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Case work for Porsche bearings
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bialzi
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PostPosted: Wed Feb 08, 2017 3:31 pm    Post subject: Case work for Porsche bearings Reply with quote

Hi all,

I have been researching the case work for Porsche bearings to run a 356/912 crank in a 25/36hp case and i could never find any pictures of the work so as i got my case back today i thought i would share them with you all.


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Ultramoron
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PostPosted: Wed Feb 08, 2017 9:03 pm    Post subject: Re: Case work for Porsche bearings Reply with quote

Is this work so you can run a 50mm main journal Porsche crank from a A/B with A/B main bearings? Or is it something more than that?
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Mr. Okrasa Premium Member
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Joined: May 20, 2000
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Location: Newport Heights, So. Califa.
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PostPosted: Thu Feb 09, 2017 1:39 am    Post subject: Re: Case work for Porsche bearings Reply with quote

Ultramoron wrote:
Is this work so you can run a 50mm main journal Porsche crank from a A/B with A/B main bearings? Or is it something more than that?


The later 356 and 912 crankshafts have their 2nd and 3rd main bearing journals at 55mm. I thought of converting over to the larger sized main bearings but that would require on modifying the bearing saddles in a 36hp block in order to use the crank as is. The problem with removing extra material from the already "weak" magnesium case didn't sit too well. Remember: Porsche used 74mm stroke, non counter weighted crankshafts in their magnesium blocks with 50mm main journals upto Nov. 1954. From Nov. 1954, Porsche switched to aluminum for added strength and still used 50mm main journals until much later when they ultimately went and stayed with 55mm mains.

Another "situation" I came across: Cutting an oil grove in the block at the flywheel end can result in a oil leak through the main 2 rear studs as they are real close to the oil path. You can see this in the photos in this thread. When oil pressure is increased, oil sometimes comes out at the hex nuts. What i'm using now on the 2 rear through bolts are "acorn" style nuts with a soft copper washer instead of the regular steel type. See attached photo.

I called SCAT and talked to Tom Lieb about their Superlite Porsche 74mm stroke billet crankshafts. I asked him if there would be any weak areas on their billet crankshafts if all the large bearing journals were cut down from 55m down to 50mm. He said, "good question! Let me check with my engineering dept and get back to you". A couple of days later, we spoke again and he said there would be NO loss of strength nor the integrity of the crankshaft would be compromised if modified to 50mm journals.

With that news, I order my first SCAT Superlite 74mm Porsche crankshaft with 50mm journals. I also orders several sets of Carillo rods. Cheers! Mr. Okrasa Cool

BTW bialzi. What crankshaft are you using in this thread?

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1950 Split Window 356 Coupe / Black / #500X
1950 Split Window 356 Coupe / Adria Blue Metallic
1951 Split Window 356 Coupe / Radium Green Metallic
1952 Split Window 356 Cabriolet / Azure Blue
1959 VW Karmann Ghia Coupe / Bamboo-Green / Denzel 1300cc / OG. owner, paint Wink

VW www.Okrasa.com
356 www.PreA356.com
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52 deelux
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PostPosted: Thu Feb 09, 2017 1:42 am    Post subject: Re: Case work for Porsche bearings Reply with quote

Looks like it's been align bored 0.25mm and cut for tanged bearing shells.

This would allow you to run 912 crank and bearings with 55mm centre and end mains.

Groove in bearing saddles is also necessary for oil feed.

This work is not required when using A/B cranks, as you can use 36hp standard bearings.
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bialzi
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PostPosted: Thu Feb 09, 2017 2:05 am    Post subject: Re: Case work for Porsche bearings Reply with quote

Hi,

The crank in the picture is a Scat super light crank. I was looking at cheaper versions but i decided to do it right first time. The block in the picture is an aluminium case so i hope the extra strength allows every thing to work fine. I have carrillo rods and im in the process of getting some 83.5mm nickies. At the moment im pondering over which Camshaft to use with 1:25 rockers? Any advice would be appreciated.

Thanks
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Mr. Okrasa Premium Member
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PostPosted: Thu Feb 09, 2017 10:36 am    Post subject: Re: Case work for Porsche bearings Reply with quote

Whichever camshaft you select, make sure you use the correct lifter profile/design intended for that camshaft! I have read in another forum that people are "sleeving"
the lifter 36hp lifter bores for flat tappets (mushroom style) and machining the first cam bearing saddle (to fit 356/912 camshaft).

I'm using a NOS Porsche 2pc. Pre-A 356 camshaft in my 1300cc Denzel powered lowlight Ghia. Idles real smooth!

See this link below:


Link


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_________________

1950 Split Window 356 Coupe / Black / #500X
1950 Split Window 356 Coupe / Adria Blue Metallic
1951 Split Window 356 Coupe / Radium Green Metallic
1952 Split Window 356 Cabriolet / Azure Blue
1959 VW Karmann Ghia Coupe / Bamboo-Green / Denzel 1300cc / OG. owner, paint Wink

VW www.Okrasa.com
356 www.PreA356.com
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bialzi
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PostPosted: Thu Feb 09, 2017 10:50 am    Post subject: Re: Case work for Porsche bearings Reply with quote

Hi,

Thats what i was thinking. There's 2 cams i am looking at Stefi g and BBT do Porsche pre a 1500 super cams that have a curve in the ramp on the lobes before max lift to gradualy open the pushrods to make everything smoother.
I have some of the lifters that AA uses so i can use cut to length pushrods. Have you used either of those cams?

Thanks Neil
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