Stroke & bore size?

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moronic_kaos

moronic_kaos

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Apr 6, 2010
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Lol yea I'm sure this has been shared 100 times already but it's kind of hard to search for "stroke size" since you get all the results for "2-stoke engine acting funny" and "what's the difference between a 2 and 4 stroke" and "what size bicycle does a 4-stroke fit", etc

So what is the stroke & bore size of these motors. According to the bikeberry site:

Disclosure of accurate engine size: While we have chosen to use the long standing factory branding engine size of "80cc", the true displacement of the bicycle engine is 66cc. Down through the years China bicycle engine manufactures have advertised their biggest engine as 80cc, therefore we have listed them in the same way on our website. However, the bore and stroke of an 80cc being 47x38mm equals 66cc.
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Is this correct? Plus, this equals 1786.... What am I missing here?

Edit: Whoops, cubically it would be 67.868, my bad...
 
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Bikeguy Joe

Bikeguy Joe

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Jan 8, 2008
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I can only add that I have gotten 50cc engines that had differing bores but the same stroke. One was 47cc the others were 45cc.


Have you measured you stroke and bore to see what you actually have? I believe I have read of two different stroke measurements when talking about the classic chinese bicycle engine kit.

Once you know what you have, maybe call the vendor you bought it from, or others to confirm what they are selling?
 
moronic_kaos

moronic_kaos

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Bikeguy Joe said:
I can only add that I have gotten 50cc engines that had differing bores but the same stroke. One was 47cc the others were 45cc.


Have you measured you stroke and bore to see what you actually have? I believe I have read of two different stroke measurements when talking about the classic chinese bicycle engine kit.

Once you know what you have, maybe call the vendor you bought it from, or others to confirm what they are selling?
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I know how to measure the bore (diameter of the cylinder, duh), but not the stroke. Unfortunately my personal motor is being welded up and I'm not about to take apart the one a friend let me borrow in the meantime.

Plus, I don't think you can call BGF. The two different stroke measurements (I could be dead wrong here) one is the Chinese which includes the space in the head, which technically doesn't contribute to the stroke and the other is the American standard. There's a description of it somewhere on one of these sites that says something like that.

Just kinda wanted to do some online window-shopping, for perhaps a compatible billet cylinder (more for bragging rights than anything) or if I got really really lucky, a compatible top-end kit that a reed would fit on. Of course I know that space is cramped and some custom exhaust & intake stuff would have to be made, but I need an excuse to learn how to use my welder, and I didn't want my engine mounts to be it. Feel much safer with a $30 exhaust pipe and a $10 intake.
 
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MotorBicycleRacing

MotorBicycleRacing

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Jul 28, 2010
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Dogtown Burner said:
I have found an engine advertised as a 60cc. looks like our 66's. this fella asked me for some cylinder mods and i'm scratchin me head!

www.cyclepromotors.co.nz/assets/Doc...rs-TB-2011.09.13-Street-60-Specifications.pdf

any takers? what the heck is this thing?
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On that page they say the specs are:
60.45 cc
45mm Bore x 38mm Stroke

So it must be a Grubee GT33 which also has 45mm Bore x 38mm Stroke.

I have never seen one and who knows if they were ever imported to the US?
 
2door

2door

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If you have the capability to measure the bore then you should be able to measure the stroke. The stroke is the length of travel of the piston from top dead center to bottom dead center. Simply bring the piston up to the top of it's stroke and call that 0 (zero) then rotate the crankshaft until the piston is at bottom dead center and measure the distance down the cylinder wall that it traveled. That's the length of stroke, or simply, 'the stroke'. It is determined by the centerline of the crankshaft connecting rod journal or bearing. Connecting rod/piston size or length has nothing to do with the length of the stroke. The connecting rod could be four inches long or ten inches long. The stroke will remain the same.

Use the formula, 3.14 x cylinder diameter x length of stroke, for finding the volume of a cylinder and you'll have the size of your engine, displacement, in cubic centimeters, or CCs if you used metric measuring equipment.
The 80cc figure comes from using the volume of the combustion chamber added to the volume of the cylinder. We're not generally concerned with combustion chamber size in determining engine displacement so we come up with the 66-70cc engines that many of us use.

If the engine has more than one cylinder you simply multiply the answer you get from the formula times the number of cylinders you have to give you total displacement.

Tom
 
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