piston slap or lifter knock... problem solved, header bolts not tight enough

[silver]

I did get the overflow open and there was maybe 1/4 of a teaspoon that came out, so seems normal there.

Just to re-itterate, this sound has been wtih the motor since it was new but the last 2 times I've taken it out for a drive the sound was there, and on previous drives it may or may not show up....I just need warmer weather so I can drive it more and get a feeling for how often it's doing it

ohh and i've lost my earplugs, which i usually wear everytime I take the car out...so the knocking maybe more obvious since I don't have the plugs.....or maybe it's "knocking" because of bad gas..I dunno

[DarthChicken]

No, knocking from bad gas is detonation, and it sounds like BBs in a tin can.  That sound in your video sounds like a midget with a hammer.

I'd take the car to a chevy dealer/service center, and have them listen to the noise. 

[McFred]

The frequency is low enough that my bet is valvetrain.

[silver]

If it was the valvetrain what does that mean for danger and repair?

[bolus]

Is it coming from the timing chain area?  That's the passenger side of the engine.    THere are reports of manufacturing problem wit the timing chain tensioner and the new ones are much diffeent design.  If it breaks there will be a rattle from the passenger side of the engine. 

This is the tensioner. 


http://www.crateenginedepot.com/store/E ... 216C0.aspx

[silver]

It is the passenger side as best as I can tell

bolus I posted my video on the cobalt forum for them to take a listen too since they've had this issue commonly, I did find the thread about it, and I'm very hopeful that is the problem, becaue $50 is a cheap repair.

It looks like I'd need to remove the catch can to get at the tensioner, but it still looks totally doable at home!

Thanks very much for pointing this out as it could very well be the problem.........I guess I won't be driving my car today....but better safe then sorry.

[DarthChicken]

I hope that's what it is.  That would be an easy 5 minute repair.  The instructions to change out that part are pretty crazy though (valve cover removal, locking it in place, smacking it with a wrench..).  All completely unnecessary, as you can leave it unlocked (sprung) and just thread it in.

[silver]

Yeah there's 2 sets of instructions..

set 1
step 1 uninstall tensioner
step 2 install tenstioner..


set 2

The timing chain tensioner is released by compressing it 2 mm (0.079 in) which will release the locking mechanism in the ratchet. To release the timing chain tensioner, use a suitable tool with a rubber tip on the end. Feed the tool down through the cam drive chest to rest on the cam chain. Then give a sharp jolt diagonally downwards to release the tensioner.

If the timing chain tensioner is not in the compressed state, perform the following steps:
17.1. Remove the piston assembly from the body of the timing chain tensioner by pulling it out.

17.2. Install the J 45027-2 (2) into a vise.

17.3. Install the notch end of the piston assembly into the J 45027-2 (2).

17.4. Using the J 45027-1 (1), turn the ratchet cylinder into the piston.

Inspect the bore of the tensioner body for dirt, debris, and damage. If any damage appears, replace the tensioner. Clean dirt or debris out with a lint free cloth.
Install the compressed piston assembly back into the timing chain tensioner body until it stops at the bottom of the bore. Do not compress the piston assembly against the bottom of the bore. If the piston assembly is compressed against the bottom of the bore, it will activate the tensioner, which will then need to be reset again.
At this point the tensioner should measure approximately 72 mm (2.83 in) (a) from end to end. If the tensioner does not read 72 mm (2.83 in) (a) from end to end repeat steps 17.1 and 17.4.

Inspect to ensure all dirt and debris is removed from the timing chain tensioner threaded hole in the cylinder head.
Important: Make sure the timing chain tensioner seal is centered throughout the torque procedure to eliminate the possibility of an oil leak.

Install the new timing chain tensioner assembly.
Tighten
Tighten the timing chain tensioner to 75 N·m (55 lb ft).

The timing chain tensioner is released by compressing it 2 mm (0.079 in) which will release the locking mechanism in the ratchet. To release the timing chain tensioner, use a suitable tool with a rubber tip on the end. Feed the tool down through the cam drive chest to rest on the cam chain. Then give a sharp jolt diagonally downwards to release the tensioner.


I took another video with my phone....keep in mind the microphone isn't some super duper directional mic but it does work

[positron]

Cold beer says... exhaust/manifold/header leak... at first will be worse when cold, may subside when it warms but will eventually get worse..  put a tissue on a telescoping roach clip and place around exhaust mating surfaces..

or look for evidence of wear/breach.. my header shield cover edge was touching and wearing a hole on the side top of #1 header tube...

[silver]

Well as I mentioned the reason for my 1 month sit was I was waiting for the exhaust therefore I will definitely check it like you mentioned right now since maybe I didn't torque it down enough

[positron]

Did you reuse gasket more than once?

Exhaust gasket
9230949

[silver]

Just checked...no leaks. I did reuse the gasket but I have the fortress exhaust with a thick copper gasket....anywho definitly didn't blow the tissue around at all.....WAIT A MINUTE...LEMME UPLOAD A NEW VIDEO

[silver]

OK so it didn't blow the tissue around but I thought maybe I just didn't torque down the header enough......torqued the header bolts a little more and here's the result




it's a marked improvement therefore I think Positron nailed it on the head with the problem.....I felt it seemed strange that this would occur right around my "reinstallation" of the exhaust.

So now to look at the thread with the brammo torques and go use my torque wrench to check them as soon as the header cools down a little more.

Originally they weren't torqued down very tight I guess....it's my tendency not to force things and I guess I should have looked for the torque requirements first.

[bolus]

See, our only job is to keep you occupied with misinformation until Positron figures it out.   He da man

[silver]

I sincerely appreciate everyone's efforts....feels like I'm using the forum for what it was intended for....weird huh