Why don't expert automobile mechanics design engines or are mechanical engineers that design engines by nature expert engine mechanics?

You need to know physics to tee to design an engine.
I know how to take apart my PC and reassemble it and do trouble shooting, but I have no idea how to design a processor or board pathway layouts.

No, they are different but related areas of expertise. One gives some level of insight and ability in the other, but expertise in one does not give expertise in the other. Not that one couldn’t learn both, and it wouldn’t help, depending too on what your design parameters were.

Nowadays, computers and megacorporate profit margins influence car design to a great degree, in ways they did not in the past. Computers do lots of calculations, and are involved in the design and engineering of modern cars. Also involved is creating an expensive product that passes modern legal regulations, and that is engineered and designed to break and require repair by the company’s own proprietary equipment, or that is only feasible by replacement with the company’s own expensive replacement modules.

I just bought a 1988 VW Fox, a discontinued line and type of car, and I was amazed by its simplicity and efficiency. The thing gets like 40 MPG and may run to 300,000 miles, and just looking at it, I can pretty much see most of the parts and they are mechanical and functional, and look like they could be fixed or replaced or swapped for something else (like a cool 1970’s Jaguar I also saw which has a Buick engine swapped into it successfully). Looking into a modern car, it’s full of air bags and computer modules etc., and there’s little to no hope of replacing much unless it comes from the factory, and unless the mechanic has a bunch of very expensive computer equipment from the manufacturer.

Mechanics are very good at following instructions, Mech Engineers generate the instructions. Engineers come up with the general parameters (big picture) that make it work, mechanics would be able to tweak the settings (smaller picture) to make it work better.

Design is a separate discipline. It is not at all clear to me that mechanics would be good designers. (or vice versa).

I’m sure with TIME, money, and the right tools, I can take apart and reassemble an engine. I’ve taken a good chunk of engine off my motorcycle to replace some gaskets no problem, and I am not a mechanic by any means. I just wasn’t scared to break something, and I had a manual.

With that being said, there’s no way in hell I can just design an engine.

And an ability to put things together doesn’t infer an ability to design. To design you must have knowledge and creativity. To put something together, the ability to follow directions is pretty much it.

Great answers above. I would guess that there are a few mechanics who would have great design ideas, and a strong understanding of the technology, but most likely they would need an engineer to actually consult with and create the final product. Within any discipline there are sometimes people who have more knowledge and creativity than the majprity of people in the field. Sometimes if circumstances had been different their education and knowledge would be different, but they might self educate themselves to broaden their understanding of the field they work in and have some strong sound ideas.

The input of expert mechanics who have to work with the final product could be useful at the early stages of the design process. Their experience with previous models might help prevent some needless design problems.

It might make sense that this bolt or that widget which is most likely to be accessed often be moved to a more accessible place within the constraints of sound structural design. Some engineers obviously did not take this step, for instance, designers of engines that were mounted in ways that many parts were difficult to access. The Previa may have been one of those.

This is such a natural and logical step that I am sure many car manufacturers already do it.

Yeah, in some cars, to change the spark plugs you have to pull the engine out!

I would bet most good engine designers are also good engine mechanics.
However, the designers have engineering skills and knowledge that a mechanic would never need, especially in materials science. Also skills in evaluating/adapting engine performance across a range of loads and conditions most individual mechanics will never experience.

@RocketGuy That is exactly what I was talking about! Which cars?

Gremlin, Monza, Astro van – genius designers.

I think that the designer has to be extrememly knowledgable, but because he or she, doesn’t have to do the labor, they do not always take into account the extra work they are putting on the machanic to get to certain areas, to replace or repair parts. Also usually the part has to be removed, to be repaired or replaced. Also the new technology of electrical systems may be easier to use for the driver, it is very costly and much more demanding work, and sometimes a puzzle to search, find, buy and repair for the machanic. Not to mention the high expense of modern technology of electrical designs. Oops, lol, sorry I got a bit carried away…