funelling the lowere transfers

[Evan]

is there any reason not to widen the lower transfer passage out closer to the piston skirt.
the pic explains more, I've all ready blended the lower transfer to the cylinder base. to me it looks like there might be benifit to angling the lower transfers towards the piston skirt. as it is the piston windows are wider then the lower passage by quite a bit.

what do you think

thanks
Evan

 

[troutfisher]

If you widen them out a lot, be aware of where the ring end gap is, it can be very difficult to assemble. The ring will expand out into that area and not travel up the bore. Once it's together it's fine, but getting the piston in can be a real pain.

 

[Evan]

even if i only came widend it out halfway from where its at now. shouldnt have any ring problems then. the ring ends ride just inside the piston skirt.

 

[troutfisher]

I did a 046 that snagged rings. The ring ends are right out at the edge of the skirt. something like a 281 wouldn't bother at all.

 

[Tzed250]

Why didn't Stihl do it?

 

[Evan]

thank you for the advice.

im thing im going to leave it alone, im getn tired of grinding on this thing. but im waitn on parts i may have it ground all to heck by the time they show up.

work came to standstill so ive got to much time to on my hands. to much tiime to think and grind. i think im going chucker hunting now

 

[Evan]

i dont know why they didnt do it.
they also left casitng flaws and hiccups in the ports that could have been much wider.

im not sure why they didnt lower the transfer to cylinder base either.

atleast they got rid of the nipples in the intake ports

one thing i was thinking is that that bare cylinder wall would be fuel washed and promote better cylinder wall oiling

 

[Tzed250]

i dont know why they didnt do it.
they also left casitng flaws and hiccups in the ports that could have been much wider.

im not sure why they didnt lower the transfer to cylinder base either.

atleast they got rid of the nipples in the intake ports

one thing i was thinking is that that bare cylinder wall would be fuel washed and promote better cylinder wall oiling

They didn't do it because it won't help. The port won't flow any more than the smallest point, so if the bottleneck is 125mm² then a 250mm² funnel mouth will not increase flow. Blending corners is OK, but big cross section changes hurt.


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