Here you see one of our borescope units illustrating the piston and connecting rod are aligned properly and ready for insertion of the wrist pin and retaining clip. If you have trouble identifying what is what in the image, you can see the connecting rod pin end bushing (a goldish color) with the two oil holes for pin oiling.
Who said engine Building wasn't surgery! This is literally all that can be done to visually inspect the work area deep within the M96 engine while assembling the #6 piston assembly onto the connecting rod.
Having aligned the piston with the connecting rod and checking my work with the borescope here I am inserting the wrist pin into the access port that leads into the #6 cylinder where it will marry the piston and connecting rod forever. This is done with yet another special tool...
Here the clip that retains the wrist pin into the piston. It is loaded into the end of another special tool that is designed to insert it into the piston. This tool is fed deep into the engine, where it must be inserted with extreme care into the piston to ensure it is seated properly and deep enough to drive the clip home. This is done with only the sense of feel and some measurements and index maks we have scribed onto our tools.
STOP!! This is what you DO NOT want to see! This retaining clip was inserted into the piston without the tool being seated properly and deeply enough into the piston! It will not retain the wrist pin, as it is not inserted into the groove in the piston! If left alone this engine would have failed within the first 30 seconds that it ran! Once the clip dislodges itself, the wrist pin would slide out, ruining the block, piston, rod, and likely the rest of the engine!
When this horrible instance occurs there is no way to remove the clip without it flying wildly inside the crankcase, requiring tear down to allow for removal of the clip. When this occurs, you are officially screwed!
Flashlights, mirrors, borescope, and tools with depth index are my friends during these processes...
This is what a properly seated wrist pin retaining clip looks like through the borescope. The components are dyed different colors before assembly so we can differentiate between them with the borescope. This clip installation is textbook perfect!
Wise assemblers will etch all their tools and use a pointer to orient the tools for proper clip insertion. This ensures that both the proper depth and clip orientation occur simultaneously. If these marks do not align the tool is not deep enough into the piston and the tool is not rotated correctly to insert the clip. Each and every bore size will have a different set of indices too!
No book or instructions will tell anyone to do these things. The Porsche assembly and tool instructions are worthless in this regard. It takes practice and common sense coupled to some Innovation to create these procedures. For the novice doing this for their first time, practicing many of these techniques prior to final assembly is a wise precaution.
Another shot of how we indexed the clip installation tool to ensure proper clip installation at each piston.
Cylinder #4 is a breeze to install the wrist pin and clip into place, since it's only 4" deep within the engine and most work can be done without the borescope. Once this piston is in, the work that takes all day to accomplish is behind us and it'll be smooth sailing until we set the cam timing.