A couple of notes on this subject as I have a little bit of experience with the subject:
1) I *HATE* powder coating. I didn't start doing it to have it become part of the business--it just kinda worked out that way. I simply wanted a way to clean up parts in-house when doing rebuilds and other customer jobs. It's painful to put a 20 year old valve cover on a freshly built motor, but at the same time, I had replaced too many oil pumps and rebuilt too many engines for people due to the place before us either blasting the head when they rebuilt it, or from media trapped under the baffles of their "pretty" valve cover.
2) Doing valve covers, unless I'm doing it for an in-house build, I couldn't care less if we get the business or not. With the process I use, at $75 for a single-coat color, I'd make about as much per hour working at Mc'D's, with less headaches.
Now that the whine-fest is out of the way, this is how *we* do valve covers.
Step 1: Degrease. These things are typically filthy when they come in the door. I'm talking, pick it up and oil is still dripping out of it, and wherever you touch them, your hand come away black. Let's face it, they've lived a hard life the last 15-25 years. I spray them down with degreaser inside and out, let them sit an hour, then spray them down again. After that, they get hosed down liberally until the bulk of the grease is off of them.
Step 2: Cleaning. They get put in our $4K high temp, high pressure parts washer. First they go in upside down so that the water is flushing out the inside and running through the baffles for about 60 minutes, then get flipped right side up, and washed for another 60 minutes.
Step 3: Oven. After rinsing with fresh water, and drip drying for a while, they go in our one oven and cooked at 475 degrees for about an hour. This serves several purposes. It dries any remaining moisture out of threads/under baffles, and also out-gases the aluminum. Outgassing is CRITICAL on these. I don't care if you buy a brand new valve cover that has never seen 1 drop of engine oil. Mitsubishi's castings are ridiculously dirty. If you doubt this statement, I invite you to weld ANY cast aluminum piece from Mitsubishi. You'll quickly see how much crap floats to the surface of the weld. Outgassing isn't to prevent the coating from peeling up or longevity of the coating. It's to *HELP PREVENT* fisheyes, and spotting in the coating. Notice the emphasis on "help prevent". Unless you do several coats on a used valve cover, I guarantee you that I'll be able to find outgassing in anyone's coating. You're simply not going to avoid it 100% on a porous casting that's been oil coated for the last decade and 1/2. This cooking process also cooks off any sticky oil/grease residue under the baffles.
Step 4: Blasting. The valve cover is mounted to an aluminum plate with two cam caps welded to it with both the outer gasket and spark plug gaskets used to seal it to the plate. A PCV valve that's been welded shut it threaded into the PVC hole, a modified metal valve cover cap with gasket is put in the oil fill hole, and the vent is covered with a thick rubber cap to seal it off. Pickling a valve cover is great for cleaning it, but without removing the loose skin metal on top, and roughening up (profiling) the surface, your coating will peel off in thick chunks in a relatively short time. Been there, done that when I first started coating. The assembly is then blasted.
Step 5: Cleaning (again). The cover is removed from the plate and given an air bath. The baffles/ports all get blown through so that any small amounts of dust (if any) get blown out. Then it goes back into the high temp/high pressure parts washer for another cycle to wash any remaining blast dust off of it.
Step 6: Oven (again). 475 once again.
Step 7: Acetone bath. The cover is hung from a rack and washed top to bottom with acetone, inside and out. It is then dried again.
Step 8: Coating Process. Finally. Powder is applied, then blown out of the ports/underside. Nothing clogs oil pickups quick as well as strips of powder that peels off of the underside of a valve cover by a sloppy coating. Ask Harry Blanchard about this. The part is then baked at the appropriate temperature for the appropriate time.
Step 9: Thread Cleaning. The threads for the spark plug cover and timing belt cover are tapped to remove any powder in them.
Step 10: Air bath (again).
Step 11: DONE. The cover is then wrapped in plastic stretch wrap, or put in a heat sealed bag, then wrapped in bubble wrap, put in a box and shipped back to its rightful owner. I then get my $75 which after the costs for powder, acetone, degreaser, and electricity, I celebrate by calling my favorite 900 telephone number for 5 minutes. ;-)
1) I *HATE* powder coating. I didn't start doing it to have it become part of the business--it just kinda worked out that way. I simply wanted a way to clean up parts in-house when doing rebuilds and other customer jobs. It's painful to put a 20 year old valve cover on a freshly built motor, but at the same time, I had replaced too many oil pumps and rebuilt too many engines for people due to the place before us either blasting the head when they rebuilt it, or from media trapped under the baffles of their "pretty" valve cover.
2) Doing valve covers, unless I'm doing it for an in-house build, I couldn't care less if we get the business or not. With the process I use, at $75 for a single-coat color, I'd make about as much per hour working at Mc'D's, with less headaches.
Now that the whine-fest is out of the way, this is how *we* do valve covers.
Step 1: Degrease. These things are typically filthy when they come in the door. I'm talking, pick it up and oil is still dripping out of it, and wherever you touch them, your hand come away black. Let's face it, they've lived a hard life the last 15-25 years. I spray them down with degreaser inside and out, let them sit an hour, then spray them down again. After that, they get hosed down liberally until the bulk of the grease is off of them.
Step 2: Cleaning. They get put in our $4K high temp, high pressure parts washer. First they go in upside down so that the water is flushing out the inside and running through the baffles for about 60 minutes, then get flipped right side up, and washed for another 60 minutes.
Step 3: Oven. After rinsing with fresh water, and drip drying for a while, they go in our one oven and cooked at 475 degrees for about an hour. This serves several purposes. It dries any remaining moisture out of threads/under baffles, and also out-gases the aluminum. Outgassing is CRITICAL on these. I don't care if you buy a brand new valve cover that has never seen 1 drop of engine oil. Mitsubishi's castings are ridiculously dirty. If you doubt this statement, I invite you to weld ANY cast aluminum piece from Mitsubishi. You'll quickly see how much crap floats to the surface of the weld. Outgassing isn't to prevent the coating from peeling up or longevity of the coating. It's to *HELP PREVENT* fisheyes, and spotting in the coating. Notice the emphasis on "help prevent". Unless you do several coats on a used valve cover, I guarantee you that I'll be able to find outgassing in anyone's coating. You're simply not going to avoid it 100% on a porous casting that's been oil coated for the last decade and 1/2. This cooking process also cooks off any sticky oil/grease residue under the baffles.
Step 4: Blasting. The valve cover is mounted to an aluminum plate with two cam caps welded to it with both the outer gasket and spark plug gaskets used to seal it to the plate. A PCV valve that's been welded shut it threaded into the PVC hole, a modified metal valve cover cap with gasket is put in the oil fill hole, and the vent is covered with a thick rubber cap to seal it off. Pickling a valve cover is great for cleaning it, but without removing the loose skin metal on top, and roughening up (profiling) the surface, your coating will peel off in thick chunks in a relatively short time. Been there, done that when I first started coating. The assembly is then blasted.
Step 5: Cleaning (again). The cover is removed from the plate and given an air bath. The baffles/ports all get blown through so that any small amounts of dust (if any) get blown out. Then it goes back into the high temp/high pressure parts washer for another cycle to wash any remaining blast dust off of it.
Step 6: Oven (again). 475 once again.
Step 7: Acetone bath. The cover is hung from a rack and washed top to bottom with acetone, inside and out. It is then dried again.
Step 8: Coating Process. Finally. Powder is applied, then blown out of the ports/underside. Nothing clogs oil pickups quick as well as strips of powder that peels off of the underside of a valve cover by a sloppy coating. Ask Harry Blanchard about this. The part is then baked at the appropriate temperature for the appropriate time.
Step 9: Thread Cleaning. The threads for the spark plug cover and timing belt cover are tapped to remove any powder in them.
Step 10: Air bath (again).
Step 11: DONE. The cover is then wrapped in plastic stretch wrap, or put in a heat sealed bag, then wrapped in bubble wrap, put in a box and shipped back to its rightful owner. I then get my $75 which after the costs for powder, acetone, degreaser, and electricity, I celebrate by calling my favorite 900 telephone number for 5 minutes. ;-)
