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Old 09-04-2005, 01:11 PM   #1
Mike1967
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Default blackened pistons - PICS ADDED

My pistons have a coating of what appears to be burnt oil. (I got my engine very hot)

Is it necessary to clean this material off of the top of the pistons. It appears to be several mils thick.

I am concerned with agressive cleaning of the heads because of potential of scraping off / scoring of the aluminum surface

Last edited by Mike1967; 09-04-2005 at 05:16 PM. Reason: Pictures Added
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Old 09-04-2005, 01:14 PM   #2
Rokkit
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I would have to say you would need to resurfce the pistions... however... if you got the engine that hot, i would be worried about the block warping...
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Old 09-04-2005, 04:41 PM   #3
Mike1967
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Quote:
Originally Posted by Rokkit
I would have to say you would need to resurfce the pistions... however... if you got the engine that hot, i would be worried about the block warping...
One head is warped to .005" in one area.

I ran this engine for 10 miles with zero coolant. What are the chances that this block is warped ?
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Old 09-04-2005, 02:47 PM   #4
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Clean it off! If it's packed on that thick, it's only raising the compression ratio. Also, get your block deck and your heads resurfaced if it's that bad.
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Old 09-04-2005, 04:35 PM   #5
Mike1967
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Quote:
Originally Posted by El_Kameleon_G
Clean it off! If it's packed on that thick, it's only raising the compression ratio. Also, get your block deck and your heads resurfaced if it's that bad.
Glad I asked !

I was already planning on taking my heads in for resurfacing. I will also take the block in for resurfacing.

Is the block deck the surface area around the piston wells ?
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Old 09-04-2005, 04:40 PM   #6
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Quote:
Originally Posted by El_Kameleon_G
Clean it off! If it's packed on that thick, it's only raising the compression ratio. Also, get your block deck and your heads resurfaced if it's that bad.

What are your recommendations for cleaning ? I don't want to get in there and start scoring the piston surfaces and well walls.

Is there a chemical and scrubbing device that you recommend ?
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Old 09-04-2005, 05:08 PM   #7
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Last edited by Mike1967; 09-04-2005 at 05:15 PM.
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Old 09-04-2005, 05:14 PM   #8
Hayes
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Subaru coats and bonds the piston skirt with moly to reduse friction. DO NOT remove it.
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Old 09-04-2005, 05:17 PM   #9
Mike1967
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Quote:
Originally Posted by Hayes
Subaru coats and bonds the piston skirt with moly to reduse friction. DO NOT remove it.
After going back and re-inspecting I see that the skirt looks to be clean. It is the piston heads themselves that are coated with the burnt "residue"
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Old 09-05-2005, 02:54 PM   #10
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carbon build up is normal, scrape it off without chunking the aluminum and you're golden! scotch brite pad is good!
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Old 09-05-2005, 02:59 PM   #11
Mike1967
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Quote:
Originally Posted by kheff46
carbon build up is normal, scrape it off without chunking the aluminum and you're golden! scotch brite pad is good!
THANKS !
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Old 09-05-2005, 03:47 PM   #12
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I have a 2.5 that warped both heads .008, beyond machine. the short block survived. amazing imo but may give you hope. the carbon comes off easy with the wire brush. you can soften it with deep creep, from an autoparts store. the carbon is from many miles, not the overheating. if anything the overheating blasted some of it out before you tore it down. you have a poor burn situation. crappy/too high octane gas maybe, or tune issues maybe. don't just get the block resurfaced, check it. only resurface things if they're out of spec
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Old 09-05-2005, 04:00 PM   #13
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Quote:
Originally Posted by 00Maddog
I have a 2.5 that warped both heads .008, beyond machine. the short block survived. amazing imo but may give you hope. the carbon comes off easy with the wire brush. you can soften it with deep creep, from an autoparts store. the carbon is from many miles, not the overheating. if anything the overheating blasted some of it out before you tore it down. you have a poor burn situation. crappy/too high octane gas maybe, or tune issues maybe. don't just get the block resurfaced, check it. only resurface things if they're out of spec
Maddog,

I took a straight edge and feeler gauges to both heads.

Found several areas in the .003 to .004" range. (Assuming that my measurement method was correct). The area that I suspected the head gasket being blown was measuring at .005

I have a local shop that will mill both heads for $ 43.00.

They will also do a compression test for $ 53

Right now I am planning on

(1) Running compression test on heads
(2) Having heads resurfaced and cleaned
(3) replacing the head gaskets
(4) cleaning the carbon on the pistons myself
(5) replacing the CAM seals
(5) replacing the valve cover gaskets and grommets
(6) Re-using the exhaust gaskets...(Throttle Body and front to back exhaust) as they appear to be in good order.

(7) Slapping it all back together and hoping that my over heating problem has been solved !
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Old 09-06-2005, 01:16 AM   #14
ballitch
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if you scrub, use something soft like a brillo pad as mentioned, or brass wire brush, anything softer than aluminum, and it would help to use some sort of solvent to loosen things up a bit.

~Josh~
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Old 09-06-2005, 11:38 AM   #15
Matt Monson
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I actually you liquid gasket remover to dissolve the crap on pistons like that. Let it sit for 5 minutes, scrub with a brass brush. and repeat.

Your heads are at the limit. .005 is the max you can shave off those heads and stay within spec. If you would prefer to get a replacement head, shoot me a PM. I have a pair. One head has a couple of bent valves, but they only have 20k mi on them and are not warped. The only thing I would want from your heads is the cams since I bought these heads strictly to have the cams reground.
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Old 09-06-2005, 02:39 PM   #16
Mike1967
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Quote:
Originally Posted by Matt Monson
I actually you liquid gasket remover to dissolve the crap on pistons like that. Let it sit for 5 minutes, scrub with a brass brush. and repeat.

Your heads are at the limit. .005 is the max you can shave off those heads and stay within spec. If you would prefer to get a replacement head, shoot me a PM. I have a pair. One head has a couple of bent valves, but they only have 20k mi on them and are not warped. The only thing I would want from your heads is the cams since I bought these heads strictly to have the cams reground.
Matt

They had to shave .009 off the heads. They are telling me that a difference of .004 should not make any difference. They are head experts...but they are not Subaru experts.

What is the potential issue that could result from using my heads ?

Also, I would really like to know your opinion on whether I should have the block decks resurfaced as well.

I have received differing opinions on this question. Currently I am leaning towards not resurfacing the block decks.
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