I need this guidance and your tolerance of my lack of knowledge and experience. And if there's anyone who gets ahead of himself it's me .......... always trying to avoid messing up and since I don't know much it's really easy with this.

 

The straight edge test showed most valves on one side fairly flat across the edge but on the other side it wobbled with one valve a full .010 beneath the edge. Checked the gap with a feeler gauge. Another was maybe half that. Verdict? Per Patrick's worst tip of .017 and not enough to worry about should I proceed with measuring one piece pushrods? BTW - when I released the tension from the rocker arms the pushrods were clearly bent because of so much pressure as I watched them flex after pressure was relieved. Wow! So lucky to have had this conversation from its' inception. Saved by V8 Buick.com

 

I would wait for others to comment on the low valves being an issue or not, just because I choose to basically ignore it doesn't mean that it was the correct decision . . .