Plastic engines

[TheEnemy]

I am not aware of any plastic that doesn't deform under stress. Also, I mentioned that

unless it has a metal structure that is then covered in plastic that the head, and bearings bolt to,

Which I can't tell if they did or not.

I don't know if carbon fiber has the same issues with stretching as plastics, but if it doesn't then that would be a truly light, if not expensive as heck engine.

[Christ]

Truly expensive.

From what I've been able to glean through limited reading and images, I don't see that there is a structure that is molded into the plastic, but it appears that there are two structures on the block, a bedplate for the crank which also has the sleeves, and a cap which installs on the block deck, then a matching cap which installs on the lower deck surface of the head, so that when the head bolts are installed, everything (including the composite block) is compressed together.

I have decided through thought exercises that a potentially better design would be to have a bedplate for the crank bearings, with only a small portion of the sleeves attached, and a groove into which the upper deck plate (which now contains the majority of the sleeves) fits. There are two good designs which could be used to mate the upper and lower portions of the sleeves, namely stress fracking, which creates uneven, but uniform mating surfaces, but is potentially timely and not always predictable, and groove/insert, in which one sleeve's ID is widened while the other portion's OD is reduced so that they interference fit together.

The reason I feel this to be superior to what I've seen is that the piston's travel never reaches a certain portion of the cylinder, and that portion of the cylinder is where the two portions of the sleeves could be mated. The sleeves having to mate each piece of the upper and lower plates prevents the plastic from being strained, and ensures that stresses are somewhat evenly distributed between upper and lower deck surfaces.

[TheEnemy]

I was figurin that the head (metal) would bolt to the cylenders, and the main bearings would also bolt to the cylenders. The plastic portions would hold the oil and coolant in where its needed.

One thing to note it that the engine pictured was an expereimental race engine, if it lasts through the race thats good enough for them. What I find interesting though is it wasn't a plastic part that failed.

[Christ]

Originally Posted by TheEnemy

I was figurin that the head (metal) would bolt to the cylenders, and the main bearings would also bolt to the cylenders. The plastic portions would hold the oil and coolant in where its needed.

One thing to note it that the engine pictured was an expereimental race engine, if it lasts through the race thats good enough for them. What I find interesting though is it wasn't a plastic part that failed.

Wouldn't that be the way, though... LOL.

My suggestion comes from casting the cylinder heads in plastic, also, and bonding that plastic to the metal "caps" which form the combustion chambers in the cylinder head.

Of course, I have no clue who to send a suggestion like that to.

[Christ]

I also suggest that for a DIY'er, plastic is probably a more viable option to prototype engine parts than most metals, and can be had in larger quantity by digging through your neighbors' trash! LOL.

Considering that grocery bags get thrown away in the thousands every day in many communities, and they melt easily in olive oil at ~240* (as opposed to 1000+ for metals), and reform into a very dense plastic, which can then be chemically plated or coated with high-temp ceramics, etc... all things that a DIY prototype engineer could achieve in his home "lab".

[Christ]

I also still question the viability of self-lubricating plastics such as Nylon or Delrin for use in very slow-speed engines.

[shovel]

I really don't see what the difficulty is.... you make the actual "engine" (cylinder sleeves, head, valvetrain, crank, and a little webbing to hold them together) out of metal as usual and then wrap the whole thing in a cast plastic jacket with lubricant/coolant channels. Sounds pretty simple to me.

[Frank Lee]

The point is...

[shovel]

Originally Posted by Frank Lee

The point is...

plastic weighs less, costs less, and potentially requires less machine time than steel?

this is, after all, the age in which Mazda re-engineered their rear view mirror to save 15 grams.

[Christ]

Requires much less machine time, that's for sure. Even the most dense composites can be cut with carbide tools in a very short time compared to steel. Aluminum is better, but still not as fast.