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Old 12-06-2017, 10:41 PM   #1
rawdirt
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Default odd shiny "eyebrows" on piston

2008 outback with ej253 2.5 and 85k on engine. I pulled the motor to fix a head gasket and this is what I found.

There was also some oil in the intake air box thing. I am not sure if it is valve strike or not. It almost looks sand blasted. The pistons have the pits from the factory casting right?




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Old 12-07-2017, 07:31 AM   #2
Elbert Bass
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Generally on internal head gasket leaks (cooling jacket to combustion chamber) any place carbon is cleaned of like that is an indication of the source of the leak. What has happened is the carbon has been "steam cleaned" by water seeping into the combustion chamber.
That is an unusual pattern - usually the cleaned area is is more of a crescent on the piston next to the cylinder wall. Look closely at your head gasket seal and see if you can see flares at those two spots that look like coolant/combustion gas has been passing across the mating surface.
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Old 12-07-2017, 02:20 PM   #3
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I see a similar pattern on the next piston. Looks like where fuel enters the cylinder and has dissolved the carbon. Just a different type of cleaning.
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Old 12-09-2017, 08:02 AM   #4
Elbert Bass
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Quote:
Originally Posted by yarrgh View Post
I see a similar pattern on the next piston. Looks like where fuel enters the cylinder and has dissolved the carbon. Just a different type of cleaning.
You know, that carbon does look thin for the mileage... Wonder if he Seafoamed or used some other induction cleaner? For fuel to do that it would have to be a rich enough that there was too much fuel to vaporize.
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Old 12-09-2017, 10:36 AM   #5
Charlie-III
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The grain in the piston looks too coarse for casting marks. If I had to guess, it actually looks like detonation, possibly due to tight intake valve clearances creating hot spots.

The marks do NOT look like a valve strike.
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Old 12-09-2017, 08:04 PM   #6
Elbert Bass
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Quote:
Originally Posted by Charlie-III View Post
The grain in the piston looks too coarse for casting marks. If I had to guess, it actually looks like detonation, possibly due to tight intake valve clearances creating hot spots.

The marks do NOT look like a valve strike.
Actually in that model engine they are cast grainy in that spot - note how smooth the raised edge of the crown is right next to it in the last photo. Valve strikes leave marks in the recesses.
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Old 12-10-2017, 10:46 PM   #7
IanT-EJ22
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Quote:
Originally Posted by Elbert Bass View Post
Actually in that model engine they are cast grainy in that spot - note how smooth the raised edge of the crown is right next to it in the last photo. Valve strikes leave marks in the recesses.
Probably abnormally hot spots due to more exposed surface area of the grainy casting and also likelihood of fuel building up on this area?
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Old 12-11-2017, 06:10 PM   #8
Charlie-III
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Quote:
Originally Posted by Elbert Bass View Post
Actually in that model engine they are cast grainy in that spot - note how smooth the raised edge of the crown is right next to it in the last photo. Valve strikes leave marks in the recesses.
Not arguing, just looks really grainy unless it was a "metal shop project" where you poured molten aluminum into a crude sand mold.
Yes, valve strike would be in the recess, totally agree.

Quote:
Originally Posted by IanT-EJ22 View Post
Probably abnormally hot spots due to more exposed surface area of the grainy casting and also likelihood of fuel building up on this area?
Not likely unless the cylinder is not firing. Just compression and piston top heat should ignite excess fuel, or, you would likely have misfire codes.
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Old 12-15-2017, 01:45 PM   #9
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Default its back together

machine shop said the valve guide seals were leaking but otherwise the heads were in good shape. I forgot to ask how much he took off when he decked the heads.

I got it running last night and the engine is way smoother and more responsive.


However, there is valve noise. It seems normal at idle but loud during acceleration. It could be that I am over sensitive

but there is also a engine light on with code O2 bank 1 sensor 1 error code along with the cruise control flashing. I am going to reset the connectors tonight. Is that the one by the passenger exhaust that you can see by looking down? I haven't had a chance to look to see if there was one off the driver side head that I forgot to connect or something.
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Old 12-15-2017, 04:04 PM   #10
Charlie-III
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Great to hear, keep us posted.

As to B1 Sx, if a flat or V engine, bank 1 usually refers to the side with plug/cylinder 1, thus, on a Subaru, yes, bank 1 is passengers side.
On an inline engine, bank 1 is the end of the engine with cylinder 1, some inline engines split the exhaust manifold to front and back....sheesh.......
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Old 12-15-2017, 09:27 PM   #11
rawdirt
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The code was P0134. I'll probably get back to work on it on Sunday. Probably start with re-seating the connection.
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Old 12-30-2017, 03:20 PM   #12
rawdirt
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Default code fixed, intermittent valve noise still there

turns out that the front o2 sensor was not plugged in all the way. I drove it to work and back for a week and the noise is not getting any better. No engine codes are detected now.

I spent a lot of time listening to it and comparing valve noise to my neighbor's outback:

(1) I sounds like it might be one valve or maybe two
(2) I think it is coming from the driver side.
(3) it only happens under certain loads, engine speeds, and conditions.

So given (3), it idles smoothly, runs reasonably well, no codes, and it happens only at certain speeds:
(a) I don't think it is the timing belt alignment
(b) I am wondering if it is an intake valve controlled by the AVCS
(c) which has me wondering if I got the AVCS barrels and springs all back to ether correctly.


I am checking the valve clearances and inspect that what I can of the AVCS barrels/springs of the driver side first. At present, I can't quite get the valve cover out and might remove the fuel rail next to see if can clear that. .
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Old 12-30-2017, 06:07 PM   #13
rawdirt
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Default valve clearances were fine.... but

one of the AVCS springs was off of its post. Happy I found it.

Now I am trying to figure if I missed it (I specifically checked them but could have been high on lacquer thinner fumes), if i did not get it all the way onto the post and it jumped, of if it jumped off its post due to another issue.

now that I have thought about it for a few minutes, I should double check that the other side of the spring is on its tab.
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