Plans for a water cooled gas 3.5cc (per cyl) DOHC I4

I know that the title sounds a little absurd but here's the backstory! During the pandemic I found myself cooped up inside, (as I'm a type 1 diabetic and therefore high risk) and saw this channel JohnnyQ90, and spun down the rabbit hole that is model engines! the first engine I got my hands on was a GP 43 from my grandfathers nitro plane, which he passed down. I had my fun with that motor and the guys at the airfield were ecstatic to have a young guy interested in flying planes, so I now have a garage full of old nitro planes that all need work, but this post isn't about that. Anyways last year I got a small internship that I got some money from an bought myself my first gas engine, as I am not that biggest fan of nitro engines, that fuel is SUPER expensive for some one like me! The first engine I got was the Toyan L200 and I got the gas conversion kit for it. The thing only worked 3 times and I have been in a battle with customer support to get a new ignition system, so eventually I was like, well to hell with it, I'll design my own engine and it'll be better then theirs'. So around Christmas I started design this engine and only yesterday did I get my first look a what a final version might look like! And I've been having fun scrolling through some older post here and figured I might as well show what some of these post have helped with without them realizing. Mind everyone that sees this, it's not finished and needs a bunch of stuff like, and oil pump, scavenge tank (it's a dry sump oil system), a water pump and some timing gears (I didn't want to use a chain) and a bunch of other stuff, but here you go!


Here's the block and everything




Internal mechanisms
And yes, those are some really long spark plugs!


Top down view of the head, without the cover

Bottom view of head
There is a complicated oiling system in the block and head and head cover and I don't quite know how best to show them so I might revisit this post with better pictures or videos later, but onto the pistons!

Simple piston to use 2 piston rings

Said ring

Crankshaft, it's the typical flat-plane, and has no oil passages as I have no clue how I would implement those into this design currently without having to rework it completely and the block and current crank bearings, which are next!

Current 2 part bearing design, is it the best, no, but it is what I think might work.


Bottom of block, the slots cut out with a hole in the middle of them (bottom left of each cylinder cavity) is for oil squirters, I know that these are more typical on life size engines, but from my understanding it helps keep the pistons cool and con rod lubricated so I thought no harm in designing them!


The oil squirter, this really only redirects the oil to be pointed at the bottom of the piston.

This is where the oil squirter would sit and redirect the oil.

Top of oil pan if any of you are curious.

Any way that's it for now! If anyone has any suggestions or questions I be waiting!

Vincent Piechocki

Yes I'm using onshape, it's free

Vincent-

That is a pretty cool engine design.
I looked up OnShape, and it looks like a nice program, especially if it is free.

I must admit that I am not a fan of some of the ready-to-run or ready-to-assemble kit manufacturers, since they really seem to be flooding the market.
They have some fantastic engines for sure, but for me, having someone else do the design and machining takes all the fun out of the build.

For someone without machine tools, ready-built engines are one way to get into the hobby sort of; at least one would be familiar with the small parts, and how they fit together.

I like your design.
I don't know enough to comment on how to improve it.
I am very much into old-school engines, generally from pre-1900, both steam and internal combustion.
And I like one-cylinder engines, and so all my motorcycles are one-cylinder, generally in the 500cc range.

I did build a two-cylinder steam engine.

You plan on making this engine, ie: casting/machining/CNC, or whatever ?
Building and running the engine would reveal how solid the design is.

.

GreenTwin said:

Vincent-

That is a pretty cool engine design.
I looked up OnShape, and it looks like a nice program, especially if it is free.

I must admit that I am not a fan of some of the ready-to-run or ready-to-assemble kit manufacturers, since they really seem to be flooding the market.
They have some fantastic engines for sure, but for me, having someone else do the design and machining takes all the fun out of the build.

For someone without machine tools, ready-built engines are one way to get into the hobby sort of; at least one would be familiar with the small parts, and how they fit together.

I like your design.
I don't know enough to comment on how to improve it.
I am very much into old-school engines, generally from pre-1900, both steam and internal combustion.
And I like one-cylinder engines, and so all my motorcycles are one-cylinder, generally in the 500cc range.

I did build a two-cylinder steam engine.

You plan on making this engine, ie: casting/machining/CNC, or whatever ?
Building and running the engine would reveal how solid the design is.

.

Click to expand...

I have no way of currently machining this engine as I'm still in high school and have no money to externally manufacture the parts, but I do plan on making it a reality in the near future. And yeah for the price ready to run kits are not the way to go, and I say this from experience. Customer service is ok, but all the parts are made in mass and defects are really common. I got the engine in August and ran it 3 times, not it just sit in my garage.

Does OnShape allow motion studies ?
I have found those to be extremely useful in Solidworks, since if you assemble the engine in 3D, and run a motion study, the engine will not run if there are any conflicts.
That one option (motion study) is worth its weight in gold in Solidworks.
.

From a practical point of view what I would say if you intend to make it is can it be done. In those crank case halves I see a lot of very small internal radii that are proportionally very deep. This will be very hard to machine due to needing small long cutters, even if you had 5-axis CNC it would be difficult and also costly due to run times as the smaller cutters can't remove as much or be fed as fast. larger radii wil make machining easier but then you nee dto consider the reduced crank and big end clearance these larger radii create

Likewise the end bearing housings will be difficult to bore with the reduced diameters on the external faces

Kosiba said:

The thing only worked 3 times and I have been in a battle with customer support to get a new ignition system, so eventually I was like, well to hell with it,

Click to expand...

Welcome to the fascinating world of home shop designed model engines. Your ignition comment caught my eye. Do you plan to integrate spark ignition or start with glow plugs or...? Some folks have harvested the ignition modules from some of these same Asian ready-to-run vendors with various degrees of success. And yes, instructions & language barriers had the potential to add challenges. I've seen some YouTube videos where (non-engine builder) guys happened to catch some shots of the distributer & though to myself, wow that works huh? And obviously many run perfectly fine.

I'm curious through your 'support' if you think you had distributer/pickup problems or CDI module problems or maybe something else? If this is outside your subject post or you don't want to get into it for other reasons, I'd be happy to hear via PM. Look foreword to continued development work on the DOHC-I4

GreenTwin said:

Does OnShape allow motion studies ?
I have found those to be extremely useful in Solidworks, since if you assemble the engine in 3D, and run a motion study, the engine will not run if there are any conflicts.
That one option (motion study) is worth its weight in gold in Solidworks.
.

Click to expand...

I'm not quite sure if onshape has the same thing, but it has a feature called "assembly" and it allows you to put all the components together, an check how everything fits.

Jasonb said:

From a practical point of view what I would say if you intend to make it is can it be done. In those crank case halves I see a lot of very small internal radii that are proportionally very deep. This will be very hard to machine due to needing small long cutters, even if you had 5-axis CNC it would be difficult and also costly due to run times as the smaller cutters can't remove as much or be fed as fast. larger radii wil make machining easier but then you nee dto consider the reduced crank and big end clearance these larger radii create

Likewise the end bearing housings will be difficult to bore with the reduced diameters on the external faces

Click to expand...

Well, I can see where you're coming from, but I have no current access to any type of machining tool, and most of the smaller radii are hole features that can be drilled out, so you can just use a punch and drill press! And I can see that the smaller engine in of itself is not that best idea due to clearance issues and the smaller features causing problems, but in onshape there is a scaling feature, so I can easily make the engine larger! I also just wanted to make a system that could be expanded and allow for way more engine configurations based off of the already existing toyan brand of ready to run model engines.

Thanks for the feed back I hope I answered some questions of why I did things the way I did them!

petertha said:

Welcome to the fascinating world of home shop designed model engines. Your ignition comment caught my eye. Do you plan to integrate spark ignition or start with glow plugs or...? Some folks have harvested the ignition modules from some of these same Asian ready-to-run vendors with various degrees of success. And yes, instructions & language barriers had the potential to add challenges. I've seen some YouTube videos where (non-engine builder) guys happened to catch some shots of the distributer & though to myself, wow that works huh? And obviously many run perfectly fine.

I'm curious through your 'support' if you think you had distributer/pickup problems or CDI module problems or maybe something else? If this is outside your subject post or you don't want to get into it for other reasons, I'd be happy to hear via PM. Look foreword to continued development work on the DOHC-I4

Click to expand...

I would like to keep everything very transparent and open, so I really want to discuss everything on this thread so other people can chime in! For ignition I want to start with the spark plugs, the spark plugs have to be very long and thin in order to fit within the space in-between the valves, and if anyone is wondering the valve diameters here you go! In valve ~9.3mm in dia, and exhaust is ~7mm in dia. the spark plugs have to be an M5 screw, so they can fit and are roughly 30mm long, as shown in the original pictures the cam rockers along with the adjustment screw (that can't be seen) that have to be fitted with them take up a lot of space so that's why the plugs are so long. And like I said above I really don't want to make a nitro engine as the fuel is super expense, especially since I don't have a job. So I want to stick with making gas engines, and for everything else ignition related, For the coils, wires, and CDIs, I have contacted the person at cncengines asking about their advice regarding some of the things they have made and are selling. As for a distributer system, I would really like to make a distributer and stick it on the end of one of the camshafts, and see how I can time it from there, but I'm open to suggestions if anyone has a different idea or opinion on the matter.

If anyone is wondering here is the criteria for the ignition system, it has to be able to handle multiple cylinders, and engine configurations (inline 4s to V8, V10, and even possibly a V12 unit) and must be able to handle a max rpm of 12k. I know it seems like it there are some tough criteria, but I think for something this small, it could reach a pretty high rpm so I think it is somewhat reasonable. But I'm open for a middle ground, I would first like to have the engine become a physical object!

I'm also looking at https://www.model-engine-ignition.com/model-engine-ignition, and https://www.hemingwaykits.com/category-105, for spark plug kits, wires, distributers, and CDIs.

It was not the round holes which as you say can be drilled out.

It is the square internal corners in the top image and the deep internal small radius in the lower photo. Even with long neck micro dia cutters the radius x depth ratio in high. What is the radius and depth?

If the radiu can be increased and still give room for other parts then that will make it easier to build an dif the squirt block could have it's corners rounde dover then you can easily mill a rounded internal corner to match, a square internal corner is not easy.

Jasonb said:

It was not the round holes which as you say can be drilled out.

It is the square internal corners in the top image and the deep internal small radius in the lower photo. Even with long neck micro dia cutters the radius x depth ratio in high. What is the radius and depth?

If the radiu can be increased and still give room for other parts then that will make it easier to build an dif the squirt block could have it's corners rounde dover then you can easily mill a rounded internal corner to match, a square internal corner is not easy.

View attachment 165217

Click to expand...

Got it, I'm sorry I didn't quite get it right, but for the first pic, the oil squirter, it is just straight cut, and has a depth of ~5mm-5.1mm, and I will definitely make changes to corner radii, and for the bottom pic, most of the fillets on the block and oil pan range between 2-5mm radii, and I'm getting these dimensions from the toyan L200 I based most this engine off of,
https://www.stirlingkit.com/collect...oke-2-cylinder-engine-kit-that-runs-fs-l200ac
here's a link to the website but I want to also show some pics,

This is a pic of the oil pan from the engine I have, and as you can see I based most of the dimensions for my engine off of this engine, as it is the only model gas engine I have, and have seen run irl

JohnnyQ90 on youtube has a build vid where you can see where a lot more inspirations for my engine come from, I will link below

I thought they looked smaller so had a quick measure.

On th eleft if we say the pistons are 17mm dia then the OD of the liner is likely to be 19mm the rest can be proportioned from that. which gives a radius of 0.8mm. could be 1mm radius at a push if you are mixing 2mm diameter which is 1mm radius.

Your pockets for the squirt blocks are 3mm wide with square blind internal corners.

If it could be modified as on the right to have the 0.8mm radius corners increased to 2.5 -3mm and the pocket for the squirter given a rounded end (squirter to match) then that would make manufacture a lot easier be it with manual or CNC machines