Reusing the proven good washer might be OK if the seating area on the new plug is the same as the old plug to which the old washer has been pressure form fitted. I have actually heard compression leakage after replacing plugs and using the new washer. The washers appear to be just punched out of copper sheet stock and usually have burrs around the edges which should be smoothed before installation to help insure a good seal with out the need to be over tightened. When changing plugs in full size aircraft, the compression washers are always replaced, as is the washer used to seal the oil drain plug. However, these are NOT simply punched out of copper sheet.
The Belleville washer previously mentioned is for an entirely different application and is made of different material---not soft copper as are plug washers.
I have recently begun using a 1/4-32 die to clean up the threads on glow plugs before they are installed; some glow plug threads are slightly damaged/deformed and can damage threads in the relatively soft head material.
I have noticed that most model engines no longer are supplied with brass or other harder material cast into the head and threaded to receive the glow plugs-------now just the relatively soft aluminum head material.
Edited to add: Installing the concave side down may not be correct in any/all cases. Some plugs seem to have a slight taper or radius at the area of the plug body that will contact the washer. In that case, it may be better to install the washer concave up to better fit the washer to the radius............
More than you wanted to know............
Jim
Topic: Non-Flat Glow Plug Washers (Read 1073 times)
