In the process or replacing the head gasket, should I clean the piston tops?

Maintenance/Repairs
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1

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.
imgur.com/a/EbFCZ#0

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?

Cheers,
Ben

2

I’ve cleaned piston tops many times when the head(s) been removed. The only other thing I do after scrapping the deposits off the pistons is follow up with a shop-vac to make sure everything has been removed.

Tester

3

Cleaning the tops off is the corect way to do it. Carbon retains heat, and the pistons and cylinders should be as clean as you can get them before reassembly. If you’re concerned about any of that gunk having gotten into the engine’s pan, you can remove the oil pan and take a look…and clean that all out too.

If you can do it on that engine, you’ll also want to run the oil pump, turning the crank slowly by hand, prior to starting the engine.

Also, you’ll want to check the top of the block and the head for flatness. But I have a feeling you already know all that.

Persoanlly, I’ll bive you a B+. I’d give you an A if you were willing tot go he rest of the way and do the bottom end too…(just kidding).

4

If I’d had my druthers, I’d have pulled the engine out completely and done a full rebuild. It would have been easier and faster, not to mention more thorough. However, the tinyness of my garage made this impossible. There just isn’t enough room for the car and a shop crane in there.

If I ever had to do it again, though, I’d just contrive to borrow someone’s larger garage and use a crane. It’s worth it, I think.

I have another Saab 9000 Aero (yeah, I’m that kind of Saab nut) stored at my mother in laws’ house, and I will be using a crane to pull the engine out of that to get it back on the road.

5

I wouldn’t worry one minute about it. Any loose debris that has been missed will be spit out of the cylinders or vaporized in the first few seconds after engine startup.

The only question might be whether or not the oil consumption and gooped up piston tops is related to valve seals only or if piston rings may be involved.

6

I tended to suspect the valve stem seals for this reason :
If I let the car sit for a while, like a week or so, then there’d be a puff of blue smoke out the tailpipe when you first started it up from cold.

Commonly, with these cars, that’s one of two things :

  1. oil seals within the turbo are shot
  2. valve stem seals are leaking

Since I replaced the turbo about 20,000 miles ago with a brand new unit, I was inclined to believe option #2.

If I understand the symptoms of leaky piston rings correctly, I should have been getting constant smoke when the engine idled, and more smoke in direct relation to engine RPM (more revs == more smoke).

I do plan to change the oil and oil filter after the first 100 miles of driving, in the hopes that anything that wound up in the oil will have been caught in the filter by that time.

I primed the oil pump with vasilene when I put the engine back together, and I did turn it over several times by hand before pulling the fuse for the fuel pump and running it with the starter for a few seconds.

I took the opportunity to do a bunch of maintenance and “while I’m in there” type replacements.
I replaced the oil pump gears with new ones, installed a brand new water pump, replaced the voltage regulator, replaced hoses, gaskets, seals, and o-rings of every variety, and installed all new hardware under the timing cover.

It’s much, much quieter than before. In addition to the weepy head gasket, the timing chain was also way stretched out. It sounded a bit like a tin can full of spoons rolling down a steep hill.

Now it sounds like it’s practically brand new, and there isn’t a single drop of fluid on the ground!

7

I understand your reasoning and applaud your work.

My suggestion with the oil pump was not for the sake of the pump, but rather for the sake of the engine’s upper half. It’s always good to get the top end full of oil before starting the engine again.

Actually, amend that to include prelubing the lower end too. What WAS I thinking!

8

Ahhh! Gotcha. I was lead to believe that priming the pump with vasiline would provide sufficient suction to get the oil flowing, but I can also see no harm in turning it over by hand before starting it (which I was doing anyway to double re-check that I had the timing right). Sounds like good enough reason to make it standard procedure.

9

You didn’t do anything wrong, but you may end up with an oil burner now. There are a lot of variables that determine whether this will happen to you or not, but at some point in the mileage of an engine, any top end wok will increase the compression enough to unseat the rings. The old rule of thumb was about 80k miles but that has gone way up with better metallurgy and oils used today.

In most cars, you can replace the valve stem seals without pulling the head and in your case, that is all I would have done, actually I wouldn’t have even done that unless there was another issue with oil retention around the valve guides.

What TSM was referring to is that a lot of engine designs with overhead cam(s) have a sort of dam or trough that holds a pool of oil so that the bottom of the camshaft is always under oil, even at start up. You could fill this trough up just by pouring oil into it with the valve cover off.

Good luck, I hope you duck the bullet on the rings, but if you didn’t, it wasn’t because you cleaned off the tops of the pistons, it was going to happen anyway.

10

As many have said. Clean is good. My 2c is you do what you can and let oil sort it out. Your engine ran many years with crap in the block. The total teardown vs the enough. Its like coke or pepsi. Good luck.

11

@Kieth - considering that this is a turbo engine (where CR is 8.5:1), does that make a difference? I’d imagine any slight increase in the compression of the pistons would be lost in the face of the incoming 14 psi from the turbo. Perhaps I’m grasping at straws, but I’m also curious if the rule of thumb applies in this case.

12

What I was actually thinking of was prelubing the engine by spinning the oil pump with a hand drill…if it can be done on this engine. Good point about the oil pools, however. I hadn’t thought of that.

13

There are a lot of variables so I can’t really answer that question. You maybe OK, my intent was to say that if you do start burning oil, it’s not because you cleaned the piston tops.

14

Gotcha, thanks for the info. Bottom line is, it might happen, it might not, but I’ve already done what I could given the circumstances.

In the end, I gather it would have been better if I’d pulled the engine and put new rings and/or bearings in as needed. I think that’s what I’d do next time anyhow - the engine is by far easier to work on when it’s out of the car (though this was quite doable in-car, there’s a fair amount of room in the old 9000’s).

15

@TSM - can’t spin the pump separately, as it’s driven directly by (and is coaxial to) the crankshaft on this car.