Edelbrock heads engine overheating steam vent question

[2+2GT]

To prevent a hotspot from forming in that part of the head, being as aluminum shrinks and contracts at a different rate than iron, it only becomes a problem when your using aluminum heads on the iron block. I went thru the same thing about 4 years ago.

That would explain why my 71 Vega went through 4 head gaskets in 40,000 miles. Doesn't explain how it got though Chevy Engineering, though.

 

[Loup-garou]

You had a Vega that lasted 40,000 miles? Amazing.

 

[danledford]

It is the original 68 block

 

[65ShelbyClone]

Then it doesn't have the offset holes.

That's why I am trying to make a habit of taking pictures of everything even if I don't think they will be needed later. I have photos of my roller 302 shortblock from nearly 10 years ago. I didn't think I would need them until this thread came up. Sure enough, I went back to look and it has both coolant holes whereas the roller blocks that came in production vehicles only have the offset hole AFAIK. That's because my block is a service replacement intended to be backward compatible with earlier heads. It doesn't have a normal decade/year casting number, either.

 

[rbohm]

That would explain why my 71 Vega went through 4 head gaskets in 40,000 miles. Doesn't explain how it got though Chevy Engineering, though.

the vega was an all aluminum engine. its problem was the lack of support for the top of the cylinders, and the open deck design.

 

[65ShelbyClone]

No, the block was aluminum and the head was iron.

 

[2+2GT]

the vega was an all aluminum engine. its problem was the lack of support for the top of the cylinders, and the open deck design.

You are incorrect, sir, the cylinder head was iron. I was the one who lifted it to repair. The open deck didn't help, but the head was iron. The real weakness was the block, supposedly cast so silicone would form the surface of the cylinders. Didn't always work out, and within a year or two would end up with the rings riding on aluminum. A few years later they came up with the "Iron Duke" engine, with iron sleeves, even restyled the car and changed the name, but they couldn't save it.

And yeah, we managed to squeeze 48,000 miles out of it before we'd had enough. In that time it went though the aforementioned head gaskets, all the rear axle bearings, tailpipe, alternator (seized bearing) and distributor. During a repair discovered the body panels (fenders, etc) were bare steel on the back, meaning it would have rusted out like Swiss cheese in a couple more years. Guess they wanted to save 5¢ per car on primer.

 

[65fastbackresto]

Chevy engineering?

That would explain why my 71 Vega went through 4 head gaskets in 40,000 miles. Doesn't explain how it got though Chevy Engineering, though.

Doesn`t sound like they did too good a job either.

 

[rbohm]

The real weakness was the block, supposedly cast so silicone would form the surface of the cylinders

nope, the real weakness of the vega block was in fact the open deck. it would allow the tops of the cylinder to move around thus abrading the head gasket and causing head gasket failures. it was made even worse when machine shops would mill the block to flatten everything out, when the cylinder were supposed to stand proud a few thousandths to seal the head gasket against the head and prevent the cylinders from flexing freely. the iron duke used a closed deck design that supported the tops of the cylinder.

by the way, you are right about the head being cast iron. the vega engine was a stupid design all the way around.

 

[2+2GT]

A nice write-up in Wikipedia:

GM Research Labs had been working on a sleeveless aluminum block since the late 1950s. The incentive was cost. Engineering out the four-cylinder block liners would save $8 per unit. Reynolds Metal Co. developed an eutectic alloy called A-390, composed of 77 percent aluminum, 17 percent silicon, 4 percent copper, 1 percent iron, and traces of phosphorus, zinc, manganese, and titanium — suitable for faster production diecasting, making the Vega block less expensive to manufacture than other aluminum engines. Sealed Power Corp. developed chrome-plated piston rings that were blunted to prevent cylinder bore scuffing. Basic work had been done under Eudell Jackobson of GM engineering. Then suddenly, Chevrolet got handed the job of putting this sleeveless aluminum block into production. The Vega blocks were cast in Massena, NY at the same factory that had produced the Corvair engine. The casting process provided a uniform distribution of fine primary silicon particles approximately 0.001 inches (25 µm) in size. The blocks were aged eight hours at 450 °F (232 °C) to achieve dimensional stability, then inpregnated with sodium silicate to help eliminate porosity.[2] From Massena, the cast engine blocks were shipped to GM's engine plant in Tonawanda, NY where they underwent the etch and machining operations. The cylinder bores were rough and finish-honed conventionally to a 7-microinch (180 nm) finish then etched removing approximately 0.00015-inch (3.8 µm) of aluminum, leaving the pure silicon particles prominent to form the bore surface. A four-layer plating process was necessary for the piston skirts, putting a hard iron surface opposite the silicon of the block. From Tonawanda, the engines went to the Chevrolet assembly plant in Lordstown, Ohio. The technical breakthroughs of the block lay in the die-casting method used to produce it, and in the silicon alloying which provided a compatible bore surface without liners. With a finished weight of 36 pounds (16 kg), the block weighs 51 pounds (23 kg) less than the cast-iron block of the 153 cu in (2,507 cc) inline-4 used in the Chevy II Nova.

Further reading, however, reveals this info:

"After the engine had been in production for a while, customers would go back to the dealer complaining about oil consumption... the mechanic would peer down the bore scope and observe cylinder scuffing. We eventually found out that the problem had never been the scuffing of the (cylinder) bore. The real problem was the valve stem seals. They'd harden, split, fall off, and oil would leak down past the valves and into the combustion chamber. So we did some experiments. When we got an oil burner, we simply replaced the valve-stem seals, and that cured it." 1976-77 Dura-built engines had redesigned seals that reduced oil consumption by fifty percent.

The car was initially well like by the automotive press. That didn't last:

In 2008, Popular Mechanics editor John P Huffman's web article, 10 Cars that Damaged General Motors said, "the Vega was actually a sales success. But ultimately that meant there were just that many more people disappointed by the Vega." and "Throw in haphazard build quality and sheetmetal that you could practically hear rusting away, and the Vega truly rates as one of GM's great debacles." The 2009 Car and Driver feature, Dishonorable Mention: The 10 Most Embarrassing Award Winners in Automotive History, Car and Driver.com editors listed the 1971 Vega third, criticizing Motor Trend's Car of the Year stating, "That’s not to say the choice of the Vega as 1971 Car of the Year didn’t make sense in context..compared with Ford’s Pinto, the Vega at least seemed better. The Vega’s aluminum engine block even seemed like a technological leap forward. However, the aluminum block’s unlined cylinder bores scored easily, and the (usually misaligned) iron cylinder head let oil pour into them." In 2010, John P. Huffman of Popular Mechanics referred to the Vega as "the car that nearly destroyed GM."

 

[rbohm]

2+2, everything you posted points towards oil consumption, not head gasket failure. again the problem with constant head gasket replacement is the lack support for the upper cylinders, which allows them to move around and abrade the head gasket causing leaks. and it is made at the machine shop when the machinist does not let the tops of the cylinders stand proud of the outer edge of the block to enhance sealing.

 

[65ShelbyClone]

Going further off-topic...

What was particularly bad about the Vega's open-deck design? I think just about all Hondas made since the late '80s use that block design and they're not prone to losing gaskets. All I can think of is their iron liners adding some rigidity and the fact that they are truly all-aluminum engines. They do tend to crack cylinders with forced induction, though. Posting the cylinders or welding in an upper support was popular before Dart started making aftermarket closed-deck blocks.

 

[2+2GT]

2+2, everything you posted points towards oil consumption, not head gasket failure. again the problem with constant head gasket replacement is the lack support for the upper cylinders, which allows them to move around and abrade the head gasket causing leaks. and it is made at the machine shop when the machinist does not let the tops of the cylinders stand proud of the outer edge of the block to enhance sealing.

What machine shop? The friggin POS was brand-new!

 

[rbohm]

Going further off-topic...

What was particularly bad about the Vega's open-deck design? I think just about all Hondas made since the late '80s use that block design and they're not prone to losing gaskets. All I can think of is their iron liners adding some rigidity and the fact that they are truly all-aluminum engines. They do tend to crack cylinders with forced induction, though. Posting the cylinders or welding in an upper support was popular before Dart started making aftermarket closed-deck blocks.

part of the problem was the thin cylinder walls on the vega, and the lack of steel liners that were put in later. however even the honda had minor issues with the cylinders moving around at the top, but since the honda is all aluminum, compared to the vegas aluminum block and cast iron head, the hondas expansion rates were the same which also reduces stress on the head gasket.

What machine shop? The friggin POS was brand-new!

maybe the first time, but subsequent gasket replacements should have had the block machined to true the surface otherwise you are just asking for more gasket failures in short order.