You may need to resurface your cylinder heads to improve the finish of the surface, restore flatness to the head. After welds or other repairs have been done to the cylinder head such as increasing the compression ration, the cylinder head may need resurfacing. Regardless of why you need to resurface the head, the important part of the process is getting it done quickly and correctly. If you make a mistake, it can cost you. You can not remove too much metal because you can not put back what has been taken away, resulting in having to purchase a new cylinder head.
Here are some of the most common mistakes that result from resurfacing cylinder heads:
Wrong Finish on the Surface
A head gasket needs a surface finish that will allow it to seal properly. The range will dpend on the type of head you are working with. Surfaces that are too rough or too smooth will result in the gasket not sealing properly, causing it to leak. Don’t ignore the recommendation for the type of head gasket you are working with. The finish may appear to the naked eye to be correct but you can’t be sure it is within the recommended range. You will also not be able to feel if a finish is correct. The only accurate way to tell if the finish is complete and correct is by using a profilometer. This instrument uses a diamond-tipped stylus that is dragged across the surface. It calculates the profile of the surface and will display the values necessary for the surface. The values include roughness average, average valley depth, average peak height, and waviness of the surface. These values are especially important when you are building a high-performance engine.
Not Aligned Properly
You need to line up your surface with the resurfacing equipment before you start cutting away. The surface must be parallel with the cutter head and side to side. Then you can set up the depth of your cut. You can not make the mistake of moving the head after it has been aligned. Some machines now have indicators that make it easy to set and be more accurate in your resurfacing efforts but some will still allow for movement that can mess up your proper alignment. During resurfacing, you need to ensure that the part and the machine do not move or you can negatively affect the finished surface.
Incorrect Speed
The quality of the surface finish will be high if you are using the correct feed rate and speed for the tool bit type you are using, which varies based on the diameter of the head cutter.
Old Equipment/ Wrong Tools
If you are looking to achieve an exceptionally smooth finish, you’ll need to invest in quality resurfacing equipment like a milling machine. It will not matter what kind of tool bits are used to resurface the cylinder head provided the feed rate and speed are correct. When it comes to the tools you need, experts recommend using CBN on cast iron cylinder heads and PCD on aluminum cylinder heads. Some experts say that CBN will work on both kinds of metals however. PCD is not recommended for cast iron cylinder heads because the diamond becomes too hot at the high cutting speeds. It will chemically react with the cast iron, causing a break down. CBN is capable of handling the higher temperatures and disperses heat four times faster than silicon carbide so it stands as a good choice when you are doing high-speed resurfacing.
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