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

The rod bolts are hand started into the rods.

The second set of rods is installed.

The rods are lightly torqued down with an electric impact. The crank is flipped over and the other two rods are installed.

Next, the crank and rods are placed into this bespoke assembly fixture so they can be held firmly without damage while the rod bolts are finally tightened.  IAG uses bolt stretch to reach the correct torque. The amount of bolt stretch is measured with the special micrometer from ARP.

When the bolts are tightened they are marked with a confirmation mark.  This way no bolts will be forgotten.

All the rod bolts are tightened via this method.


  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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