The absolute state of cheap engine design

[zoomzoom]

In relation to this video:

 

A few things in here really made me facepalm. It uses belts to drive the cams and oil pump, which wouldn't be too remarkable except that they're INSIDE the engine, and while I would hope that they used a special composition belt, the state of the belts in a short service life leads me to think they're pretty much standard rubber timing belts that last about as good as you'd expect bathed in hot oil their whole life. In this teardown, the belts appear to have caused the destruction of the engine.

Also, the timing belt isn't keyed to the crank. Yep, that's right, it only keeps timing if the toothed pulley remains torqued enough.

I shouldn't be surprised that this exists, but I keep wondering why it exists. Even an amateur engineer can see these obvious failure points, and yet a company with more than a century of experience in motor design has made this engine.

Some things might be easily explained by cost cutting. Not keying the crank technically saves on a machining step. But belts inside the engine?

The more sinister side to all this is 1) planned obsolescence after about 5 years, and 2) difficulty in maintenance and repair by either the consumer or 3rd party repair.

Take for example the timing belt, it's no longer a matter of simply synchronising the belts teeth to the correct teeth on each pulley. It now has an infinitely variable pulley which needs some special tools to get it synchronised.

Does anyone have any insight into the industry? I can't believe these are ideas originating with engineers, but rather the accounting department. Or is that even too generous to all engineers, is there also a culture of amorality in which they're in the business of creating the ultimate disposable consooooomer item? Let's not forget VW's dieselgate, there's plenty of engineers willing to go along with some shady stuff.

[joshuaho96]

24 minutes ago, zoomzoom said:

In relation to this video:

 

A few things in here really made me facepalm. It uses belts to drive the cams and oil pump, which wouldn't be too remarkable except that they're INSIDE the engine, and while I would hope that they used a special composition belt, the state of the belts in a short service life leads me to think they're pretty much standard rubber timing belts that last about as good as you'd expect bathed in hot oil their whole life. In this teardown, the belts appear to have caused the destruction of the engine.

Also, the timing belt isn't keyed to the crank. Yep, that's right, it only keeps timing if the toothed pulley remains torqued enough.

I shouldn't be surprised that this exists, but I keep wondering why it exists. Even an amateur engineer can see these obvious failure points, and yet a company with more than a century of experience in motor design has made this engine.

Some things might be easily explained by cost cutting. Not keying the crank technically saves on a machining step. But belts inside the engine?

The more sinister side to all this is 1) planned obsolescence after about 5 years, and 2) difficulty in maintenance and repair by either the consumer or 3rd party repair.

Take for example the timing belt, it's no longer a matter of simply synchronising the belts teeth to the correct teeth on each pulley. It now has an infinitely variable pulley which needs some special tools to get it synchronised.

Does anyone have any insight into the industry? I can't believe these are ideas originating with engineers, but rather the accounting department. Or is that even too generous to all engineers, is there also a culture of amorality in which they're in the business of creating the ultimate disposable consooooomer item? Let's not forget VW's dieselgate, there's plenty of engineers willing to go along with some shady stuff.

The lack of keying the crank hub to the crank is a cost cutting measure. Getting everything to be perfectly clocked on the crank and keyed correctly takes more time in production and assembly. Modern engines use nickel-diamond one time use washers that generate incredible amounts of static friction when torqued to spec. All of that can work as long as you do the math correctly. Obviously the problem is when you look at stuff like the BMW N54/N55 they don't do the math correctly and there's not a sufficient factor of safety to avoid spinning the crank hub when people use the DCT kickdown too often. You don't hear about Mazda's MZR/L-series engines/Duratecs spinning crank hubs and losing time en masse even though they are built the exact same way. Also let's not forget that people absolutely mangle crank keyways on RBs so it's entirely possible for the timing gear even on traditional designs to be held on purely by crank bolt torque.

Belt in oil is not the same as a traditional dry timing belt where oil causes it to fail rapidly. The belt is built for engine oil, although like timing chains if you stretch oil change intervals too far it will cause the belt to age faster. The design logic behind using those is first and foremost about fuel efficiency. Belt in oil has less friction than a timing chain. This alone is enough for most manufacturers to go for it when fleet average fuel economy drives so much at these OEMs. On top of this though belts don't transmit crank harmonics as strongly to the cams as a traditional timing chain. The belt can be narrower than a timing chain which means the whole engine can be smaller to cram more electronics in the engine bay or whatever else is fighting for space. Unlike a dry belt you don't have a bunch of oil seals on the front of the engine to separate the timing components which is another win for production time, part count, and cost. Those belts are also designed to last something like 150k mile change intervals which is about when the whole front of the engine has to be taken apart anyways. Anything that doesn't use hydraulic lash adjustment will also need a valve adjustment at the same time so either way you're doing a pretty major overhaul. RTVed front timing covers are usually also leaking pretty nicely by that point regardless, especially when engine mounts are attached to them for transverse FWD commuter cars.

Personally I think when assessing what engine/car is worth buying boiling it down to simple spec sheet comparisons like "belt in oil" vs "timing chain" vs "dry timing belt" is really not a good idea. I can show you timing chains that need service at frankly incredible intervals like the BMW N20/N26 engines that frequently self destructed themselves at 60-80k miles from timing belt stretch. I have seen RBs turn their timing belts to shreds well under 60-80k miles because of unexpected interactions like overboost fuel cut causing the belt to catch the crank trigger wheel. I can show you GDI engines like the BMW N63 that are an absolute nightmare to service or something like a Toyota M20A which is comparatively hilariously easy. It is tempting to boil the world down into "after x feature all engines suck" but it's really not that simple.