08-08-2008, 10:29 AM
Many mechanics and machinists will remove forged pistons from the box and install them. There is a significant gain to be made in properly deburring the crowns so I thought I'd post up a few photos of the process. The idea here is that the sharp machined edges tend to stay much hotter than the face and therefore lead to detonation. I did some work on an engine and gained 2 degrees of timing (MBT for the engineers) with just deburring the crowns. This winter I will be installing some custom sodium filled valves for more knock resistance. It may not sound like much but just this change was good for about 4ft/lb at peak torque and it made 3hp more.
All you need is a sheet of 1000grit sandpaper (wetsanding paper from a body shop supply store). NAPA sells it too... and about an hour of time.
I usually start with the sharpest edges and do each operation consecutively. In other words I will smooth over the first sharp edge on all the pistons first then move to the next edge. Each time I will move to a fresh part of the paper. It probably doesn't make that much of a difference but I like to be consistant and i can be a little anal that way sometimes. Some people use scuff pads but I haven't found these to work well as you really just want to round the edges. I would also avoid any motorized tools because it's really easy to take off more than you want.
You do have to be careful not to touch the outside of the piston at all. This can be easy to do if you make a mistake. Since the outside edge is generally in close quarters with the cylinder wall and the quench area of the head I don't think it contributes a lot in terms of hot spots. Obviously this is engine dependant. On these pistons I did opt to smooth a really sharp edge around the intake and exhaust valve ring seats.
-Michael
All you need is a sheet of 1000grit sandpaper (wetsanding paper from a body shop supply store). NAPA sells it too... and about an hour of time.
I usually start with the sharpest edges and do each operation consecutively. In other words I will smooth over the first sharp edge on all the pistons first then move to the next edge. Each time I will move to a fresh part of the paper. It probably doesn't make that much of a difference but I like to be consistant and i can be a little anal that way sometimes. Some people use scuff pads but I haven't found these to work well as you really just want to round the edges. I would also avoid any motorized tools because it's really easy to take off more than you want.
You do have to be careful not to touch the outside of the piston at all. This can be easy to do if you make a mistake. Since the outside edge is generally in close quarters with the cylinder wall and the quench area of the head I don't think it contributes a lot in terms of hot spots. Obviously this is engine dependant. On these pistons I did opt to smooth a really sharp edge around the intake and exhaust valve ring seats.
-Michael