I am the former owner of a 1997 Ford Taurus SHO. Even though the Taurus SHO has a long and peppered history, Ford Motor Company recently reintroduced the model. In earlier years, the SHO came with a host of troubles.
At first, the SHO was one of Ford’s flagship performance sedans. The difficulties began when Ford took over the engine program from Yamaha. The monkeys went to work and quickly changed this proud vehicle from a stellar product to a vehicle that Consumer Reports actually warned people against buying as a used car.
To make a long story short, the Generation 3 SHO came with a 3.4-liter (207cid), 32-valve V-8, which was a major change from the 3.0-3.2-liter, 24-valve V-6 that Ford used in the first two generations of the SHO. When Ford developed the four-camshaft V-8, it designed the camshaft sprockets without any keys or pins. Instead, it pressed the sprockets on to the cams to create an "interference fit" to hold the sprockets on to each cam.
This proved to be a very unwise decision. It was considered to be a zero-tolerance engine, meaning that if the timing goes, the valves won’t get bent. Not so with the SHO. Many of these sprockets have slipped, usually without warning, causing catastrophic damage to the valve-train and engine.
I recall (from rebuilding and souping up several Ford flat-head V-8s) that 1930s-vintage flat -heads used a molded or pressed-on fiber camshaft gear. They were designed to be silent, but on occasion stripped their teeth or slipped on the camshaft, assuring a perfectly silent (dead) engine. Of course when modifying a flat-head, I installed a racing-type camshaft with a metallic gear.
Good design says that if position or rotation on a shaft matters, they must be keyed or splined or welded. So there are a number of options. I hope that the problem cost Ford enough so that they decide to never make that mistake again. At least I hope that they learned something. It is probably not possibe to lock the shaft to the gear if it has not moved yet, sometimes a bit of advanced maintenance is what is needed.
The "and 30 degrees" is included to stretch the bolt, giving a a very uniform clamping force. Once tightened in this manner, the bolt will not return to its original length if loosened. This permanent stretch is why manufacturers generally recomment against reusing TTY bolts. Will you likely get away with reusing the bolts? Sure, but a set of bolts doesn't cost that much when you look at the cost involved in redoing the job if a bolt fails or doesn't clamp correctly.
You can re-use the head bolts if they are not damaged, as long as you omit the "and 30 deg" part that is meant to crush the washer the first time. I did this during a head gasket replacement on a 6 inline engine, because I saw that the recommended replacement of the OEM headbolts was already done earlier and I did not want to spend more money than necessary to get this "mechanics special" running again. I drove it a year, then borrowed it for another year to a lady with young child who lost her car and when she returned it I finally sold it, the new headgasket and old bolts held up pretty well.
NOTE that for the pressed-on cam sprockets, the only thing that stands between you and disaster are the manufacturing tolerances of the interference surfaces!
Now go back and review how much interference (thousandths of an inch) is required, which interference is designed and how much accumulated tolerance you can get...
This is not the only place Detroit is up to something strange. I was working on a Malibu and the torque spec for the heads was x footpounds plus 30 degrees. Is that a spec? Where do I get a torquewrench that measures in footpounds and degrees?
===============
These are called Torque-To-Yield (TTY) fasteners and are not unusual.
Many years ago I was engineering manager at a small company building a line of standard machines for manufacturing plants to use in their production. Our machine shop and fabrication people wanted to eliminate the keys I had designed in to keep two aluminum arms locked parallel to each other in a steel shaft. They felt that since there was little torque involved, it would be OK.
I made it known that we would continue to use the keys period! That may have been blunt and it caused a stink up and down the ladder but I never had to wonder when a maintenance man would put one back on too loose or out of parallel. Sometimes the person in charge of the product design has to put his foot down even at the risk of being fired.
...Well...in my 55+ years of working on various mechanical and electrical stuff...pressed-on cam shaft sprockets are 2nd only in stipidity to letting people talk on cell-phones while they drive...
Some 13 years ago an engineering friend of mine told me something that explains a bit of this. "Roy" was with Texas Instruments on the team designing the control system of the yet to be released f-22. I was visiting with him one day in his home and said I'd been getting unsatisfactory performance from newly purchased computer periferals, specifically printers. I said that it seemed to me that these things weren't tested before being released to the public. Roy replied that this wasn't just a perception, that it was true: new products weren't being tested any more, like we both remembered most products had once been. "That's because," he went on, "companies no longer have field testers or in many cases, no field testing department." If that's so, I replied, then how do they determine if a product is ready for general release? His answer: They don't; they use the consumer as the field tester. He doesn't know he's the tester, but he is. That's why they encouraged people to bring an item back to the point of purchase to be picked up by a company rep or ship it directly to them with specifics about the problem. Since the selling price actually covered the cost of making 3 or more, it was cheaper to just replace it with another item -- which by the time the problem was encountered may have been upgraded -- than to have an entire department on salary to do the field testing. In company field testing also increased the time in which a product would be rolled out. Time is money in most businesses these days. All important to get your "new" product on the shelves ahead of the competition even if not the best it can be. In short: If doing it this way saved even a few pennies on each item, even if it resulted in the loss of a customer, then that was the way to go. Your business was expendible. The market was always groing; they could always get more customers. It's still being done this way.
The issue of institutional knowledge is growing now that the baby boomers are starting to retire. Some companies are trying to capture that knowledge before they leave the building. In most cases, decades of knowledge will just walk out the door on retirement day.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
2 
