Formula 1 RC 1/3 with V8 engine

[bernimodels]

Gents, interesting discussion here! I am not a professional engine designer myself so this is good for learning.
The process I followed to dimension the engine was:

- V8 F1 Engine (roughly) based on existing literature: Bore 97 mm, stroke 41 mm, con rod about 102 mm. This scaled equals to 32.3, 13.7, 34 mm. The dimensions chosen for my engine are 35 mm, 20.8 mm (bore / stroke). The reasons for the difference are that I wanted to achieve more displacement to get more power. Bore is mainly based on the actual scaled value (so engine length on the V8 is true scale). There are hardly any model engines with such a short stroke and so I did not want to risk it. Still, with 20.8 mm stroke I am sure I can achieve above 14000 rpm to max 20000 rpm. The closer I can get to the 18000 rpm the better, as the whole transmission will be easier to scale down from the real thing (all gear box / final drive ratios) and frequency of noise will be on the same range of real engine. F1 engines were limited to 18000 rpm.

- With a longer stroke than the scaled value, I had to reduce con rod length so the overall height of the engine was the real scaled value. The engine cover on the car is so tight to the engine, that otherwise I would have to modify the external shape . Therefore the con rod length is under scaled. This produces a more aggressive maximum angle of the con rod during, so more compression load and wear on the bearings and piston. The acceleration profile on my engine due to a smaller con rod / stroke is flat around for about 40 deg b/a TDC, more similar to the Cup engine on the article. The only advantage I can think is less weight/inertia, but mainly this will have a negative effect on power.

- Valve design: I chose a 0,85 inlet / outlet valve diameter ratio. Based on that, and recommended flow speeds from literature I determined valve lift for IN / EX. Basically, I could use all the available cylinder area.

F1 engines have such a short stroke to rev higher and achieve more power. This is the main reason. Rod lengths are optimized to reduce friction losses, mass, and maximize flow efficiency.

Let me know what you guys think.

 

[dman]

ahh, so you have made some alterations.. with the stroke and displacement up that much and by making the ports to match recommended flow speed then you avoided the things i was talking about. if it was 100% to scale you'd rev too high. this will be fun to see come together.

 

[johnny1320]

I just want to see it built, it's something new and it will be used in a model. I am designing a parallel twin based on Per Bengtsson's supertwin fuel bike, I am hoping to start machining soon. I will be building the bike as well

 

[SixSixSevenSeven]

Interesting discussion, hopefully I can take some info away from that for my "eventual" engine build.

 

[e.picler]

I have got an Optimus BF20 L vario with CNC kit and rotary table. I am still a long way behind with CNC machining, but I have been learning a lot with the recent engines. Also a manual lathe.

HI Bernimodels!
I also have the same milling machine you have with original cnc kit. Are you using the NCDrive software controler (supplied with the cnc kit) from Optimum?
As I observed you are using the 4th axis to machine the engine block.
Are you using a sort of cam software to generate the G codes?
I`m trying to machine the crankshaft on this machine using the all the 4 axis. Fisrt test showed to be promising.
I also recently got a SIEG Slant mini CNC lathe with 8 tools turret. I`m still getting used to it. For now I`m manually programming but plan to do it on the Master Cam software, I alread use it for the milling machine.

Congratulations for your project. It will be very interesting to follow this project.
Where are you located? I`m in Brazil.


Good luck on you construction.

Edi

 

[bernimodels]

I also have the same milling machine you have with original cnc kit. Are you using the NCDrive software controler (supplied with the cnc kit) from Optimum?
As I observed you are using the 4th axis to machine the engine block.
Are you using a sort of cam software to generate the G codes?
I`m trying to machine the crankshaft on this machine using the all the 4 axis. Fisrt test showed to be promising.
I also recently got a SIEG Slant mini CNC lathe with 8 tools turret. I`m still getting used to it. For now I`m manually programming but plan to do it on the Master Cam software, I alread use it for the milling machine.

Thanks for your comments e.picler. I am using Visual Mill for CAM and Mach3 as the controller software. I only use the CAM software, although for really simple operations I type the code at the machine as it is quicker.

I have a Belflex BF 520c TME manual lathe. To be honest I have not missed that much the CNC capability on the lathe, but on the milling machine it is great.

I am based in Surrey, UK. Good luck with your project too and to johnny1320 as well.

 

[johnny1320]

Thanks, I look forward to seeing your finished project

 

[bernimodels]

This weekend I have made some progress with the engine head. The inlet and exhaust ports have been polished and valve seals have been pressed in. It all went quite nice together. I used some Dremel tools and polishing compound to polish the ports in the inside, with extreme care to not damage the mating surfaces for the inlet and exhaust and valve seats. On the pictures you can see the dedicated fixtures to press the valve seats and guides into the head.

The upper assembly with the camshaft carriers and little brackets has also been put together. As the top of the engine will be open, it will be possible to see any leaks or other issues inside the head. The brackets are only for the test engine as the V8 holds the cam shafts with the head covers.

The valves were almost finished, I just had to grind the top and bottom surfaces to final dimension. So they are ready to install. The material for valves is SS AISI 316.

During the week I expect to finish the bores for the cam shafts, including the bronze split bearings installation. Also the countersunk on the valve seats.

 

[barnesrickw]

Nice detail and excellent work.


Sent from my iPad using Model Engines

 

[johnny1320]

Bernimodels nice prgress, my question is why not make the head the same way as the V8 to see how it works and if the cam cover holds the cams in how will you be able to check the valve clearance?

 

[bernimodels]

Bernimodels nice prgress, my question is why not make the head the same way as the V8 to see how it works and if the cam cover holds the cams in how will you be able to check the valve clearance?

the reason for not using the same design is that the cam cover is quite a complex part to design and machine, as it is very thin and full 3D machining on both sides. Using the brackets is a simpler way to do the same job. The function of the brackets is to hold the cam shafts as the covers will do. I will probably get a lot of oil spillage once the cams spin at full speed but this is easy to put a transparent plastic cover.

Valve clearance is set with the brackets on. After that, the brackets are replaced with the cam cover. It does not affect the valve clearance adjustment.

 

[bernimodels]

Hi there, it´s been a while after last post, but batteries fully charged after the summer break. Hope you all had a good time too.
The engine head has been assembled and is almost completed. All four valves, rockers, cam shafts are working together. All is left is the valve lapping and cups to be ground. I pretend to adjust cam clearance by grinding the cups, so each cup will have to be numbered according to its position and valve.
The valve seats were already cut with an HSS custom made tool. This tool is basically a countersinking tool with a pilot steam to achieve good concentricity with the valve guide. I am sure most of you use the same system.
I hope I can grind the cups and lap the valves this weekend, so I will be posting more pictures soon.

What grit do you apply for polishing valves cups and cams?
What clearance do you use on valve/cams?

 

[canadianhorsepower]

Nice work,
hope not to many "my opinion says you are wrong " will ruined your great project:hDe:Thm:Thm:

 

[Swifty]

I don't have a lot of experience on IC models, however on the Lynx that I recently finished, I allowed 0.10mm (.004") clearance between the cams and the valve caps. I suppose that the amount of clearance would depend on how long the valve stems are and the expansion rate when hot.

Paul.

 

[bernimodels]

Thanks Swifty, what you say makes a lot of sense. I just wanted to make sure that there was no other reasons.

 

[bernimodels]

The spark plug is almost ready to assembly. Last weekend I almost finished the individual components, including the ceramic bits machining. The ceramic machined quite easily, but it was very challenging because of the wall thickness required (<0.5mm in some cases). The only bit missing is the electrode which will be from a HSS drill bit (Ø1mm). I will use epoxy adhesive to seal the bits together, and then swage it to ensure the electrode is not ejected when the engine is running. The thread will be M5, still to make.
The head and block are now together with he timing belt on. On the V8 engine, the distribution will be made with gears only, but I though I could save a bit of work and money on this one by just making the upper stage with gears and the rest with a chain. The rubber belt is only as a temporary replacement before the actual spring is assembled.
Also see a comparison with a RC plug and the my own spark plug.
Only left: finishing of spark plug, mounting of carb and exhaust. Can´t wait!

 

[artist334]

Unbelievable work! Can I ask how you machined the valve stems and to what kind of tolerances did you bind yourself in to?
I tried to do similar valves on lathe but I had taper of perhaps 0.04mm over the length of 40mm stem.

 

[bernimodels]

Hi artist334, thanks for your comment. Valves are within 0,01 mm tolerance, measured with a digital Vernier Calliper, so cannot guarantee this is absolutely correct. I usually turn up to 0,02-0,01 oversize, and then use SiC paper to achieve better surface finish and the desired final size, up to grit 1200.

To reduce the taper you might have, I used the tailstock, but I cannot guarantee more than 0,01 as I cannot measure beyond that. To be honest there should not make a big difference, maybe more oil consumption.

 

[petertha]

bernimodels, I wanted to inquire about your neat chain drive.
- what reference size is it & where did you acquire it?
- did you make the sprockets or adapted from commercial stock?
- is there some sort of calculation that specifies max velocity, particularly as a function of sprocket diameter?

 

[bernimodels]

Hi peterha!
The chain is a 6mm pitch, from Chiaravalli (Ref. CAT. RCX P.6 SEMPLICE ISO9001). I bought the sprockets from Technobots, 04B, z=8 and 16 (Ref. 4804-008, 4804-016).
Spur gears are from HPC Gears, m=1mm, z=24 (Ref. G1-24).
Both sprockets and gears are then machined to suit my design.

This is a good design guide for chain transmissions http://www.crossmorse.com/pdf/DriveDesign-Cross-Morse.pdf

The chain/sprockets I am using are outside recommended design allowables, but since engine life is going to be relatively short it can be tolerated. On the V8 I will use gears only. Also minimum recommended Z is 17 and I am using 8!