Hi there,
make sure that the correct spark plug is used, there are some special "long reach"plugs used and if you have fitted one of these the piston could strike the plug. But this would happen on the first compression, so just make sure that it is set (gap) correctly and see what happens. The only other way it can happen is the piston travel is excessive and anything that can cause that will make a loud engine knock.
Mark (mhpautos)
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Wednesday, May 14th, 2008 AT 7:25 PM