Why does half my Transam reqiure metric fasteners and the other half SAE. Did GM have a problem in the mid 80's choosing which one to use?

 

LOL!! Mid-80's...better step back about 10 years ...I seem to recall metric fasteners on my '78 Camaro (also none as slow-as-frozen-goo).

 

It was the period of changeover. The holes in the engine case that were common to the old design and drilled and tapped on the Ingersoll automatic lines remained as fractional sizes. This prevented any significant retooling and incompatibility with older cases, heads, and such. Smaller and less expensive parts, like intakes, accessories, brackets, and other components were changed over to metric sizes as soon as there was a redisign or new item released.

You would be very upset if your Dart heads and ARP bolts didn't fit the block because the "new" case was made for metrics.

This is another reason for Torx fasteners, There are no metric or fractional sizes for Torx, just the international standards. While the body of the fastener may have a metric or fractional diamter and corresponding pitch, the heads are the same for both.

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Later,
Vader
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"Let the bodies hit the floor!"
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[This message has been edited by Vader (edited August 12, 2001).]

 

SAE? Society of Automotive engineers? There is a "society"? How old are these guys =P Are new cars made in the US still incorporating SAE fasteners? If you're gonna have one standard you might as well use metric. It wont hurt anyone if all new cars were all metric becuase every darn garage already has metric tools.

 

My 91 truck has a mixture of standard and metric. Even the Hubble telescope has standard and metric. The trouble is where the parts were assembled. The USA still assembled parts with standard fasteners while components that were assembled out of the country (Canada and Mexico being the largest assembled parts suppliers) were already using metric. Until everything was standardized to all metric there can be a real mixture of fasteners. At least were not using british standard sizes.

Depending on the metric size required, most standard tools will still work. Common metric sizes for nuts and bolt heads that don't convert very well are 10, 15 and 18 mm. The sizes in between are either not a common size to use or will have a standard size close enough that it will work.

Even my 91 truck still has standard and metric sizes. There aren't a lot of standard but they're still there.

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If I'm correct, the newer generation SBC III engines are all metric. Many of the newer GM engines are all metric, as well. Since the SBC was designed and first produced in 1954, the fasteners in the main components are still all fractional.

Consider your self lucky that you don't have to deal with clutch head bolts and Robertson heads, like some of the '40s and '50s cars and trucks used. Or better yet, the 19/32" heads used on 7/16" bolts. Then again, explain why some Toyotas (Land Cruiser) have a 120.65mm bolt circle for the wheels. I thought they were all "standard" metric sizes. ¿?

------------------
Later,
Vader
------------------
"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

No kidding! Try finding a gauging tool for a BSP fitting. Depending on what part of the country in which they were manufactured, the "standards" change. Look in an engineering manual for exact sizes for some British standards and you'll be lucky if you find an asterisk, let alone any numerals. This is all from a place smaller than Wyoming. And we're whining about having only two systems, both of which actually have some standards.

------------------
Later,
Vader
------------------
"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

What's wrong with Robertson heads? I've never seen one stripped yet. Any good Canadian has a dozen Robertson drivers in his toolbox.