2007 Chevrolet Cobalt 2.2L Ecotec L61 Engine Rebuild

Hints from my BlueDriver

It's a long story, but the car is a 2007 with fewer than 60,000 miles on it, and the engine needed some serious work done to it.  It all started with a pretty aggressive oil leak, followed shortly by an "open wallet soon" light on the dashboard.

The oil appeared to be leaking from both ends of the engine.  On the front from behind the crankshaft pulley, and on the back out of the bell-housing where the engine attached to the transmission.  It had blown the main seals on both end.

I pondered what could have caused both seals to fail and then remembered the check-engine light.  It occurred to me they might be related.  One of the suggestions was to check for leaks in the PCV (Positive Crankcase Ventilation) System.  This system is supposed to recover a nominal amount of pressure from the inside of the engine and draw it back into the intake.  Could the misfire be related to a pressurization of the crank case?  But the PCV in this car is overly simple, and it is fine.

I continued to ponder and read.  Could excess exhaust be leaking out of the cylinders and into the crankcase?  How would I test for that?  I tried my compression tester, and the standard compression tests came out reasonable.

80 psi in, all leaking out.  That's not good.

Then I thought about how airplane mechanics do compression tests.  On my airplane we perform "Leak Down" tests.  Take a look at this Eric the Car Guy video -- it is a pretty good dive into the differences.  Instead of letting the engine's normal action create the pressure for a moment, a leak down test injects compressed air into the spark plug hole, and measures how much stays in the cylinder.  I bought a leak down test set and went about testing.  Here I discovered that neither of the end cylinders would hold any compression.  Out of 80 psi in, nearly all leaked out.

The interesting thing about this type of compression testing is that you can HEAR the hissing of the air escaping.   If the leak is occurring out the valves, you can hear the leak either in the intake system or the exhaust system.  I could hear this leak out the oil passages in the top of the head -- the air was escaping into the crankcase and venting up the oil return passages.

Left the A/C hoses in place so I would not have to recharge it.

I had to get the engine out of the car.  I started by draining all the oil and coolant, then removing all of the stuff hanging on the outside of the engine...  Fuel injection rails, ignition system, intake manifold, alternator, air conditioning pump, starter, exhaust manifold...  Basically stripping it down to just the engine block left in the car.  I then removed the bolts holding the engine to the transmission (this was a mistake) and the engine mount, attached a lift and started to pick it up.

The torque converter was still attached to the back of the engine, and when it came loose from the transmission, the transmission fluid drained all over my shoes.  Bummer.  And there was not enough space in the engine bay to slide the engine far enough away from the transmission to get the torque converter to clear the transmission's bell housing.  So I went to the internet.  On YouTube I discovered there are three bolts accessible through the starter hole holding the torque converter to the flex-plate.

Boom.  10 minutes later the engine was hanging in the lift.  (note to self:  watch YouTube before starting any major repairs.)

I tore into the engine, removing the front cover, timing chain, heads, connecting rods, crankshaft and pistons.

It was not until I got the pistons out of the engine block that I found the cause of the engine's problems.  The rings had pretty much corroded into the pistons, preventing them from moving freely.  This resulted in a poor seal between the piston and the cylinder walls, allowing exhaust gas to escape past the rings and into the crankcase, pressurizing it and blowing the main seals out each end of the engine, and allowing oil to drain out, along with lighting up the "open wallet soon" light on the dashboard. 

I brought the block and head to a local machine shop where they could assure me that it was still within tolerance for rebuild.  A complete new gasket kit was obtained.  The head got new seals around the valves, and the cylinders were honed so they would suspend engine oil after rebuild.

I bought the repair manual so I would have specifications for the more technical aspects of the repair and reassembly started in earnest with attaching new pistons and rings to the connecting rods, renting a ring compressor, and putting the pistons back into the engine block.  The crankshaft got all new bearings, new "torque to yield" bolts were installed, torqued, and then rotated the specified number of additional degrees (I got a new tool).

Aligning the timing marks

Soon the balancing shafts were being installed with the water pump. The oil pan was going back on, and the head, with it's new torque specifications, and the camshafts were being realigned with the crankshaft and timing chain.

With all of the parts set out in front of me, I could also see that there was plenty of room to reinstall the engine with the exhaust manifold in place, so it was installed too.

Back in place

Eric showed up at the house just in time for the installation to occur, and together we slid the engine back into the car and started reattaching bolts and connectors.  And I discovered I had lost TWO bolts.  By then it was too late to go buy them and I had to wait for the next day to finish installing and connecting everything.  Then next morning the engine fired up without a hitch.

A new engine would have cost over $4,000.  For about $1,000 and several days out of my life, I was able to complete the repairs.  I've driven the car around the neighborhood a couple of times, and am monitoring the engine, and so far, so good!

All secure

Here are some photos.