Author Topic: 1/4 scale Porsche 917 180 degree V12 Build  (Read 57543 times)

Offline Vixen

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #495 on: January 26, 2023, 12:00:27 AM »

Valve timing for model engines along with Compression ratio's vary significantly from full size practice.   Generally lower CR's and much less overlap on cams to make them much easier to start, tune and run.     As I understand it, a much milder cam timing is required to make a good running MODEL engine.    Valve timing and events such as those published by Westbury are generally to be preferred.


I totally agree with all of that. Mild valve timing will always make an easy starting, well mannered MODEL engine. And it also helps to fit a smaller carburetor than you thought necessary.

However, if you want POWER (to drive something other than the running stand); fit a wild cam with plenty of overlap, higher compression and a bigger carburetor; but it may be a pig to start and run.

Mike
« Last Edit: January 26, 2023, 12:03:50 AM by Vixen »
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Offline steamer

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #496 on: January 26, 2023, 12:01:58 AM »
Dave - I misspoke... its not ASME, it was the Proceedings of the Institute of Mechanical Engineers Vol 186 2/72 - "The development of the Porsche Type 917 car"
https://journals.sagepub.com/doi/pdf/10.1243/PIME_PROC_1972_186_005_02
Regards
John

EDIT - trying to fix the URL link.

Thanks John!
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Offline jcge

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #497 on: January 26, 2023, 12:02:51 AM »

Offline steamer

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Offline RReid

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #499 on: January 26, 2023, 12:34:33 AM »
There's a ton of good stuff in that PDF. Thanks for posting it!
Regards,
Ron

Offline petertha

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #500 on: January 26, 2023, 04:46:06 AM »
Dunno,  :hellno:     

 Ask Steamer, the 917 is his project

Mike

Sorry about that Mike, I actually knew that LOL. Late night typing & getting my exotic engines crossed. Anyways I continue to tinker with my cam spreadsheet tools & its been somewhat revealing (to me). I've also been working on a kind of cookbook cam phasing/orientation procedure... well lets just call them personal scribbles & kind of a symbol matrix for now. This came about because I as suspicions of a certain cam & getting it wrong in real life seemed like a lot of work to be avoided. There are quite a few variables that enter the picture. Anyways, it was good to work through the problem on my own. So I look forward to whenever the topic comes up in discussion.

Offline steamer

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #501 on: January 26, 2023, 10:50:51 AM »
Dunno,  :hellno:     

 Ask Steamer, the 917 is his project

Mike

Sorry about that Mike, I actually knew that LOL. Late night typing & getting my exotic engines crossed. Anyways I continue to tinker with my cam spreadsheet tools & its been somewhat revealing (to me). I've also been working on a kind of cookbook cam phasing/orientation procedure... well lets just call them personal scribbles & kind of a symbol matrix for now. This came about because I as suspicions of a certain cam & getting it wrong in real life seemed like a lot of work to be avoided. There are quite a few variables that enter the picture. Anyways, it was good to work through the problem on my own. So I look forward to whenever the topic comes up in discussion.

Hi Peter,
I enjoy your ruminations on timing as I too would like to internalize the nuances of engine parameters with model engines.   Feel free to post what you think appropriate.   If this was a Compound steam engine, I'd know EXACTLY what was needed....been there done that.     This is all still new to me, but I'm learning as I go.

Dave
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Offline steamer

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #502 on: January 26, 2023, 10:56:02 AM »
Been giving the cylinders a lot of thought as of late.     I think trying to drive a slitting saw through 12 of them ( minimum) is asking for drive problems.....and I don't need drive problems.

That said, I'll be going at this a little differently.    I'll take a page out of the Edwards 5 radial design, and  I'll make a aluminum cylinders with cast iron liners.   This is a lot more work, but I think the risk reduction is worth it.    Making fins in the lathe will be easy in comparison with aluminum.     The cylinder heads will still need to be milled, but with aluminum, it should be far less of a drama as compared to 1144SP steel.

Best way to keep going on a project,  make a decision and then execute.....onward!

Dave
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Offline ozzie46

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #503 on: January 26, 2023, 10:39:58 PM »
Hello Dave,

You seem to want/need to avoid the use of 1144SP steel for the cylinders because of potential fin cutting issues. Instead you are considering aluminum finned cylinders with cast iron liners. What is the objection to making the whole finned cylinder from cast iron? I am sure that's what Craig did on his big 'Le Craig' rotary engine.

Just thinking




Mike


Or use 12L14 leaded steel. I cut fins in the cyls for a nine cyl radial that were .031 grooves in the stuff, no issues . Ground up 2  HSS cutting bits
 to .031. Broke 1 ,my fault , lost concentration.

12L14 is a pleasure to machine.

Ron

Offline steamer

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #504 on: January 28, 2023, 11:01:45 PM »
Thanks Mike and Ron for your responses.

Looking at the machinability of the materials, it's attractive to go with Aluminum with an iron liner, like the Edwards and the Ohrndorf.    Running on methanol, there is concern about corrosion.  I have seen engines built with both 1144SP and Iron.   Petertha was concerned about corrosion with methanol on the steel parts, and decided to go with cast iron liners as they have a good reputation with iron rings.      I too will have these problems with a multicylinder that I know I wont get EVERY last drop of methanol out of after a run.   After run oils are out there, but I'm not convinced that I'll get it all.  Petertha also had issues with the liners shrinking and going out of round on the Ohrndorf after pressing them into the sleeves.

Machineability of 1112 Carbon steel being 100%   1144SP is 83%, 12L14 is 170%,  while Gray Iron is about 48%.    Aluminum alloys of the wrought material variety are at about 360%.

The above facts would point to a two piece solution.....Armed with that and a closer look at the design,   the manifest problem and there is a problem became obvious.....

1.   The sections of the cylinder are thin....real thin.    Making this cylinder in two pieces would be a challenge and keeping the parts together ....I'm not sure I'm going to
2.   Mixing Steel with Aluminum and then soaked with a substance that corrodes metals sounds like galvanic action taking over quickly.......hmmmm.  Getting the heads off this engine is going to be a right royal PITA!.....the cam boxes have to come off.   Like it might be easier to split the case! :hellno:
........ :zap: :headscratch:

So   hard to starboard and come about!    back to 1144SP.     And in one piece.
1.  One material....less chance of corrosion.
2.  Better machinability than Iron, and Im not burying my lathe in iron chips.....
3.  If I'm thoughtful enough, and do all the fin making in the right order, I can cut all 8 x 12 plus extra's    lets call it 120 grooves   1mm wide x 5mm deep fins on the lathe.....time to buy some more thin bit!

Nicole thin bits      .043 wide by .236 depth of cut.   Best price so far is $21 EACH.      ( I have a holder for them.)   I'll keep looking, but Bubba! (Steve Huck )   if you know a cheaper place to buy...let me know.

4.   I won't need to worry about the liner closing down and going out of round after final machining and lapping....
5.  One less turning fixture to make....

It's also clear to me that I will need a good after run procedure that flushes the cylinders and the block with after run oil.   




   

 



« Last Edit: January 28, 2023, 11:10:54 PM by steamer »
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Offline steamer

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #505 on: January 28, 2023, 11:58:40 PM »
Model Cam timing

Thanks to Petertha for his great work! 

Im liking the OS FS26.....its very similar to the bore stroke and compression ratio that I'm going with, and is described as a beautiful engine that is very easy to start on methanol and 10% nitro with synthetic oil.

Something to shoot for

Dave

http://sceptreflight.com/Model%20Engine%20Tests/OS%20FS-26%20Surpass.html
« Last Edit: January 29, 2023, 12:02:36 AM by steamer »
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Offline petertha

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #506 on: January 29, 2023, 07:37:55 AM »
I think you might be referring to this post. Sheesh, has it really been that long? I really must get on with my documentation. I promise!

https://www.modelenginemaker.com/index.php/topic,10155.120.html

Anyways, maybe some commentary. The way I initially went about my liners & cylinders was not efficient or correct. I was initially after a very mild interference fit between CI liner aluminum cylinder mostly because that was my RC experience. Just a little bit of soak time in a 350-400F toaster oven & the liner could be removed & replaced. But those engine bodies are almost always die cast & under close examination the cylinder bores are very well finished, maybe  honed or lapped. The liner OD's are extremely well finished. I lapped my liner OD's but I now believe my cylinders were a little more 'lively'. The shape is not symmetrical, for sure more mass near the top & rectangular base; possibly conditions for post machining stress relief. I also depended on a reamer for the cylinder bore which I thought was pretty good, but lapping exposed it wasn't quite perfect either. So a 1/10" here, 2/10" there..my fit was OK but not perfect.

Then I read the fine print of another builder (Jung) & his interference recommendation amount was more than a slip fit & he wrote necessary for dissipating heat. So when I went down this path, I still used heat to assemble liner & cylinder, no pressing or adhesive. But aluminum can expand a lot & if you don't get the diameters right it is possible/likely for the liners to get squeezed especially if they are thin wall. But all I was really trying to say in this episode was don't waste effort lapping the bores unless you are going for that magic light slip fit. Next engine I would simply leave enough material in the liner ID for lapping & save that operation for very last. Ie. assemble cylinder & liner the same way (thermally), let them stabilize over some reasonable period & let them do what they may. Then do the final liner lap. I had my finished assemblies sitting in a box for quite a few months while building other components & I could no detect any bore deviation from last lapping dimension. Hope they stay that way.

In terms of materials, I also oscillated between alloys mentioned. I opted for CI because of its stated good wear properties with a CI ring. I am very happy with the finish & stability. It was a bit messy but fun to machine & you can achieve a mirror finish if desired. Apparently CI was used in glow engines before chrome/hard coating came into the picture (castor oil days). 12L14 machines like a dream but my only concern was possibility of 'a bit more' corrosion rate. Purely based on unscientific data: machined 12L14 stock in my scrap box shows some discoloration over time & I live in very dry air environment. But I have also seen 12L14 used in many built engines, but predominantly gasoline which I think are not as aggressive corrosion wise as methanol? I considered 1144SP as well, my crankshaft is made from it. It finishes very well too but it was my impression it was tough stuff. I did lapping on OD surfaces & it just seemed to take forever. Diamond helped. But this might just be my imagination, a lot of time expired between crankshaft & liners. Lapping is mind numbingly slow, I dream about access to a Sunnen hone. But I'd say have a fun R&D day & try a liners of each material on your top list, see what you think. You have so many more to make on the V12 than I did.

Anyways, I will continue to be quite religious about interim engine storage liberally soaked with oil & stored in Ziplock bags, even if it means partial disassembly to ensure everything is coated. Come running season, drain & wipe. I've done this for years on expensive RC engines back in the day. Aside from running wear they look spotless. Whether its pneumatic tool oil, or (non additive) hydraulic oil, or Klotz.. doesn't seem to matter as long as its coating everything & doesn't react to other alloys used in the engine. Hopes this helps!

« Last Edit: January 29, 2023, 04:58:10 PM by petertha »

Offline steamer

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #507 on: January 29, 2023, 10:41:44 AM »
Hey Peter,
We violently agree!
I am fond of CI as it does finish nicely but I do want/need1 piece cylinders and I want them to last a bit....this engine is a real "Stack of parts" and identical bore and length are critical....yes 1144sp isn't as friendly as 12L14 but it will lap up nicely in my experience.  Again   some tooling will be required lol.  I think 2 piece construction is out if I want to stay at least NEAR prototypical.  For after run I plan on flooding the engine internally with oil and draining it. Cylinder bores as well through the glow plug ports.   Thanks for looking In! :praise2:
Dave
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Offline steamer

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #508 on: February 04, 2023, 01:50:09 AM »
Hope this is useful for you Dave
Top left spiral gear is the tacho drive on the inlet cam.
Notches at either end of the exhaust cam (lower) drive the scavenge pumps at front and rear.
Thrust bearing in the center (flanges), and drive gears attached via vernier plate integral to the shaft. Gear is located with standard bearing nut KM series.
Regards
John

EDIT - timing as per typ.906   Mezger details the lift and accelerations in the ASME paper
INLET   12.1   mm
EXHAUST   10.5   mm
Amax   0.0143   mm/°/°
Dmax   0.0056   mm/°/°

typ.906 cam timimg
INLET OPEN      104   °BTC   
INLET CLOSE      104   °ABC      
EXHAUST OPEN      100   °BDC   
EXHAUST CLOSE   80   °ATC

A friend of mine pointed out that cam receipt makes for 388 degrees of duration and 185 degrees of overlap......his comment was....."holy mother or god"   LMAO!
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Offline Jasonb

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #509 on: February 04, 2023, 07:15:46 AM »

 lets call it 120 grooves   1mm wide x 5mm deep

Nicole thin bits      .043 wide by .236 depth of cut.   Best price so far is $21 EACH.      ( I have a holder for them.)   I'll keep looking, but Bubba! (Steve Huck )   if you know a cheaper place to buy...let me know.
 

If you go with their Grooving & Cutoff inserts (neutral) rather than standard grooving you will get closer to your 1mm with their 0.039" width and an extra mm of depth capability. These are what I use most of the time in my holder for parting small parts and grooving, even parted some 200mm dia streel tube the other day with them. Never found them cheap but they are good.
« Last Edit: February 04, 2023, 07:46:52 AM by Jasonb »

 

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