Advisibility of 'fettling' new cast pistons

Road-race engines and ancillaries - general discussion
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Graham Stewart
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Location: Sheffield, UK (A)
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Advisibility of 'fettling' new cast pistons

Post by Graham Stewart » Tue May 30, 2017 2:36 pm

I'm in the early stages of renovating/rebuilding the engine in my 2 litre Lancia Beta Spider. The engine will be almost entirely for road use, and will have ported and 3 angle valve seat cylinder head, twin DCOE 45s with 36mm chokes, Vick Auto cast 10:1 (allegedly) pistons, standard cams (thanks Guy!), GC Cunningham rods, GC balanced and modified crankshaft and lightened and balanced Volumex (280mm) flywheel.

The question I want to ask is this; is there any advantage or point in me cleaning up the casting marks, sharp edges and general excess material on my new cast pistons or would this be unnecessary, unwise or just simply not worth the bother? I was thinking that I could save a few grams of mass and at the same time balance the pistons to each other and/or the rods they will be paired with. Is this worthwhile doing or not? And if it is worth doing, what areas of the piston should I concentrate on for material removal and what areas should I avoid?

It goes without saying that I will not be touching any of the bearing surfaces, of course.

Thanks in advance.

Spider 1969
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Re: Advisibility of 'fettling' new cast pistons

Post by Spider 1969 » Wed May 31, 2017 8:48 pm

Hi Graham,

Not a subject matter expert but I'd say that depends on how much difference in weight there is between the pistons.
Your spec looks promising.
One thing sprang to mind concerning the the 10:1 cr of your pistons: this may be based upon standard TC chamber volume.Your valve seat modifications will cause the valve will seat deeper into the head thus increasing chamber volume and lowering compression. Deshrouding the valves will also increase the volume. May be worthwhile to determine dome volume and burette the chamber volume after modifications to check if you have a sufficient cr.
Have fun with the build and it would be nice if you'll post progress and pictures of it!

Regards,
Charles
GC_26

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