Hi Richard and all you are amazing knowledgeable people out there. This thing is really starting to beat me:((
So acquired a wartime 16 H engine and fully rebuilt it but actually all the internal components were really good to really. I've just restored what was already there but the piston had picked up.
Replaced it with identical piston new old stock and all good however when the Piston reaches TDC it just touches the copper of the head gasket.
I noticed on the old piston it looks like it has been turned a fraction maybe just to clear the gasket in its previous life now I know the chap I bought it off. He said his father used to race it and there's been a few Tell Tail signs of this.
Could this be the wrong piston for this bike with the crown so high?
Please give me some direction to go as I'm losing the Will a little bit.
cheers
16H Pistons
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Hi Richard. Thanks for the…
Hi Richard.
Thanks for the info. Yes, it looks like the ball has been radiused If that's the right term.
what I did this afternoon was to gently push back the copper in the head gasket which I believe is a new old stock gasket and it took it very well. I've now got the clearance I need but it's close obviously now these things are so simple to work on on the top I thought when I get to the point where I can run it, it's only a five minute job to take the head off to see what's happening.
I guessed it was to do with the rebore to 60 thou.
I do have another barrel but this one is in exceptional condition and measures are only 78.3 mil which means there's plenty of scope for a rebore to 10 thou I believe.
just waiting for the oil tank to be restored and I've got to try and locate the right magdyno complete as it's a clockwise rotation and my Lucas unit is a anticlockwise.
will let you know, sir. Thank you so much. If you do happen to know of a complete unit.
cheers
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I suspect that you have a number of factors causing problems here. The piston looks to have the standard 16H domed form.
I suspect that the cylinder has been skimmed as the piston body is usually level with the cylinder deck. Yours has certainly been radiused / flowed which makes it even more obvious.
This probably wouldn't be too much of a problem, except that the standard composite head gaskets have an internal diameter just shy of 80mm. Norton didn't show oversized pistons in the pre-war civilian parts lists, but in the WD lists from 1937, they went in .010" increments up to + .030" only. This would be roughly 79.8mm. In 1939, they included a +.040" oversize but no larger size was officially listed. You're going to be at about 80.5mm on that oversize.
I have seen solid copper gaskets that were slightly over 80mm but the composite gaskets don't seem to have changed. I think that I would prefer a solid gasket with a tweaked engine.
Your alternative is probably to machine the piston as the previous owner seemed to have done. Obviously, you'll have to check everything.
This photo shows mine on an occasion when it had become a bit hot and bothered...From memory it's on +.040 - No gasket in place but you can see the witness marks.