Plastic combustion engines and why aren't they used

[Unrest]

but the plastic combustal engine was made practical in 1980 or so! Literally making cars far lighter

It's not clear that there would be much benefit. Car buyers don't want light-weight cars and they don't want fuel efficient cars. This is demonstrated by all the over-sized and over-powered cars that people choose to buy. When was the last time you saw a 3-wheeled covered motorcycle? Many people don't need much more than that but they still buy much more.

The production cost may actually be higher. The article mentioned longer cycle times. There are also all the metal inserts that are needed on a plastic engine, but can be cast directly into a metal block.

Furthermore, this material is likely to be non-recyclable (it's a thermoset), and produced from oil (ever increasing cost). Aluminium and steel are heavily recycled, which makes them more sustainable.

 

[Unrest]

It's a good idea and it will work. But, the question is how long will it work before you encounter problems.

Yes I think that's the reason a lot of wonderful sounding ideas never end up in production. There are a million and one novel ideas for engines. Even the original Diesel engine was a complete failure. The inventor thought it would revolutionize engines, but it turned out blowing coal dust into the cylinders wasn't good for reliability.

 

[256bits]

I have to say, when I first looked at the thread title, I was expecting to see ICE's that used plastic as fuel. Haha

ICE's made out of plastic are equally impressive though. Though I don't know how long they would last. As a mechanic, I usually hate plastics in the engine bay. They almost always become brittle in the dry heat over time. Also they usually give you nice scratches all over your arms when you work in proximity to them.

There are a couple things that would be needed to take into account for this to be feasible in my eyes. One, if the cylinder heads are also made out of plastic I would try to opt for a springless valvetrain. The immense tension put on the springs from the cam would easily pop a cam bearing cap over time or possibly even crack the head... If an aluminum head is used with the plastic block, you'd have to watch the heat expansion of the head to make sure you don't pull the threads out of the block.

Not to mention, novice mechanics tend to over tighten everything. I would expect a lot of parts to crack just from the mechanic tightening the bolts.

It's a good idea and it will work. But, the question is how long will it work before you encounter problems.

I also wonder if it such a good idea - ie reliable and easily manufactured - that it hasn't caught on, less alone tried, with other types of machinery besides automobiles. Weight is a criteria in chain saws and leaf blowers, especially when using one of these in a full time occupation. Who also would not like a light portable generator to lug around in the back of his pickup?
I presume that after time vibrations would just cause the plastic engine to self destruct. I doubt if its life cycle could be made as long as a metal engine block and header, as the plastic engine would suffer horribly from fatigue. I am surmissing here, but if that is true the engineering tolerances would have to be reduced and up goes your cost of manufacture.