Love your theorizing on flow characteristics of pop-ups, LOL until recently I thought "why wouldn't all 2-strokes utilize this? all my echo's are domed!"and then I spent some time learning re comb.chambers, compression ratios, knock/pre-det., and the surprisingly slowly occurring combustion-event pushing down for the piston's powerstroke -- I LOVE your theory because I came to same one IE that domed/pop-up is inherently inferior, I like your thinking Re scavenging though I suspect there's multilpe reasons, the one I'd thought about the most was simply the true-ness of the piston's movement, IE the downawrd force of the cylinder pressure, on a domed-top, is encouraging air to the sides (and even to/past the rings), whereas a flat-topped piston (or even one w/ the slightest inward-dishing!) would have that force nailing the piston "dead-center true" in its downward travel to BDC, considering the rock of a piston heck the rock of it just as the exhasut cracks and pressure rushes to the exhuast-side pushing the rear/intake skirt's bottom into the intake-side plating of the jug (always the 1st worn-areas on a piston IME!), can't help but want slight dishing or at least flat if nothing else (which sucks as I built both chinesium 660's around pop-up's, and am now wanting to take them out :P You don't work the pistons much, and you cite *customer-friendliness*...what of performacne? On a 660, my understanding is that transfer functionality is resultant from the transfer-ports AND the piston windows, as theyr'e required pass-throughs for transfer charge to get from crankcase to lower-transfers (which is why I open-up the windows on 660 pistons, and flare the lowers to the same width, so at BDC there's maximal "potential", the potential being "tapped" by way of how much I enlarge the lower-to-upper passages in the transfers, and how large the top transfers are, I don't really raise mine much - blowdown of 24 on current build - but do extend them a bit laterlly, towards intake of course!) Thanks so much for posting this stuff, you & @BayouCountyPowersaws are like the only 2 that come to mind as "great minds of the chaisnsaw porting world"!!
Oh and btw when sanding/working on squish band w/ tools like you were, when you show how the alum slurry 'creeps' and hits the "circle of death"of unplated cylinder-wall-top, just **TAPE** it :D I don't have the gear you do, but - since it's just my own saws IE not *that* many - I couldn't help going for at-home machining of band & base.... Using painters tape or mark-off tape on the plating is surprisingly easy to set, you 'stick' a ~1.5-2" long piece on the end of a screwdriver and let the bottom 'hit' the squish band, then press that sucker into the plating from the center and work-outwards, you'll be amazed how quick, easy and precise you can wrap that plating to way under 10thou close to the band (even bumping-itno the band) I do small time-increments because of the heat, that could surely get through tape :P But I cut real amoutns off my band (actually OPE says the angle is too steep & I ruined it so am doing it again now but I took 19thou off band using 2" sanding discs on my drill, then used the sandpaper-on-glass, by hand, method to remove 14.25thou from the base (an f.tec 660 jug), tolerances only got tighter/better each round (I did *many* rounds, checking depth-measurements from base-to-band, repeatedly through the process since I didn't know for sure it'd work!)) Tape lasts a session or two if using petrol based lubes (I use marine grease..)
Great videos you have made. Can you please explain a little more, what you were saying about free porting when you scribed the bottom of the piston skirt. My brain is a little simple and slow and I didn't get all if your explanation.
Basically if you take material off the skirt or port to increase exhaust duration, you end up with an open port, meaning that since you have dropped the cylinder down and then in addition removed material from the piston skirt and/or exhaust port, that creates a scenario in which the exhaust port is never fully closed. His scribed line showed where the bottom of the port was with the piston at bottom dead center. I'd you were to remove material past that line to increase duration, that port would never close.
the old 1st 22r toyota has a doughnut ring pop up on top it just popped into me head i think it may work better than just being flat on top .i am wanting to/// mod a ms090
this is golden!
Love your theorizing on flow characteristics of pop-ups, LOL until recently I thought "why wouldn't all 2-strokes utilize this? all my echo's are domed!"and then I spent some time learning re comb.chambers, compression ratios, knock/pre-det., and the surprisingly slowly occurring combustion-event pushing down for the piston's powerstroke -- I LOVE your theory because I came to same one IE that domed/pop-up is inherently inferior, I like your thinking Re scavenging though I suspect there's multilpe reasons, the one I'd thought about the most was simply the true-ness of the piston's movement, IE the downawrd force of the cylinder pressure, on a domed-top, is encouraging air to the sides (and even to/past the rings), whereas a flat-topped piston (or even one w/ the slightest inward-dishing!) would have that force nailing the piston "dead-center true" in its downward travel to BDC, considering the rock of a piston heck the rock of it just as the exhasut cracks and pressure rushes to the exhuast-side pushing the rear/intake skirt's bottom into the intake-side plating of the jug (always the 1st worn-areas on a piston IME!), can't help but want slight dishing or at least flat if nothing else (which sucks as I built both chinesium 660's around pop-up's, and am now wanting to take them out :P
You don't work the pistons much, and you cite *customer-friendliness*...what of performacne? On a 660, my understanding is that transfer functionality is resultant from the transfer-ports AND the piston windows, as theyr'e required pass-throughs for transfer charge to get from crankcase to lower-transfers (which is why I open-up the windows on 660 pistons, and flare the lowers to the same width, so at BDC there's maximal "potential", the potential being "tapped" by way of how much I enlarge the lower-to-upper passages in the transfers, and how large the top transfers are, I don't really raise mine much - blowdown of 24 on current build - but do extend them a bit laterlly, towards intake of course!)
Thanks so much for posting this stuff, you & @BayouCountyPowersaws are like the only 2 that come to mind as "great minds of the chaisnsaw porting world"!!
Outstanding commentary on pop up pistons. You've saved me some money and time. Thank you, sir!
Oh and btw when sanding/working on squish band w/ tools like you were, when you show how the alum slurry 'creeps' and hits the "circle of death"of unplated cylinder-wall-top, just **TAPE** it :D I don't have the gear you do, but - since it's just my own saws IE not *that* many - I couldn't help going for at-home machining of band & base.... Using painters tape or mark-off tape on the plating is surprisingly easy to set, you 'stick' a ~1.5-2" long piece on the end of a screwdriver and let the bottom 'hit' the squish band, then press that sucker into the plating from the center and work-outwards, you'll be amazed how quick, easy and precise you can wrap that plating to way under 10thou close to the band (even bumping-itno the band) I do small time-increments because of the heat, that could surely get through tape :P But I cut real amoutns off my band (actually OPE says the angle is too steep & I ruined it so am doing it again now but I took 19thou off band using 2" sanding discs on my drill, then used the sandpaper-on-glass, by hand, method to remove 14.25thou from the base (an f.tec 660 jug), tolerances only got tighter/better each round (I did *many* rounds, checking depth-measurements from base-to-band, repeatedly through the process since I didn't know for sure it'd work!))
Tape lasts a session or two if using petrol based lubes (I use marine grease..)
Thanks mate, I’ve been learning so much. Almost keen to have a go at my Chinese saw... But there is no way I will ever touch my 462. 😅
You check with the solder right over the wrist pin?
Great videos you have made. Can you please explain a little more, what you were saying about free porting when you scribed the bottom of the piston skirt. My brain is a little simple and slow and I didn't get all if your explanation.
Basically if you take material off the skirt or port to increase exhaust duration, you end up with an open port, meaning that since you have dropped the cylinder down and then in addition removed material from the piston skirt and/or exhaust port, that creates a scenario in which the exhaust port is never fully closed. His scribed line showed where the bottom of the port was with the piston at bottom dead center. I'd you were to remove material past that line to increase duration, that port would never close.
What is the tool called that you use to hone out the squish band?
the old 1st 22r toyota has a doughnut ring pop up on top it just popped into me head i think it may work better than just being flat on top .i am wanting to/// mod a ms090