This article details installing floating pistons onto floating rods, using the Spiro-loc type spring clips.
You should first thoroughly clean your parts in solvent and then dry them with compressed air. If you are going to have your parts balanced at the machine shop, do not assemble your rods and pistons until after the machinist has completed his work.
Examine the large end of the rods. You will find that one side of the bearing surface has a taper to it. This taper should always face the un-finished portion of the throw of the crank. The tapered end should never be butted up against another rod end. On a SBF, the left hand cylinders (1-4) the taper will be aligned with the front of the crank journal (engine front.) For cylinders 5-8, the taper will be aligned with the rear of the crank journal (engine rear.) Do not get this messed up!!!
If you are working with used rods, the original rod location may have been marked by the disassembler. It is a good idea to permanently mark the rod before removing it from the crank.
Now examine the pistons. Some piston tops (primarily factory types) will have a witness mark that signifies which side of the piston that should face the front of the motor. Look to the right of the picture below:
Aftermarket type pistons normally do not have such marks. So how do you determine which way the piston is to be installed? On a SBF, the piston valve reliefs will always be orientated toward the top of the motor, nearest the lifter valley.
Here is how the pistons would be oriented in relationship to the crankshaft:
The trick to installing the Spiro-loc clips is to pull the ends of the clip apart so that the clip resembles a spring and does not try to collapse back on itself. It if stays separated around ¼”, that is about right.
Now put one of the ends of the Spiro-loc into the piston pin groove. Next take a small common screwdriver and locate it 180 degrees from the inserted end. Carefully push that side of the spring into the groove, without disturbing the end that has already been installed. Carefully slide the screwdriver slightly away from the portion that you have just inserted, but continue to maintain pressure on the clip. Again, push more of the clip in to the groove. Continue working around the clip until it is fully in the groove.
Some pistons, like the Probe’s shown in these pictures, use 2 Spiro-locs on each side.
Once you have the Spiro-loc(s) installed on one side of the piston, then it is time to install the piston pin. Lightly oil the pin, the small end of the rod, and the pin retaining holes in the piston.
Next take the pin and partially insert it into the side of the piston which does not yet have a Spiro-loc installed. It should be a tight fit and yet easily done with you hands once you have it aligned. Do not fully install the pin at this time.
Now it is time to install the rod onto the piston. Orient the rod properly into the piston (as detailed above) and carefully push the pin through the whole assembly until it is full inserted in the piston.
You will now need to install the Spiro-locs on this side too. Before you do, carefully examine the piston and rod orientation. You will not want to unexpectantly remove the clips should the parts be installed improperly. Once installed, you should be able to rotate the rod freely in the piston, and you should be able to slide the rod side to side with no effort.
Once satisfied, move on to the next piston.
An old piston box is a handy way to keep your pistons and rods in order.
In conclusion, assembling pistons to floating rods is not a difficult task and is one that you can easily accomplish at home with no special tools. This is one area where the home engine builder can save some money by doing it himself.
Today
