I have a '94 Saab 9000 Aero with 180,000 miles on it.
Recently, I did a major top-end overhaul on the car, replacing all the timing and balance gears and chains, had the head cleaned, checked, and a valve job done on it, and put in a new head gasket.
The car apparently had leaky valve stem seals, and the piston tops were covered in a sticky black gunk, which I can only imagine was the residue left over from the thousands of miles of burning oil.
I searched a variety of internet forums about what to do, and got differing opinions. The camps seem equally divided. Half said, “Sure! Get that gunk offa there! Just be careful not to mar the piston crowns”. The other half said “Are you crazy? All that crud will get down in the engine and you’ll need to re-bore the cylinders and have the bottom end bearings fail shortly”.
I opted to believe the former. I used a plastic drywall knife and brake cleaner and got them fairly clean. I stopped up the holes in the block so that chunks of crud wouldn’t go down in there during the process. Then, after I was done, I wiped out the cylinder bores, rotated the crankshaft, and wiped them out again, and repeated until there was no grit left on the cylinder walls.
An important point to note here is that I did all this work with the engine in the car, so I did not ever remove the pistons or crankshaft.
Below is a photo gallery of the work I did, including photos of the cruddy pistons.
So, what do you guys think? Is my engine doomed? Have I only got a few miles left before I’ll need new rings and crank bearings, or did I take adequate precautions? Is there anything else I could/should do to mitigate the damage?