Can someone tell me the diameter of a 66 piston head?

Got one laying around?- don't want to take the head off mine
What is the diameter of a 66 aka 80 cc piston?

the 50 I have out here is 40mm at it's widest point-

Nobody's got a 66 piston around and a ruler w/millimeters?

Nashville Kat said:

Nobody's got a 66 piston around and a ruler w/millimeters?

Click to expand...

What do you mean....Nobody??

Bought this,http://www.harborfreight.com/6-inch-digital-caliper-47257.html this past week on special. $10.00 + tx. Just so I can answer questions like this (and anything I might need to measure). It's my first use of it.


A 66cc piston diameter is
1. 47 mm
2. 1.85 in
3. 17/9 or 1-8/9 in

Thank you

or 117.5% of surface volume of the 50cc piston.

So it stands to reason, if the stroke is still the same- and boygofast at least seems to be advertising the same bottom end for both engines- at least with 6mm studs-

the 66cc is 117.5 percent larger than the 50cc, or then actually 58.75 cc?
What am I missing here?

Here's some math- correct me if I'm wrong-
and I don't know the depth of the stroke or the formula for cubic cc's

but isn't the surface volume of a piston head pi x radius squared?

50 cc motor- 40mm diameter means 20mm radius
20 x 20 (squared)= 400
400 x pi or 3.14= 1256 square mm.

"66" motor 47 diameter means 23.5 radius
23.5 x 23.5= 552.25
552.25 x 3.14= 1613.4065 square mm


the second figure should be roughly 117.5% ?
This is the surface area of the piston heads

It's obviously not - it's almost another 1/3 again- or 33% more- so I guess I'm leaving the pi r squared formula off the percentage figure.

33% more then gives us an 18.888 figure- making the motor, with the same stroke- actually a 68.888 cc motor

but of course I've roughed up on the figure to 33- it's not quite and I'm through doing math for the night.
so anyway it's then a little bit LESS than 68.888 cc so maybe 66 is pretty acurate

I think
interesting