It is a start...

[user 13000]

So, as my intro post explains, I have no experience making model engines. I'm working on my BS as a MechE, so I have no problems diving in head first. I'm making all the parts in Inventor first. I'm posting my work/thoughts here for constructive criticism. I will warn you ahead of time, many of my ideas/plans may seem odd or uncomon for what I'm building first. Just give me the pros/cons instead of turning it into a flame war.

The Idea:
I eventually want to work on making a supercharged V12 (similar to the Artus V12 from Germany). For now, I'm going to make a 4-stroke, 2-cylinder opposed engine. The idea is to actually use this on a scale model aircraft (so it has to work). I'll be experimenting on production techniques on this 2-cylinder for experience/ideas on the much bigger V12.

The plan is to run pure methanol with a manual mix of pure nitromethane (not the mixed 'nitro' from hobby shops). Oil control is separate, and pressurized/forced/whatever-have-you. This should allow me to run high compression with slight supercharging.

So first up, the piston design. So far, 1in diameter dished piston. Two rings (will be fine-grained iron - Tremble method). I'm still debating on an oil control ring.

Thoughts?

 

[Cogsy]

I'm too new at this to be able to offer any thoughts, but I can tell you that we don't do 'flame wars' here. I'm sure you'll get lots of feedback and help though Thm:

Good luck with your build!

 

[trumpy81]

MrBaz, two things, why the dished piston? and is the wrist pin location correct? It seems a little low to me.

I'm no expert mind you, I'm asking for my own knowledge as much as anything else.

Other than that, it's a very nice Inventor model. What version of Inventor are you using? I have 2013 Pro.

 

[Minerjim]

MrBaz,
Nice rendering. i can use the AutoCAD, but i like to revert back to the paper and pencil i was originally taught with. if you are schooling to become an ME, you are smart to try and balance all that book learning with hands on experience building things, you will find it will help you become a much better engineer over the long run.( has worked for me for over 35 years inthe business) Have always thought my machinist friends have had it over me because they could design and build their designs. Look forward to seeing more of your renderings, and hopefully pix of your model.

 

[kuhncw]

Nice looking piston, though the ring grooves look rather wide for a 1 inch bore. I'd expect the Trimble method to specify a pretty narrow ring, perhaps 0.040 or so.

Good luck and please keep us up to date on your project.

Chuck

 

[user 13000]

MrBaz, two things, why the dished piston? and is the wrist pin location correct? It seems a little low to me.

I'm no expert mind you, I'm asking for my own knowledge as much as anything else.

Other than that, it's a very nice Inventor model. What version of Inventor are you using? I have 2013 Pro.

It will be a semi-high compression setup that will eventually get supercharged. I'm controlling the compression and piston-to-deck travel with the dish in the piston, just like how they do it on the full-size boosted conterparts.

The wrist pin could possibly use a little more meat on the bottom. Otherwise, I'm not sure what you mean by its location. I've been using JE and Weiso performance pistons as a guide -- they have short piston skirts.

 

[user 13000]

Nice looking piston, though the ring grooves look rather wide for a 1 inch bore. I'd expect the Trimble method to specify a pretty narrow ring, perhaps 0.040 or so.

Good luck and please keep us up to date on your project.

Chuck

I was wondering about that. I believe I have the grooves set for a 1/16" (.063in) thick ring. I wasn't sure if I could safely go thinner. Keep in mind that this will be a high compression, supercharged engine.

I forgot to mention a few things:
rings - fine grained cast iron (Durabar 6000 maybe?)
sleeves - cast iron
pistons - 4032 aluminum

 

[trumpy81]

MrBaz, normal practise is for the wristpin to be located at the midpoint between the piston crown and the bottom of the skirt. It may be parallax error and or the picture, but your wristpin location looks lower than that midpoint.

 

[user 13000]

MrBaz, normal practise is for the wristpin to be located at the midpoint between the piston crown and the bottom of the skirt. It may be parallax error and or the picture, but your wristpin location looks lower than that midpoint.

I see what you mean. Like I said, I was just trying to model off of a typical performance piston from JE, Weisco, etc. If midpoint is preferrable for small scale engines, I'm more than happy to change the design. I do want this to work after all!

Attached is an example of what I'm talking about. You can see how the wrist pin is darn near dead-bottom.

 

[trumpy81]

MrBaz, wow, they are really nice pistons!! Now if you could just use those it'd be great ... lol

I'm wondering if using such a piston in a model engine, what effects it would have. Would there be too much pressure on the skirts or too much expansion of the crown, given the reduced size for model use?

I have often wondered why modern piston design is not used in model engines. They obviously work in full size engines so why not model engines?

Will your engine be glow or spark ignition?

 

[user 13000]

MrBaz, wow, they are really nice pistons!! Now if you could just use those it'd be great ... lol

I'm wondering if using such a piston in a model engine, what effects it would have. Would there be too much pressure on the skirts or too much expansion of the crown, given the reduced size for model use?

I have often wondered why modern piston design is not used in model engines. They obviously work in full size engines so why not model engines?

Will your engine be glow or spark ignition?

I wonder the same thing. Maybe I'll just build a 2-cylinder with such pistons and see? :hDe:

I'm planning on spark ignition using a custom solid state system, including spark advance.

 

[user 13000]

MrBaz, two things, why the dished piston? and is the wrist pin location correct? It seems a little low to me.

I'm no expert mind you, I'm asking for my own knowledge as much as anything else.

Other than that, it's a very nice Inventor model. What version of Inventor are you using? I have 2013 Pro.

I forgot to answer your other question; I'm using Inventor Pro 2013.

 

[user 13000]

Update: 0.04" ring gap. Distance from crown to wrist pin hole midpoint is 0.735". Piston is a total of 1.088" long. Still debating the oil control ring. How does one make one?

 

[trumpy81]

MrBaz, There are several techniques for making oil control rings. The one that sticks in my mind is to use a jewelers saw to cut small slots in the periphery of the ring. Another method of oil control is to drill a few holes aligned with the fore/aft piston skirts (where the most friction occurs) and that are tangent to the top of the ring groove but may extend past the bottom of the ring groove depending on the diameter of the hole. For a .040 ring groove an .080 drill bit would be used. It's easier to model than it is to describe .... lol

Love that Inventor!! (Hate the new materials and appearances though

 

[Leucetius]

Another method of oil control is to drill a few holes aligned with the fore/aft piston skirts (where the most friction occurs) and that are tangent to the top of the ring groove but may extend past the bottom of the ring groove depending on the diameter of the hole.(

Which is the same method used in the pictured pistons, if I'm not mistaken.

Inventor 2013 is a neat piece of software indeed, but I'm most sure, that in 2012/11 it was possible to place a hole on a round surface ... this is gone.

 

[trumpy81]

Leucetius, the second picture of a piston is mine and yes it is still possible to place a hole on a round surface in 2013 ... maybe a different technique is needed than what you were used to?

That piston was drawn in 2013 Pro.

 

[user 13000]

... Another method of oil control is to drill a few holes aligned with the fore/aft piston skirts (where the most friction occurs) and that are tangent to the top of the ring groove but may extend past the bottom of the ring groove depending on the diameter of the hole. For a .040 ring groove an .080 drill bit would be used. It's easier to model than it is to describe .... lol

Love that Inventor!! (Hate the new materials and appearances though

So, would it be possible to use the second ring as a dual-use friction and oil control ring? I was thinking about doing something exactly as you described, but wasn't sure.

 

[Leucetius]

I think so. The picture I meant was this: (posted by yourself). You can see that the holes overlap the lowest ring groove other than emerge fully in it. (sorry for bad english)

Leuc

 

[user 13000]

Like so? 3 on each side. Should they be farther apart? A hole is then drilled through the underside of the piston until I hit the oil passageways. Is this the correct method? Oil scraped from the cylinder wall flows through the oil passageways into the center hole 'in' the piston so the oil then 'drips' onto the small end of the connecting rod, right?

 

[trumpy81]

MrBaz, Not quite, but that is one way of doing it. My piston crown bisects the oil holes at about the midpoint of the hole so they are open to the bottom of the piston crown. The holes would be drilled before the interior of the piston is milled out.