Found an old unused genuine yamaha yz80J experimental "Torque Piston"

[OverTheHill]

Were sent this by Yamaha to try but never did, wonder if anyone else ever tried one or have i got the only one ever made!!. By the time it arrived we'd worn ours out to oversize. Has super skinny rings but not sure what happened to those if i ever got them, or possibly they're just standard ring thickness for that year but think 'not'.

[OverTheHill]

pics not 'that' good but can just make out that the transfers are advanced by a 2 or 3mm, obviously weren't too worried about squish etc. Bit more of that & she'd look like a 'real old' villiers deflector top piston [or not].

[Slakewell]

I guess it allows a bit more port timing. I did something similar back in the 90,s to try and get more power from my WR 200

[evo550]

I did something similar back in the 90,s to try and get more power from my WR 200

Me too, but I gave up and went looking for a stone I could get some blood from instead 

[OverTheHill]

yes, just thought it a bit unusual for the factory to be trying something like that with a genuine piston. maybe we had the only one in existance, [i smell money now, must be worth lots--or not] they'd be pushing shit uphill trying to get extra torque out of an 80 anyway [me thinks], in saying that i don't recall our 80J being particularly bad in any respect apart from having the radiator sticking out like [heavy] dogs balls. Did a few sets of sea;s at work on the J's [& was it from the H model on 125's!!]. Sir my steering head's leaking water?, keep the head bearings tight too so there's no play to pull on the seals i used to think. Yamaha had a bad problem with [mainly little road bikes] where the top cone used to bare on the threaded portion of the stem & the threads would get flattened & leave movement in the 'stem to bearing fit'. --Yes dear i know my tea's getting cold--mmmm gotta go. Haven't proof read--YES DEAR.

[Lozza]

Has anybody worked out why this is a crap idea?

[head]

squish band

[oldyzman]

If it was a great idea then every small bore two stroke would use it, if it were half reasonable then some would use it. Still an interesting way to modify port timimg without messing with the barrel.

[OverTheHill]

just remembered yamaha sending us 'thinner reeds' back in the 125E days, don't recall them being 'better' in fact back in the bucket days with wild port timing i had to double up on standard reeds to stop a crazy blubbering just as it tried to 'come on the pipe' [so to speak], worked too--but wasn't me that thought of it & i was trying to carburate it out, mind you i'd welded a big yamaha reed block into the back of a mudbug 100 cylinder [don't ask]. Gosh i remember the early bucket days at our 'local airforce base' running no flywheel cover on the mudbug to let the heat out & the end broke off the crank complete with flywheel & disappeared into the fuel storage area [never did find it]. Next time out the crank pin broke right through the middle while at 10 grand+ [big vibes all of a sudden], had a new [old stock, free] cranckpin with the oil hole in the middle [for slinger oil feed] where as mudbug is solid, mind you they're not meant to be ported & piped to 13000 [well, that was the theory--not sure if got there but sure revved hard].

[mitch75]

I am new to two stroke tunning so I am interested in why it is a crap idea.
The raised section is on the exhaust side making it's timing earlier unless you raised the exhaust port this would be a crap idea 

[Lozza]

Nothing to do with reeds or the squish band

[OverTheHill]

Please Sir, can i have a guess?, ummm, speak up boy, does the 'step up' bit tend to hinder the transfers from helping to excavate the spent exhaust gases. [No boy, back in the corner] Ok. How many guesses do we get!!. Cheers.

[Lozza]

Back to remedial class .Transfers don't evacuate spent gases . NO guesses, educated guestimates are unlimited

[OverTheHill]

did think the charge coming up from the bottom helped the last of the exhaust gas out the door & got to port just in time to stop any exhaust getting back in. Willing to learn but just have trouble retaining it long term haha. Have to admit i started googling the answer [bloody cheat] but just couldn't make myself push 'search', feel much better after 'not' doing that.

[OverTheHill]

Re-thinking what i said--does the chamber draw the exhaust out after the initial opening plus helps draw the next charge up from the crancase then the shock wave coming back [if all chamber calculations are correct] arrives just in time to stop the fresh charge from escaping out the door?. Sorry this isn't getting to the answer as to 'why advancing the transfers is a crap idea'!!. Or did you mean doing it by modding the piston is a bad idea?. I'll just watch for a bit as run out of ideas. Cheers.