TEXT FPO - Driving Sports TV

2007 LEGACY GT PROJECT
36. Our fresh short block from Subaru. You can buy a newly built
STI short block straight from any Subaru parts department. Since
we are using forged pistons, we will have to remove the stock
slugs from this block.
39. Pull the wrist pin free and continue cranking the engine over.
The rod will push the piston out.
42. The ring in the bore. This is how you will check the gap. Once
the initial measurement is taken (it should be very tight) grind a
bit of material off, re-install the ring and re-measure. This is a
long and tedious process.
45. Of course there is a proper tool for installing rings, but if you
are careful you can slide the rings on with your hands. Do the
secondary first, then the top ring. Also, install a new retaining clip
into the inboard side of the piston. Once the piston is in the bore,
there is no way to get to the inside of the piston. If you forget this
clip and start the car, the wristpin will slide out and bad things
will happen.
58 July 2008
37. To remove the pistons, first remove these inspection covers
with a 17mm star drive in the front. You’ll need an impact driver on
the rear plates. Install the crank bolt and rotate the engine over with
a 22mm socket so that the wrist pins line up with the inspection
holes. Remove the wrist pin retaining clips with needle nose pliers.
40. With the stock pistons out, push the forged units into place
to check the piston to cylinder wall clearance.
43. A ring “gapper.” This is the proper tool for grinding off ring
material to get the proper gap. Take your time and don’t grind
too much off in a fit of trying to get done faster. Doing so will
remove too much material; then you will have to get a new ring
and start over.
46. Installing the pistons. Lubricate the rings and pistons with
fresh motor oil. This will make everything easier to work with, will
save parts from damage, and reduce bore scoring. Note: Most
pistons have markings on them, which tell you which side of the
piston is up, especially with offset wristpin-type pistons. Installing
the piston incorrectly can result in skirt slap and excessive
noise, requiring you to completely take the engine apart for a
do-over.
38. Using a long screwdriver, push the wrist pin out from the
opposite side of the engine through the inspection hole (there are
inspection holes on both sides of the engine).
41. Piston ring gaps: Your piston rings will grow when they get
hot, so we will have to set a proper gap so that they don’t bind
or let excessive oil by on cold-start. To do this, push the rings
into the bore with a piston to make sure they are square with the
bore all the way around. Then, use a feeler gauge to check the
gap. The top ring on our engine was gapped to .22-inches and
the secondary gapped to .18-inches. The oil scraper rings do not
have to be gapped.
44. Your pistons should have five rings each; the top, secondary
and three scraper rings. The top and secondary are self-explanatory.
The scrapers have a top, middle and bottom. Slide the
middle “sectioned” ring on first. Then the bottom ring. The top
ring will have a notched end on one side. Slide this one into one
of the oil ports on the piston (small machined holes). This will
keep the oil rings from rotating around on the piston.
47. To install the pistons into the bore, you must first compress
the rings with a ring compressor. This is a specialty tool that you
can get at most auto parts stores and Sears.