MistrGoodwrench

New guy here. Just took this car in on trade for my son's Tahoe tonight. Drove it, came back, turned it off swapped titles and sent the seller on his way in the Tahoe. Go out to start the C230, it cranks (I was standing in front of it) but my son didn't think it did (too quiet) and shut it off. Try to restart and the motor will not budge! Starter is engaging. I get a breaker bar and try to turn it with the crankshaft pulley bolt....NO GO! I can rotate it backward, but not forward!

Dropped valve and/or broken timing chain as I suspect or something specific to these cars that I'm not aware of?

Here's what I've tried so far...

Pulled the serpentine belt to rule out any external accessories. - No change

Pulled all of the spark plugs - No change (plugs all look good, no fouling, no damage)

I didn't pull the starter due to the difficulty of removing it and the extremely unlikely chance of that being the issue. It appears to function fine UNTIL the motor hits whatever is stopping its rotation.

I put a small paint mark on the timing chain and observed it as I turned the motor backward via the crank pulley bolt. Made a full revolution with no issues.
Attempting to rotate it forward results in an abrupt stop whether rotating it by hand or via the starter. Oddly, it doesn't always appear to happen in exactly the same place.

The only issue I've seen so far is that the engine was overfilled with oil by quite a bit (completely above the plastic indicator on the dipstick and onto the shaft). I drained it, looking for metal shavings, water, coolant, gasoline or anything abnormal. I started with a completely clean drain pan and observed a bit of metal shavings (small glitter size) in the oil. Not good but not more than I'd expect in a 175,000 mile motor.

I am open to suggestions, obviously. I'm not afraid to tear into it.

Russell Ormerod

I am busy with a m272 motor now, clk350 was also jammed solid. The timing chain rail broke and eventually broke a chunk of alloy out the front cover, and then bent all the intake valves. Possibly you have a guide rail that is getting wedged when you turn in one direction, If I was you i would remove valve covers and inspect the rails. Also my balance shaft was completely shot no more teeth left. Stripped it completely and rebuilt it.
Good luck

MistrGoodwrench

Thanks, Russell.

ItalianJoe1

Agreed with the above, i'd suspect a broken chain guide jamming. That it turns backwards makes me think it's quite salvagable, I just would not try to start it until you know what's going on, so you don't do any further damage.

MistrGoodwrench

Thank you, ItalanJoe. It'll be this weekend before I get another shot at it. I'll update with my findings.