49cc vs 80cc questions on differences

[wildone]

first off is there a difference in the stroke of the 49cc verses the 80cc i know the bore is not the same but what about the stroke on a stock motor set up???

 

[crassius]

I think stroke is same on the older models (some new 80s have diff stroke), but I haven't seen a 49 in many years. 49 is faster on flat roads (prob due to swinging less weight), but here where the hills are steep, only the 80s will climb them.

 

[The_Aleman]

Yeah, the small chinagirls tend to out-rev the bigger ones simply because of less rotating mass. They also don't have as many balance issues in general.

The bigger chinagirl will make ~50% more torque simply because of displacement. This of course translates to roughly 33% more horsepower.

 

[wildone]

i just bought a 2011 model 49cc from my friend and he said he only rode it maybe 20 times but i cant get it going much faster than a idle after sitting for about a year i even changed carbs but it still would not pick up any speed so i pulled it off the bike and replaced it with a new 80cc using the new clone carb the bike runs great now so im thinking of putting a bigger bore piston and liner on the 49cc motor. thats why i m wondering if the stroke is the same.. the 35 bucks for parts is cheaper than a new motor and i might learn how to port the jug while i m at it if the parts will fit

 

[crassius]

never seen a big bore fitted onto a 49cc - tho some folks say they can do it

your 49 is probably good and just needs something adjusted a bit - head gasket & ignition are common fails

 

[KCvale]

You can't 'bore out' a 48cc cylinder and put a 66cc piston in it, there is no room.
The 66cc's have fatter and wider apart head bolts to accommodate the fatter cylinder and won't go on a 48cc bottom end either.

If you plan to re-use the 48, just do the basics first.
Pop the head and check inside for damage and debris, check the head gasket, then use an actual torque wrench and tighten the head to 12# ~4# at a time.

 

[wildone]

well i guess ill look for some one with a couple of old 49cc barrels to experiment porting on them before i try it on a new one..And your rite about poping it apart to see what i can see..i suspect he burnt the piston or liner or both.. ill let ya know after i pull it down today. And last but not least by any means thank you guy you already save me some headache and put me farther up the learning curve than i was a while ago

 

[crassius]

if he has 6mm studs, I'd recommend 8# +/-2# for that torque

 

[wildone]

well sure as shooting the head gasket is showing signs of being blown. i should of known when i saw 6 washers on each stud it was a tell-tale sign of a pre-existing problem not disclosed at time of purchase (go figure) thats why he flattened the tires so it could not be riden.. never the less its a easy fix.. on to the next problem the air filter wont fit against the seat post down tube.. need to find a flex hose to fit the clone carb and build a air box

 

[wildone]

next question are the head gaskets reuseable on this motor ??? they dont look like they smash down like a exhaust gasket