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Hello, I have a 2007 Cobalt that is running very rough. I just changed the head gasket and after job was done it doesn't run correctly. Someone said it seems like a problem with the timing. does that sound correct If so how do I fix it?
 

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I assume you are saying you did the work yourself. I always rotate the engine 4-8 times after installing a timing chain, doesn’t matter what engine it is. Actually I always do it after a timing belt too. I always want to verify that I didn’t install it a tooth off before putting things back together. I figured it is basic practice to do so, especially on such a tight engine bay like the Cobalt. If you didn’t verify things were in the correct place, you may have a problem.

You should definitely get a camshaft or crankshaft correlation code if the timing is off in either direction.

If the timing was done correctly there can be other problems though. Did you have a machine shop check the cylinder head for cracks? Also did you make sure to have the head machined? If you have only just swapped out the head gasket without machining the head, you could have made a big mistake. Usually you will want to machine the sealing surface, and probably have the valve seats cleaned up. Also wouldn’t been a great time to install new valve guides, they are know to wear on these engines.

If you have access to a scanner with live data capability you can see what is happing with the timing and other things. I would also recommend you do a compression test if you haven’t done so already. Also, was the engine using a lot of oil before the head gasket problem? Piston ring problems are also another common issue on these cars.

Why exactly was the head gasket being replaced? Was the engine overheated because of a low coolant condition or was this just a simple head gasket failure?
 
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