Metal knock
 

{See below for the fix}

[Background]
I have a challenge for the group that is driving me nuts.

2013 Automatic Scion FRS with KW C30 SC and other accompanied upgrades. I developed a metal knocking noise that can be definitively heard with a stethoscope on the passenger head. It's erratic in rhythm.

{I also had issues stalling on startup that I didn't know were related until I found the fix below}

So I decided to have my engine rebuilt - chose Outfront Motorsports as they are Subaru rebuilding experts with FRS experience.

They pulled the engine and while they found some scoring on the bearings - they didn't find anything in the heads that would be causing the knocking.

I had the whole thing rebuilt - forged pistons (custom stock compression CP) and rods (turbo tuff), new stock bearings, machined heads, new Ferrea valves, new double springs, titanium retainers and even new rockers just to be safe.

I don't drive the car all that much and have only put 2-3k miles on the new engine with no track time and a few oils changes for good measure.

Well - the damn knock is still there...

Hate to pay to pull the engine again as they didn't find anything the first time.

Even more so, hate to buy new heads as I've already paid for mine to have all of the upgrades.

Any thoughts?

https://vimeo.com/172263792


[Confirmed Fix!]
Automatics have a special vacuum pump that is attached to the cam (instead of just a cover) on the passenger rear of the engine. This pump had gone bad causing stalling issues AND the metal knocking. Since it is attached to the cam, it was masking itself as potential rocker noise. Pump, O-ring and gasket maker was $170. Install was 20 minutes taking my sweat time. Fix is confirmed! She purrs like a kitten with no stalls or clanking noises! I've been chasing this over a year and have spent $12k in upgrades trying to get rid of it. Hopefully others can shortcut this :)

I um, well, okay. I guess I'll be the first to ask the question.

Why did you pay all that money to have your engine rebuilt without diagnosing the problem?

Dang shame you had all that work done and still have a unidentified sound ...... :(

If the "metal knocking noise" is what I hear as a "ticking", I don't think it's related directly to the engine running (innards of the engine).

I'd guess it something else ..... like something lose ...... sort of flopping around ...... :iono:

If it doesn't get any louder, I wouldn't worry about it.


humfrz

Hey Xan, in hope to have it resolved and it was a great time to build it up anyways. Pushing double the HP always had me worried about the internals.

Humfrz - it does sound like something lose and rattling but I can't find anything external that could be causing it...hmmm

That's odd. Good recording. It sounds like something external but if you're sure you hear it on the head... hmmm...

hmmm.......I suggest you listen/look closely around the serpentine belt ...... maybe one of those covers are lose ..... ??


humfrz

I have a very similar sound on the passanger side too. (stock 2013 BRZ) .Its a random knock like yours that is most noticble if I turn the car off when it is hot, then restart 4 min later, and let it settle to idle without driving it. Someone else had it diagnosed at the dealer and they wound it was a rattle from the rocker arms. When he had the rocker arms replaced, the sound was gone. I have noticed the sound is much less since I change from 0W-20 to 5W30 for the summer. Did they rebuild the upper engine rocker arms with you??

Yeah, had the rockers replaced thinking that could be the issue (even though nothing seemed wrong with the previous ones). I'll try the oil - I'm running 0w20 redline but I just purchased some motul 5w40 that was recommended for me by PRT.

I'm thinking rocker as well now that I found this post: http://www.ft86club.com/forums/showthread.php?t=81496

Maybe the new rockers were also crap...

yup, that was the guy I was referring to and his video is closer to the sound that I have. Interesting that you replaced the rockers and still have the sound, unlike that guy.

Gotcha, if you were going to build it up anyway then that makes sense.

Yeah, it sounds external on that recording, that's what's really stumping me.

There's a local with a similar sound. Has had the car since 2012, been boosted since 2013, still running strong.....

It sounds like something is loose in the rocker arm area. He has never taken the engine apart or worries too much about it.

Holy crap people - just stumbled on what could be the fix. Two more pieces to the puzzle - I have an Automatic and I'm also having stalling issues that my tuner can't figure out.

I found out that Automatics have a vacuum pump on the passenger side cam cover that feeds the brake booster. Not only does this bad vacuum pump sound like bad rockers in the head, it also causes idle stalling issues.

$160 pump ordered which I will install on Wed or Thur when I get it. Best news of the day (hopefully)!

Thanks for the update.

Please let us know if that was the problem.....:)


humfrz