Cylinder Porting for Dummies....

[troutfisher]

Just my opinion, but I feel that if I'm not going to raise the compression on a woods port, it's not worth doing. Just mod the muffler and run it.

 

[teacherman]

Brad, if you look at an optimally ported cylinder from the top, and if you took a cross-section so you could see the port from the top, would the sidewalls of the port space be relatively straight, or would the port space have more of an hourglass shape?

I know the opening into the cylinder is to be an oval, I mean the space between the port openings. Thanks.

 

[Boleclimber]

Below is a link to a discussion discussing 2 stroke books. I recommend you use the search function for the words port timing, duration, porting and any other word associated with porting a chainsaw.

Using the search function and purchasing two books on 2 strokes I was able to learn enough information to woods port my saws. This worked for me and will work for you. The largest step is taking the risk and diving into a project, you will learn quick.





http://www.arboristsite.com/showthread.php?t=4175&highlight=tuning+books

 

[blsnelling]

Brad, if you look at an optimally ported cylinder from the top, and if you took a cross-section so you could see the port from the top, would the sidewalls of the port space be relatively straight, or would the port space have more of an hourglass shape?

I know the opening into the cylinder is to be an oval, I mean the space between the port openings. Thanks.

Straight side walls if at all possible. That way you get maximum port width the fastest as the port opens.

 

[Tree Sling'r]

Just my opinion, but I feel that if I'm not going to raise the compression on a woods port, it's not worth doing. Just mod the muffler and run it.

I have gotten pretty good compression numbers just by widening ports.

 

[blsnelling]

This 361BB was the first time I ever significantly raised an exhaust port. But it was really low to begin with and did not have the port timing I wanted.

 

[troutfisher]

I have gotten pretty good compression numbers just by widening ports.

Usually step one for me is setting the squish and see what I get for compression, If I'm not happy I go to a pop up piston. I guess I've never tried widening first. Does compression raise much just widening the ports? Usually I'm looking for at least another 50psi on the guage. Thanks for sharing this Sling'r.

 

[blsnelling]

Widening the ports will do nothing to affect compression. I'd love to have a mill and lathe to do popups and the like.

 

[lovetheoutdoors]

great info here...thought about some tinkering myself. can someone post a pic of the main tools you grind with like the grinding stones and so forth...i have several die grinders i just need to know the size and shape of the attachment you guys are using.

 

[blsnelling]

Nothing but a corded Dremel with a carbide burr, 1/4" diameter cylinder radius-tip double-cut. Finish shaping up and flaten out with a chain sharpening file. Use sand paper to finish.

 

[parrisw]

Remember to measure to the narrowest part of the skirt. Unlike I did and measured to the bulge of the skirt, and farked up a good 395 cylinder.

 

[Martinm210]

I still don't understand what timing to look for, but I have experimented with some tools. I found my dremel with the pencil extension to work best for me as the grinder. One of those micro pencil die grinders would probably also work really well, but the dremel seems to have enough power.

The other thing I found is for polishing. They sell these little brown and blue polishing bits that work pretty well for polishing. I found them at harbor freight for $2 for a six pack.

Anyhow, after redoing the exhaust port about three times I finally started using this sort of method:
1) Grind with either sanding drums or carbid bits, sanding drums seem to work best when cutting down the coating as it's pretty hard and sand is harder than carbide. Just rough it out with these bits, and don't try to get it perfect, it won't be smooth or straight, that's where the needle files come in.
2) Needle files work great to take the rough cutting down to a nice flat surface. They leave a rough finish, but it's straight which will show later
3) Wrap sand paper on the needle files and sand. Seems like I start with 150, then 220 grit paper. That's plenty good for intake ports, but exhaust you can continue, sand down to 400
4) polish with those little brown and blue polishing bits. They were down to nothing fast, but they work much faster than any cotton buffs and compound.
5)finish with some compound and a soft cloth by hand.
6) Chamfer edges of ports with a ball stone, then polish those same edges with a round blue polishing bit. I still worry about the coating missing on the chamfer, so I figured a nice polishing is a worthwhile second step.
7)Wash it all up and check with a ring for level. Probably to do a good job, you'd need to check and touch up several times until everything was perfectly symmetrical.

Last but not least take your time. I still managed to slip up twice doing my piston and made a few nicks where I didn't want them. I'm hoping my light sanding will have taken care of that.

Anyhow, I didn't go too far with my first one. Mainly just clean up the ports and spent most of my time port matching the muffler and cleaning up the piston windows. I'll do my MS290 as soon as they come out with a 390 kit..

 

[Tree Sling'r]

Usually step one for me is setting the squish and see what I get for compression, If I'm not happy I go to a pop up piston. I guess I've never tried widening first. Does compression raise much just widening the ports? Usually I'm looking for at least another 50psi on the guage. Thanks for sharing this Sling'r.

I guess I should have followed through with my statement:
You don't have to lower your squish a bunch to get high compression readings. The last 5 460s I have built have had the squish set at .023-.025 with compression @ 195-210lbs. Granted a little bit of that is coming from a pop up on the piston, but not that much. Just raising ports back up to stock numbers.

 

[troutfisher]

I guess I should have followed through with my statement:
You don't have to lower a your squish a bunch to get high compression readings. The last 5 460s I have built have had the squish set at .023-.025 with compression @ 195-210lbs. Granted a little bit of that is coming from a pop up on the piston, but not that much. Just raising ports back up to stock numbers.

Yup, that's where I like squish readings at too.....and stock numbers usually work good for work saws. If I deck the jug and cut the popup on the piston, and compression goes way high, I'll raise the exhaust a bit to keep it down around 190psi. Big changes in timing numbers usually go along with pipes and heads and stuff like that.

 

[volks-man]

Widening the ports will do nothing to affect compression. I'd love to have a mill and lathe to do popups and the like.

I guess I should have followed through with my statement:
You don't have to lower your squish a bunch to get high compression readings. The last 5 460s I have built have had the squish set at .023-.025 with compression @ 195-210lbs. Granted a little bit of that is coming from a pop up on the piston, but not that much. Just raising ports back up to stock numbers.

hey guys,
since this is the 'dummies' thread...
would you mind explaining the pop-up?
you machine off a ring of material around the top edge of the piston right?
how does this raise compresion?
thanks,

one of the dummies.

 

[Martinm210]

How do you go about raising the bottom of an exhaust port. If I were to mill down the base of my jug and turn the piston to make a pop up, I'd have a problem with the bottom of the piston skirt clearing the bottom of the exhaust port on my 066BB kit (Is that the sub piston induction term?). It already does a very small amount.

Is JB weld or something else used to fill in stuff like that?

Obviously the fill would need to remain away from the piston enough to prevent contact.

A longer piston would do the trick too, but I'm not sure what would be compatible in 56mm.

 

[Tree Sling'r]

How do you go about raising the bottom of an exhaust port. If I were to mill down the base of my jug and turn the piston to make a pop up, I'd have a problem with the bottom of the piston skirt clearing the bottom of the exhaust port on my 066BB kit (Is that the sub piston induction term?). It already does a very small amount.

Is JB weld or something else used to fill in stuff like that?

Obviously the fill would need to remain away from the piston enough to prevent contact.

A longer piston would do the trick too, but I'm not sure what would be compatible in 56mm.

If you cut the base and make the pop up the same you should not have any issues. But, then again, the BB kits are weird. Waste of money if you ask me.

 

[Tree Sling'r]

hey guys,
since this is the 'dummies' thread...
would you mind explaining the pop-up?
you machine off a ring of material around the top edge of the piston right?
how does this raise compresion?
thanks,

one of the dummies.

The pop up goes into the compression chamber, creating more compression.

 

[Lakeside53]

If you don't want to grind on a cylinder, or lathe a pop-up.


I saw a pretty interesting way to raise compression - take out the decomp valve and wind in a bolt that protudes even slightly into the cylidner. Sure make a difference. I suspect it messes with gas flow though... However.. the saw ran remarkably well....

How about building up the top of the chamber with a tig, then grinding it smooth with a big ball cutter?

 

[Martinm210]

If you don't want to grind on a cylinder, or lathe a pop-up.


I saw a pretty interesting way to raise compression - take out the decomp valve and wind in a bolt that protudes even slightly into the cylidner. Sure make a difference. I suspect it messes with gas flow though... However.. the saw ran remarkably well....

How about building up the top of the chamber with a tig, then grinding it smooth with a big ball cutter?

Neat idea! Just a slightly over length plug hmmmm...


Has anyone tried cutting the jug into separate head pieces?

Maybe with some careful measuring and a nice large thin kerf slitting saw, you could make it happen on a mill?

Ahh probably too much headache, but it would allow some more tinkering with compression/domes without messing with your port timing.