spewing i think i fuc'd a new piston

[Freakshow]

can some one tell me if on the74  TM 250 the standard piston has both transfers fully open or is there overlap on the small transfer ? ( closest to INLet)

i just stuck a new wisco in it and it seemed to be over half way over the small transfer,so i cut it back but now i can see light on the sides of the inlet. i think i may have forked the piston cause im assuming if i can see inlet peeking through on the sides its basically raised the inlet port by about 4 mm.    :'(

# standard piston overlaps small transfer window?
# am i screwed ?

[Lozza]

 

[pokey]

Hows about a few pictures Freaky to save a 1000 words

[Freakshow]

is that a question?   what im trying to say is does the stander piston  transfer area normally cover some of the smal transferr >   And if so and i trimmed to much off and can see the main inlet when i move the piston up to TDC thus charge come in the small gap down the sides of the rear piston base " before" the bottom of the piston opens the inlet port have i just essentialy opened the inlet port way to early cause the chage can sneak past before the timiing should be ?

if the missis didnt steal my camera to dtake away on the weekend, i post a piccy up. i might try drwing it    well i guess i got 2 choses any way put it al back together and see if it runs, or sook and never know, who knows i may have stumped onto a rare factory 2 stroke technique, then again i may have just killed a piston

[pokey]

Removing  that much from a wiseco aint the way to go. Most ive removed  from a piston that was made for the engine is about 0.5mm .basicly if the skirt is too short or tooo long in a PP engine it throws the port timing out and you lose  untill it wont run.
 The request for the pics was to ascertain how the hell you managed to  decide to take that much from the skirt and how you measured it to benefit the transfers.


 Im scratching my head

[cyclegod]

When you say "trimmed" do you mean trimming down the piston skirt? to open the intake earlier and for longer?
(Piston skirt length on ts125 is 5mm longer than tm125 for example)

[Freakshow]

no as in the transfer was partially covered by the skirt width, so i trimed the sides so the transfers where no longer covered it wasnt until i ran the piston up in the bore i realised the wall between the transfer and the intake was only a  mm, so when trimmed the sides of the piston transfers may have gone too far, i didnt realise it was so close and the intake is now exposed slightly from the side when you run it back up past the intake window.

Yes i know  i was on a roll at the time and it was getting late and it was the last thing i noticed before i packed up for bed. i  should have asked the question before i went too far.  Hindsight 

the piston that was in was a wisco 380P - is that the right one ?

[pokey]

ummm the transfers are covered partially when the piston is Up and the intake is open, thats normal.. The transfers are controlled by the crown of the piston not the skirt.. . You  trim skirts for intake or clearance on the counterweights.

[Freakshow]

ahh ok, i though there was a charge from the transfers on the way up aswell to put pressure on the exhaut stroke on the way out ? woops......... stuffed that up then. it  just didnt look right at all.  ahhh wel you learn. 

I might just get another base gasket stick it back together and see if it still runs. if not guess its a new piston.  ON the up side at least i can see the bottom end has been rebuilt so thats good news. ill will pull another one apart this week and see how differant that piston is.  Originally all i was doing was getting the piston out to drill some holes for the bridge, cause i could see they hadnt dont that, and then i think once i had the file in hand for a clean up, i got a bit out of control :O)