2001 Oldsmobile Alero Engine knocking

AARONLU

MEMBER
2001 OLDSMOBILE ALERO
3.4L
6 CYL
FWD
AUTOMATIC
142,317 MILES

I have a 01 olds sleep 3.4. I had a head gasket leak I replaced gasket heliocoiled all 12 rocker arm bolts put it back together. Runs fine until it gets to operating temp. No tick. It's a knock from the engine. I can't tell if it's a piston a rod or it's the head. I didn't have it machines but I am a machinist and I checked it and it wasn't even a.01 out of tolerance. So what could it be? It's not a constant knock it's spatatic but sounds like a guy with a hammer in there. Oil flow is fine

Tuesday, October 6th, 2015 AT 3:51 PM

4 Replies

HMAC300

MECHANIC
48,601 POSTS

Short cylinders out one at a time to see if you can find out what cylinder it is. Then check oil pressure with a manual gauge. If engine ran without noise it may be something in cylinder which if small enough you may be able to remove a plug start motor and it will get blown out, especially if it seems to be going from one side to the other. Other than that have a local guy look at it. A we can't give a good diagnosis as we can't hear it.

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Wednesday, October 7th, 2015 AT 7:13 AM

AARONLU

MEMBER
3 POSTS

What does a bent valve sound like? Would the car run? Would you hear a tick instead of a knock? I've narrowed it down to timing chain or bent valve. Thank you for your info. Helpful

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Thursday, October 8th, 2015 AT 9:46 AM

HMAC300

MECHANIC
48,601 POSTS

If it were a bent valve you may not hear anything at all except the predominant miss. If this is the 3.4L engine the timing chain has a tensioner so you wouldn't hear that. A piston would knock when cold unless it has a lot of clearance. Do what I said in first reply. It's a lot easier to get the CORRECT diagnosis.

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Thursday, October 8th, 2015 AT 11:59 AM

AARONLU