Porsche 917 flat 12 engine

[Foketry]

Engine mounting bracket

To support the engine the time has come to abandon pieces of wood, so I designed some aluminum brackets. The brackets are made by casting aluminum, so I printed the foundry mold .

undergoing 3D printing

2-piece mold

aluminum castings

sandblasted and drilled

assembled with motor

 

[ddmckee54]

Foketry:

I know that you printed the molds for these parts, but when you cast these parts, were they sand-cast or was it lost PLA like some of your other parts?

Don

 

[Foketry]

Foketry:

I know that you printed the molds for these parts, but when you cast these parts, were they sand-cast or was it lost PLA like some of your other parts?

Don

these pieces are sand cast (Petrobond first layer in contact with the mold , green sand all the rest .
I use lost PLA when the pieces are complex and need some cores.
Lost PLA is expensive, takes many hours in the oven, plaster and electricity cost a lot. If I make a mistake, I have to redo everything from the beginning.
Sand casting , the whole process is simple, visible and more controllable.

 

[Steamchick]

I am simply impressed....
Enjoying your endeavours!
Well done!
K2

 

[Foketry]

Ignition, first step

For this engine model I prefer to put 2 ignitions, one for the six cylinders on the right, one for the 6 cylinders on the left. If this engine does 3000 rpm (I hope) 36,000 sparks per minute will be needed.
I think that dividing the necessary sparks by 2 ignitions will give me less problems to solve.
Place the pick ups directly on the crankshaft instead of on the camshafts, it will give me a more precise timing, not affected by gear backlash.
Each of the 4 camshafts is driven by 6 gears and backlash is inevitable.

I chose 2 GY6 CDI ignitions normally used on small motorcycles, reliable and very cheap
Pick ups can be Trigger or Hall type , in this post tests with Hall sensor
https://www.homemodelenginemachinist.com/threads/model-engine-cdi-easy-and-cheap.31128/post-363965Inside the gearbox I have the useful space to hide 2 pickups, I chose this solution

the pick ups can be rotated to find the correct timing

 

[Foketry]

2 distributors

CDI ignition

Hall sensor circuit

 

[ajoeiam]

2 distributors

CDI ignition


Hall sensor circuit

I can't wait to see this thing when its all done.
Then a short video to hear it - - - - that's going to be wonderful!!!!!!!!!!!

Great work by the way!!!!!!!!

 

[michelko]

Hi have you thought about some sealing around the dizzy shaft? I made the experience that after some time oil made its way into the cap and the engine stoped running.
I made an return screw onto the shaft. Why do you use ballbearings there? I had good results with just bronce or brass buschings in the dizzy.
Can you say something about that hall circuit?
Somewhere i saw a thread about those chinese cdi having trouble be triggered with a hall.
As allways fantastic work !!!!!

Michael

 

[Foketry]

Hi have you thought about some sealing around the dizzy shaft? I made the experience that after some time oil made its way into the cap and the engine stoped running.
I made an return screw onto the shaft. Why do you use ballbearings there? I had good results with just bronce or brass buschings in the dizzy.
Can you say something about that hall circuit?
Somewhere i saw a thread about those chinese cdi having trouble be triggered with a hall.
As allways fantastic work !!!!!

Michael

Hi Michael
The crankshaft has 2 oil seals at the ends, has 1 axial stop on each side and rotates on bronze bushings, but the bearings should work too, I have already built the Bugatti engine on bearings.
About the Hall sensor applied on the CDI, I did some tests on the lathe and it works well, the final test I will do it on this engine, but I am confident, there is a very long thread on this forum about this, you can find it in my previous post.

 

[michelko]

Hi Lules,
maybee a little misunderstanding
the question was not directed to the crank or camshaft bearings. The drawing of the dizzy showes also two bearings. i am affraid that through these bearings oil will creep up into the Cap. I noticed this on my bugatti and also on the W.T. Seal.

Michael

 

[Foketry]

Hi Lules,
maybee a little misunderstanding
the question was not directed to the crank or camshaft bearings. The drawing of the dizzy showes also two bearings. i am affraid that through these bearings oil will creep up into the Cap. I noticed this on my bugatti and also on the W.T. Seal.

Michael

ok, I understand, you refer to the distributor, in this engine the oil level is very low, the pump sends it through the crankshaft, I don't think it will arrive inside the distributor, if the first tests highlight this problem I will put a small oil seal.

 

[Foketry]

Check for piston and valve leaks ,tappet thickness adjustment, valve timing, engine painting

Before timing all the cams I checked the air leaks once again with this instrument, it is composed of 2 pressure gauges that measure the difference in pressure between the air inlet and leaks through valves and ring. Air inlet through the spark plug hole.
I adjusted the thickness of tappets, measuring, reducing the thickness on lathe, checking the backlsh, again lathe, again checking, etc etc , 2 days only for the tappets

Valve timing

I adjusted the opening and closing of the valves using a digital angle measuring instrument, all the cams are independent of each other and then I adjusted 24 cams. For now they are temporarily locked by grub screws , then I will put a spring pin. I chosen to make 24 single cams instead of 4 camshafts because it is easier to mill them .
To find the opening and closing point I put compressed air in the cylinder and rotated the single cam, when I hear blowing air, the noise is very audible, that is the precise point.

 

[a41capt]

I love the precision of your build. Valve timing on 24 valves for 12 cylinders! I’m glad it’s you and not me, I’m damn sure I’d never be able to get it right. I had a hard enough time getting my Ford Kitchen Sink engine running.

John W

 

[Foketry]

Ignition , distributor caps with cables and 12 spark plugs

I screwed the spark plugs on an aluminum plate, I mounted the distributor caps on the engine and by rotating it with the cordless drill I checked the firing order 1-9-5-12-3-8-6-10-2-7-4-11

Ignition test

 

[michelko]

Those are some nice boots on the dizzy cap.
From where do you get them?

Michael

 

[Foketry]

Those are some nice boots on the dizzy cap.
From where do you get them?

Michael

They are spare parts for Dellorto carburetors
https://www.motogiovane.com/cappucci-cavi-carburatori-vhbt-phbh-moto-guzzi-p-1071.html

 

[Foketry]

I spent several days doing the tests, ignition and carburetors.

Regarding the carburetors I have tried many different sizes, from Venturi 14 mm to Venturi 7.6 mm
I thought that for a 26 mm diameter piston and 9 mm valves a large carburetor was needed, at least 11 -14 mm, in fact I learned that 8 mm venturi bore is optimal for this 12 cylinder engine.
This is because through a small Venturi the speed of the gases is greater and therefore there is a better mixing between air and petrol. in addition to this, a higher speed reaches bettere the cylinders far from the carburetor.

Also one of the 2 electronic ignitions gave me problems, the timing was not constant, it jumped back and forth.
I discovered after several tests that the pick up for cylinders 1-6 lost its pulses and delayed them, but not always.
I waited 10 days for a new pick up and now everything seems to work.

It is very complicated to fine-tune the timing and carburetion of an engine with 2 carburettors, 2 ignitions, 2 distributors.
I did all the tests on only 6 cylinders on the left (1-6), removing the spark plugs in the other 6 cylinders. The 2 carburettors must also be synchronized with each other, the valve must open at the same time and by the same quantity

The engine is not perfect yet, but I hope to optimize everything to the fullest

 

[Foketry]

Display base with electronic ignitions

after painting, primer and top coat

 

[petertha]

Regarding the carburetors I have tried many different sizes, from Venturi 14 mm to Venturi 7.6 mm
I thought that for a 26 mm diameter piston and 9 mm valves a large carburetor was needed, at least 11 -14 mm, in fact I learned that 8 mm venturi bore is optimal for this 12 cylinder engine.
This is because through a small Venturi the speed of the gases is greater and therefore there is a better mixing between air and petrol. in addition to this, a higher speed reaches bettere the cylinders far from the carburetor.

I know its more complicated than this, but FWIW the carb orifice size you eventually selected lands like so on these cross plots I made of various 4-stroke OS brand (methanol glow) engines.

 

[mayhugh1]

What coil are you using? Also, could you say bit more about how you're using the electronic protractor to set valve timing? Is there a remote sensor or is the whole protractor attached to a degree wheel? Thanks - Terry