piston sizes

[hillbilly]

a bit of info needed lads and lasses,ive just measured a standard piston(903cc)its about 65.16mm.ive been offered some pistons at 67.05mm.what cc would they be for.

[paulmceleney]

1mm is about 30cc

[Gus]

According to Wiseco

70mm is 1015

71mm is 1045

[ruffle]

Short answer: around 950cc


Long answer:

It's the area of the bore times the swept volume

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(((bore/2)^2* pi) * 4) * stroke

so for a standard 6.6cm bore (piston is a bit less) and standard 6.6cm stroke....

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(((6.6/2)^2*3.1415)*4)*6.6 = 903.16 cc

for your 6.7cm pistons its...

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(((6.7/2)^2*3.1415)*4)*6.6 = 930.74 cc

but that's not allowing for any piston/bore clearance so add 1 mm (not actually sure what the bore should be for your pistons) and that makes it:

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(((6.8/2)^2*3.1415)*4)*6.6 = 958.73 cc

[hillbilly]

so would that make them one mm overbored.

[zed1015]

Yes.

[hillbilly]

cheers lads,it was clear as mud at first.

[ruffle]

You'll still need to find out what the right bore is for those pistons (assuming they're not NOS with known part numbers).

Wiseco talk about bore size not piston diameter; so their 70mm/1015cc pistons are not actually 70mm wide. The 70mm is what bore the cylinders need to suit those pistons.

[hillbilly]

i understand that ruffle,my mate has lent me some barrels that are one mm overbored,so can take a measurement off them to get correct bore.cheers. i think they will be two mm overbore,and not one,as the piston i have here is one mm over,and reads 66.9 mm.

[zed1015]

The bore needs to be the same dia as the piston and then honed to give the correct clearance . Simple.

[garyd]

I do recall some 'big bores' were 960. Not very popular as the engine could easily take more.

What make of piston are they?

[hillbilly]

waiting to find out what make they are.

[steve.w]

waiting to find out what make they are.

genuine kwak i think

[hillbilly]

cheers steve,