How to Install Spirolox

September 25, 2018 / by Mike Magda

Most engine builders have a love/hate relationship with Spirolox. However, with a few tricks, they install easily. Here's how to do it. 


While there are numerous methods of securing the piston and wrist pin to the connecting rod, a double dose of Spirolox on each side of the pin is one of the most popular for high-performance and racing engines.

Pin locks, which Spirolox are a type of, are necessary on pistons with full-floating wrist pins. With this design, the pin pivots freely within the little end of the connecting rod and the two pin bosses on the piston. The pin must be held in check between the pin bosses to keep it from shifting around and scratching the cylinder wall.           

Here are the three types of wire wrist-pin locks; from left, Tru Arc or snap ring, round-wire clips and a Spirolox, which is sometime called a spiral retaining ring. There are different styles of the round-wire clip, often called a circlip. Note the tang on the upper style to help with installation.

Spirolox are preferred by many engine builders due to their low cost and very effective operation. They’re heat treated, hardened and available in two sizes.

On the downside, Spirolox have sharp edges and there is a learning curve on installing them properly and quickly. High-performance applications usually require two Spirolox on each side of the wrist pin, which doubles the installation time. On the upside, when an engine builder develops a personal style for installing the clips, the job goes very quickly.

Engine builders have used dental tools, jeweler’s screwdrivers and other tricks to speed up the process. Perhaps the simplest method relies on fingers and small screwdriver, as demonstrated by John Himley of CNC Motorsports in Brookings, South Dakota. It took Himley less than 10 minutes to attach dual Sprilox on each side of eight Diamond pistons once all the components were prepped and organized in the assembly room.

Part of the preparation includes checking the retaining grooves to make sure they're clean and free of grit or metal flashings. Also, make sure you are aware of the proper orientation of the piston and rod. You don’t want to pull them all apart after realizing the rod chamfer doesn’t face the fillet radius on the crankshaft when the piston is installed into the cylinder, or that a valve relief is in the wrong place!

Follow along for more tips and tricks on using Spirolox with Diamond pistons. And a final note wrist-pin locks are inexpensive and it is always advisable to replace them during a rebuild! 

It helps to pull the Spirolox apart slightly in preparation for installation. Note all the reciprocating components are numbered and organized. This is a good time to ensure that you have 32 Spirolox, four for each piston.
Two Spirolox are installed on one side of the piston before attaching to the wrist pin and rod. Here’s a closeup of the starting point. Himley uses a forefinger to keep the Spirolox spread apart while he starts the leading edge of the clip in the groove. Note the notch just to the right of the Spirolox leading edge. This is useful for helping dig out the wire when removing the Spirolox.
The small screwdriver helps push the wire lock down into the retaining groove as Himley “walks” around the hole. Avoid scratching the piston with a screwdriver. A deep ding can lead to a stress riser.
The final step is to ensure that the Spirolox is completely in the groove.
Repeat the routine for the second Spirolox on the first side of the piston.
Prep the connecting rod by applying a dab of engine assembly lube to the pin hole.
Apply assembly to the pin bores on the piston. Position the little end of the connecting rod between the pin bores and slide the wrist pin into place. The Spirolox on the other side will keep the wrist pin in position.
Again, here’s a closeup of starting the leading edge of the Spirolox into the groove.
Walk the lock into the groove with a firm and steady hand.
Make sure the lock is completely flat and bottomed out against the retaining groove before starting the final lock for each piston. Use a small screwdriver or dental pick to carefully dig out the top coil wire of the Spirolox, then walk the remainder of the lock out of the retention groove. You don’t have to worry about damaging the lock since it shouldn’t be used again, but don’t be too aggressive that the piston groove or finish is scratched.

Topics: ENGINE BUILDS, featured, PISTONS 101, Tech

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Written by Mike Magda

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