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Discussion Starter #1
Hello
First thanks for all the info I have already gleaned from this forum!
Now the question...
I recently had a good mechanic replace the head gasket on our 1996 2.5 L legacy outback at 150,000 miles...I love this car!!
Since the head gasket replacement there is a loud knocking noice at initial COLD start up. After HG work mechanic used full synthetic oil. I just changed oil and used hi mileage synthetic blend. This defiantly helped the noise some. But it is still present at cold morning starts.
Initially I thought this was just a piston slap. However, after some research it sounds like a piston slap lasts for minutes. My noise only lasts for about 3 seconds after start up.
Please, WHAT IS THIS NOISE??
KNOCK KNOCK KNOCK KNOCK
 

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01 Outback H6 VDC, 97 GT wgn w/ ej22, 98 OBW w/ej22
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the 96 has HLAs, hydraulic lash adjusters for the valves. if these leak down it may take a bit to pump them up. this is particularly true on the ej22 engine.

i'm not 100% sure about the design on the ej25 since it uses ''buckets'' with the HLAs so i can't really speak to a fix.

in later years, 97 - 99, the ej25 used ''bucket and shim'' type valve lash adjusters.

it may be that the HLAs were dismantled, can't imagine why, during the head gasket job and that played a part.
 

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Discussion Starter #3
hmm. so if the noise IS coming from the HLA's, is this a problem? somthing to worry about? or just another noise common on a car with 150,000 miles?
THANKS
 

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my 2001 was a little more noisy than before the HG job by Subaru. They claimed they didn't adjust the valves at 65K that they were spec when they did the HG. By the time I sold it at 180K it had quieted down and ran great. Cold mornings it would thump a little shaking the car in a mild rythm - but that never seemed to cause any issues and after a few seconds it was smooth.

The old piston slap name has been used more or less to describe cold starts where the engine might shake the car a little in a different manner than the standard i4's.

Given the age of your car I wouldn't worry about it as long as its running fine when warm and everything else seems OK oil consumption - coolant is fine then keep running and don't worry about it.
 

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Discussion Starter #5
thanks Subbie salior.
ya, after the first 5 seconds, the engine quiets rite down and runs great. It does still lose a bit of oil, but not as bad as pre HG replacment.
I love this this old car!
 
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