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66cc Vs. 68.5cc engine What different?

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  #1  
Old 06-07-2011, 10:31 AM
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Lecheroandpuertorro Lecheroandpuertorro is offline
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Default 66cc Vs. 68.5cc engine What different?

Hi friends
i have a 66cc in my bike with angle fire head one day i test the compression and the gauge read 150 psi i dont know this number is good but i need to know is good or no.The solution for me is visit a friend and check your bike he had a 68.5cc engine when i check the compression WOW 250 psi i check other 66cc engine and i read 150 psi now i believe 150 psi for a 66cc is normal but now my question why the 68.5 engine have 250 psi and the 66cc have 150 psi? i check and the engine in the outside is same as 66cc i believe if he have some differences that is inside the engine. i ride the bicycle of my friend and she have good torque more that mine and he ride the bike with 87 octane fuel and i ride my bike with 93 octane but dont see result with high octane but this is other history.Please any friend in the forum i need help to know the different of this 2 engines.
Thanks....
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Old 06-07-2011, 10:48 AM
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Default Re: 66cc Vs. 68.5cc engine What different?

150 psi is a good number for the 66cc engine.

I can't believe an extra 100psi is coming from the extra 2.5cc of the other engine.(must be a buster to pedal start)
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Old 06-07-2011, 10:51 AM
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Default Re: 66cc Vs. 68.5cc engine What different?

Could be squish band, head gasket thickness, piston configuration, or ring condition.
Or all of the above.
Take your pick.
150psi is respectable.
Ride it like you stole it!
rc
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Old 06-07-2011, 05:24 PM
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Default Re: 66cc Vs. 68.5cc engine What different?

thanks for the answer but i like to know if the 68.5cc have more stroke or more bore than 66cc.let me know if you have this info for this engine.
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Old 06-08-2011, 03:25 PM
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Default Re: 66cc Vs. 68.5cc engine What different?

Best of my knowledge the "68.5cc" is still just the same ole 66cc and being called a 68.5cc, I know BGF on ebay sells soem of his engines with the claim "68.5cc" and I have one that was claimed at that size and it has the same everything as the other 66cc engines best I can tell, I think it is just another sales gimic just like some call the 66cc an 80cc which it isn't.

Just my $.02

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Old 06-08-2011, 04:17 PM
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Default Re: 66cc Vs. 68.5cc engine What different?

Pop the head off of your engine and measure the diameter of the cylinder, then go to your friend with the 68.5cc engine and measure his cylinder and see if same or not.
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Old 06-08-2011, 07:25 PM
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Default Re: 66cc Vs. 68.5cc engine What different?

i dont understand one point i measure the compression of two 66cc engines and the measure is same 150 psi and i measure the 68.5cc engine and have a compression of 250 psi my friend is a maniac with your engine and dont head off only for a suspect i need a biker with this two engines and with the experience of disassembly this engines and compare both s..i believe this person exist in this forum...thanks my friends
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Old 06-08-2011, 07:58 PM
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Default Re: 66cc Vs. 68.5cc engine What different?

Quote:
Originally Posted by Lecheroandpuertorro View Post
i dont understand one point i measure the compression of two 66cc engines and the measure is same 150 psi and i measure the 68.5cc engine and have a compression of 250 psi my friend is a maniac with your engine and dont head off only for a suspect i need a biker with this two engines and with the experience of disassembly this engines and compare both s..i believe this person exist in this forum...thanks my friends
No matter where you look you will never find any parts listings for a "68.5cc" engine.

49cc 66cc are the most common and 66cc is the biggest of the China Girl 2 smokers.....

Myself and many others have rebuilt these engines from the ground up and there is only a 66cc engine that gets called 68.5cc, 70cc or 80cc

As to the 250lbs compression I have no answer for that.

Go to this link and scroll down, read and you will see this engine is called a 66cc, it's called a 80cc and in the final description it is refered to as a 68.5cc engine, the truth of the matter is that this is a 66cc engine and this is the biggest displacement of this type engine that is made

80cc Motor Bike Motorized GAS ENGINE KIT black X-80BK | eBay

I dont see one of these engines being capable of being roll started if the compression was actually that high, that is about like diesel compression ratios and not typical for one of these loosely built chinese engines, that kind of compression would require a much better built engines than these are to have any durability in my opinion.

Peace
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Old 06-09-2011, 01:04 AM
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Default Re: 66cc Vs. 68.5cc engine What different?

is that a slant.... and do you recommend that motor for a first time builder?

Thanks!
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Old 06-09-2011, 10:16 PM
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Default Re: 66cc Vs. 68.5cc engine What different?

Quote:
Originally Posted by jtgolden View Post
is that a slant.... and do you recommend that motor for a first time builder?

Thanks!
Here is the one I would choose between the two, I just used that other kit for referance for the point I was making about the advertised 66cc-68.5cc-70cc-80cc.

80CC BICYCLE MOTOR gas ENGINE KIT MOTORIZED silver X80A | eBay


This is the engine that I will be putting on my next build, and a good friend of mine has this same kit and he got an excellent engine, very smooth and strong. all of my engines that I have bought came from BGF and I've had good results.

Peace
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