Hi guys first post here. I bought a 2008 cobalt s off my brother in law last november. Its just under 90k. I'm due for an oil change, but I noticed a rattling sound recently. I spent 6 weeks in china and my car sat, but the first or second time driving after I got back (about 2 weeks ago) I noticed the rattling sound.

It's only noticeable on the low-end, especially just after you let off. It will make the rattling sound for a second or two, and seems to be in tune with the rpm. After doing a little research I read about timing chain tensioners going bad on ecotecs.

Can anyone help me identify the sound, and give an estimate on the cost to repair?

Thanks in advance,
Matt

 

A video would help in this situation

 

Sounds like youre on the right track but post a video of it idling and try to get ones driving too

 

Check the tensioner, but also pull the plug on the front of the head (10mm allen wrench) and make sure the upper guide bolt hasn't backed out. When that happens you hear the rattle more on deceleration in my experience.

 

Can you tighten it again or does it need to be replaced?

 

If the bolt backs out the threads will be all opened up from the bolt bouncing around in the head, so no you can't put it back. In some cases the bolt snaps off, which in that case it may be possible to remove the piece and install a new or upgraded bolt. But in my experience they've all backed out and damaged the threads in the cyl head.

 

Anything that can be done to check or prevent this? I'm at 110k. No noises at idle but I'd like to keep it that way.

 

MR. B on here sells the upgraded ARP bolts that won't snap off, if your bolt hasn't backed out by now it won't IMO. My car I bought new and by 40K it was rattling, when I pulled the head closer to 60 to do pistons I found the damage, just had the hole drilled and helicoiled back to the correct M6 thread and it was fine.

During assembly you should always use a drop of red loctite on an otherwise clean and dry thread on bolts like that to ensure it stays put.

 

Gotcha. I'll leave it alone. I installed the updated tensioner as soon as it came out so maybe that helped save it.