[Maylands Performance]

Hi Pitmaster.
The piston crown has an odd carbon pattern on the RHS.From the pic it almost looks as if the top of the piston has been coming in contact with the cylinder head or head gasket.In the pic there appears to be a ring of clean aluminium on the RHS outer.!!!???Is it possible you have previously been rough with the con rod ie:driven the gudgeon pin with a hammer and bent the conrod ?? Sorry dont be offended I have seen it done by customers previously !!..
If the conrod was bent the piston would float or shuttle sides ways in the bore causing a knocking sound. [But the noise would increase hugely under increased revs]
The easiest way to check if the con rod is bent is to re-assemble the piston and cylinder minus the cylinder head.If the rod is bent the piston crown will be tilted or cocked sideways slightly !!
Note :If the conrod was bent the very bases of the piston skirt would would have odd angled wear patterns.[The piston crown above the ring lands directly above the pin circlips on one side would also contact the cylinder bore !]

Check your ring gaps
Check your piston to bore clearance
If these are ok at least you can count them out of the equation !!

Ps .Perhaps the knocking sound is Clutch or Trans related

Cheers Brian