Engine Knocking....

[Denis Sweeney]

Thanks for the comment John, the original noise came on under load in third and fourth, revving the engine whilst stationary nothing was evident.
Later it started to sound just generally rough, a member of the local A7OC came for a spin to try to diagnose the issue. Nothing conclusive was detected but he said it sounded pretty rough and so that’s when I decided to stop driving her and investigate.
You are not the first to suggest a “hotter” plug to assist in reducing carbon deposits.
I do not know what the acceptable limits on piston clearances are but I did read +0.003 on bore to piston diameter for pistons up to 2.5” this was from a Pitman’s book. But not sure if this was for new build or maximum wear??