Measuring pushrod length for your LS or LT engine is a crucial part of building an engine, swapping a camshaft, changing lifters to a different type, changing cylinder heads, and more. To that end, we’ve made a video to help anyone with an LS or LT engine be able to properly measure their pushrods. We cover how to measure pushrods using the two different types of pushrod length checkers. The video also explains the difference between measuring for hydraulic lifters and measuring for solid lifters, as well as how to properly set valve lash.
Why Is Pushrod Length Important?
Pushrod length is a critical component of proper valvetrain geometry. Measuring the length incorrectly can cause broken lifters, bent pushrods, piston to valve contact, rocker arm damage, worn valves, and broken valve springs.
Consequences of Pushrods Being Too Short
When your pushrods are too short your valves won’t be able to fully open, resulting in lost power and very loud valvetrain.
Consequences of Pushrods Being Too Long
Pushrods that are too long are more dangerous because they can lead to mechanical interference in the engine such as piston to valve contact. The valves will be hanging open in this scenario, which causes loss of engine compression, and if the valves make contact with the piston it can bend or break valves, or even shatter cast pistons.
Calculating Lifter PreLoad for hydraulic lifters
Once you’ve measured your pushrods, you also have to account for lifter travel. Different types of lifters will have different “travels” that allow you to determine a safe range for your pushrod measurement to fall within. Stock LS lifters, such as LS7 lifters have a .200 total travel. This means the safe range for preload within that window is .050 to .130. If you’ve come up with a pushrod length, and it falls within that window you are safe. We typically recommend finding the closest commercially available pushrod length to your measurement and choosing to order that, as long as it is still within the window.
Beware, not all lifters have as long of a travel, meaning your preload calculation has to be much more specific. One example of this would be Johnson Reduced Travel Lifters. These lifters have a plunger travel of .093, half of the LS7 factory lifters. They also have a manufacturer suggested preload of .025" – .045". Now all of a sudden the window to land your pushrod measurement within has gone from .080 to a mere .020. We also don’t like to recommend running at the outsides of the window, so now you’re left likely trying to target around .030-.040, a comparatively very small range. For a range this small you will need to measure each intake and exhaust pushrod on each cylinder of the engine to ensure that your pushrods will all be within the window, and you will likely need to order custom pushrods. This is where quality of machine work on your engine build will be abundantly obvious as well.
Lastly, if you have a solid roller engine the process is entirely different. Solid lifters do not have travel, so there is no window of preload. Our video below dives into measuring pushrods for solid lifters and setting valve lash.
Setting valve lash
Lashing your valves is a process that is unique to solid lifter engines. There is generally a “cold lash” specification, and a “hot lash” specification. Cold lash is set while the engine is cold and hot lash is checked while the engine is at operating temperature, which can make it much harder to do. To set lash, determine what amount of cold lash your engine needs (this will be different depending on build, components used, etc) and use a feeler gauge to begin to snug your rocker arm’s adjuster until there is no play up and down, but the feeler gauge still slips in and out between your rocker time and valve tip when everything is tight.
If you have any questions after reading this article, we have this helpful video representation to guide you! Take a look below and drop a comment if anything wasn’t clear, or if this answered your questions!
