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Author Topic: Engine bore sizes  (Read 343 times)

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Offline lash

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Engine bore sizes
« on: February 07, 2019, 01:39:11 am »
How much is 1 over on a 750 engine? Does that make it an 836 or ?
« Last Edit: February 07, 2019, 09:24:40 am by lash »
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Offline robvangulik

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Re: Engine bore sizes
« Reply #1 on: February 07, 2019, 01:45:22 am »
760.
Do the math....

Offline bryanj

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Re: Engine bore sizes
« Reply #2 on: February 07, 2019, 02:18:02 am »
3.1472x diameter(in cm)squared ÷4 x stroke(in cm) x 4
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline lash

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Re: Engine bore sizes
« Reply #3 on: February 07, 2019, 09:26:08 am »
760.
Do the math....

Not getting this one at all...
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Offline slikwilli420

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Re: Engine bore sizes
« Reply #4 on: February 07, 2019, 09:43:44 am »
1mm over is 760, as that is the class limit on my race bike and I had custom 62mm pistons made.
All you gotta do is do what you gotta do.

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Offline Tracksnblades1

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Re: Engine bore sizes
« Reply #5 on: February 07, 2019, 11:05:49 am »
Lash,

Like stated 1 over in this case is 1mm.
Stock bore diameter = 61mm,    radius = 1/2 bore diameter or 30.5mm
1mm over diameter = 62mm,    radius = 1/2 bore diameter or 31mm
StockStroke      =  63mm

Using the old formula for "volume of a cylinder".  Several variations exist now.

Volume of a cylinder formula is stated as  V=πr2h
V (Volume)  =(equals) π (pi 3.1415) r2 (radius x radius) h (height/ stroke)
Entering your values in the equation
V= 3.1415,  times,   (31)2 or 961,  times,  63 (stock stroke)
V= 3.1415 x 961 x 63
V= 190,195.834 cubic Millimeters or 190.195834 cubic centimeters
Volume for 1 cylinder with a 62mm bore and 63mm stroke equals 190.195834cc
Total displacement for all 4 cylinders = 4 x 190.195834
Total displaced Volume = 760.783338 cc

That's the Math their talking about. This example doesn't include piston to cylinder wall clearance. Their are other equations that help eliminate "order of operations" mistakes. Better yet there are online displacement calculators that don't make any mistakes.

👍

« Last Edit: February 07, 2019, 11:31:24 am by Tracksnblades1 »
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Offline lash

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Re: Engine bore sizes
« Reply #6 on: February 07, 2019, 11:11:37 am »
Thanks for spelling that out! Now I get it..even us old guys can learn something new every day!
I think...therefore I ride..

Offline david 750F

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Re: Engine bore sizes
« Reply #7 on: February 07, 2019, 11:20:43 am »
There are four factory oversized pistons.
1st is +0.25mm =742cc
2nd +0.5 mm.   =748cc
3rd + 0.75mm.  =754cc
4th + 1.00mm.  =760cc

Anything over 1mm (62mm actual diameter) is considered a “big bore”.


1976 CB 750F

Offline robvangulik

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Re: Engine bore sizes
« Reply #8 on: February 07, 2019, 02:51:07 pm »
Thanks for spelling that out! Now I get it..even us old guys can learn something new every day!
What is old? ;D

Offline Tracksnblades1

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Re: Engine bore sizes
« Reply #9 on: February 11, 2019, 08:19:11 pm »
Thanks for spelling that out! Now I get it..even us old guys can learn something new every day!
What is old? ;D

Some DMV's consider anything older than 20years are "Classics". 45years and older are considered "Antiques".  I never thought I'd be an antique.

😩
« Last Edit: February 11, 2019, 08:26:04 pm by Tracksnblades1 »
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Offline pjlogue

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Re: Engine bore sizes
« Reply #10 on: February 12, 2019, 12:36:36 am »
Thanks for spelling that out! Now I get it..even us old guys can learn something new every day!
What is old? ;D

Some DMV's consider anything older than 20years are "Classics". 45years and older are considered "Antiques".  I never thought I'd be an antique.

😩

So 20 years = classic, 40 years = antique, what does 60+ years =?  Fossil? :D

-P.

Offline lash

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Re: Engine bore sizes
« Reply #11 on: February 12, 2019, 12:48:49 am »
In my case that would be a fossil riding an antique!
« Last Edit: February 12, 2019, 03:04:04 am by lash »
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Offline bryanj

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Re: Engine bore sizes
« Reply #12 on: February 12, 2019, 01:25:45 am »
Does that make me a fossilised antiqu dealer?
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

 

;
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