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

Now the crank and rod assembly is ready to be put into the cases.  The plastic caps are to prevent the cylinder walls from being scratched during this part of the assembly process.

Next, the ring end gaps are set.  This tool is used to push the compression rings a consistent distance into each bore.

Next feeler gauges are used to measure the gap. IAG uses oversized rings and handsets the gaps for each bore.  This gives the best seal.

All of the compression rings are put in place and measured.

This tool helps to precisely grind the ring end gaps to the perfect dimensions.

The ring is held by a fixture and the ends can be ground with a small wheel. After grinding the ends are lightly stoned to remove any burrs.


  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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