Retro tires

[Ross Flora]

When I bought my '72 LT-1 it had Goodrich radials on it. It get more original, I matched the spare with Firestone Bias ply F70-15. I haven't actually mounted the tires yet because several people have told me that is it unsafe to do this! How can useing the style and model of tire originally on the car be unsafe? I understand there are performance differences, but unsafe? Gosh, I drove a '70 Chevy Vega in High School, that was unsafe! But it might have had radials. Anybody know why the concern?

[Duke W.]

Re: Retro tires

It's not clear to me what you did. You bought a used, period set of F70-15s or a new set of repro F70-15s?

BTW, the first model year for the Vega was 1971, and they were never accused of being unsafe, just unreliable due to engine cylinder wall scoring and a propensity to rust.

Duke

[Ross Flora]

Re: Retro tires

Duke, I bought new reproduction tires from Coker. You're right it was a '71 Vega, and actually the only problem I had with the motor was the timing belts. Also, by the time I sold it the only thing holding the fenders on was that great looking Chevy orange paint. I was commenting more on the 16 year old driving the Vega, not the car itself. Wow, I guess Corvette aren't the only cars NCRS members know about!

[Dick W.]

Re: Retro tires

On a quiet night you could listen to your Vega rust

[Duke W.]

Re: Retro tires

Some reproduction tires have questionable quality. For example, out of round problems seem to be more common on repro than modern tires. Though repro tires are only built to minimum goverment/industry safety and performance standards (which have not been updated for over 30 years) so are most low or no speed rating modern radials. Repro bias ply tires are certainly not as good from a ride or performance perspective compared to modern radials, especially high speed radials with nylon cap belts, but repro tires are okay for normal driving.

I special ordered a '72 Vega GT is August '71 - took delivery in October and drove it 90K miles in five years. In late '73 a piston skirt disintegrated, which scored the block but it was never clear which occurred first. I suspect the block scored first, which loosened the piston clearance, and the subsequent banging around disintegrated the skirt. I later received a refund for the repair cost under GM's so-called "secret warranty".

In late '76 I bought Cosworth Vega from dealer inventory at a "close out" price, and sold the '72 GT.

I still own the Cosworth Vega, and just recently rebuilt the head at 70K miles, but it's seen at least 4K miles of race track hot laps and time trials, so the engine has a lot of high rev time. The block is in good shape with some minor scoring on one cylinder, but there was no measureable taper at the tops of the bores.

If you visit www.cosworthvega.com you can see my 7000 rev dyno pull and lots of pictures from our national "Roundup" last June, and the Cosworth Vega Owner's Assc. sells a 200,000 word compendium of Cosworth Vega history and technology called "The Twin Cam Times" that I researched and wrote.

Duke

[Michael H.]

Re: Retro tires

Duke,

I well remember the problem with the Vega. The official GM term used for the failure was called "Deck Drop". That was when the individual aluminum cylinders, that had absolutely no deck surface around them, would expand and contract at different rates than the rest of the block and cyl head and the following anti freeze leak from the head gasket into the cylinders would cause rapid serious scuffing/gauling of the cylinder and piston. In 1972-74, GM wound up replacing nearly 38% of the short block assy's in Vega's under warranty, regardless of mileage. Not sure if you ever had one apart but they're a very strange looking affair with no deck at all. Looks just like a block would if you continued to machine the deck surface until it was gone completely and just the cylinder was sticking up out of the base of the block.

[Duke W.]

Re: Retro tires

I'm not familiar with "deck drop", and it's alway been my understanding that the early Vega engine problems were due primarily to an inconsistent etch. Some areas of the bores had little or no etch, so the rings would tear off bits of aluminum and score the cylinders. Overheating exascerbated the problem and both head gaskets causing coolant leaks and oil consumption due to poor valve seals have been blamed for the lack of cylinder wall durability. I also think 20 below cold starts in North Dakota were a factor.

The '72 head gasket was replaced on warranty when it developed an oil leak at the RF of the block adjacent to the high pressure oil gallery to the head, but I was not able to inspect the cylinder walls at that time, I just took it to the dealer. I don't remember that it ever consumed coolant, so I don't think the head gasket ever developed and internal leak. I rebuilt the engine with a fitted block that I bought at the dealer and received the refund a few years later. I also recently refreshed the head on the CV so I'm familiar with the internals of the block. A number of modern aluminum blocks are also open deck designs.

One of the worst things that happened was taking the '72 back to the dealer for a recall. The bowl cover screws on the Rocherster 2GC had a tendency to loosen and the "fix" was to remove them and apply Locktite to the threads. I checked mine and they were okay, but dutifully took it to the dealer for the work. A few days later I left on a road trip and a few hundreds miles down the road the car began to run rough. I finally stopped and found all the carb bowl cover screws loose with a couple missing. It was like they loosened the screws and gave the car back to me. The threads had no evidence of Locktite. Needless to say, upon my return I went back to the dealer service manager and read him the riot act. Fortunately, I never had to take the car back to them again for any reason, and they were the only Chevy dealer in Grand Forks.

Duke

[John H.]

Re: Retro tires

We even shipped them like sides of beef - yup, the Vega was unique I was in charge of the plant conversion and launch, and spent five years as the Trim/Chassis/Final Production Superintendent....got lotsa stories, all of which will be in "the book", but several folks have to die first before it's published

[John H.]

Re: Retro tires

Dick, some folks claimed the early Vega didn't need a heater due to the ongoing exothermic reaction

[Dick W.]

Re: Retro tires

John, that is the best description of rapid decomposition that I have heard. It was so rapid that if it was just a wee bit faster, it whould have been acompanied by light, then we could have called it fire! While being challanged as an expert witness on an arson case, the defense attorney asked me the definition of fire. I answered "Rapid decomposition accompanied by heat and light". That was the end of his questions.:D :

[Michael H.]

Re: Retro tires

Duke,

The bore scuffing problems were nearly all caused by the presence of PAF from the leaking head gasket which allowed PAF to run directly into the cyl, especially on a hot restart. The first GM recommended "fix" was to replace the head gasket but not long after, the campaign became more costly and the entire short block assy's were replaced under warranty, regardless of mileage.

The blocks were a mix of silicone and aluminum, the silicone being the intended wear surface on the bore. Bore finish was completed with what they called a "silicone lap", which was done after the final bore/ hone process. The silicone lap was done using what looked like felt pads instead of stones on the hone. The pad and special compound would remove aluminum but not silicone, leaving the small nubs of silicone as the wear surface for the specially plated pistons and rings. In oil, this combination would work well but as PAF was introduced into the mix, piston and cyl wall surfaces were worn away quickly and failure was just a few miles away.

This cyl wall prep procedure is the vary same as the later Can-Am aluminum big block with aluminum cyl walls. I have the silicone lap instructions here somewhere. Interesting process!

Michael

[Michael H.]

Fable?

Not sure if this is true but I once heard that junk yards were scrapping these cars the same way that GM was loading them in John's picture above. New, special equipment, that was capable of lifting Vega's three at a time, just so they could keep up with GM production. Also heard that GM made the floor pans concave so the cars would fit the roof of the car below and stack more efficiently at their final resting place.

[Dick W.]

Re: Fable?

I had two 1976's that never rusted. They were driven from the dealer and put into storage. One still only has 19 miles on it. I slip out into the garage ever now and then and listen though.

[Patrick H.]

Re: Fable?

You're kidding, right?
The same money in 76 would have purchased a low mile all-original Corvette, and you bought a VEGA to store???

Patrick

[Brian M.]

Re: Retro tires

Vega's rusted in the showroom.