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2005 Outback 2.5i - 5 speed - 191K
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276 Posts
Discussion Starter · #1 ·
With the passenger side head off I was able to examine the passenger side pistons (at least the tops of them).

They are fairly black. The guy I bought it from replaced the main bearings on the crank but didn't do much else inside the engine. He left the old pistons.

The cylinders look fantastic for 190,000 miles. There is still clear cross hatch pattern. That seems pretty good to me. I am concerned about the carbon buildup on the bottom edges in the photos.

Any ideas about this? Cause? Remedy?
 

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2005 OBXT Limited, VF37, STI intake, 5MT
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1,610 Posts
Higher mileage, gummed-up oil rings, low-load running for long periods of time (cruising at 45mph for hours on end). Could be many factors, but those don't look too bad, assuming they weren't shiny-new after the rebuild.

Draw the piston down to the bottom of the bore and check on the upper and lower walls of the cylinder for scoring. This usually starts on higher mileage cars as the piston skirt coating wears-down and gouges the walls. If you find these, the only "fix" is to either bore-over or find another short block.
 

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2010 2.5 CVT Limited
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2,112 Posts
I would expect the buildup on the lower half of the cylinders is due to gravity. Oil in the cylinder would migrate to the lower half when the engine is at rest. Upon startup, it gets burned. I'd suggest to simply clean it out and not worry about it. It is not a large accumulation nor does it appear in any one cylinder more than another.
 

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OBW H6 VDC, Tribeca, XT6
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12,385 Posts
Looks normal or common to me. I'd ignore that.

you might consider reringing it but we have no idea why it's apart. there's a chance of oil blow by from this engine in the short term.

what is more alarming is the previously replaced crank bearings and now the engine is all apart again. splitting a subaru block is not a low risk endeavor. there's a story or three somewhere in there...
 

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2005 18psi supercharged U5 Outback w/207k+ miles
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846 Posts
cthies you seem like an adventurous dude. i would yank those out and put in STI rods and pistons... then you will be all ready for the supercharger you will want to put on right after you get finished putting it all back together ha ha.....
 

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2005 Outback 2.5i - 5 speed - 191K
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276 Posts
Discussion Starter · #6 ·
Im simply replacing one of the head gaskets. I have another thread about the engine being taken out for oil leaks. Been a long journey with this car.
 

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. . Current daily driver is a 2017 Outback.
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51 Posts
. . Rings ?

. . He split the cases and didn't put new rings back in with 190k? ?
. . Why did he replace the bearings? ? Rod noise? ?
. . Doesn't sound like some I would put in one of my cars. .
 

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2005 Outback 2.5i - 5 speed - 191K
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276 Posts
Discussion Starter · #10 ·
. . He split the cases and didn't put new rings back in with 190k? ?
. . Why did he replace the bearings? ? Rod noise? ?
. . Doesn't sound like some I would put in one of my cars. .
Engine came with the car. Compression is dead on with spec

The engine had already been rebuilt and something went wrong with the rear crank main bearing. He replaced the crank bearings and she actually runs fantastic

The oil leak was bugging me so I dug into it. Turned out to be more than I thought. I replaced alot of worn parts that I came across.
 

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2005 Outback 2.5i - 5 speed - 191K
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276 Posts
Discussion Starter · #11 ·
Decided to take a wire brush to the piston tops. I was able to rotate the crank and the piston skirts look great and the cross hatch pattern extends the length of the entire piston bore. The other side had LESS oil accumulated on the bottom edge of the piston tops. I cleaned it all off.

I did see, upon close examination, that the driver side front piston had TWO gouges where it was struck by a valve. This has to have occurred prior to my purchase of the vehicle.

Piston tops are clean now and the heads are ready to go back on.
 

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