Porsche 917 flat 12 engine

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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 ?
 
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
 
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
 
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, 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.

testa e valvole new.jpg
 
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
 
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.
 
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.
 
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.
 
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 ...

 
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

IMG_1883.JPG
 
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

scatola camme.jpg


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

IMG_1816.JPG


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

IMG_1818.JPG


After burning

IMG_1802.JPG



after pouring aluminum

IMG_1810.JPG


removing plaster


IMG_1850.JPG



after some roughing operations

IMG_1886.JPG




camshaft housing temporarily screwed to the heads

IMG_1867.JPG


IMG_1888.JPG
 
Last edited:
So tell us more about the 3d printing. What wall thickness skin and %of infill used because that is a fantastic casting
 

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