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As posted elsewhere I have a knocking big end after my weekend at Silverstone, the car has done 700 miles since the rebuild and considering it's built mainly from 38 year old parts I was expecting there may be some issues, even after having to replace the head due to a crack. I suspect one of the rods or the crank are oval and have been so since the rebuild.

I will send the crank and rods away for checking and machining but I'm wondering whether I should do something with the pistons and bores? There was some wear on the bore of number 6 but nothing excessive and it doesn't seem to use any oil, but while I'm there.....

From what I understand new pistons in oversize are not available except if I have them made. Also new standard pistons are available but the cost doesn't seem to be any lest than having them made. I have a spare 320 block so boring out and having standard 323 pistons is I believe an option.

What are people's experiences, any advice, what should I do?

Hi Keith, glad you made silverstone with it but bummer if it has run a big end. Id hope that from what youve described that a new set of shells and honing of the bores would be enough to rectify this, especially with the piston replacement costs. I will see if can find shell set part numbers for you std and oversize. Have you done a compression test on this engine ever? That would help knowing the values to decide how to proceed.
I havent had any experience with these engines internally yet other than oil pump and tappet setting up so cant advise you but do hope somebody here can.

Well I've done a bit of research.

Bottom end I'm looking at a regridg with undersize bearings which are available from W+N if nobody else does them, so that's not a big issue, just slightly costly. I would have to get all the rods checked for ovality as well.

The next question is do I just leave the pistons and bores alone as they seem ok, not burning any oil etc, or should I go the whole hog this time? I can't find oversize pistons but I can get them made at a cost of $900 (plus shipping and probably some import duty), I could then get my block rebored

The 320 and 323 block have the same bore and I have a 320 block which I think is good, maybe I could have this honed and fit my old pistons?

Does anybody know what the differences are between the 320/323 block, can it be used if the bores are OK, what do I have to do?