engine timings

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

I've always wondered the same question.

How guys get timing numbers from Rc engines.

Mathematics. EAP works for me.

Ray Sametz said:

Mathematics. EAP works for me.

Click to expand...

Ray,

What's the meaning of EAP in this example? Employee Asistance Program?

JA

Jim Allen said:

Ray Sametz said:

Mathematics. EAP works for me.

Click to expand...

Ray,
What's the meaning of EAP in this example? Employee Asistance Program?

JA

Click to expand...

I think its Engine Anylisis Program? Right Ray.

I'm still confused on how you time it.

Jim Allen said:

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

Click to expand...

Please elaborate a bit, Jim.

We've always viewed it as a time/area study rather than angular. Angular degree values are just simpler to

work with in most cases, subsequent to design release.

Trigonometric calculations with geometric input is, perhaps, the valued approach using dimensional input

from the ports, crankshaft, conrod, and piston. There are dwell points that occur in the pistons linear travel

due to pin location, rod envelope, etc. (linear acceleration/deceleration)

However, when working with an increased amount of measurements, the opportunity for error increases.

Angular mensuration with a degree wheel can be sufficient to modify an existing engine, as long as it's done

with care. However, from an initial design standpoint, time/area studies and other geometric components

are prerequisite.

There has been a lot published regarding this subject from doctoral thesis.

Thanks-

Tim

Ref- Dr. Martin Hepperle

Dr. Gordon Blair

Samuel Hagan JR said:

Jim Allen said:

Ray Sametz said:

Mathematics. EAP works for me.

Click to expand...

Ray,
What's the meaning of EAP in this example? Employee Asistance Program?

JA

Click to expand...

I think its Engine Anylisis Program? Right Ray.

I'm still confused on how you time it.

Click to expand...

Engine Analysis Program is correct. Precise measurements are feed into a computer program that does the math. Results in exhaust timing, boost, transfer and so on.

I wonder what was done before EAP programs came along? How did engine builders in 1970 know that the windows cut in any cylinder were cut in the correct place? Is math or a computer program necessary to cut windows in a cylinder? What effect does the thickness of the cylinder's wall have on cutting windows that are not square to the cylinders wall, when it is the inside measurement that counts to determine the timing? Since the cylinders in question SHOULD be held from the flange end when cutting windows, how do you determine where to cut if the measurement is taken from the top of the cylinder? Is there any simple method, without using a degree wheel, EPA programs or computer programs, that any modeler could use, to determine what the timings are in a engine's cylinder????????

JA

Jim Allen said:

I wonder what was done before EAP programs came along? How did engine builders in 1970 know that the windows cut in any cylinder were cut in the correct place? Is math or a computer program necessary to cut windows in a cylinder? What effect does the thickness of the cylinder's wall have on cutting windows that are not square to the cylinders wall, when it is the inside measurement that counts to determine the timing? Since the cylinders in question SHOULD be held from the flange end when cutting windows, how do you determine where to cut if the measurement is taken from the top of the cylinder? Is there any simple method, without using a degree wheel, EPA programs or computer programs, that any modeler could use, to determine what the timings are in a engine's cylinder????????

JA

Click to expand...

Too be honest, kept it simple I used the "Trickle down theory" from you to Charney to me. My engines ran awesome after Brian worked on them.

The formulas for piston position are calculated from trigonometry. There are calculators available both on line and in many programs. I'm sure I probably have a spreadsheet somewhere that will calculate piston positions. I put tables for 28 mm and 29 mm stroke Zenoahs or clones in my Zenoah Porting 101 article in the April 2016 Propwash.

Lohring Miller

doesnt matter how they do it...just so long as your method works for you

If Excel files were allowed, I would post a piston position calculator.

Lohring Miller

I understand when machining 100's/1000's of part's you dont use degree wheel. What can a Degree Wheel be used for then?

You can use combinations of measurements and a degree wheel. The measurement is a lot more accurate, but the degree wheel gives a reality check. Again look at my Propwash articles. Below is a possible setup for Zenoah style cylinders. The second picture illustrates the method of accurately determining piston position.

Lohring Miller

Jim

Your engine timing do you still use the 30deg blow down timing

Dave

The problem isn't in the calculations, EAP does that just fine. The problem for me has always been accurately measuring the opening point with regard to TDC, especially with tapered knife edge openings. I always used the "first light method" in a dark room with a depth gauge. I was never sure if this was the best way to do it though.

Delete

I just got the EAP. A lot of info to take in.

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

Delete