Took a quick look at the 66 cc again removing a small amount of piston skirt that hangs over the intake port at top dead has been a thought today..
what did you do to your motorized bicycle today?
- Thread starter Skarrd
- Start date
instead of notching the skirt try drilling 4 holes in the skirt two 31mm from bottom ring then two more at 34mm from bottom ring helps keep the integrity of the skirt
Have you done this mod?
How is someone gonna drill holes in the very small amount that doesn't clear top of intake port when piston is at TDC when usually only 1/8" - 3/16" is all that needs to be trimmed.
drilling holes above the area that usually needs trimming is gonna be a performance killer since as piston moves downward creating the primary compression that forces the air fuel mix into transfers and ultimately into combustion chamber.
Maybe I've just misunderstood,if so please explain so someone doesn't start drilling holes in the wrong place their piston and ruin the piston.
I agree... drilling holes where there needs to be open space will kill performance as well as ruin a piston... what you're describing works with reed valves but not piston port engines and these engines don't come with reeds.... be sure you know what type of engine the guy has before recommending something that can mess up their engine or parts...
your right I was referring to a reed valve set up. I just put one on my motor and the performance is amazing !!! my top speed is 47M.P.H. im running a 36 tooth adapter from gasbike.net he has some very good priced.
ah ha.... now we know.....lol
Yep a reed set up is different, I knew this would get cleared up quickly....
Thanks DRBS
Just for curiosity and for info for others who may want to run reeds.
What diameter are the holes you drilled and exactly where didyou drill them in the piston?
This would be good info to share here since other curious about running reeds would have a chance to know what kind of mods would be needed to make the setup work right.
1 13mm from bottom ring 7/32" two then continue to drill two holes then two more below them stopping 3mm from bottom of piston so in all 6 holes you also need to make room in intake port for the top reed to work. you need to take off a little bit about 1mm. they really do make a difference while going up hill or against the wind. check this page out there is a lot of good info here I did change the hole pattern to two by two seems to work better I know I went through 3 pistons to get it right!!! http://www.dragonfly75.com/motorbike/images/drill-piston.jpg
Last edited:
Thank you for taking the time to share this, its always great to learn new things and Im sure there are those who will see this in the future and it may help them get a reed setup working for them, Ive never ran reeds in the chine girl engine's, but its something I have been interested in.
check out mimiami on ebay has a fairly good reed valve set also matt at bicyclemotorworks has them too.
I was going to buy one last week but when I went to his ebay page the reeds were gone...
There's another seller bicycle motor works who sells the genuine RSE reeds tho for $64.00 but I've been holding out to buy it from my Miami since the ones he sells have the slotted mount holes so they.will fit the 32 or 40mm bolt spacings.... also most my new jugs are coming in with the 35mm spacing so the slotted mount holes work perfect here, just gotta be sure everything stays centered when torquing down...
there the same I bought them there too. the ones that motorized bicycle works sells are a little different in the spacer but the reed valve is the same ive installed a few already everyone seems to like the power that they make
I started out today by ordering two engine sound dampening kits from sick bike parts. They're inserts of some sort that go under the clutch, magneto and output covers. Meant to dampen the engine's mechanical noise. I've had my eye on them for a while. But now that I think about it, I'm a bit surprised that I haven't seen any review threads here. I suppose I'd better review them when I get mine installed.
Then I went to work on my handlebar mounted choke adjust.
I didn't think to get a photo of my cable stop. Or I should say my cable sheath stop. But it's an L bracket made out of aluminum. Mounted to the seat tube with a hole drilled in it for that cable to pass through. A return spring fills the space between that and the choke lever.
Then run a cable up to the twist shifter on the handlebar.
I took her out for a little test run and she seemed to be okay. It was warm out today, so there wasn't much need for choke. So it wasn't the best test. Still, it felt just fine to adjust the choke with my left hand on the grip. Cold morning starts ought to be a great deal easier now.
But tomorrow will be an errand running day. It ought to be more cool in the morning. Maybe I'll get a proper test then.
Then I went to work on my handlebar mounted choke adjust.
I didn't think to get a photo of my cable stop. Or I should say my cable sheath stop. But it's an L bracket made out of aluminum. Mounted to the seat tube with a hole drilled in it for that cable to pass through. A return spring fills the space between that and the choke lever.
Then run a cable up to the twist shifter on the handlebar.
I took her out for a little test run and she seemed to be okay. It was warm out today, so there wasn't much need for choke. So it wasn't the best test. Still, it felt just fine to adjust the choke with my left hand on the grip. Cold morning starts ought to be a great deal easier now.
But tomorrow will be an errand running day. It ought to be more cool in the morning. Maybe I'll get a proper test then.
Last edited:
looks good bgw...
Ive threatened several times to make a choke cable set up mounted under the seat so I dont have to lean way over to push down on the choke lever.
more pix as you go so we can see what you end up with.
Ive threatened several times to make a choke cable set up mounted under the seat so I dont have to lean way over to push down on the choke lever.
more pix as you go so we can see what you end up with.
lets see I got my fixie 80cc bike running for first time this year replaced the carb to a run tog carb on the Astra this thing is pretty fast cant wait till someone rides it for the first time this is faster than the fixie I built last year now going to work on a Schwinn midway its a 29" bike like the Astra is so ill take the motor I bought and change the Japanese ones out for Timken ones and ramp the piston and clear out the transfer ports drill two holes near the bottom of piston and billet head 6cc ignition delay box and motorcycle coil should be pretty fast www.facebook.com/motorizedbikes that's my page
Last edited:
Scratch the ignition with retarded timing and just stay with a stock cdi unit and you'll be better off.
ive been using the timing thing my brother builds them for me, there are like 7 different ones out there mine actually do make it a tad bit more responsive and a little faster like 2-4 M.P.H. but its better than stock!! im ordering a Jake diamond head ice been using the dome top ones think ill try these and see if there any good
ive tried some of the after market cdi units, only found one that performs as good as a stock unit, but never got any of them to outperform the stock unit on my fastest build which GPS'd 52mph on a bike with 24" wheels and a 30T sprocket.
If youve got them that actually do add performance over a stock unit thats great.
I have a Jake's Diamond head and I really like it, you'll need to find an extra long reach spark plug for it, i'm using an E3 3.22 in mine and it could actually use one a bit longer.
the combustion chamber design of the diamond head is different than all the others, the squish ring in head is actually roughly 47mm, it doesn't have a flat surface for the head gasket to seal on like the other heads but instead the head gaskets bore diameter actually matches the squish areas diameter so the squish band is actually the exact height of the jug deck when a standard thickness head gasket is used and if a thin .016 gasket was used the heads squish band will actually sit down in the bore just a few thousands since the squish band is the same diameter as the bore and is beveled from the outer edge all the way in until it ends and the actual combustion chamber starts.
this design is gonna make it easier for those who want higher compression to get it without having to shave the deck height down as much or none at all if they have a 40mm stroke engine, all they will have to do is order a .016 head gasket from juicemotors and they will get a higher compression ratio than they will with any of the other 6cc chamber heads ive seen.
The diamond head is taller and a little heavier that the others, but I kinda like the looks myself, and I really like the squish band design, this head should really wick heat away from the jug also, only downside is that builds with tight space for the engine may not be able to run the taller head, but most all 26" cruiser frames and any full size fixie or mnt bike diamond type from will have plenty of room.
Last edited:
I've been considering the jake's Diamond head for my next build too since it has the different combustion chamber design to see how that works out. Another one I'm keeping a close eye on is VMB's Shark head he's still designing and perfecting at the moment.
I just picked up a Super Rat bottom end from BGF Motors on ebay last night that I'll do my next build on. I know these have ignition issues but I got a few ideas to hopefully work around that issue, and now that I can get those ignitions fairly easily I'll take the risk. First thing I'll need to do with it is check the geometry and change out all the bearings for the good stuff. I'll also check, true, and balance the crank while I got it apart since it could just as easily be engine vibes that's killing the CDI units in these as well as the heat with not enough opening in the covers to let it escape out quick enough. My other thoughts here are that other magnetos might work better with the type of rotor this engine uses.... We'll soon find out.
I also saw that the same seller has the jugs with the straight intakes installed on them so I bought one of his to see if it has the bigger flat transfers, if so that'll be great, but if not, I got other sources for these jugs. The Super Rat bottom ends he sells also come with a piston installed so that'll take the initial guess work out of piston selection too.
I'm hoping I can get one of these to work reliably because these will make for a very clean looking install on future builds.
I just picked up a Super Rat bottom end from BGF Motors on ebay last night that I'll do my next build on. I know these have ignition issues but I got a few ideas to hopefully work around that issue, and now that I can get those ignitions fairly easily I'll take the risk. First thing I'll need to do with it is check the geometry and change out all the bearings for the good stuff. I'll also check, true, and balance the crank while I got it apart since it could just as easily be engine vibes that's killing the CDI units in these as well as the heat with not enough opening in the covers to let it escape out quick enough. My other thoughts here are that other magnetos might work better with the type of rotor this engine uses.... We'll soon find out.
I also saw that the same seller has the jugs with the straight intakes installed on them so I bought one of his to see if it has the bigger flat transfers, if so that'll be great, but if not, I got other sources for these jugs. The Super Rat bottom ends he sells also come with a piston installed so that'll take the initial guess work out of piston selection too.
I'm hoping I can get one of these to work reliably because these will make for a very clean looking install on future builds.