Engine knock problem...

[87gnguy]

I just had my motor rebuilt and after driving about 150 miles (with boost never going above 10psi), I have a knock in the motor somewhere. However, when you rev the motor to about 2000-3000 rpm, the knock goes away. I've had rods knock before and when you rev it, it gets louder and more prominent. Anyone have any answers?
Thanks,
Casey

 

[phil_jordan]

Sounds like a lifter....

 

[phil_jordan]

And the only reason I say a lifter is because I'm having a similar issue. Only difference is, when my car warms up, the sound goes away. HTH

 

[87gnguy]

See I was wondering that too... They were really loud to start with and I adjusted them so they are quieter now. I'm running race lifters so I understand they are louder than normal and I'm ok with that. This knock seems to reverberate through the whole motor, not just in the valvetrain. You can even hear it more prominent from under the car... I'm wondering if it could be "piston slap"? I don't know... I've never had an issue like this. Everytime I've had a motor knock, it got louder if you revved it.

 

[phil_jordan]

Sheesh. Sounds like more than a lifter then. Sorry. Did you have someone rebuild the motor? I'd take it back to them asap if so!!!

 

[87gnguy]

Yeah, I'm going to give him a call and see. I've talked to him a few times but I haven't told him about this yet because I couldn't hear it over the lifter noise...

 

[phil_jordan]

Yeah thats definitely heartbreaking. Hopefully it turns out to be something small and silly. These cars are intimidating. Every time i hear something different or see a weird number on the scan tool, I automatically think the worse. It normally turn out to be something so silly that I overlooked mostly.

 

[dank GN]

Double check headers for cracks /leaks

 

[v6turbo87]

What is your oil pressure reading?

Posted from the TurboBuick.Com mobile app

 

[87gnguy]

Oil pressure is 20 psi at idle and 40 cruising.

Posted from the TurboBuick.Com mobile app

 

[1KWIKSIX]

Although I'm no expert on the subject.........but I am also thinking piston slap?
Forged pistons will need greater piston to cylinder wall clearance due to the fact that they will expand more than a cast piston. They will tend to be noisier when cold, however should not be prominent when your engine is fully warmed up to normal operating temperatures. Does this go away or diminish when engine warmed up? or only when cold?
What were your piston / cylinder wall clearances set at on your rebuild? If they ended up being set on the looser side, that could explain what you are hearing. May be good for a race motor, by will be noisy for a daily driver.
My son had his Subaru STI engine rebuilt with forged rods & pistons by a local race shop & they ended up being much noisier than stock......sounds similar to what you've described.

 

[SCOOBY DOO]

Inspect the flex plate for a crack. Could also be a broken cam button retainer spring.

 

[blackazz]

Inspect the flex plate for a crack. Could also be a broken cam button retainer spring.

Cam button will make a loud knock. Put a listening device on the cap an see. Mine did the same knock when the cam button Spring broke.

 

[84BuickGNYorkPA]

I think I would pull the pan and have a look under some of the caps... just don't mix them up or turn them around and of course re-torque them back on.

Chuck

 

[v6turbo87]

I have forged pistons and do have any noise. I agree with pulling the pan and checking some rod bearings.

Posted from the TurboBuick.Com mobile app