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Piston protrusion head clearance

Hello all, been a while since I posted on here, I have just put a new piston in my 1943 WM20, 1941 engine, I didnt notice before if there was any protrusion above the barrel, but the new piston certainly does protrude, .021" above the liner/barrel deck, I use a solid copper head gasket (not composite) which is .042" thick, so logicaly I would have 020" clearance, but is that normal ?

Piston used is a 060" over size GANDINI brand from Draganfly

Cheers
Mick

email (option): michael.skehan@downergroup.com

Re: Piston protrusion head clearance

I've experimented with squish clearance and have found .035"-.040" is the minimum practical figure to avoid contact with the head...Expansion and more to the point, flexing of the crankshaft assy. determine this figure....

It is generally accepted that a figure of MORE than .040" results in the 'squish' effect being lost...

So, a piston that is flush with the top of the barrel and the head gasket you have would result in the correct working clearance...Possible solutions are to fit an appropriate extra gasket under the barrel or to skim .020" of the crown of the piston. There will be plenty of material in the crown for you to remove that amount...Alternatively, fit a thicker head gasket...The drawback with that is that it complicates replacement in the future unless you have a handful laser cut....Ian

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

Re: Piston protrusion head clearance

Thanks Ian, just the info I was after, yeah pull the piston n take 020” off the crown sounds the go, just when I thought it was going back together....😂

Cheers
Mick

email (option): Michael.skehan@downergroup.com

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