Engine displacement vs stated CC's ???

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Engine displacement vs stated CC's ???

Postby Cb673 » Sun Oct 07, 2018 10:29 am

Hello all,

So the cb650 is bore x stroke is actually 627cc, with head chamber of (?) 24cc.
Making roughly 650 when added together.
If a motor were bored out, and one wanted to put cb"XXX" on the side covers, should the head 24cc's be added as well?
I'm doing a 62mm overbore soon, and don't know if I want to put cb673, or cb696 on the side covers...
673cc is only bore x stroke, 696cc is bore x stroke +head cc's

What's your opinion?


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Re: Engine displacement vs stated CC's ???

Postby Volker_P » Tue Oct 09, 2018 1:58 am

Welcome here! :D

At http://irfanview.com you find a nice, free tool for picture view and resize.

With regard to your side cover label issue, I would prefer the "696" just because of the visual beauty of the sequence of digits.
In case you really cannot decide for sure, there is still the option to preliminarily put "cb XXX" on the side covers, too. :lol:
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

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Re: Engine displacement vs stated CC's ???

Postby kerryb » Mon Oct 29, 2018 6:01 pm

I'm not an engine guy, but I know enough to get myself in trouble, so here goes with an opinion with my reasoning to back it up. Engines are labeled with the displacement of the engine. Displacement indicates movement..."displaced" or the amount of of air moved by the piston. The volume of the head remains static, the mixture gets squeezed into it but the piston doesn't move through it. So the actual volume displaced does not include the volume of the head. That being said, I would label the side covers with "696", it's got a better ring to it. If someone takes issue with that after they learn the size of your new pistons...congratulate them on their mastery of engine math. :D

It's all part of the adventure.

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Re: Engine displacement vs stated CC's ???

Postby Cb673 » Mon Oct 29, 2018 10:52 pm

The cb650 displaces 627cc. The 750 displaces 726cc....

And I'm going with the 696. Comes to the displacement plus the 23 head cc's(noticed I said 24 earlier..oops)


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