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Old 02-01-2018, 05:11 PM   #1
AspirinWhite
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Default EJ207 Cold knock or piston slap?

I recently completed my version 7 EJ207 swap into my 03 WRX and it fired up with a noise that was similar to a engine knocking noise. However when the engine was warmed to temperature, the noise disappeared.

I've been looking up through a lot of threads and most of the answers leaned toward piston slap while a handful claimed it was rod knock.

I'm quite stumped about this problem and really paranoid if the engine I've purchased was bad from the start. I tuned the engine immediately via open source to eliminate the possibility of pinging/detonation due to crappy California 91 gas. The engine runs very strong but the cold knock doesn't seem to go away.

Any help would be great.

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Last edited by AspirinWhite; 02-04-2018 at 05:01 PM. Reason: video upload
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Old 02-01-2018, 06:16 PM   #2
danger1138
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You just said the noise goes away after it warms up. So essentially you have no issue.
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Old 02-01-2018, 06:45 PM   #3
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Quote:
Originally Posted by danger1138 View Post
You just said the noise goes away after it warms up. So essentially you have no issue.
So is it pretty normal make that noise when cold? I will post a vid of the sound once the car gets cold again
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Old 02-01-2018, 07:57 PM   #4
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Well,
For the most part yea; it is normal. Ive had a built motor that was pretty noisy, particularly when cold. But remember it was a built motor.

My stock ej251 on my 04 legacy wagon is also loud and has piston slap when cold. My oil levels are above the "F" mark btw too. So not a low oil scenario in my case.
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Old 02-01-2018, 08:02 PM   #5
AspirinWhite
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Quote:
Originally Posted by danger1138 View Post
Well,
For the most part yea; it is normal. Ive had a built motor that was pretty noisy, particularly when cold. But remember it was a built motor.

My stock ej251 on my 04 legacy wagon is also loud and has piston slap when cold. My oil levels are above the "F" mark btw too. So not a low oil scenario in my case.
I'm running with valvoline synthetic 10w30 and I religiously check for oil levels to make sure it's in the right level as well.
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Old 02-01-2018, 08:16 PM   #6
Cobrakai
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I'm in the same boat, my V7 swap is noticeably loud during cold starts but it quiets down at operating temperature.

It's a slapping/knocking sound only audible on reversing and taking off in first during cold engine conditions.

The car has been looked at by numerous Ej207 guru's and Subaru Mechanics, they've said everything is A-OK, which puts me at peace.
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Old 02-01-2018, 08:26 PM   #7
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Quote:
Originally Posted by Cobrakai View Post
I'm in the same boat, my V7 swap is noticeably loud during cold starts but it quiets down at operating temperature.

It's a slapping/knocking sound only audible on reversing and taking off in first during cold engine conditions.

The car has been looked at by numerous Ej207 guru's and Subaru Mechanics, they've said everything is A-OK, which puts me at peace.
That does put me in the ease a bit. How many miles have you put on your engine so far?
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Old 02-01-2018, 08:32 PM   #8
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Quote:
Originally Posted by AspirinWhite View Post
That does put me in the ease a bit. How many miles have you put on your engine so far?
~2800.

Few late night canyon carving sessions and daily WOT pulls on the freeway onramps, hasn't gone boom yet.

If the noise is present at operating temperatures I'll start worrying haha.
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Old 02-01-2018, 09:04 PM   #9
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Originally Posted by Cobrakai View Post
~2800.

Few late night canyon carving sessions and daily WOT pulls on the freeway onramps, hasn't gone boom yet.

If the noise is present at operating temperatures I'll start worrying haha.
Yours is still relatively new then. I officially went through one full tank so far. Lots of power for sure but that cold slap/knock really is annoying.

Did you get yours tuned at Churchs?
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Old 02-01-2018, 10:55 PM   #10
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Forged piston cold slap, normal. Even my 97 ej20k with cast pistons did it, worse in cold weather, but ran silky smooth and never skipped a beat. I believe the flat engine design makes it easier to hear as well.

It could also be the timing belt tensioner, did you replace it with new?
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Old 02-01-2018, 11:01 PM   #11
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Old 02-04-2018, 05:19 PM   #12
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video uploaded
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Old 02-05-2018, 01:29 AM   #13
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Quote:
Originally Posted by AspirinWhite View Post
Yours is still relatively new then. I officially went through one full tank so far. Lots of power for sure but that cold slap/knock really is annoying.

Did you get yours tuned at Churchs?
No but I wish I had.

I went with another big name shop in socal, good tuner - terrible customer service.


From what everyone tells me Church is fantastic with a 207, if I had the choice to do it over again I'd go with him.

Quote:
Originally Posted by AspirinWhite View Post
video uploaded

That's exactly how my car sounds.
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Old 02-05-2018, 02:05 PM   #14
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Quote:
Originally Posted by 2slofouru View Post
Forged piston cold slap, normal. Even my 97 ej20k with cast pistons did it, worse in cold weather, but ran silky smooth and never skipped a beat. I believe the flat engine design makes it easier to hear as well.

It could also be the timing belt tensioner, did you replace it with new?
I haven't yet but it won't be a bad idea replacing all the idlers and belts
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Old 02-05-2018, 09:19 PM   #15
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my car does that too (exactly the same sound when blip the throttle) but its an EJ205 stock motor. it did not always do it. it slowly got louder. i replaced all my pulleys because i thought it was timing belt related. it still runs ok but it makes noise when hot too now. i dont trust my det cans now because the mechanical noise is so loud i cant hear anything.
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Old 02-06-2018, 10:10 AM   #16
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Quote:
Originally Posted by 2slofouru View Post
Tensioner noise. Imagine how many subaru owners have gotten screwed out of money or even sold their cars because they were told it was a "spun bearing".
I'd lean toward this ^^^ before cold piston slap.
There have been a number of posts re: people having what they thought was rod knock only to discover later that it was a bad tensioner.

... and no, I'd say it is not normal. I don't have cold piston slap on mine.
I think many people just call it piston slap because the v7s have forged pistons so they call it normal, because they are comparing it to a built motor w/aftermarket forged pistons.
Easy answer so they don't have t look into it.

You should check the tensioner to be sure before it's too late.
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Old 02-06-2018, 10:21 AM   #17
AspirinWhite
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Quote:
Originally Posted by Samurai Jack View Post
I'd lean toward this ^^^ before cold piston slap.
There have been a number of posts re: people having what they thought was rod knock only to discover later that it was a bad tensioner.

... and no, I'd say it is not normal. I don't have cold piston slap on mine.
I think many people just call it piston slap because the v7s have forged pistons so they call it normal, because they are comparing it to a built motor w/aftermarket forged pistons.
Easy answer so they don't have t look into it.

You should check the tensioner to be sure before it's too late.
Is the bad tensioner noise temperature dependant though? The noise I'm hearing disappears once it's warm and appears only when lower rpm from cold start.

The tensioner noise sounds like it's constant
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Old 02-06-2018, 10:26 AM   #18
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My IAG stage 1+ block does the same thing on cold start especially in the winter.

Just piston slap from having forged pistons until they expand when they warm up.
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Old 02-06-2018, 12:17 PM   #19
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My IAG stage 1+ block does the same thing on cold start especially in the winter.

Just piston slap from having forged pistons until they expand when they warm up.
You can't compare a "built" motor to an OEM motor. "Built" motors do normally have some piston slap. How much is dependent on which brand pistons you use and the piston material and how the builder set the PTW clearances.
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Old 02-06-2018, 12:19 PM   #20
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Quote:
Originally Posted by AspirinWhite View Post
Is the bad tensioner noise temperature dependant though? The noise I'm hearing disappears once it's warm and appears only when lower rpm from cold start.

The tensioner noise sounds like it's constant
It may only be the tensioner. It may be showing up when it's cold, but could continue to deteriorate. Worth checking the tensioner than just ignoring it and wish you did. All I am saying is it is worth checking now just to rule it our, or in
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Old 02-07-2018, 01:13 AM   #21
AspirinWhite
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Quote:
Originally Posted by Samurai Jack View Post
It may only be the tensioner. It may be showing up when it's cold, but could continue to deteriorate. Worth checking the tensioner than just ignoring it and wish you did. All I am saying is it is worth checking now just to rule it our, or in
Well, I ordered the Gates blue kit and gonna change everything when it comes in. It may or may not fix the issue but I think it's a good idea to change it.
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Old 02-07-2018, 08:32 PM   #22
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Quote:
Originally Posted by Cobrakai View Post
No but I wish I had.

I went with another big name shop in socal, good tuner - terrible customer service.


From what everyone tells me Church is fantastic with a 207, if I had the choice to do it over again I'd go with him.




That's exactly how my car sounds.
Have you replaced your belts/tensioner yet?
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Old 02-08-2018, 01:26 PM   #23
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Quote:
Originally Posted by AspirinWhite View Post
Have you replaced your belts/tensioner yet?


No, the timing components are brand new. Tensioner was bled properly, Iím swaying towards piston slap.

My friends gf has a V7 swapped bugeye and it makes the same sound as well.

Iím going to drive it until something breaks
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Old 02-08-2018, 01:28 PM   #24
AspirinWhite
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Originally Posted by Cobrakai View Post
No, the timing components are brand new. Tensioner was bled properly, Iím swaying towards piston slap.

My friends gf has a V7 swapped bugeye and it makes the same sound as well.

Iím going to drive it until something breaks [IMG]

https://media1.tenor.com/images/b8a3131f330d1dd7d73c64a37f5fd132/tenor.gif?itemid=10570702[/IMG]
Sounds good. If you're in oc, let's do some ej207 meet haha
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Old 02-08-2018, 02:28 PM   #25
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My v7 ej207 piston slaps at cold start but quiets down fairly quick, under a minute. Keep in mind when buying a used motor you are trusting the vendor is representing the mileage accurately. A higher miles motor will have more wear and looser tolerances.
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