Dan what current do you use? AC or DC? DC can pick up shallow sub-surface indications while AC will normally only pick up indications that are open to the surface. Also product do you use to check alluminum heads/rods? I know alot of people have seen Magnaflux red dye penetrant but I'm willing to bet very few have seen flourecent penetrant which is actually way more sensitive then mag particle depending on the level of penetrant you use.
Just to give you guys who are interested an idea how the magnaflux works. You have a few different ways you can magnatize a part. 1. you can use a hand yoke. The advantage of these is they are portable and can get into smaller areas. You can use a yoke for pretty much any part you want to mag. but you can only cover a 6" area at a time. The second way of magnatizing a part is to use a magnaflux bench. The advantage of these are you can control the amount of amperage that you put into a part. You also can magnetize a whole part at once which saves time and money if you have multiple parts to do. Third way is you can use another type of magnaflux machine that uses cables. (kind of like welding cables) The advantage of these is they are fairly portable and can do very large parts.
Now for how the process works its pretty simple you magnetize a part while applying flourescent particles. These particles are made up of kerosene/water and iron. If there is a crack in the part it will break the magentic field and cause the flourescent particles to line up along the break, when this happens you get indications that look like the pictures that Dan posted.
