Engine Refresh 27
With the bottom end complete, it's time to move to the big job- cleaning and preparing the block deck for the new head gasket. I have seen so many very, very bad ways of doing this on the internet. Basically anything that involves any kind of hard abrasive (sandpaper, scotchbrite, roloc wheels, etc.) is
NOT what you should do. All of these products contain small particles of very hard abrasives like silica and aluminum oxide. They're basically tiny, jagged edged rocks. When you start scrubbing, you create a cloud of these particles, which fall into the cylinder and all of the other engine crevices. If one of these abrasives gets into the bearings, or between the cylinder and piston ring- you're looking at a rebuild. Also, the abrasives remove the soft aluminum of the block, and completely ruin the machined flat surface necessary for proper head gasket sealing. So, I use a different method. First, I tape off the rest of the block to prevent any contamination of areas where I'm not working.
Then, I plug the water jackets and oil drain ports.
Next, I lower the piston to about where the oil ring sits- about 3/8" below the deck. I have a reason for that, discussed below, but it also helps keep the razor away from the piston crown.
Then, I begin the cleaning process. First, I take a fresh razor blade and very, very carefully (the hard steel will gouge the soft aluminum if you make a mistake) start lifting off the major chunks of old gasket, carbon and graphite. You also could use a ceramic scraper too, I suppose. The key here is to go slow and have a light touch. If you feel the blade resist at all, STOP. Reset and try again from a different angle. You'll know the scraping phase is over when you can run the razor over the deck and feel no resistance- it will feel flat and smooth. At this point, lots of debris will have fallen into the various crevices. It's mostly carbon and graphite, but still, you have to keep it tidy. I use my shop vac (exhausting oustide so as not to make a cloud of aerosol particles in my work space) with a crevice tool to very thoroughly vacuum out all of the debris.
Next is the really tricky part. What is left on the deck is mostly very hard carbon/graphite that is baked into imperfections in the metal surface. It's too close/low to the surface for the razor to pick it up without risking gouging the surface by digging in a corner of the blade. But, it is raised just enough to prevent uniform gasket seating, meaning you will get hotspots and/or leaks. [MENTION=25737]Kaz-kzukNA1[/MENTION] mentioned using "the oil stone" to finish prep the surface, but never explained it on his blog. I envisioned something like
this, soaked in machine oil, and being gently passed over the surface at a 45 degree angle, and then the opposite 45 degrees until the surface was clean and flat- like a cross-hatch. Without Kaz's guidance, I had some concerns. First, where does the oil paste full of dirt and stone grit go? Second, stone is harder than aluminum- how can I be sure I'm not removing any metal? Third, how can I be sure it is truly flat? What if I hone the deck at a tilt? This all scared me too much. So, I went to my old standby: fine grain steel wool. I use high-strength remover like
this, which does a great job of emulsifying the carbon. The steel wool is rough enough to scrub the carbon off, but leaves a completely smooth aluminum surface. I use a very small ball of wool- maybe the size of a small marble, to minimize shedding and focus the pressure where I am trying to clean. Working very carefully, you get this:
The reason I lower the piston is that the steel wool does shed. If you leave the piston at the top, your scrubbing will jam that wool into the small crevice between the piston and the head, where it will sit on top of the fire ring. By lowering the piston, it lets the wool settle gently on top of the crown instead of getting jammed against the fire ring. It drops tiny pieces off like falling snow. This is where the vacuum comes in. Once you're done cleaning, the vacuum lifts it all away. I vacuum twice and wipe with a microfiber in between. The microfibers cling to and lift away any debris as well.
Once I'm sure there is no more loose debris on top of the piston (I inspect obsessively using a flashlight), I'll raise it back up and clean the crown. Again, I use steel wool and remover, taking special care not to get too close to the edges. Then more vacuuming and wiping with the microfiber. I found that a plastic scraper works well to get the carbon out of the valve recesses in the crown. Once the piston is clean and I'm sure there is no loose debris anywhere on the head, I lower it all the way down. Using a clean microfiber, I wipe the interior of the cylinder to remove the old oil and any small contaminants that made it past the piston rings. Then, I vacuum out the cylinder and wipe again, this time with acetone to clean the carbon rings near the deck surface. I do one more vacuum (to grab any carbon bits that might have fallen down) and wipe, and then I wipe down the inside of the cylinder with clean Mobil 1. This engine will not be started until December or January, so I want to ensure there is no corrosion in the cylinders.
Here is another trick- I rotate the engine a few times and check the cylinder. Any leftover debris sticks to the oil.
#4 had some bits leftover, which I wiped out with the microfiber and re-oiled. # 5 and
#6 were clean. Each cylinder took over 2 hours this way, but I ended up with this:
