Porsche 917 flat 12 engine

[Foketry]

do you machine them conventional or with an cnc lathe?

Regards Michael

Hi Michael
I bought a small Italian lathe from a school a year ago that I converted CNC, it is suitable for pistons, valves, small parts.
If I have to build a few pieces I use the manual Chinese lathe, over 2/3 pieces I use the CNC

And about your Holt 75 ?

 

[davidyat]

When machining the two valves, how do you control "tool push"? Do you use a steady rest on the middle of the part?

 

[Foketry]

When machining the two valves, how do you control "tool push"? Do you use a steady rest on the middle of the part?

I work a single valve with collet chuck and tailstock, the second valve is hidden inside chuck , 1600 rpm, stepover 0.2mm
Perhaps this short video clarifies the procedure

 

[davidyat]

Great video. Maybe at some time in the future, I'll figure out and get a CNC machine.
Grasshopper

 

[JonnyC]

Hi, love the posts, this is a major undertaking and made to look so easy. I'm watching with interest on how the various issues are approached regarding scaling a real engine.

It looks like (from the bore in the cylinder head as though you are going to use some sort of valve/seat/spring catridge, is that right?

Jon

 

[michelko]

realy nice swarfs.
what tolerances / free play are you aiming for the valvestem to guide.
I did some test with cnc on my lathe but i had a little problems to get the numbers constant.
Jules:
the holt is on hold ;-) because of the other hobbies, children, building a pool etc.
the case is ready, the cam also, the cylinder jackets are cnc turned(see above).
here is a video from my first cnc turning work.
I think i will go on with the project in fall.
You are doing awesome work. Can´t wait to se the updates.

Regards Michael

 

[Foketry]

Hi, love the posts, this is a major undertaking and made to look so easy. I'm watching with interest on how the various issues are approached regarding scaling a real engine.

It looks like (from the bore in the cylinder head as though you are going to use some sort of valve/seat/spring catridge, is that right?

Jon

this is my design for valves: bronze cage , oil seal , spring . 2 spring retainer , upper and under, Seeger, tappet.
The camshaft pushes directly on the bronze tappet
The valve on the right has a different solution, instead Seeger I thought of a spring ring to save space in height. I opted for a traditional seeger solution, easier to make, but keeping the solution of cages on right which reduces the overall dimensions in height and more spring stroke.

 

[Foketry]

realy nice swarfs.
what tolerances / free play are you aiming for the valvestem to guide.
I did some test with cnc on my lathe but i had a little problems to get the numbers constant.
Jules:
the holt is on hold ;-) because of the other hobbies, children, building a pool etc.
the case is ready, the cam also, the cylinder jackets are cnc turned(see above).
here is a video from my first cnc turning work.
I think i will go on with the project in fall.
You are doing awesome work. Can´t wait to se the updates.

Regards Michael

Hi MIchael
I partially solved the problem of the diameter dimension variation by mounting on the X axis a Heidenhain encoder found at no cost by a friend of mine who repairs CNC motors
In addition to this I always do 2 or 3 passes of the finish, the last at zero stepover. I got a repeatability of +/- 0.01 mm once I optimized rpm and feed.
Jules

 

[DiegoVV]

realy nice swarfs.
what tolerances / free play are you aiming for the valvestem to guide.
I did some test with cnc on my lathe but i had a little problems to get the numbers constant.
Jules:
the holt is on hold ;-) because of the other hobbies, children, building a pool etc.
the case is ready, the cam also, the cylinder jackets are cnc turned(see above).
here is a video from my first cnc turning work.
I think i will go on with the project in fall.
You are doing awesome work. Can´t wait to se the updates.

Regards Michael

I machine my valves outnof 316ss in a manual lathe. Before making the valves, I make the valve guides reaming the inner bore, then I machine the valves leaving them 0.03 mm oversize in diameter to allow for lapping them to get a perfect fit on the guides. Very important to check consistency in diameter in all the stem length during the lapping process to ensure consistency in the fit along all the valve movement.

 

[JonnyC]

this is my design for valves: bronze cage , oil seal , spring . 2 spring retainer , upper and under, Seeger, tappet.
The camshaft pushes directly on the bronze tappet
The valve on the right has a different solution, instead Seeger I thought of a spring ring to save space in height. I opted for a traditional seeger solution, easier to make, but keeping the solution of cages on right which reduces the overall dimensions in height and more spring stroke.

View attachment 126744

Two nice layouts. How will the bronze cages be locked into the heads? Also, why the need for space saving on the right hand valve arrangement? When I looked back at the engine drawing I thought it was because the exhaust side sits lower than the inlet side but then realised that its the angle of the valves that is different from the centre line of the bore.

 

[Foketry]

Two nice layouts. How will the bronze cages be locked into the heads? Also, why the need for space saving on the right hand valve arrangement? When I looked back at the engine drawing I thought it was because the exhaust side sits lower than the inlet side but then realised that its the angle of the valves that is different from the centre line of the bore.

I'll make the diameter of the cages fit a slight pressure in the head and use Loctite 620 high temperatures
I need to reduce the height of heads because this engine has compact dimensions and I would like respect the exact scale.

 

[Foketry]

realy nice swarfs.
what tolerances / free play are you aiming for the valvestem to guide.
I did some test with cnc on my lathe but i had a little problems to get the numbers constant.
Jules:
the holt is on hold ;-) because of the other hobbies, children, building a pool etc.
the case is ready, the cam also, the cylinder jackets are cnc turned(see above).
here is a video from my first cnc turning work.
I think i will go on with the project in fall.
You are doing awesome work. Can´t wait to se the updates.

Regards Michael

Hi Michael , if you want to get constant and repeatable dimensions, I suggest buying the best lathe in the world for hobbyists: SCHAUBLIN, made in Switzerland, watch the final part of video ...

 

[Foketry]

The cages, 24 + 2, bronze B12 -CuSn12, partially turned on the manual lathe and on the CNC lathe
I had to build a special tool for internal front groove

a short video, turning seal ring seat

 

[Foketry]

Valve lapping
I make a pre-lapping of valves and cages before assembly in the heads
I know that a final lapping will be required because there may be deformations during the assembly and drilling of the exhaust and intake holes
I did a manual lapping with these tools, I glue a small round on the valve head, I put it in the flexible hose of the wooden handle and then I lap for about 1 minute

 

[Foketry]

Then I do a vacuum test
Lapping is OK if the gauge from 25 to 5 takes more than a minute
In this case valve has an insignificant leak (note: the oil seal is not installed)

 

[GreenTwin]

I was able to get time today to read through this entire thread.
Very nice and impressive work for sure.
.

 

[Foketry]

Lost PLA : overhead camshaft housing
To make this cast aluminum housing I used the lost PLA technique ,pattern has angled angles that do not allow an open casting, cores are required ,i chose lost PLa instead of cores

PLA pattern spilt into 2 pieces, my 3D printer has dimensions that do not allow to print a single piece
the pattern is hollow inside to burn easily and quickly when drowned in plaster, you can see the internal honeycomb in transparency , thickness of the outer skin is very small

pattern inside plaster before burning , 550° C 4/5 hours in electric oven

After burning

after pouring aluminum

removing plaster

after some roughing operations

camshaft housing temporarily screwed to the heads

 

[926wolf]

So tell us more about the 3d printing. What wall thickness skin and %of infill used because that is a fantastic casting

 

[Foketry]

So tell us more about the 3d printing. What wall thickness skin and %of infill used because that is a fantastic casting

this is my setting , Ultimaker Cura , Infil 10%, all other settings are Basic, not high quality

 

[926wolf]

Thank you i will give that a try