Project GD Subaru STI, Building the Engine Part Four: Assembling the Short Block With IAG.

Assembly lube is also applied to the pin boss of the piston.  One of the pin retaining circlips is also installed at this point.

The rings are compressed with a special tool and the piston is inserted into the bore.

The piston is pushed down and rotated until it lines up with the small end of the rod and this assembly port.

The piston pin is installed through this port.

A special tool is used to put the pin all the way in and seat it.

Next, the other pin retaining circlip is installed.


  1. Is the situation with assembly of the piston pins the same for 6-cylinder boxer engines? I can’t imagine how you would get the pin into the center cylinders.

    Also, there must be an obvious reason why the block can’t be assembled with the pistons, but I am kinda spacing it. For the Boxer builders, how does ease of assembly compare to straight engines?

    Now, I am really curious as to how Porsche assembled their flat-12s. Going to have to do some Googling, I guess.

    1. At least the older air cooled Porsche stuff is different because the cylinders come off the block individually.

      1. I forgot about the air cooling. I am sure that the same situation applies for the big 12 as Dan mentioned.

        I did find a decent build video for the Water Cooled Porsche Flat-6 but it looks exactly as hard as I thought it would be. Knowing Porsche, they probably have a special assembly tool at the factory for getting that pin in more easily. Or maybe some special jig?

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