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      04-01-2019, 02:58 PM   #1
CAOZKAN
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Engine rebuilt, new weird sound

I have just got my engine rebuilt with cp pistons and rods. There was no problem with the engine tbh I just got an itch to do it since my car is at 60k miles. Meanwhile at it, I added the vtt crank hub fix to it as well. However, now that I got the engine rebuilt I have a new knocking sound at 800-1400 on throttle. It sounds like an injector knock but in a deeper way and it feels like it comes from the top of the engine. I know it's almost impossible to understand it from video or description but I have three suspects.
-Do you change the valve lifters(rocker/tappet) when you built an engine? Do you think since I reused my old ones, they may be the problem?
-An other mechanic is saying it sounds like the HPFPs are the problem since the sound comes on throttle and only on idle.
-Finally, this can be due to cp pistons gap vs oem ones. This one is a more focused question to the people who got their engine rebuilt, do you have the same sound?

I will try to add a video later on but it's very hard to distinguish the sound on it.

Sorry for the long post but I just don't want to spend money on parts which aren't problematic meanwhile this may be an impossible issue to solve.(piston gap)
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      04-01-2019, 03:17 PM   #2
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I know what kind of sound you're talking about... it often gets associated with common DI and HPFP noise, but if yours are any louder, then it could very well be the valve lifters, or valvetronic related. Definitely get them checked as soon as possible, because you don't want this kind of issue to develop.

Also try switching to a 40w oil to see if the sound goes away a bit.
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      04-01-2019, 04:12 PM   #3
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Engine rebuilt, new weird sound

Quote:
Originally Posted by nars3000 View Post
I know what kind of sound you're talking about... it often gets associated with common DI and HPFP noise, but if yours are any louder, then it could very well be the valve lifters, or valvetronic related. Definitely get them checked as soon as possible, because you don't want this kind of issue to develop.

Also try switching to a 40w oil to see if the sound goes away a bit.
Thanks a lot for the advice. What can go wrong with valvetronic during the rebuild? Because it was working just fine before the engine got rebuild..would you use oem or the other brands like swag or ina? I'm asking because these valvelifters seem nothing like a big technology and oem ones are two times more expensive..
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      04-01-2019, 04:26 PM   #4
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Quote:
Originally Posted by CAOZKAN View Post
Thanks a lot for the advice. What can go wrong with valvetronic during the rebuild? Because it was working just fine before the engine got rebuild..would you use oem or the other brands like swag or ina? I'm asking because these valvelifters seem nothing like a big technology and oem ones are two times more expensive..
Nothing wrong with the OEM valve lifters that I'm aware of. They just tend to go out of spec after being pushed with a bit more power for a few thousand miles. The valvetronic component have also been known to fail on this platform; see: https://f80.bimmerpost.com/forums/sh....php?t=1389358

I've seen a handful of engine build list, and most of them stick to CP Pistons and Carrillo Rods, with no mention of aftermarket valves or lifters. In fact, both Carbahn and Ghassan offer the same options for their rebuilt S55 longblocks.

It may have been a good idea to change the lifters while you had the engine rebuilt... that may have saved you from having to deal with this issue now.
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      04-01-2019, 04:44 PM   #5
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Could be oil squirters contacting the piston skirt or connecting rod, larger piston to wall clearance, or a bunch of other things.
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      04-01-2019, 05:54 PM   #6
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I learned to mark everything and put everything back in the same position when doing a rebuild. Was this done with the valvetrain components? If itís clearance related, do you hear difference when cold vs operating temperature? Issue might still be there at higher rpm but not audible because of shift in frequency. I would inspect everything with a boroscope.
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      04-01-2019, 05:55 PM   #7
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Quote:
Originally Posted by maximumpsi View Post
Could be oil squirters contacting the piston skirt or connecting rod, larger piston to wall clearance, or a bunch of other things.
Do you change the valve lifters or hpfp by default when you rebuild an engine? Or did you have similar sound issue when you did ?
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      04-01-2019, 05:58 PM   #8
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Quote:
Originally Posted by G4BR13L View Post
I learned to mark everything and put everything back in the same position when doing a rebuild. Was this done with the valvetrain components? If it’s clearance related, do you hear difference when cold vs operating temperature? Issue might still be there at higher rpm but not audible because of shift in frequency. I would inspect everything with a boroscope.
Valvetronic component, I believe so. About the temperature, it's definitely louder in the mornings when iI first time start it but doesn't get much silent after it gets warm too but definitely slightly more silent.
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      04-01-2019, 05:59 PM   #9
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Does it go away once warmed up? If it does then its just piston slap while cold but if its there all the time you got an issue in the rebuild somewhere I think
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      04-01-2019, 10:48 PM   #10
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Having built a few of these, pushing them to over 900+ HP, I'd presume this is typical "built engine" noise.

Slightly more loose PTW and Oil clearances.

Speak with your builder to understand the specs/tolerance that they've setup in the engine.

~Anthony
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      04-02-2019, 01:18 AM   #11
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Quote:
Originally Posted by OpenFlash View Post
Having built a few of these, pushing them to over 900+ HP, I'd presume this is typical "built engine" noise.

Slightly more loose PTW and Oil clearances.

Speak with your builder to understand the specs/tolerance that they've setup in the engine.

~Anthony
But if it was the ptw, sound should go away when it gets warmer, right?
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      04-02-2019, 07:05 AM   #12
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Not always.

If they've setup/specified a unique PTW clearance it could have lightly audible piston slap until power pulls are done and the engine is hot.

Most CP pistons are made with 2618-T61. This material is more ductile, which allows it to resist cracking, and can tolerate high cylinder temperatures. Because it has a low silicon content, it also requires a larger PTWC. Its the best material for high power/boost applications.

Again, speak with your builder to know what they've spec'd.

~Anthony
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