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Below are pictures of two heads that were nearly ruined with a Roloc disc. A Roloc disk is mildly abrasive disc mounted to high speed die grinder used to remove old gasket material. It is a useful and timesaving tool when used for appropriate applications, but too many mechanics don't seem to know that the same abrasive that removes the old gasket can also remove metal. Rolocs should never be used on cylinder head or deck surfaces. These pictures were taken after we started to surface the heads. The bright areas are the high spots that the surfacer has ground. The dull spots are troughs that have been ground away with the the Roloc disc. The arrows point to areas where the combustion chamber sealing ring rides. This is the most important sealing area of the head. Roloc damage can be very difficult to detect with a straight edge because the depressions can cover very little surface area, yet be very deep. When checking a cylinder head or deck surface, a mechanic will typically lay the straight edge across the head at several different angles, measuring the gap between the straight edge and head with a feeler gauge in the center (1/2), then at 1/4 and 3/4. To find all of the divots a Roloc leaves, you'd need to measure every 1/2" all the way across on every one of the 8 straight edge angles. That would be about 240 measurements on a single head! If you could average 10 seconds per measurement, it would take 40 minutes just to check one head. When we find a head that has been Roloc'd, we set it up on the head surfacer and take a skim cut rather that wasting time on measurement.

 

 
This is a circuit board that was broken into 2 pieces. (The picture is 200% larger than the actual size.) The part had a bad "ship code" meaning it would be weeks or months before it would arrive. First I glued the two pieces back together. Then I scraped the green coating off of the printed circuits to expose the copper. Next I soldered small wires on to repair the breaks in the printed circuit where the crack had torn them. The part worked fine and the car left the same day it came in.
This is a burnt exhaust valve next to a used but not burnt exhaust valve. Note that the valve on the right still has a margin (the red arrow points to it). The valve on the left has no margin left. The cylinder that had the burnt valve had no compression. When a valve has insufficient margin, it should not be ground. It must be replaced instead. You may also notice that the valve seat contact area (the dark brown ring) on the right valve is closer to the valve face than in the diagram. This is due to valve and valve seat wear and is known as "sunken" exhaust valve. The valve on the right was also replaced because the stem was worn, but that's another story.
This is a 1991 Acura Legend engine block uncovered during a head gasket job. Note the erosion of the aluminum surrounding the cylinder sleeve. The erosion will likely cause the new head gasket to fail prematurely because there is not enough contact surface left to carry heat away from the head gasket. This type of erosion is usually caused by electrolysis. Electrolysis is erosion caused by an electrical current generated by dissimilar metals bathed in acidic fluid, in this case old coolant. Changing the coolant every 2 years will prevent electrolysis.
This is another example of the damage electrolysis can do. This is a picture of a waterpump impeller that has eroded so much it's paper thin and the impeller blades folded over from the force of the water. This could have resulted in a melted engine. Funnily, this car was just in for a routine timing belt job, and there was no complaint of overheating.

To whom it may concern:

These are the parts Elizabeth needs for her 4Runner.
This is a circuit board from an Infiniti G20 automatic window control unit. It looks like there was excessive current pulled though this solder joint. By resoldering the broken connection, we saved our customer some money. Many control units can be repaired in this way. Once we find that a control unit is bad through standard diagnosis, we disassemble the control unit. Sometimes control units come apart easily, other times they are glued together at the factory. Most control units are made of plastic, so some careful work with a hacksaw blade makes it possible to disassemble just about anything, and a little work with a hot glue gun will put it back together. Once the control unit is apart we stare at it for a long time, looking a each individual solder joint for any signs of damage. All solder damage is not as obvious as the damage on this unit. Sometimes the solder joints just have a tiny crack that is causing an intermittent connection. Cracks are usually caused by vibration or movement. There are some control units, such as heating and air conditioning control units, that can be very expensive - $700 and more. These are definitely worth spending some time fixing.

 

This is a heater blower motor switch for a 1989 Honda Civic. The contact strips (the copper colored pieces on the half on the left) were dirty, charred, and grooved from years of use. All of the dirt and charring was removed by careful surfacing with fine flat file, followed by dressing with a fine knife sharpening stone, followed by polishing with an electric pencil eraser. However, there was still some pitting and grooving on some of the contacts, so I tinned the contacts with solder and redressed it. It took about 20 minutes total. At $82 per hour and a switch cost of $42, this was probably not the smartest use of time. Sometimes I just get carried away with a project and leave common sense behind. Oh well, it was a fun repair.

This is a control unit from a 1981 Toyota 4X4 pickup. It's pretty basic; it's main output control of the air injection system. This is a discontinued unit that is not available from the dealer anymore. This one was broken, and with no way to buy a new one, the only option is repair or hunting for a used unit.

Brad disassembled the unit and found several broken solders, (see red arrows). After resoldering all of the pins, the control unit works again and the truck is on it's way to lower emissions.