80CC OHC V8

[Coopertje]

Inspired by builds on this site (I follow most of them quietly, sorry for that) I have started to put together a V8 in Solid works. It will be

based on the Schillings plans (I have bought them many years ago at www.vth.de), although I do not like the square box looks of that engine. I

will try to get a more detailed and realistic look on this engine, change the water flow through the cylinder block, different valve covers,

electric starter etc. Do not know if this will make the engine “my design”, on the other hand when it is finished it will be a unique one. If

the moderators think it is more appropriate in the “from plans” section please let me know.

My main goals with this project are:

1)   Build a working V8 with a combination of manual as well as CNC machines
2)   Learn to draw and design with Solid Works
3)   Generate G-code of the 3D Solid Works parts with SprutCam V9 CAM software
4)   Make the missing tools / accessories for my machines (have a long to do list here) needed to build this engine

I plan to only use the CNC machines where it is required due to part shape or when I have to make multiple items of the same. The crank will

be a build-up style and all the rotating parts will have ball/needle bearings. Initially it will be a glow-plug engine, in this way I

eliminate the distributer and ignition timing. When it is running well on glow plugs I might convert it to sparkplug and even fuel injection.

Since this is my first multiple cylinder engine I prefer to take things step by step....

Below some pictures of the design as it is today, guess I have about 70% – 80% finished.










The very nice thing about 3D CAD software is that you can really tackle design issues in a very early stage. If you look to the section view

below you will see a collision between conrod and cylinder block. Normally I would see this at assembly time, now it becomes clear before the

first piece of material is cut saving lots of time and frustration in a later stage. There is another error visible in this picture, the left

cylinder bore was off by 0.25mm (see the connection between combustion chamber and cylinder bore).



I had a last opportunity to buy material against trade prices (got it over a friend and the department he is working is sold...). I bought

some lengths of 3mtrs of free cutting steel, aluminium, C45 steel and Stainless steel tubing, all in different sizes.






From the scrap yard I collected some aluminium blocks, one piece of 7075 and some pieces unknown but they have milling marks so it should be

ok for machining. The 7075 will be for the cylinder block.





Although the design is not finished yet, I am eager to start making some chips! It will be a very long project and most likely parallel to

others since I cannot focus on a single project for more then 3 to 4 months.... Hope that positing the build here will help me keeping

motivated to bring this project to a proper end....

Suggestions / design idea's etc are more then welcome!

Regards Jeroen

[steamer]

That's exactly the type of crank I want to do on the V12 I sketched out a while back!    NICE!

Dave

[fumopuc]

Hi Jeroen, the plans,the book and also Mr Schillings single/two cylinder plans are under my pillow since 3 years now. Everythink in my entire current projects is to get the kwnollage to build this engine. So I will follow your build with very big interest.

[Coopertje]

Thank you for checking in Dave and Achim. I believe that this type of crank construction is the most simple and straight forward way of making a multi cylinder crank. For sure it does not have the looks like the master pieces from for example George Britnell or Keith5700, but I am quite sure it will work. 

I have a doubt about the lubrication on the needle bearing though. Would they need lubrication when the engine is running? I am thinking on adding an oil pump and some piping that will feed the oil in the direction and hopefully will reach the bottom of the pistons. This would cool the pistons and at the same time all the needle bearing would get some lubrication by the mess caused. If possible some guidance / advice on this would be much appreciated.

Regards Jeroen

[Roger B]

That's an excellent challenge you have set yourself    I will be following along   

Like Achim I am trying to improve my skills with the current builds to move onto the 'dreams' (I will collate and post them one day).

[Coopertje]

Isn’t funny how the grass always looks greener on the other side! My skills are fur sure not better then yours Roger or Achim’s. When I look at the work of both of you I always think to my self that I still have a lot to learn. In my opinion it is better to have a project that has your true interest to improve your skills then to do “simple” things only. More complicated projects pushes you over your own limits and then you really improve your skills. And if it goes wrong, think, ask and learn and redo the part. Sometimes with Solid works I spend evenings to figure out how to draw that one thing I have in my mind. Great feeling of victory when it is finally achieved. Same with machining, I finally have reached a point that I can get my parts to good tolerances, but I have to work really slow and concentrated. As soon as I speed up it goes wrong.....
My piece of advice, just start to build your dream engine, your skills will develop along the way!

[gbritnell]

Hi Jeroen,
I know the engine is in the preliminary stages but here's few things you might consider.
1. The wrist pins don't get enough radial movement to require a bearing so you could eliminate that.
2. Even though the engine is spinning on bearings they will need some type of lubrication. For a bearing engine a splash type would be more than adequate. You only need a pressure pump if you're going to be sending oil to the heads or elsewhere.
3. You will need at least 2 rings per piston and possibly 3. The third one being some type of oil control ring. (holes drilled to return the oil from the cylinder walls)
4. Although some engines (full sized) don't have the piston coming to the head deck it's common practice to to do this. This way the shape of the combustion chamber in the head can be designed to facilitate the burning of the fuel efficiently.
5. Just looking at your drawing it seems like the compression ratio will be very low. (total area of piston recess and combustion chamber shape) versus the stroke length.
gbritnell

[Coopertje]

Hi George,
Thank you for your input and suggestions, they are appreciated. Related to your input:
 
1)      I could make them from bronze, I am just afraid that they will wear out because they do not get a pressurized lubrication. I have already bought the bearings so for the moment I will stick with them, I do not believe they will hurt.
2)      I have considered a splash lubrication by mounting small blades on the conrods. The disadvantage I see here is that the oil level in the engine should reach let say up to half the crank. I am afraid to have leakage at the crankshaft ends when the engine sits for a while. If I add an oil pump and guide the oil flow by piping I can keep the oil level below the crankshaft end bearings and prevent leakage. 
3)      In my other engine I made the piston 0.005mm smaller then the cylinder bore. It has a lot of compression even without piston rings. I would have expected that it would get stuck quickly when the engine is running due to the different expansion coefficients (cast iron liner and aluminium piston) but to my surprise it doesn’t, keeps running without a problem. My idea is to run the engine without rings, only cut the grove in the pistons just incase I need to add piston rings.
4)      This I do not understand, do you mean that the top of the piston should be at the same level as the top of the liner when the piston is in TDC?
5)      I did not calculate the compression ratio, I took the shapes and volumes from the Schillings plans. The engine should run with this, it is a proven design. I think you are right that it is not optimal, if I look at the engines from Luther (google on “luther model engines”) I see that he has made pistons with a “head” to increase the compression ratio. Since building this engine on its own is already a very big challenge for me, I will stick to the plans for this part. If the engine is running  it is not so much work to make another set of pistons and start to experiment.
 
Thank you again for thinking with me and preventing me for my beginners mistakes
 
Regards Jeroen

[Roger B]

Hi Jeroen,

My projects are all things that I want to make, it's just that I realise that if I start with the simpler ones the mistakes cost less. Either of the next two will push me, a version of the 1898 Saurer opposed piston engine with paraffin (kerosene) injection or a horizontal two stroke diesel (Field Marshall style) to operate as a true diesel with high pressure fuel injection using pump diesel. The one to follow will be a Hulsebos-Hesselman (maybe you know this one?) 5 cylinder wobble plate semi diesel. There is also the possibility of a Junkers/CLM opposed piston diesel.

[Coopertje]

Hi Roger,

Most of the mistakes normally can be rescued, it is more the mental damage then the waste of materials 

Those are indeed some challenging engines you mention there. Do not know any of them, did some google on them and I like the wobble plate design! Not an easy one but should be do-able in a home shop. Do you have experience with CAD?

Regards Jeroen

[dieselpilot]

Another Solidworks driver! Save as --> .jpeg makes for easy screenshots. Otherwise, the snapshot button copies the screen to the clipboard which you can paste into a new file in your photo editor. That looks nice.

What does Schillings suggest for lubrication? I assume the typical model airplane glow fuel with 15-20%oil in the fuel. It seems that sump oil and splash lubrication would require an oil level high enough to put the crank bearings in oil which would cause a substantial load. The little rod end with rollers doesn't need much oil at all. Many utility two strokes use a bushing here with 50:1 oil. Most RC four stroke engines get by on just what oil gets past the single ring and bronze bushings in the rods. I don't think piston cooling is much of a concern, unless the engine is making a lot of power and run at high load.

Combustion efficiency and fuel consumption are not a concern in model engines. A deck height of zero is OK, but production model four stroke engine's pistons are usually around 1mm below the top of the liner. This has no adverse effects. The main reason for a small deck height is to allow more control of the squish band design.

Schillings compression ratio is high enough to work well with glow plug ignition and fuel so that must be in the region of 6-7:1.

The truth is that all of this stuff has been done so many different ways that for a display engine that occasionally runs almost anything that's square and straight works. It's when you try to run at peak power/rpm for hundreds of hours and sell it for a reasonable price that the smallest details matter.

Those crank roller bearings look like they run directly on the crank journals. How hard will the journals be? Typically they ask for <57 HRC in real applications. What's more amazing is that it was used at some point in full size engines, by Tatra according to the interwebs.

[Coopertje]

Hi Greg,

Yeps and I must say that I like Solid works a lot. Most of the things are really intuitive, the only thing I keep fighting with is the reference planes, when you want to have them in a specific angle and position it is not so easy. Thanks for the tip to save as jpg, I had found this already but was lazy and took some quick pictures with my mobile phone to send to a friend (my hobby PC is not connected to internet).

I looked in the book of Schillings and he is speaking about lubrication caused by the mess in the crankshaft housing. So he uses a higher oil level and splash lubrication. I will see what I will do, took the basics from his plans and I like to work out the rest of the engine to my own ideas.

The crank disk will be made of C45 steel not hardened. This because the rollers in the needle bearing are already hardened, and as far as I know hard on hard does not work well. 

You are right about the fact that these engines do not need to perform and last 200.000km, so keep things realistic in material usage and optimal compression ratios etc. However it would be fun to experiment a little when the engine is running, at least that is if I have any motivation left at that time.

Nice picture of that Tatra crank!

Now it is not wise but this weekend I will start on machining the cylinder block and lower block, had enough of working behind the PC. I will leave enough stock left for detailed outside shape finishing, did not bother about that yet.

Regards Jeroen

[Roger B]

Hi Jeroen,

I have limited CAD abilities I use 2D DraftSight as a sort of electronic sketch pad but have never tried any 3D systems.

Maybach made a series of tunnel crankshaft petrol and diesel engines that were used in tanks and locomotives. There are a couple of pictures of a crankcase about 1/3 of the way down this page:

http://sp9010.ncry.org/mechanical1.htm

[dieselpilot]

I'm surprised, that he uses splash lubrication with all those bearings inside. The point of rolling element bearings is to reduce the oil requirement. I've had his book on my list for a long time, but still haven't purchased it. If you do splash lube then I would follow George's suggestion about oil rings.

Rolling bearings need a hard surface to run on. There the hardness difference between rolling elements is too great, problems arise. Take a look at the engineering manual for the bearings you've selected. The manufacturers recommend using their race components if the running surface can't be produced to the required hardness and surface finish.

Roger, I saw mention of the Maybach but didn't see any photos. More recently, Timken proposed a needle bearing crank with normal proportions for the main journals for truck engines.

You have to start cutting metal sooner or later, or you'll end up like me tweaking a design for years. Though it did save me from making parts for an engine that I couldn't assemble, even after many checks for assembly procedure. I mostly modify RC four stroke engines for now.

This is a section of an OS FS-30.

[Roger B]

This link has better pictures of the Maybach engine:

http://sp9010.ncry.org/Maybach.htm

And this is a small cutaway drawing