Author Topic: 1/4 scale Porsche 917 180 degree V12 Build  (Read 2110 times)

Offline RReid

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #30 on: September 13, 2021, 03:19:31 AM »
Looking great! I can hear the satisfaction loud and clear in your post.  :ThumbsUp:
Regards,
Ron

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #31 on: September 15, 2021, 12:32:15 AM »
Ok  had an epiphany, and it resulted in reduced set up and machine time...light dawns over marble head...anyway I'll be finished with half the crank webs tonight....and then I can start the rest.  I'll order gear cutters tomorrow.  32Dp and 48 Dp    14.5 degree PA  and the rest of the stress proof.   I also ordered some ttstool holder blanks to make cutter arbors from.    As cheap as the steel id make them out of.  Starting to get some momentum here.
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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #32 on: September 15, 2021, 02:59:26 AM »
A cranks done with a spare   In the middle of making the holding fixture for the Bs.

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Offline crueby

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #33 on: September 15, 2021, 03:40:12 AM »
What was the epiphany?  Pictures!

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #34 on: September 15, 2021, 05:23:24 AM »
 :lolb:  Instead of having a finished and unfinished A and B, I changed the assembly to a finished A side and a unfinished B side.  That means 2 set ups instead of 4 set ups.....so significant..

My biggest challenge this evening was ME!    Did some dumb things and broke tools....but I didn't lose parts! so I got there eventually!
I need to arrange to have the crankpins hardened....

Finished A sides on the left.   Unfinished B sides on the right


Dave
« Last Edit: September 15, 2021, 05:29:47 AM by steamer »
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Offline Craig DeShong

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #35 on: September 15, 2021, 08:47:42 PM »
Lots of parts !  I assume you have some type of assembly jig planned to keep everything square?
Craig
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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #36 on: September 16, 2021, 12:59:36 AM »
Lots of parts !  I assume you have some type of assembly jig planned to keep everything square?

Thanks for looking in Craig

Yes    There will be 2.   One to press the B side onto the assembly, to keep is close to aligned, and a second one to hold the A side while I machine the bearing diameters on the B side to size and concentric to the A side.

After that.   It's all about stringing all the sections together into a single crankshaft just like stringing together beads.
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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #37 on: September 16, 2021, 01:54:00 AM »
I don't think I've explained how this crank gets made very well, Shilling was quite clever!    His design allowed for some very high power outputs, with a fairly simple crank design.   It requires careful work, but it's doable

Hi approach was to create a ball bearing crank via many small pieces     If allows for large ball bearing mains, and also can provide for a ball or roller bearing connecting rod bearing as well.    If you've ever been into the bottom end of a modern 2 stroke or even 4 stroke motorcycle engine, you have seen this construction before.

So what I'm doing, is creating 2 crank webs, and a crank pin.   The A side has M4 threaded holes, while the B side has M4 clearance holes
The crank pin fits with a interference fit.   Seems simple right?

But how to you make sure that the two bearing diameters are concentric?   And it NEEEDS to be concentric!
There are 8 main bearings on this crankshaft,

One way that Shilling did it was to machine one side complete, assemble the 3 parts, and then FINISH machine the second side using the finished side as a datum both radially and axially.

Rinse and repeat 6 times.....plus a gear....and some end caps....and you have a 917 crankshaft

It's slow going as there are quite a few parts to make, but it seems to be coming together quite nicely.   I'm still torn as to finishing the second side in the lathe, with a fixture, or in the mill with some soft jaws to hang on to it.      but I'll figure that out when I get there.     

The OD and FACE in blue below are the two surfaces that get finish machined after assembly to assure concentricity....I've left material on the second web specifically for this purpose.

I am going with ball bearing mains 32 x 25 x 4, and bronze bearings on hard pins for the rod bearings.   Simple, and hopefully durable.

Dave
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Offline RReid

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #38 on: September 16, 2021, 02:00:03 AM »
Thanks. That does help to clarify what you're up to. And what you're up against! :ThumbsUp:
Regards,
Ron

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #39 on: September 16, 2021, 02:04:01 AM »
Thanks Ron,

I think it's the best way forward.   Making that crank any other way would be daunting!

Dave
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Offline Art K

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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #40 on: September 17, 2021, 01:31:52 AM »
Dave,
I have been following along just not saying much/anything. I do have one thought though.
Quote
Making that crank any other way would be daunting!
As if doing it this way isn't daunting!
Art
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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #41 on: September 17, 2021, 10:57:44 AM »
Well   you can do (1) 6 throw  crank...or (6)  1 throw cranks....like I said if I can.make this crank...I can make the engine.
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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #42 on: September 17, 2021, 11:45:07 AM »
Additionally...cutting the center gear on a solid crank would be tough without a gear hob.
« Last Edit: September 17, 2021, 12:14:45 PM by steamer »
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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #43 on: September 19, 2021, 07:44:20 PM »
B sides underway!   I think The program is good now....now to run 6 good ones

Plug gage fits just a scouch tight, but alright
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Re: 1/4 scale Porsche 917 180 degree V12 Build
« Reply #44 on: September 20, 2021, 01:13:32 AM »
Ok   Progress!     Other than 18 holes to tap M4, and general deburring, the crankwebs are done with spares.!   The crankpins are also done with spares and I'm setting up now to get them heat-treated.   Lot of work there!....next is assembly fixtures, and gear cutting.  The 917 engine took power from a gear at the center of the crank.   I have some cutters coming.....fun  challenging project!
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!