my journey begins and never ends
- Thread starter MacZulu
- Start date
well I am handing the bike and engine over to my machinist buddy tomorrow, so hopefully I will have it back in a few days. I have my next work set off, so it would be nice to have running for that break.
thanks Davezilla, it is coming along. as for pics, well the next ones should be of a motorized bicycle in a relatively finished state. I am still doing some detail work while I wait for the mounting.
after getting the crankcase back together I relaxed a bit, that whole bottom end experience was a little exhausting.ended making my own crankcase gasket, it is gasket material and just a little bit thicker than the torn waif of a thing that came in my gasket set. I know, lost compression. it's a good fit, and stayed well in place. I used a touch of copper gasket goop, a mimic of the big "copper" brand I think. but there's sweat and blood lubricating this china doll now.
so Davezilla I don't know if I even want to ask. port timing? I will do more research, as my preliminary search left me feeling a little lost. I'm thinking, first get her running and see if she's strong. I will ask Legwon for his opinion of her running condition (he's local and knowledgeable, helpful) then look at finishing her off. make sense?
thanks Davezilla, it is coming along. as for pics, well the next ones should be of a motorized bicycle in a relatively finished state. I am still doing some detail work while I wait for the mounting.
after getting the crankcase back together I relaxed a bit, that whole bottom end experience was a little exhausting.ended making my own crankcase gasket, it is gasket material and just a little bit thicker than the torn waif of a thing that came in my gasket set. I know, lost compression. it's a good fit, and stayed well in place. I used a touch of copper gasket goop, a mimic of the big "copper" brand I think. but there's sweat and blood lubricating this china doll now.
so Davezilla I don't know if I even want to ask. port timing? I will do more research, as my preliminary search left me feeling a little lost. I'm thinking, first get her running and see if she's strong. I will ask Legwon for his opinion of her running condition (he's local and knowledgeable, helpful) then look at finishing her off. make sense?
Davezilla
New Member
think of port timing and porting like putting a hot cam in a 4 stroke engine... it pretty much does the same thing, the hight of the exhaust and transfer roofs controls the duration and the width of the port would equate to the lift of a cam in a 4 stroke engine.
There are a different set of rules for duration and timing on a 2 stroke, but for the most part, they work the same way and the whole idea is to get the biggest bang to push that piston down and make power. The problem is that one can't just start cutting and enlarging the ports and expect more power, this tactic does work if the porter don't get too greedy, or just gets lucky somehow, but to squeeze the most power out of these (or any 2 stroke for that matter) we need the exhaust port to start to open at exactly the right time, then get the exhaust out of the cylinder before the transfers start to open. Then down on the other side we need to get the fresh air/fuel charge into the case and get as much of it in there as possible for each cycle so we want to lower the floor on the intake port so the enging can pull in the fresh sharge as soon as possible and keep pulling it in as the piston goes up. The problem here tho is that the piston has to come back down and will push this charge back into the intake and carb, and even out the carb. This is referred to as Blow back and blow back needs to be avoided or low rpm power will suffer, at higher rpm, the air/fuel charge has enough momentum to keep going the right direction as the piston returns down and closes the port so we definitely can't get too greedy with the intake duration on a piston port 2 stroke. The ideal situation here is to pull in the fresh charge and pull in enough that most of it stays in the case when the piston comes back down before the intake port can be closed (This is why reeds make a lot better low end power). The intake port also needs to be closed so the pressure inside the case builds up enough to force the charge up the transfer tunnels and into the cylinder as the piston heads toward the bottom of the cylinder.
The idea of port timing is to optimise when each port opens and closes in order to get the most fresh charge into the cylinder and get the exhaust out before the transfers start to open as well as get the intake closed as quick as possible as the piston returns down, but leaving it open as long as possible while it goes up, we do have to rely on the air/fuel charge's momentum to keep this happening and it will happen at a certain rpm range, but we still need to be conservative to a certain point so the engine will run decently out of this rpm range.
There's a lot of different details that go into doing a good port job and knowing what effects doing each part of the job does will really help in making the engine run the way you want it to whtther you want a street engine with some mild upgrades to get the best top speed without sacrificing too much acceleration or hill clim ability or you want an all out race engine that'll only perform well in a certain rpm range, but will have the most power, but the throttle becomes much more like an on/off switch. Knowing the effects of each step in the job will give you the control of how it's going to run.
It would easily take over 100 pages of explanation to explain everything, but there are some good books you can usually find online for free like the 2 stroke performance books by Graham Bell or Gordon Jennings, if you can download a copy of The 2 Stroke Tuner's Guide by Gordon Jennings, this is a really good start. There are also some good articles and discussions at mopedarmy.com that can be very helpful as well. The more you can read and learn about this, the easier it will be to design and build up one of these engines for excellent street performance
There are a different set of rules for duration and timing on a 2 stroke, but for the most part, they work the same way and the whole idea is to get the biggest bang to push that piston down and make power. The problem is that one can't just start cutting and enlarging the ports and expect more power, this tactic does work if the porter don't get too greedy, or just gets lucky somehow, but to squeeze the most power out of these (or any 2 stroke for that matter) we need the exhaust port to start to open at exactly the right time, then get the exhaust out of the cylinder before the transfers start to open. Then down on the other side we need to get the fresh air/fuel charge into the case and get as much of it in there as possible for each cycle so we want to lower the floor on the intake port so the enging can pull in the fresh sharge as soon as possible and keep pulling it in as the piston goes up. The problem here tho is that the piston has to come back down and will push this charge back into the intake and carb, and even out the carb. This is referred to as Blow back and blow back needs to be avoided or low rpm power will suffer, at higher rpm, the air/fuel charge has enough momentum to keep going the right direction as the piston returns down and closes the port so we definitely can't get too greedy with the intake duration on a piston port 2 stroke. The ideal situation here is to pull in the fresh charge and pull in enough that most of it stays in the case when the piston comes back down before the intake port can be closed (This is why reeds make a lot better low end power). The intake port also needs to be closed so the pressure inside the case builds up enough to force the charge up the transfer tunnels and into the cylinder as the piston heads toward the bottom of the cylinder.
The idea of port timing is to optimise when each port opens and closes in order to get the most fresh charge into the cylinder and get the exhaust out before the transfers start to open as well as get the intake closed as quick as possible as the piston returns down, but leaving it open as long as possible while it goes up, we do have to rely on the air/fuel charge's momentum to keep this happening and it will happen at a certain rpm range, but we still need to be conservative to a certain point so the engine will run decently out of this rpm range.
There's a lot of different details that go into doing a good port job and knowing what effects doing each part of the job does will really help in making the engine run the way you want it to whtther you want a street engine with some mild upgrades to get the best top speed without sacrificing too much acceleration or hill clim ability or you want an all out race engine that'll only perform well in a certain rpm range, but will have the most power, but the throttle becomes much more like an on/off switch. Knowing the effects of each step in the job will give you the control of how it's going to run.
It would easily take over 100 pages of explanation to explain everything, but there are some good books you can usually find online for free like the 2 stroke performance books by Graham Bell or Gordon Jennings, if you can download a copy of The 2 Stroke Tuner's Guide by Gordon Jennings, this is a really good start. There are also some good articles and discussions at mopedarmy.com that can be very helpful as well. The more you can read and learn about this, the easier it will be to design and build up one of these engines for excellent street performance
silverbear
The Boy Who Never Grew Up
Dave,
Thank you for this very informative post and for your help in general. For most of us this is pretty esoteric stuff.
SB
Thank you for this very informative post and for your help in general. For most of us this is pretty esoteric stuff.
SB
alright Davezilla, I'm a reader. I have found the pdf of two stroke tuners handbook. he gets pretty deep right off the bat with the kawi vs yami example and the equations for bhp and piston speed. but I have laymen's interest in quantum mechanics, so I'm used to re-reading a point until I can get my head around it.
I hope to pick the bike up on monday, my first day off. then I can sort out some details and mount the engine. a friend at work will lend me a 2" x26" tire if my tire rubs. I probably need to get a smaller tube, my tire is 2.35". and KC informed me that bigger than 2.18..." will probably rub, so atleast I will be ready for it. I did read something about fat tiresrubbing, but forgot about in the ensuing frenzy of engine work.
I found a before and after of one side of the port matching job, I didn't want to begreedy. just took down the little "step" that was there.
I hope to pick the bike up on monday, my first day off. then I can sort out some details and mount the engine. a friend at work will lend me a 2" x26" tire if my tire rubs. I probably need to get a smaller tube, my tire is 2.35". and KC informed me that bigger than 2.18..." will probably rub, so atleast I will be ready for it. I did read something about fat tiresrubbing, but forgot about in the ensuing frenzy of engine work.
I found a before and after of one side of the port matching job, I didn't want to begreedy. just took down the little "step" that was there.
Last edited:
so I picked up the bike today with the mounts. I guess there was an accident and some fins were broken, luckily it was the head which I have plans for anyways. also the frame took a bit of a beating, I should have taped her up.
I like the mounts, they need paint yet. but I'm set.
it looks like I'll have room for the big diamond head from Jakes, but I'm also like Fred's. Fred has a 45 day holding period for 1st time international buyers due to bad experiences, so something I need to keep in mind. I still have niggling doubts about my engine work but I'll find out soon. just eyeballing it, I think I'll be using my back up narrower tire(maybe, it too may not be narrow enough). a shift kit is in the works, and then I'll put my 2.35" back on.
I like the mounts, they need paint yet. but I'm set.
it looks like I'll have room for the big diamond head from Jakes, but I'm also like Fred's. Fred has a 45 day holding period for 1st time international buyers due to bad experiences, so something I need to keep in mind. I still have niggling doubts about my engine work but I'll find out soon. just eyeballing it, I think I'll be using my back up narrower tire(maybe, it too may not be narrow enough). a shift kit is in the works, and then I'll put my 2.35" back on.
well this has been a trial, had some serious starting issues, swapped out; plug, cdi, coil, carb, exhaust, put on a pull start. nope. so what can you screw up in assembly which will sabotage all attempts to start a simple 2 stroke?
put the magnet in backwards. mine is a 12:15 position slot, but I had it at 11:45.
so she needs alot of detail work now to clean her up. it will come.
oh ya. so here whats running.
jet 66cc
sbp spark plug wire
jnm engine sound dampeners
after market fuel filter
replaced rear sprocket hardware with 7/16, and tensioner with 3/8s
sbp twist throttle
stock exhaust with hole at port
back tire swapped to 1.95"
custom mount
ports matched
intake/exhaust ports cleaned up
piston ramped to transfers
transfer ports cleaned up
head milled
reinforced fuel tank posts (thanks Chaz)
running 94 octane with lucas 2 stroke semi synth at 20:1
so MAJOR shout out to Legwon, who helped me through patience, knowledge, and determination(hours). I would have smashed and thrown her in the corner if he hadn't been there to keep pushing to keep trying.
and a thanks to Davezilla of course for all the tips and guidance. I will clean her up and get some proper pictures and put a photo thread in the right area.
put the magnet in backwards. mine is a 12:15 position slot, but I had it at 11:45.
so she needs alot of detail work now to clean her up. it will come.
oh ya. so here whats running.
jet 66cc
sbp spark plug wire
jnm engine sound dampeners
after market fuel filter
replaced rear sprocket hardware with 7/16, and tensioner with 3/8s
sbp twist throttle
stock exhaust with hole at port
back tire swapped to 1.95"
custom mount
ports matched
intake/exhaust ports cleaned up
piston ramped to transfers
transfer ports cleaned up
head milled
reinforced fuel tank posts (thanks Chaz)
running 94 octane with lucas 2 stroke semi synth at 20:1
so MAJOR shout out to Legwon, who helped me through patience, knowledge, and determination(hours). I would have smashed and thrown her in the corner if he hadn't been there to keep pushing to keep trying.
and a thanks to Davezilla of course for all the tips and guidance. I will clean her up and get some proper pictures and put a photo thread in the right area.
Last edited:
im just glad you finally got her fired up dude. (god knows we tried forever!!!!)
one thing ill mention, keep on the bolt maintenance. ensure they are tight after every ride for the first couple tanks, otherwise you gonna be back to the "smashed and thrown her in the corner" mode. lol.
but most importantly, have fun!
one thing ill mention, keep on the bolt maintenance. ensure they are tight after every ride for the first couple tanks, otherwise you gonna be back to the "smashed and thrown her in the corner" mode. lol.
but most importantly, have fun!
Davezilla
New Member
Glad to hear you got her up and running... Yeah, a backward mag rotor will give you all kinds of fits because it just won't start... Now that it's running its time to get those rings to seat and like Legwon said, keep an eye on those bolts as they will work their way loose the first few times before they decide to stay put.
I gotta agree with the others... now it's time to have fun with it
I gotta agree with the others... now it's time to have fun with it
thanks guys, I will stay on top of the bolts. patched the exhaust last night, if I replace it right away I will probably try the "little bomber" style. a little spit and polish and she'll be ready to model.
should it be cold be for re tightening? or generally crank everything hot?
should it be cold be for re tightening? or generally crank everything hot?
Chaz
Well-Known Member
Also keep an eye on the chain tension. They stretch a fair bit for the first while. If I had rear dropouts on my bike I would be using some kind of axle adjusters like these. Keeps the axle from creeping forward and makes for easy and precise wheel alignment. That is assuming you have enough axle thread to accommodate. I can't recall if any of our sponsor vendors offer these. They also use them on pocket bikes. Also keep an eye on the tensioner itself to monitor its proximity to the spokes.
so many things to keep in mind... but still have fun!!!
so many things to keep in mind... but still have fun!!!
Attachments
I will torque the head cold tonight and warm when I run her tomorrow. I checked everything out after installing the new muffler, and things were pretty snug. I got a little on the upper crankcase bolts. Tensioner holding well, chain is not contacting anything I can see. I will probably take it off and paint it tonight and maybe adjust the strap. It's pretty solid, muffler was contacting the crank guard before installing and now it's good. seems a nice solid mount with this unit. Also cleaned up the cdi/killswitch wiring. now it's cables, cables, cables. I will try shorten then zap strap them. there is just too much slack to strap them down right now.
here's the little bomber.
the shifter cable isn't pinched but it is cradled snugly.
I will take the end cap off when I paint it tonight and maybe I'll do the same mods if they apply, holes and cut stinger. Ran very nicely today, goes well and smooths out at half throttle'ish. a little rough at lower rpms, but idles ok.
here's the little bomber.
the shifter cable isn't pinched but it is cradled snugly.
I will take the end cap off when I paint it tonight and maybe I'll do the same mods if they apply, holes and cut stinger. Ran very nicely today, goes well and smooths out at half throttle'ish. a little rough at lower rpms, but idles ok.
Last edited:
silverbear
The Boy Who Never Grew Up
Congratulations on your build.
SB
SB
thanks Silverbear, I'm looking forward to when she is broken in and seeing how much torque she has for the hills.
little bomber internals
I'm going to leave it as is, after break in I might drill holes in the cap again if that is helpful on this style of muffler.
well it's hanging 3 pieces with 3 coats of paint, and looking good. I will pull out my camera gear and go shoot her somewhere.
also going to get some thread sealer for electrical, as my plug seems to leak. all in all, I'm pretty happy with her o far. but it's ben maybe 40 minutes run time total.
little bomber internals
I'm going to leave it as is, after break in I might drill holes in the cap again if that is helpful on this style of muffler.
well it's hanging 3 pieces with 3 coats of paint, and looking good. I will pull out my camera gear and go shoot her somewhere.
also going to get some thread sealer for electrical, as my plug seems to leak. all in all, I'm pretty happy with her o far. but it's ben maybe 40 minutes run time total.
went for a good ride this morning, a few hills. half throttle and pedal assist and I flew up any hills I tried. Lots of cooling and inspection breaks. some vibration, but at around half throttle it gets smoother. so I think she likes the higher rpm.
I am going to call her Sithunzi, which means shadow.
I am going to call her Sithunzi, which means shadow.
thats awesome dude!!
im glad you getting some time out on her. your gonna have a blast
just take care of her, and she'll take care of you!
give her a few shots of WOT now and again... nothing long or overbearing... just to work all the power ranges during break-in.
what i did for mine is wind it up, keep it for 10-15 seconds then bring it down a bit slowly, then hit the clutch.
ooo... also!!!
a lot of ppl LOVE doing this, but makes sense not to ...
dont ride the clutch like an engine brake. burn out the piston and rings.
so now its seems we have a bit of a group happening here... we need to get a ride happening!!! haha ;-)
im glad you getting some time out on her. your gonna have a blast
just take care of her, and she'll take care of you!
give her a few shots of WOT now and again... nothing long or overbearing... just to work all the power ranges during break-in.
what i did for mine is wind it up, keep it for 10-15 seconds then bring it down a bit slowly, then hit the clutch.
ooo... also!!!
a lot of ppl LOVE doing this, but makes sense not to ...
dont ride the clutch like an engine brake. burn out the piston and rings.
so now its seems we have a bit of a group happening here... we need to get a ride happening!!! haha ;-)
Ya Legwon we'll all meet up at the clubhouse on Brunette, I'm sure they'll give us honorary patches if we flex a bit.
I'll watch the clutch thing, I was pulling the clutch going down hills and at stops. I'll see how wot feels next time using your technique.
I need to look at shortening the cables too, and just waiting for my dual lever now
I'll watch the clutch thing, I was pulling the clutch going down hills and at stops. I'll see how wot feels next time using your technique.
I need to look at shortening the cables too, and just waiting for my dual lever now