Pushrod Length and Rocker Adjustment
When putting together an engine after having machine work done, it's important to ensure that your valve train is set up properly.
Part 1 - Making Your Adjustable Pushrod
Having an adjustable pushrod is a must when working out the length of pushrod required. When you have machining work done to your engine, it can change the required length of your pushrod. For instance, surface grinding the heads and/or block will change the height of your rockers in relation to the lifters. Changing to aftermarket heads, installing roller rockers etc can all change the length of pushrod required.
Making an adjustable pushrod is a simple process. You'll need an old pushrod, a high tensile or stainless ¼" bolt of around 1½" length and a couple of ¼" nuts. My preference was to use UNF threads for better accuracy, but I could only get UNC at the local hardware store, so coarse thread it is.
Cut the head off the ¼" bolt and clean up the thread so you're left with the threaded rod.
Cut one end off the pushrod around 20mm from the end
Work out an aproximate required length for your pushrod and cut some extra off the main rod remembering to factor in the thickness of two nuts. I ended up removing around 30mm from mine
Drill the main pushrod and the 20mm piece using a 5.5mm drill bit
Tap both the main pushrod and the end piece that you originally cut off
Screw the nuts onto the threaded rod, then screw the rod into each pushrod piece
You now have yourself an adjustable pushrod.
Part 2 - Checking your Pushrod Length
Torque your heads down with gaskets to the recommended settings
Using a black marker, colour the top of the valve stem. This will provide a tell tale of rocker contact on the valve stem
during the engine cycle
Install the adjustable pushrod and rocker arm to the manufacturers specs (particularly if using roller rockers)
Turn the engine so that the valve is opened twice
Remove the rocker and inspect the mark left on the valve stem
Ideally, you want the contact to be as close to the centre of the stem as possible.
Mine were set up so that at full lift, the roller is in the centre of the stem.
Once you are happy with the rocker contact, remove the rocker and adjustable pushrod and measure the length of the pushrod. You can then order the correct length rods for your engine.
Having an adjustable pushrod is a must when working out the length of pushrod required. When you have machining work done to your engine, it can change the required length of your pushrod. For instance, surface grinding the heads and/or block will change the height of your rockers in relation to the lifters. Changing to aftermarket heads, installing roller rockers etc can all change the length of pushrod required.
Making an adjustable pushrod is a simple process. You'll need an old pushrod, a high tensile or stainless ¼" bolt of around 1½" length and a couple of ¼" nuts. My preference was to use UNF threads for better accuracy, but I could only get UNC at the local hardware store, so coarse thread it is.
You now have yourself an adjustable pushrod.
Part 2 - Checking your Pushrod Length
Ideally, you want the contact to be as close to the centre of the stem as possible.
Mine were set up so that at full lift, the roller is in the centre of the stem.
Once you are happy with the rocker contact, remove the rocker and adjustable pushrod and measure the length of the pushrod. You can then order the correct length rods for your engine.