New style of 66cc engine:To port or not to port

pjamin10

New Member
Feb 18, 2019
9
3
3
24
Hello everyone,
This is my first post.
Some background on myself in regards to motorized bicycles is that I have already built on 66cc motorized bike. It was pretty junkie bike but I really enjoyed working on it. Also I got it going about 27mph with all stock on 24" wheels. It became so reliable that I used it as my commuter to college every day!
Long story short it got stolen last January but now I am going to build a better and faster bike to use once this Midwest snow melts. (Pic of my old bike:blue bike with motor.)

To my point:
I received this 66cc engine off of amazon from the same seller as my last engine and first off you'll notice there are no header/jug bolts. The head and the jug are one piece with 4 hex heads at the bottom of the jug to connect to the lower part of the motor. Has anyone else seen this style engine before?
Also the ports seem pretty clean and smooth, not perfect.

I have two questions:
What are your thoughts on this motor?
Do these ports need porting??

Hopefully I get some responses.
Thanks guys!
IMG_9733.jpg
IMG_0546.jpg
 

Attachments

Greg58

Well-Known Member
May 1, 2011
4,143
1,033
113
62
Newnan,Georgia U.S.A.
That is like most chain saws and string trimmers are designed today, one advantage is no head gasket to leak. I wouldn't do much till I ran it other than cleaning up the rough spots if there are any. The disadvantage is if the squish band is not correct you are stuck with it, you can't upgrade to a after market head to improve Cooling and compression either.
 
Last edited:

pjamin10

New Member
Feb 18, 2019
9
3
3
24
That is like most chain saws and string trimmers are designed today, one advantage is no head gasket to leak. I wouldn't do much till I ran it other than cleaning up the rough spots if there are any. The disadvantage is if the squish band is not correct you are stuck with it, you can't upgrade to a after market head to improve Cooling and compression either.
Thank you for the response Greg58

I decided to take off the jug(if I am using incorrect terminology please tell me) look inside.

What I believe I should do is bevel the edges of the intake and exhaust ports.
Also what are those ridges in the middle of the transfer ports??
Can I remove them to allow better flow?
IMG_0611.jpg
IMG_0613.jpg
IMG_0614.jpg
IMG_0615.jpg
 

Greg58

Well-Known Member
May 1, 2011
4,143
1,033
113
62
Newnan,Georgia U.S.A.
Be careful not to get into the cylinder with the rasp, don’t remove the dividers in the transfer ports, they keep the rings from hanging at the top of the port. Without the divider the width may be too large.
 

cannonball2

Well-Known Member
Oct 28, 2010
3,662
150
63
Colonial Coast USA.
Anyone have any experience with one of these? I just ordered one thinking it might be the basis to use in a Stihl cylinder/piston build. Wondering how it is stock. I like the idea of a cylinder jug. My BT80 has been an excellent engine.
 

pjamin10

New Member
Feb 18, 2019
9
3
3
24
The engine works well and with all stock parts from the kit I am able to hit 34MPH flat out on an aluminum mountain bike frame. The only down side I have seen of this motor is it is balanced quite roughly in my opinion. It runs smooth until you hit 10MPH and then vibrates quite badly from there and faster.

I will be re balancing the crankshaft here soon.
 

cannonball2

Well-Known Member
Oct 28, 2010
3,662
150
63
Colonial Coast USA.
Sorry to hear that. Not surprised though if the maker just put a top end on it with no regard to piston weight. I would have thought the piston would be lighter which should have helped balance. Who knows what they have cobbled together. Did you measure the bore size?