Custom Length Push Rods
Cutting your own push rods to length for your custom motor
When building high performance engines, especially strokers, you need to resort to using cylinder shims to get the deck height (DH) necessary to achieve the desired compression ratio (CR) for the motor. As with anything in life, every action has an opposite and equal reaction. Using the cylinder shims causes the motor to grow slightly wider which in turn causes the pushrods to end up too short. This throws the rocker geometry off, then add a set of swivel foot adjusters to the mix and everything goes south in a hurry. You soon find that your push rods are way too short for the motor you're building, but there are only 2 sizes of push rod that VW made and they only come in short and shorter! The solution is a custom length set of pushrods.
Buying them is easy; just call your favorite VW parts retailer. I bought these steel push rods from CB Performance in Farmersville, CA. The set comes with 8 pushrods w/ one hardened end installed and 8 separate hardened ends. The pushrods are extra long, so they can be cut for virtually any motor out there.
The first thing to do is to measure the length of the tip from the shoulder (where it will rest against the top of the blank push rod to the top of the rounded tip). These measured .405" which happened to be the same length as the tip of my adjustable push rod.
I used an adjustable push rod and a variety of rocker stand shims to determine what length push rod I needed so that my rocker geometry was perfect with the valves at half lift. Once I had the rocker geometry perfect I could lock down the jam-nut on the adjustable rod and I had my length measurement for my custom push rods. Since my adjustable push rod tip was the same length as the tips on my push rods, all I had to do was to set the two rods squarely against a flat surface and carefully mark with a fine point Sharpie pen where to cut.
I use a tube cutter to make the first cut. I put the cutter blade just beyond the mark so that it's cut just about 1/32" too long. The reason for this is two-fold; (1) the blade cuts in a "V" causing the outside of the tube to be shorter than the inside and (2) the cut will need to be de-burred and flattened with a sanding disc.
With the length rough-cut I can then move to the finishing process on the disc sander. I used a framers square to square up my table and guide on my 12" disc sander. Getting the end absolutely square is critical when cutting your push rods. If they are not cut square, the load will be uneven on the rod and they will bend under load. Do not try and free-hand this process; you WILL get it wrong. If you can't get the tip absolutely square and flat, have a professional do the job. Once the table and guide are adjusted at 90degree angles to the sanding surface, I'm ready to begin.
When using a sander to de-burr/shorten push rods, you need to be aware that heat WILL build-up on the end being sanded and this could effect the head treat of the push rods. So what I recommend is only contact the disc for a few seconds at a time and have a cup of water to cool the tip in. I like to hold the push rod with one hand firmly against the guide while the other hand lightly pushes the tip against the disc while simultaneously turning the rod. This turning will ensure the tip is nice and flat and keep burring from building up on the inside of the rod.
Once the tip is exactly the right size, I be-burr the outer edge of the rod by turning it at a 45degree angle to the disc with VERY light contact; you're just trying to remove the sharp corner, not angle the tip. The next step is critical. Thoroughly clean out the push rod of sanding dust and metal debris. Any dirt missed here will be injected directly into the motor causing damage in a hurry.
Now that the rods are clean, you're ready to assemble them with the tips. I use a pair of old lifters to hold the top and bottom of the lifters. If you have a hydraulic press or arbor press, you just press the tips in place and you're done. If you don't have a press, you can use a hammer to tap the tips into place. Be sure to use the old lifters to hold the tips firmly.
What you have now is a custom set of push rods that will work perfectly for your motor.
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Revised: June 06, 2008 .