engine timings

[stan simpson iv]

I have been asked a very intelligent question about how the exact timing dimensions are found for the exhaust, transfers & boost ports by a manufacturer of hundereds of engines. I can assure you that a "degree wheel" is NEVER used to determine or check any timing point in any manufactured or custom built engine's cylinder!

Jim Allen

What #'s should we be shooting for Ex,Boost,Side's,and finger port's. Does it differ from rig to mono...21's to 101's. What is simple,Mild and WILD.

 

[Timbo Whalen]

The most accurate and consistent way for me of taking measurements of the piston-to-port or the rotor-to- back plate closing timing with a degree wheel on nitro engines is with a simple tool similar to what Lohring is using on the gas engines. However with the very close tolerances of the fit in the nitro engines a much thinner tool can be usedI

I made a simple tool that works. I take a .002 feller gauge blade and trim a section from the side of it about 1/8 inch wide running the length of the blade. I then put one end of this blade into a piece of brass tubing and crimp it to make a handle. I use a piece of tubing about 3 to 4 inches long for this. On the other end, I make a bend about 1/4 inch from the end of the blade at about a 45 degree angle. That is all there is to making this tool.

To use this tool, slip the bent end into the sleeve port and GENTLY bring the piston up against it then take your reading from the degree wheel. If this is done with a little finesse, it will be very consistent. Use the same procedure for the rotor-to-back plate position. As with using a micrometer, developing a feel for exactly when the surfaces make contact will reward you with a very accurate reading.

One other thing, when finding TDC (top dead center) on the degree wheel, position the piston stop far enough down in the cylinder so that it stops the piston at about 90 degrees to each side of TDC (one half of the piston stroke) then adjust the degree wheel to make these readings exactly the same. When the piston stop is removed, this gives you the most accurate TDC setting.

Enjoy,

Charles

That's a great method, Charles... and you have the math supplied through the gauge thickness, as Dave mentions. Or close enough, anyway.

Thanks-

Tim

 

[Samuel Hagan JR]

Where do you all get those small degree wheels?

 

[Charles Perdue]

Charles I like the gauge tool idea,, so if I understand the use ,You slip the .002" gauge into the port and bring the piston up to read your wheel ok,so then if using digital tools as I do then subtract or add the .002" to or from your measurment because of the gauge in the port,and because the piston will be .002" lower than than the top of port is that right?I guess I would in my case because I use digital tools.

David, I think that it is close enough for us. Say if you were trying to put the exhaust timing at 186 degrees and you were using the tool to set this. I do not think that if it were 185.9 or 186.1 degrees that you could tell the difference. However it you wanted to make sure that it was exactly 186 degrees then you could add or remove a .002 sleeve shim. I have never been able to tell the difference by taking out or adding a .002 shim.

Anyway I have been using this tool for many years so that all of my notes take this .002 into consideration.

Some of the top engine tuners just use the degree wheel to set the initial timings close and then add or remove sleeve shims in combination with head shims to dial the engine in to their particular setup or the changing weather and/or altitude. From what I have seen, shims ranging from .005 to .010 in different combinations is what they are using. To keep the head clearance at where you like it the best, when you use a shim to raise the sleeve you then lower the head by removing the same thickness shim and vice versa.

Charles

 

[PaulHail]

I have been asked a very intelligent question about how the exact timing dimensions are found for the exhaust, transfers & boost ports by a manufacturer of hundereds of engines. I can assure you that a "degree wheel" is NEVER used to determine or check any timing point in any manufactured or custom built engine's cylinder!

Jim Allen

What #'s should we be shooting for Ex,Boost,Side's,and finger port's. Does it differ from rig to mono...21's to 101's. What is simple,Mild and WILD.

There is no magic number for ideal port durations as you need to look at the entire picture of intake tract length, intake duration, the volume and shape of the internal flow paths in the engine, the width of the ports, the compression ratio and the tuned pipe shape and length.

I think you'll find that with modern engines that flow fairly well and run a tuned pipe that an inlet/exhaust duration of 120/180 to 126/186 is going to make pretty solid power across the board, but reasonable to tune and can rev as much as you want with an appropriate pipe and it doesn't matter if you're talking 3.5cc or 500 cc.

Some people like to run much higher durations, and those engines can really scream, but they can also struggle to pull a prop off the beach, can be hard to tune, can be hard to drive and can be less likely to finish a race. IMHO there is more power to be made or lost in the needle valve, pipe and combustion chamber than going to radical port timing and a solid tractable engine that finishes races all season in various water and atmospheric conditions is faster than the wonder engine that makes crazy power one race a season.

 

[dwilfong]

I have a easy and reliable way I check the port highs. Pull the sleeve out of the eng and hold it in you hand. Get a good pair of glasses if need be and use the bottom side of the calipers. Rest the bottom on the top of the sleeve and run the center rail that comes out down the inside of the sleeve. When the end lines up with the port edge you got the measurement.

Give it a try and you will see what I mean.

Of coarse TDC can be checked the same why with the sleeve installed in the eng.

Put the # in a eng analysis program and there you have it.

Don't be afraid to raise the transfers and boost timings. The ex dose not need to be sky high. stock has work best for me so far.

Look at the VAC .91 trimming when thy first cane out we all thought the intake ports where over the top at 136. Well thy worked just fine.

 

[LohringMiller]

If you look at the pictures I posted you can see the wire method I use. Fixed head engines are tougher than removable sleeve engines to measure. The hooked wire in the first picture fits into the exhaust port to measure the transfers. The 45 degree method in the second picture gives a system to measure radiused exhaust ports. A radius on the exhaust and piston as shown in the attached pictures greatly improves the flow in the early opening phase of both exhaust and transfers.

Lohring Miller

 

[BobBonahoom]

I really like what is being taught here. Lohring's drawings are a great help. It doesn't matter how long you do this, there is always something new to learn here. Thank you all !

 

[Lennard Cuenco]

If you look at the pictures I posted you can see the wire method I use. Fixed head engines are tougher than removable sleeve engines to measure. The hooked wire in the first picture fits into the exhaust port to measure the transfers. The 45 degree method in the second picture gives a system to measure radiused exhaust ports. A radius on the exhaust and piston as shown in the attached pictures greatly improves the flow in the early opening phase of both exhaust and transfers.

Lohring Miller

exhaust edge radius.png

piston edge radius.png

interesting stuff Lohring,

what improvements did you notice with the top of the window radiused like that?

you worry at all about the piston trying to sneak out the window?

 

[scottmeyers]

Ok fellers here's a little "port timing" video I shot for our buddy Lennard some time ago.

Please forgive the sarcasm. If you know Len you'll surely understand why it was necessary...

https://youtu.be/UR8NaSUrrgQ

 

[Samuel Hagan JR]

Nice video.

Where did you get the degree wheel?

 

[BobBonahoom]

Scott,

That was a nice video. Where did you get that degree wheel? I use the EAP so I don't use a wheel, but it might be good to have one for use at a race when you don't have a computer, etc.

For a 1/2" diameter drum, a 0.015" wire would be about 3-1/2 degrees.

 

[scottmeyers]

Scroll down a bit http://www.sdp-si.com/products/Hardware-and-Miscellaneous-Components/index.php

 

[Lennard Cuenco]

Ok fellers here's a little "port timing" video I shot for our buddy Lennard some time ago.

Please forgive the sarcasm. If you know Len you'll surely understand why it was necessary...

https://youtu.be/UR8NaSUrrgQ

yeah yeah yeah

thanks skotty....

for clearing things up and not playing the vagueness game....

great stuff

 

[stan simpson iv]

I have been asked a very intelligent question about how the exact timing dimensions are found for the exhaust, transfers & boost ports by a manufacturer of hundereds of engines. I can assure you that a "degree wheel" is NEVER used to determine or check any timing point in any manufactured or custom built engine's cylinder!

Jim Allen

What #'s should we be shooting for Ex,Boost,Side's,and finger port's. Does it differ from rig to mono...21's to 101's. What is simple,Mild and WILD.

There is no magic number for ideal port durations as you need to look at the entire picture of intake tract length, intake duration, the volume and shape of the internal flow paths in the engine, the width of the ports, the compression ratio and the tuned pipe shape and length.

I think you'll find that with modern engines that flow fairly well and run a tuned pipe that an inlet/exhaust duration of 120/180 to 126/186 is going to make pretty solid power across the board, but reasonable to tune and can rev as much as you want with an appropriate pipe and it doesn't matter if you're talking 3.5cc or 500 cc.

Some people like to run much higher durations, and those engines can really scream, but they can also struggle to pull a prop off the beach, can be hard to tune, can be hard to drive and can be less likely to finish a race. IMHO there is more power to be made or lost in the needle valve, pipe and combustion chamber than going to radical port timing and a solid tractable engine that finishes races all season in various water and atmospheric conditions is faster than the wonder engine that makes crazy power one race a season.

So 210 ex..135/130 boost/sides and(fingers) on a NR 35plus 21 is to much?

Crank #s will not get into right now.

Does it "REALLY" cause a sensitive needle and hard launch...with right setup??? Rigger(JAE)... Pipe(SPP).... NR (Engine)... ABC prop(NEW Style) ...Technology Fuel(HOT). Where is the cut off point? Where is Twilight Zone?

P.S. Timing done with a Degree Wheel.

 

[El Zorro]

WOW, Stan! That NR must be cranking 40 K ( and a slingshot launch ) just to get it around the corners and stay on the pipe with that much exhaust timing. What the hell? Who needs torque??? Throw the proprylene (?) oxide to it!!!

Dick Tyndall

 

[stan simpson iv]

No just asking what is "Twilight Zone"...played with planes(control line),car's,and boats. Learned a lot from my father(still picking his brain). Just picking at people's mind,what is their thought's on what they do with setup's,and why.

 

[Jack ODonnell]

I have been asked a very intelligent question about how the exact timing dimensions are found for the exhaust, transfers & boost ports by a manufacturer of hundereds of engines. I can assure you that a "degree wheel" is NEVER used to determine or check any timing point in any manufactured or custom built engine's cylinder!

Jim Allen

What #'s should we be shooting for Ex,Boost,Side's,and finger port's. Does it differ from rig to mono...21's to 101's. What is simple,Mild and WILD.

There is no magic number for ideal port durations as you need to look at the entire picture of intake tract length, intake duration, the volume and shape of the internal flow paths in the engine, the width of the ports, the compression ratio and the tuned pipe shape and length.

I think you'll find that with modern engines that flow fairly well and run a tuned pipe that an inlet/exhaust duration of 120/180 to 126/186 is going to make pretty solid power across the board, but reasonable to tune and can rev as much as you want with an appropriate pipe and it doesn't matter if you're talking 3.5cc or 500 cc.

Some people like to run much higher durations, and those engines can really scream, but they can also struggle to pull a prop off the beach, can be hard to tune, can be hard to drive and can be less likely to finish a race. IMHO there is more power to be made or lost in the needle valve, pipe and combustion chamber than going to radical port timing and a solid tractable engine that finishes races all season in various water and atmospheric conditions is faster than the wonder engine that makes crazy power one race a season.

So 210 ex..135/130 boost/sides and(fingers) on a NR 35plus 21 is to much?

Crank #s will not get into right now.

Does it "REALLY" cause a sensitive needle and hard launch...with right setup??? Rigger(JAE)... Pipe(SPP).... NR (Engine)... ABC prop(NEW Style) ...Technology Fuel(HOT). Where is the cut off point? Where is Twilight Zone?

P.S. Timing done with a Degree Wheel.

210 degree exhaust ??? J.

 

[LohringMiller]

I wish I could take credit for the radius ideas. I believe Jim Allen has tried a radius on a Quickdraw piston with good results. The pictures are courtesy of Frits Overmars and has been tested in motorcycle two strokes. Remember that adding a radius will raise the timing.

Lohring Miller

If you look at the pictures I posted you can see the wire method I use. Fixed head engines are tougher than removable sleeve engines to measure. The hooked wire in the first picture fits into the exhaust port to measure the transfers. The 45 degree method in the second picture gives a system to measure radiused exhaust ports. A radius on the exhaust and piston as shown in the attached pictures greatly improves the flow in the early opening phase of both exhaust and transfers.

Lohring Miller

exhaust edge radius.png

piston edge radius.png

interesting stuff Lohring,

what improvements did you notice with the top of the window radiused like that?

you worry at all about the piston trying to sneak out the window?

 

[stan simpson iv]

I am not running 210ex 135/130boost/sides,just a hypothetical question. The Nelson 45 outboard engine is at 197ex,that only 3 degrees from 200. Just asking what people are doing and why. Years ago when we use to race the Rossi 45 they were 186ex and back then that was CRAZY#'s to most people.