Checking Rod Clearances & Hanging Pistons - Tech - It's In The Measurements - CHP Step By Step

Although an easy step to overlook, pay close attention when installing the rod bearings. All race bearings indicate whether they are supposed to be placed in the piston cap or the actual rod, labeled upper or lower. Uppers should be placed in the rod, whereas lowers needs to be placed in the cap. Lastly, locate the bearing in the rod with the tang for proper fitment.

To torque the rods, QMP suggests using a rod vise (standard vises with teeth will damage the sides of the rod when applying pressure) and torquing the rod bolts as specified by the bolt manufacturer with the required amount of lube for final assembly in the engine.

Once the bearings were in the rods and torqued to spec, we used our set bore gauge to measure. Place the gauge in the big end of the rod, in the center of the upper and lower bearings, and do not measure the bearings at the parting line (where the rod and cap meet), because the bearings are not perfectly round and will give you a false measurement. Also, assuming the rods were machined correctly or are brand new, QMP suggests that, depending on the application (steel or aluminum), there should be a maximum of 0.004 inch variance in bearing clearance.

With everything measured, we then disassembled the rods by placing the rod back into the vise, removing the bolts, and separating the rod from the cap at the parting line. Once apart, we cleaned all rods, caps, and bolts for final assembly. To prevent any error in your torque specs, be sure to clean all threads completely. Any foreign material, besides lube, on the threads can skew your torque readings.

To prepare the piston-to-rod assembly, we applied a liberal amount of engine-assembly lube to the inside pin area of the piston and the pin boss, including the pin and small end of the rod.

With the entire assembly lubricated, we then slid the pin halfway through the piston, leaving enough room to place the small end of the rod into the piston. From there, we continued to slide the pin until it met the rod and came through the other end. Although it isn't required, it's still a good idea to move the rod side to side and back and forth to make sure the pin is properly lubricated; this will provide a little insurance that it won't bind up later.

While many types of retaining rings are available for various applications, we opted for the Spirolox brand. Truth be told, if you have little experience with any retaining rings, they can be difficult and stubborn. Just take your time, making sure not to stretch the coils out, and you'll know when they're in. Ideally, they should sit flush in the piston and against the wrist pin.