During the rebuilding of our prechambers we found that the socket head capscrews that secure the upper and lower halves were too long and bottoming out in their holes. This was discovered while troubleshooting oil leaking into the sparkplug bores on 6 of 18 cylinders of one unit.
Measuring the holes with a depth micrometer, we found the bore depth matched the screw length exactly, with no room for stretch. In other words, the screws were bottoming out in the bores when torqued and not providing adequate compression at the sealing faces of the prechamber.
Approx. 3 threads were cut from the ends of the screws to prevent bottoming in the bores.
Feel free to contact me via email for details and photos, as I can’t attach photos to this post.
Dave Mordecai
City of Tallahassee Hopkins Station