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Old 12-05-2012, 08:37 PM   #1
Monkey_Boy
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Default 2005 Legacy--Started making this noise


What is this sound?
+ It's a loud tap-tap-tap-tap
+ It is tied to engine revs
+ It started "suddenly" and did not grow over time
+ I had to drive it a couple of blocks to get it home.

Things I know:
+ It has plenty of oil--changed by the dealer about 2200 miles ago
+ The engine is warm
+ The car has ~170k miles, but the engine has ~50k
+ It is not leaking any fluids
+ No CEL lights or the like
+ Head gaskets were changed out about 20k ago

The car is a 2005 Legacy estate. 2.5l NA MT. It does not sound like the vaunted Subaru "piston slap". Could it be the tensioner?
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Old 12-09-2012, 11:44 PM   #2
Charlie-III
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Really sounds like a bad rod bearing.......You should be getting a "knock CEL" (P0325?) with that noise.
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Old 12-10-2012, 08:52 AM   #3
Monkey_Boy
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We'll know soon enough. It's in the shop now with the heads on that side taken off. There was no CEL, and no apparent damage to the cylinder, valves or pistons on that side. Whatever it is, it is very LOUD.

And very frustrating. The motor has ~52k miles on it....grrrr.
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Old 12-10-2012, 06:15 PM   #4
Elbert Bass
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Hard to tell in video - can't get any directional perception. I've heard loose valve tappet screws make that much racket. The noise is definitely at half the speed of the crank. If it is loudest and most distinct when standing by the fender than in the front it's a good chance it is valve train related.
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Old 12-14-2012, 09:16 AM   #5
Monkey_Boy
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I know more about it now. They scoped the engine and discovered that the wrist pin on the front passenger piston had "worked loose" somehow and gouged the cylinder wall. That put the whole thing out of alignment and is making the piston bang like that.

That is the kind of thing put in place when the engine is manufactured, and never touched again. I am not happy with that lack of quality, and will be having a few works with the engine builders.
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Old 12-14-2012, 08:43 PM   #6
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Quote:
Originally Posted by Monkey_Boy View Post
I know more about it now. They scoped the engine and discovered that the wrist pin on the front passenger piston had "worked loose" somehow and gouged the cylinder wall. That put the whole thing out of alignment and is making the piston bang like that.

That is the kind of thing put in place when the engine is manufactured, and never touched again. I am not happy with that lack of quality, and will be having a few works with the engine builders.
There wrist pin is captured by a circlip on each end. The circlip sits in a groove on the piston. Usually a botched clip install shows itself immediately. I think I have heard of a clip failing or coming loose after a few thousand miles when a used one was re installed on a rebuild but I'm kinda fuzzy on the details of why the clip came apart.
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Old 12-14-2012, 10:21 PM   #7
Monkey_Boy
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I do not know, either. The local shop and a tech from the Subaru dealer took a look--that's what they see. The good news is that the engine builders are stepping up to make it right. They are shipping out a new block and parts, and the local dealer is going to put it all back together.

That is a sound I hope I never hear from an engine again.
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Old 12-15-2012, 06:26 AM   #8
Eyedoc Orlando
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That's really scary man -- good luck with the new engine! At least it's a car, and it's repairable Merry Xmas
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Old 12-15-2012, 01:55 PM   #9
Brianteck20
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sounds like a rod knock.
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Old 12-15-2012, 07:30 PM   #10
Charlie-III
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Quote:
Originally Posted by Monkey_Boy View Post
I know more about it now. They scoped the engine and discovered that the wrist pin on the front passenger piston had "worked loose" somehow and gouged the cylinder wall. That put the whole thing out of alignment and is making the piston bang like that.

That is the kind of thing put in place when the engine is manufactured, and never touched again. I am not happy with that lack of quality, and will be having a few works with the engine builders.
Hmmmm.......not sure how a missing wrist-pin circlip would make that noise.

While is could damage the cylinder wall, I believe all Suby engines have enough wrist-pin/piston overlap so that the wrist-pin always has 3 points of contact.
This would preclude most noises that sound like a bad rod/crank bearing.

But hey, if the engine builder is going to replace the SB, who really cares?? (Other than you while the car is down)??
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Old 12-15-2012, 10:45 PM   #11
Elbert Bass
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Quote:
Originally Posted by Charlie-III View Post
Hmmmm.......not sure how a missing wrist-pin circlip would make that noise.

While is could damage the cylinder wall, I believe all Suby engines have enough wrist-pin/piston overlap so that the wrist-pin always has 3 points of contact.
This would preclude most noises that sound like a bad rod/crank bearing.

But hey, if the engine builder is going to replace the SB, who really cares?? (Other than you while the car is down)??
Like I said it's hard to tell in video, but then I am only used to diagnosing them in person.
I have never seen one do this but am told that the wrist pin clips can pop out. Apparently what happens is the pin slides out and starts eating a groove in the cylinder bore.
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Old 12-16-2012, 10:16 PM   #12
Monkey_Boy
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Quote:
Originally Posted by Elbert Bass View Post
Like I said it's hard to tell in video, but then I am only used to diagnosing them in person.
I have never seen one do this but am told that the wrist pin clips can pop out. Apparently what happens is the pin slides out and starts eating a groove in the cylinder bore.

That describes what they see exactly. I have a photo, but it's too low-res to be of much use--much more clear on the boroscope screen itself. The scariest part for me is that we drove that car to West Virginia (from Western Missouri) over Thanksgiving. If it had done this on the trip, we'd have been stranded somewhere in the wilds of Indiana instead of me only having to take it a couple of blocks to the station.
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Old 12-18-2012, 06:03 PM   #13
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The engine is on a Fed-ex truck heading for Colorado to be rebuilt with a new short block. Had a little back-and-forth with the engine builders on who is paying for what, and some changes in plan (they decided that they wanted the whole thing back to rebuild it themselves) but they have been pretty good to work with so far.

Going to look at the clutch/flywheel stuff now since the engine is out, and hoping to have it my much-loved Legacy back on the road before the end of the year!
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