Steve Best
Well-Known Member
So this is going to be an impression, not an accurate test because I stuffed these a month or more ago and got busy. Didn't write down any data about this engine. I'll never make it as a scientist.
It is my old black unknown 66cc Happy Time China Girl. My first engine.
I bought the entire bike and engine for a song but it worked well enough to get me hooked.
I cannot remember what the top speed was but I improved it a bit with a head mod, new muffler and cleaning the flashing out of the transfer ports. No porting, no timing changes, maybe a little more compression.
I stuffed the bearing retainers and spread 1-2mm of JB weld over the entire sides of the cases much like this:
I also filled in the through under the transfer ports where it went below the crank cheeks, as shown in solid red. I drilled an oil flow port to the bearings on each side, because I could see the oil had been baking in there. No pictures I am afraid, lost my darned camera again... (old guy, losing it!) New seals and bearings while I was in there.
So not a huge gain. Nothing in top speed, in fact I think I might have lost a bit. I showed 45kph and I am sure I broke 50 kph before this mod, but cannot be sure. Where it gained is rock steady idle and lots of low end torque. It would now do the steep hillclimb with only a bit of assistance now (this is not the modified Grubee, which will climb with no assistance). Previously it would not climb the hill even if assisted. Throttle response is crisper. Powerband is much lower rpm than it had been originally. I'm surprised.
Steve
It is my old black unknown 66cc Happy Time China Girl. My first engine.
I bought the entire bike and engine for a song but it worked well enough to get me hooked.
I cannot remember what the top speed was but I improved it a bit with a head mod, new muffler and cleaning the flashing out of the transfer ports. No porting, no timing changes, maybe a little more compression.
I stuffed the bearing retainers and spread 1-2mm of JB weld over the entire sides of the cases much like this:
I also filled in the through under the transfer ports where it went below the crank cheeks, as shown in solid red. I drilled an oil flow port to the bearings on each side, because I could see the oil had been baking in there. No pictures I am afraid, lost my darned camera again... (old guy, losing it!) New seals and bearings while I was in there.
So not a huge gain. Nothing in top speed, in fact I think I might have lost a bit. I showed 45kph and I am sure I broke 50 kph before this mod, but cannot be sure. Where it gained is rock steady idle and lots of low end torque. It would now do the steep hillclimb with only a bit of assistance now (this is not the modified Grubee, which will climb with no assistance). Previously it would not climb the hill even if assisted. Throttle response is crisper. Powerband is much lower rpm than it had been originally. I'm surprised.
Steve
