2 Stroke Channel Softening Question

[2_DONE_THE_TON]

hey guys!

got my cylinders today back from the workshop needed a fresh bore...one of the pistons were f+++++ .

so i just read that since this is a 2 Stroke (RD 250) that i need to "soften" the edges of the channels of the rebore...with a little round file or some sanding paper in order to keep the rings from getting caught up on the pointy eges.

so the procedure is clear to me, i´ll sand all edges of the ports inside of the cylinder but how much?do i just need to slightly break the edge or get a really round edge?

thanks in advance!!!

 

[jpmobius]

Odd that your machinist did not do this for you as it is typically part of boring any 2 cycle cylinder. Regardless, the port window edges do need to be relieved to help ease the ring(s) back into the bore as they pass the port. The vertical edges (parallel to the piston travel) need essentially nothing aside from removing any burrs. Any portion of edge not purely vertical needs a very slight "ramp" to prevent the ring from trying to catch the edge. This is a very steep tiny chamfer, closer in angle to the direction of the bore than the direction of the port. If you were to push the ring into the bore and watch it as you push it past the port windows, you can imagine the very tiny amount the ring might want to "bulge" into the port. Obviously this will be greater at the wide exhaust port window than at the transfer windows, and the size of the chamfer needs to be correspondingly greater there. While the chamfers are critical, they are typically very small, and I think not especially noticeable unless you were looking for them; Much bigger than you would reasonably achieve with sandpaper though. Hopefully someone will help out with a picture. This is typically done with a die grinder, but certainly could be done by a patient and careful person with a file.

 

[bradj]

Just round them or put a slight taper to them a few mins with a non aggressive file you don't want to change the shape or size of the port or you'll get in to trimming changes

 

[2_DONE_THE_TON]

Just round them or put a slight taper to them a few mins with a non aggressive file you don't want to change the shape or size of the port or you'll get in to trimming changes

thanks guys for your answers!

just found these two pics on a RD lc forum.i dont know if these port edges look stock.but as you said the exhaust and carb side edges look way more rounded then the little overflow ports (looks like the edges have just been slightly rounded).

should the edges get chamfered or angled?i guess chamfered so the rings wont stick to them.

 

[xb33bsa]

like brad and the other says just slightly round/chamfer the edge the most important edge is the exhaust port top and bottom
the intake port never sees the rings(only upon assembly) the transfer ports are so harrow they only need some very minor work,nothing gained overdoing it

 

[xb33bsa]

thanks guys for your answers!

just found these two pics on a RD lc forum.i dont know if these port edges look stock.but as you said the exhaust and carb side edges look way more rounded then the little overflow ports (looks like the edges have just been slightly rounded).

should the edges get chamfered or angled?i guess chamfered so the rings wont stick to them.

chamfered and angled is the same thing you are only confusing yourself

 

[2_DONE_THE_TON]

like brad says just slightly round the edge the most important edge is the exhaust port top and bottom
the intake port never sees the rings(only upon assembly) the transfer ports are so harrow they only need some very minor work,nothing gained overdoing it

thanks xb!

sorry for the stupid question.the exhaust ports are the two big openings in the cyl wall?
intake ports are the two big openings on the carb side.
the small openings are the transfer ports?

so should i chamfer the edges which are horizontal to the rings more or all the same amount of chamfering (slight rounded by file)?