thanks Ian - any guesses as to brand?

email (option): cas.vanderwoude@gmail.com

BSA used a number system to show type and overbore size...This one has a part number so probably BSA.

I don't know of any aftermarket maker in this country that used BSA part numbers but it is possible it's a USA producer...Ian

email (option): ian@wright52.plus.com

Presumably it was running a three-valve head, judging by the witness marks....

I was thinking of listing it on Ebay - is it worth selling with that "love tap"? Rings feel like they are unused...

email (option): cas.vanderwoude@gmail.com

There's a market for everything it seems..

The piston certainly looks serviceable and the marks on the crown, although unsightly, won't affect its function (though probably will affect the price...)...Ian

email (option): ian@wright52.plus.com

If a valve made those marks, and I can't think what else would have, the piston must have been fitted sideways?

That's what I thought, Ken, hence the tongue-in-cheek '3 valve' comment. I was trying to imagine a scenario whereby some idiot might have removed a barrel and head and tried in some way to check clearance...but I can't.

If a valve head had detached or a valve dropped in then the damage would have been far, far worse.

It's too big a radius to have been caused by careless use of a timing tool.

Rik, Someone spent a while wondering where that last 1/2 inch washer had got to?

.....it was here just before I put the head on....

I realised it was tongue in cheek, but now I am more delighted with the notion we are taking rivet counting to a new level, by musing on what caused this damage......

The possibilities are endless.

The source of this piston is also amusing (I think). Some time ago I bought a replacement barrel on Ebay (My original one had a bunch of fins missing). The piston came with the barrel which had been machined to accept it. So, I now need a new sleeve. Maybe I'm missing something but I can not see how a domed piston would make for an improved WM20, and how it might be damaged by a valve in a flathead engine.

email (option): cas.vanderwoude@gmail.com