Hello from California

0megaMan

New Member
Aug 9, 2016
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Escalon, Ca
I'm the type of guy that always needs a project, not that bowfishing season is over I'd like to build a motorized bike. I will be starting with this.....



A SE Racing single speed, CroMo frame that measures 16" from bottom bracket to top tube. I do not think I can squeeze a 4 stoke in there so I ask which kit do you guys recommend?

I've watched a million youtube videos and have come to 2 conclusions, it look like a lot of fun and the supplied brackets are chincy at best. Fortunately I'm a fabricator by trade and will be fabbing purpose built pieces to replace those one size fits all stamped brackets.

Thanks for any advice in advance.
 

Dave31

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Staff member
Mar 1, 2008
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Welcome to the forum 0megaMan. Looks like you have a great candidate for a motorized bicycle. Keep us updated on your prpgress
 

0megaMan

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Aug 9, 2016
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Escalon, Ca
The more vendors sites I go to the more it appears these 66cc motors are all the same.

Do I just find the best deal and go for it?
 

MotorBicycleRacing

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Jul 28, 2010
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SoCal Baby!!!
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A SE Racing single speed, CroMo frame that measures 16" from bottom bracket to top tube. I do not think I can squeeze a 4 stoke in there so I ask which kit do you guys recommend?
.
Cut a piece of cardboard 8" wide x 9 1/2" tall and place inside your frame
on the level to see if the 49cc 4 stroke motor and carb will fit.

Welcome to the forum from SoCal.
 
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Tyler6357

Well-Known Member
Mar 15, 2012
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Santa Barbara, CA
The more vendors sites I go to the more it appears these 66cc motors are all the same.

Do I just find the best deal and go for it?
Wait, not all 2 stroke china girl engines are the same. It might have been true in the past but not anymore. Here are a couple videos for you to watch that explains some of the differences. I think the PX80s are better than the GT5s but that is just my opinion.

https://www.youtube.com/watch?v=rzLWYSlpFEg

https://www.youtube.com/watch?v=MMZqayAYsWo

Also, that frame looks like a good start, it appears to be steel which is better for vibration and strength, get a front break for it.
 
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0megaMan

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Aug 9, 2016
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Escalon, Ca
.wee.
Wait, not all 2 stroke china girl engines are the same. It might have been true in the past but not anymore. Here are a couple videos for you to watch that explains some of the differences. I think the PX80s are better than the GT5s but that is just my opinion.

https://www.youtube.com/watch?v=rzLWYSlpFEg

https://www.youtube.com/watch?v=MMZqayAYsWo

Also, that frame looks like a good start, it appears to be steel which is better for vibration and strength, get a front break for it.
This is the kind of insight I was looking for.

Thanks for the links I will check those out. As for the bike frame it is Cromoly like I mentioned in my first post., probably will have to get a beefier fork possibly a suspension fork.
 
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0megaMan

New Member
Aug 9, 2016
30
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Escalon, Ca
Wait, not all 2 stroke china girl engines are the same. It might have been true in the past but not anymore. Here are a couple videos for you to watch that explains some of the differences. I think the PX80s are better than the GT5s but that is just my opinion.

https://www.youtube.com/watch?v=rzLWYSlpFEg

https://www.youtube.com/watch?v=MMZqayAYsWo

Also, that frame looks like a good start, it appears to be steel which is better for vibration and strength, get a front break for it.
I watched the videos, seems like great information on how to determine which engine you have if you're ordering parts. However I didn't take away anything from them that would help me determine which type is better and why.
 
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Tyler6357

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Mar 15, 2012
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Santa Barbara, CA
In the video he says that the PK80s are 40 stroke and the GT5s are 38 stroke, this makes a difference. The 40 stroke ones all use the type "B" piston and the shorter connecting rod except the A80 and the half breed ones which are not very common. The GT5s use the longer connecting rod and are only 38 stroke.
 

0megaMan

New Member
Aug 9, 2016
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Escalon, Ca
If I recall he said in the second video I believe he mentioned he runs a motor with a 38mm stroke, so is the consensus that the 40mm stroke is more desireable?
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,143
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Santa Barbara, CA
Yes, I think the 40mm stroke is more desireable, also, he talks about the top of the piston coming up to the very top of the cylinder which decreases the squish gap (ignition zone). A smaller squish gap creates a more powerful explosion and more power. This, I think, makes the PK80s better, however, this is just my opinion, others might respectfully disagree with me.
 
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0megaMan

New Member
Aug 9, 2016
30
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Escalon, Ca
Yes, I think the 40mm stroke is more desireable, also, he talks about the top of the piston coming up to the very top of the cylinder which decreases the squish gap (ignition zone). A smaller squish gap creates a more powerful explosion and more power. This, I think, makes the PK80s better, however, this is just my opinion, others might respectfully disagree with me.
I appreciate the help. Probably going to order a PK80 from Dax. Seems like a good place to start.
 

0megaMan

New Member
Aug 9, 2016
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Escalon, Ca
Found this on Craigslist for $100, all the cables are loose and the bottom bracket is jiggling around pretty good but everything should be easily repairable.



Pretty sure this was a screaming deal.
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,143
170
63
Santa Barbara, CA
That looks good! $100 is a steal! Nice RT Carb upgrade, that is a much better carb than stock. Kinda hard to tell if it's a PK80 or a GT5 without taking the head and cylinder off and looking at the piston and the connecting rod and comparing them to the ones in the video. It looks like a 66cc one and not 49cc. That's a stock pipe and head on it, it don't look that bad at all, nice find!
 
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