Sleeve Porting: What does what?

[Jim Allen]

Jim: In order to maintain a 50% squish band area on a .21 sized engine, it is necessary to use a 3/32" cutter. If you use this cutter, there will be some straight side to the chamber. Do you have any feeling about this? I have tried almost everything I can think of to get a chamber without straight sides and the CR would be so high that it could never work. Thoughts....

Marty,

I am aware of this problem with small bore engines. I was told that the toroidals that have been made for .21 size engines used Rossi turbo plugs & the squish ratio is reduced to 45%. The Rossi has a steeper taper than the Nelson plug, which will help in the weak area adjacent to the plug. Are you talking about talking about a 3/32" diameter ball nose end mill or one with a 3/32" radius. I haven't looked at the numbers for engines below .90 size. It is very possible that there is not enough space to enable the donut to be made, especially if you're using a 1/4-32 plug.

I don't know what will happen if the sides are straight for a short distance, maybe nothing. The compression ratio is always very high with the toroidals.

Jim

 

[Jim Allen]

Marty, I just tired to make one, and botched it up at the end, but I ended up using an 1/8" tool and got the following: Plug face .036 away from the piston face. (.026 deep from the squish band, I had planned on .010 head clearance) .096 wide squish band at 1* angle. ended up at .17cc with the plug installed. I didnt keep track of how deep I plunged the cutter in, but its possible. It wouldnt be possible if you wanted much wider of a squish band then that though. At least not with the 1/8 inch radius cutter.

That .096 nets us a squish band of about 50% in a .21 GO/Nova if Im calculating that correctly. I did not end up with hardly any straight wall in the chamber.

Rodney,

The numbers don't look to far off. My squish band width in the .90 engine is .162" wide with a 1.125" bore. The plug is .048" away from the piston at TDC. The maxium depth of the donut is .080" away from the piston at TDC. I use a .1875" radius ball nose end mill, translated .248" from the center & plunge in .080" from the bottom of the squish band that is still flat. I cut the 1 deg taper last.

Jim

 

[RodneyPierce]

Jim, what I ended up doing was cutting the 1* band first then plunging in my 1/8 inch cutter .040 to begin with to get the center plug height (I started there) then brought the cutter out making sure I had atleast a .090 squish band width. Just plunged it in until it looked pretty decent, then took it off and measured. I ended up WAY big, was at .24cc volume. So I took the face back down a ways, and started plunging in the 1/8 inch cutter again and then re-measuring. This time ended up at the above numbers, and it happened to work out. LOL. There really was no "design or science" behind my method, just seen yours and David's pictures and went to town.

I will retry it here some night when I have more time and patience. I will use your method. Now, sorry, as Im pretty new to this machining thing, and pretty much self taught (David has actually helped me alot) but is there a way to figure out how deep i need to go to get a certain cc? or is it all just guess and check?

 

[Jim Allen]

Jim, what I ended up doing was cutting the 1* band first then plunging in my 1/8 inch cutter .040 to begin with to get the center plug height (I started there) then brought the cutter out making sure I had atleast a .090 squish band width. Just plunged it in until it looked pretty decent, then took it off and measured. I ended up WAY big, was at .24cc volume. So I took the face back down a ways, and started plunging in the 1/8 inch cutter again and then re-measuring. This time ended up at the above numbers, and it happened to work out. LOL. There really was no "design or science" behind my method, just seen yours and David's pictures and went to town.

I will retry it here some night when I have more time and patience. I will use your method. Now, sorry, as Im pretty new to this machining thing, and pretty much self taught (David has actually helped me alot) but is there a way to figure out how deep i need to go to get a certain cc? or is it all just guess and check?

I measured only the chamber volume up to the edge of the squish band in the hemi head I was using with a .1 cc pipet. All the toroidals, starting with the first, had chambers with much less volumes. Guess, cut, test.

 

[Marty Davis]

With AutoCad and a little program that Brian Callahan made me to calculate the volume, it is very easy to know beforehand what you will have when finished. I have made dozens of buttons and now I know before I cut what they will be when finished. Also know the Squish velocity by moving the squish clearance around a little to get the range that I want. The .21 button is REALLY difficult to keep the 50% and have some toroidal donut.

Jim:

The cutter is 3/32" diameter. I tried an 1/8" and it was too big. I don't see any way to NOT have a little straight sides. Guess I will have to just try it and see.

 

[Jim Allen]

Marty,

Tilt the cutter about 120 degrees towards the out side. This will automatically reduce the squish band width & keep the outside wall from being verticle.

Jim

The reason for using the rotary table or dividing head instead of the lathe is that you will have to zero the tool bit, up & down, right & left, to the spindle center in order to know the exact translation amount before you plunge in. This is not impossible but it is difficult & it will be more difficult if the tool is at an angle. When using a dividing head or rotary table you will zero the spindle to the center of the work piece. This is easy to do even if the head or table needs to be tilted.

 

[Marty Davis]

Marty,

Tilt the cutter about 120 degrees towards the out side. This will automatically reduce the squish band width & keep the outside wall from being verticle.

Jim

The reason for using the rotary table or dividing head instead of the lathe is that you will have to zero the tool bit, up & down, right & left, to the spindle center in order to know the exact translation amount before you plunge in. This is not impossible but it is difficult & it will be more difficult if the tool is at an angle. When using a dividing head or rotary table you will zero the spindle to the center of the work piece. This is easy to do even if the head or table needs to be tilted.

Jim:

I can do that. Great idea. Using my lathe, I can use the compound and adjust it easily. With AutoCad, I can also draw that and calculate the volume too. Great solution.

 

[RodneyPierce]

Marty, care to post your findings here? measurements, plunge depth, volume, etc? Would be nice for others that might want to try and make one, or try out this idea.

 

[Marty Davis]

Marty, care to post your findings here? measurements, plunge depth, volume, etc? Would be nice for others that might want to try and make one, or try out this idea.

Rodney:

I really don't have any findings at this point. I just found out that Jim uses a different compression ratio calculation than I use (trapped compressioin ratio) and I will have to do some adjusting.

Jim:

Please let us know how you calculate your compression ratio so that I can figure out where I need to be. I have been using a high of 10.25:1 and have recently been using low 9:1.

 

[RodneyPierce]

Rodney:

I really don't have any findings at this point. I just found out that Jim uses a different compression ratio calculation than I use (trapped compressioin ratio) and I will have to do some adjusting.

Jim:

Please let us know how you calculate your compression ratio so that I can figure out where I need to be. I have been using a high of 10.25:1 and have recently been using low 9:1.

Not yet you dont, but after this:

Jim:

I can do that. Great idea. Using my lathe, I can use the compound and adjust it easily. With AutoCad, I can also draw that and calculate the volume too. Great solution.

you will . Just was curious is all, for us that dont have the programs that you do (like stated above) would be nice to have a starting place to work from, so we didnt have to mess up or go too deep, etc.

 

[dwilfong]

I have a little trick for checking the chamber sizes. I drill the plug hole then start to cut the chamber. Leaving it in the chuck I put grease on the button and the drill bit . Put the drill in with the shank end flush with the hole. then put the plexie glass cover with the two holes drilled in it on the button. the grease holds it in place. (nice) Then position the one hole at the top of the chamber. Put a dab of grease on the needle tip and fill. Real quick and easy to check as you cut. Quicker than a CAD drawing. Gust cut the dang thing. This thing ain't going to the moon. Its a toy boat eng. Sorry I get carried away some times. David

 

[Jim Allen]

Marty,

I measure the volume in the chamber up to the edge of the squish band. I divide that into the displacement of the engine. I do this because the squish band angle is always close to the piston crown's angle & the deck clearance is no more than .003", even in a 26 cc engines. In all the stuff I run, the deck is closed until it just begins to touch at maxium RPM. Leave the squish band, bowl edge as sharp as possible to start. Do not polish anything except the piston crown! If you run the lathe at the right speed, with the right feed, you will be able to get a 70 micro inch finish or better easily. The tool must be very rigid & the piece must be held rigidly! The slowest speed works the best.

Remember, if the thing is working properly, you MUST RICHEN THE NEEDLE SETTING!!! ACCURACY & KNOWING EXACTLY WHAT YOU HAVE MADE BECOMES VERY IMPORTANT IN ALL SMALL SIZE ENGINES, ESPECIALLY WHEN IT COMES TIME TO MAKE THE NEXT PIECE!!!

Jim

Just do it!

 

[dwilfong]

Jim using this total displacement CR where is a good starting point 20-1 ,19-1 ,18-1

You have to start some where?

David

 

[RodneyPierce]

I have a little trick for checking the chamber sizes. I drill the plug hole then start to cut the chamber. Leaving it in the chuck I put grease on the button and the drill bit . Put the drill in with the shank end flush with the hole. then put the plexie glass cover with the two holes drilled in it on the button. the grease holds it in place. (nice) Then position the one hole at the top of the chamber. Put a dab of grease on the needle tip and fill. Real quick and easy to check as you cut. Quicker than a CAD drawing. Gust cut the dang thing. This thing ain't going to the moon. Its a toy boat eng. Sorry I get carried away some times. David

David, dont make me........ LOL. Ill cut another one of the darn things here someday. When I get some time to get back down to the basement shop. Sorry for asking about helpful tools

Jim, thanks for the great explanations. Ill "just do it!"

 

[RodneyPierce]

Jim using this total displacement CR where is a good starting point 20-1 ,19-1 ,18-1

You have to start some where?

David

David, we aint makin rocket ships here! Its a toy boat engine!

 

[Jim Allen]

"Jim using this total displacement CR where is a good starting point 20-1 ,19-1 ,18-1

You have to start some where?"

I have already stated that I started with the volume of the hemi chamber the engine was running with. The first engine I tested had a chamber volume of 1.85 cc. It was a 26 cc engine & that works out to 14:1. The first toroidal head had that same volume. I found that the engine could be leaned well beyond it's previous setting with the first toroidal design, without any detonation. After three more attemps of reducing the chamber's volume, it is now 1.1 cc. That works out to 24:1. The needle is almost one full turn richer & my dyno, lake testing, prove the engine is making more power. The most noticable place where you will immediately see a great improvement is in the low & mid-range HP. Also there will be a large increase in the high end HP & RPM.

The things that will prevent this thing from working to the maxium are: poor carburetor design; poor induction design; poor transfer, exhaust geometry; poor tuned pipe design; poor mechanical design. NO ONE IMPROVEMENT MAKES A SUPER ENGINE!!!

Jim Allen

note: The chamber that I'm testing on my .90 engine has the glow plug .048" from the piston crown ATDC. The depth of the toroidal bowl is .080" from the piston crown ATDC. There is a .020" flat area adjacent to the plugs thread at the .048" dimension. It is made with a .375" diameter ball nose end mill, plunged straight in. I haven't the slightest idea what the compression ratio is!!!

 

[Marty Davis]

Marty,

I measure the volume in the chamber up to the edge of the squish band. I divide that into the displacement of the engine. I do this because the squish band angle is always close to the piston crown's angle & the deck clearance is no more than .003", even in a 26 cc engines. In all the stuff I run, the deck is closed until it just begins to touch at maxium RPM. Leave the squish band, bowl edge as sharp as possible to start. Do not polish anything except the piston crown! If you run the lathe at the right speed, with the right feed, you will be able to get a 70 micro inch finish or better easily. The tool must be very rigid & the piece must be held rigidly! The slowest speed works the best.

Remember, if the thing is working properly, you MUST RICHEN THE NEEDLE SETTING!!! ACCURACY & KNOWING EXACTLY WHAT YOU HAVE MADE BECOMES VERY IMPORTANT IN ALL SMALL SIZE ENGINES, ESPECIALLY WHEN IT COMES TIME TO MAKE THE NEXT PIECE!!!

Jim

Just do it!

Jim:

When you measure the volume of the chamber, do you include the glow plug cavity, have the glow plug screwed into the chamber?

Just interested in what amount the plug area is in this calculation.

 

[Jim Allen]

"When you measure the volume of the chamber, do you include the glow plug cavity, have the glow plug screwed into the chamber?"

Absolutely. Different plugs, hot or cold, will give different readings.

 

[Jim Allen]

Semi surface discharge spark plugs combined with toriodal head shapes allow the spark plug to be placed closer to the middle of the chamber. The plugs shown in the photos were made from existing NGK CR7EK spark plugs. The ceramic insulator is removed from the plug body by cutting off the hexagon nut. The remaining plug body is single point threaded with a 32 pitch external thread. A # 303 stainless .6875" (11/16") hexagon piece is internally single point threaded & machined to provide a high clamping force to the ceramic insulator. Alumina ceramic cement & the clamping nut give the spark plug a double seal. The two ground electrodes are machined to give a .025" gap when the plug body & the ceramic center have been disassembled.

Semi surface discharge plugs of this type cannot be fired with standard Zenoah or RCMK stock magneto systems. A power Spark electronic system is being dyno & lake tested to determine the usability of these spark plugs.

Jim Allen

 

[dwilfong]

Jim here is the plug I ran in my Cagiva 125 Champion N82S.

$35 each in 1989 and you had to buy a box of 10. We called it a side wire plug.

this was the plug in the eng from the factory. It was the best running plug if you could afford it.

David