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roverman
Art Gertz
Winchester, CA.
(2850 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Aluminum air-cooled and growing
Posted by: roverman
Date: January 23, 2017 07:45PM

No, it's not British-but... Corvair uses 7/16" diameter, LONG steel studs, to retain the cylinders/heads. These are necked-down to about 5/16" dia., likely to provide enough elasticity, as the engine thermal expands, ( with cast iron cylinders). Plan is to use Niklsil coated aluminum cylinders. My concern is, the steel studs will over compress,( barrel shape) the aluminum cylinders, when fully warmed up. Why not use full diameter 7075 T6 studs ? At full diameter, they would be "stronger" than the oem studs, but none of the thermal diferential problems ? Your "thoughtfull" input is appreciated, art.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5199 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Aluminum air-cooled and growing
Posted by: BlownMGB-V8
Date: January 24, 2017 02:24AM

I'd think they'd run cooler than the fins Art, what do the other Corvair (and VW) builders do about it?

Jim


roverman
Art Gertz
Winchester, CA.
(2850 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Aluminum air-cooled and growing
Posted by: roverman
Date: January 24, 2017 11:33AM

So many forums, so little time. This seems to be the only forum, where they aren't suggesting "lobotomy". Once again, my claimed location is, ' just east of forrest'. All the Corvair specialist I've spoken to, are bent on pushing the products they have in stock. I've tensile tested 7075 T6 aluminum at about 107 ksi., which compares favorably with mild steel. Using all aluminum cylinders, is not where I want excessive thermal preload. Thanks, art.


joe_padavano
Joseph Padavano
Northern Virginia
(108 posts)

Registered:
02/15/2010 03:49PM

Main British Car:
1962 F-85 Deluxe wagon 215 Olds

Re: Aluminum air-cooled and growing
Posted by: joe_padavano
Date: January 26, 2017 01:44PM

You're concern over the CTE difference is valid. Assuming about 10" studs and a 200 deg F delta from room temp to operating temp, my rough numbers are about 0.013" difference in the length of the stud vs. the cylinder (assuming 6.8 micro-inches/in/deg F for the steel and 13.1 for 7075). I'll let you run the numbers on the stress difference in the stud/cylinder.

The problem with aluminum studs is that the rated tensile yield of 7075-T6 is 63-69 ksi, per MIL-HDBK-5. Your 107 number is scarily high. Grade 8 bolts/studs are typically around 130ksi yield. I'd also be concerned about shear failure of the threads on the aluminum studs. I don't have a good answer here, unfortunately.


roverman
Art Gertz
Winchester, CA.
(2850 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Aluminum air-cooled and growing
Posted by: roverman
Date: January 30, 2017 12:08PM

Joe , thanks for the input. To clarify, I believe Corvair cases, ( studs thread into), are semi permanent mold, aluminum so approx. 40 ksi yield ? Corvair studs are necked down to only.312" dia. 107 ksi. is .at break. Are stock Corvair studs actually grade eight ?


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