Camshaft

Camshaft and timing gear from a 120cc 4 stroke. I’ve not seen this in an engine before. What chance of a 3D print of something like it for a model?

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Edited By SteveW on 23/06/2020 16:45:21

Good grief! Either it's the result of some pretty fancy materials development, or it's been designed to fail just outside its warranty period. I suspect the latter...

Does it have lightweight plastic valves and piston? 🙂

There's some fine engineering coming out of China these days. Obviously it does the job. Roller tappets or flat tappets, in steel or matching plastic? And side valve so valve train weight and spring pressure is low?

I guess the average lawnmower runs one hour a week for half the year so about 125 hours over 5 years. Probably last that long . Then you buy a new one.

Briggs and Stratton have had plastic gears and cams in their high volume production engines for at least 18 years. I had one such engine on my mower for 17 years, used 2 1/2 hr per week about 6 mo of the year. Never had a minute's trouble with that engine's internals, and it was running perfectly when I sold it. Last year I had an identical one 18 years old cross my workbench with extreme cylinder and valve guide wear, from running in a sandy area without an air filter for several years. During strip down I noticed that there was no visible wear at all on the plastic cams or gear, they looked just like the day they were made.

Intuitively after years working in the plastics / tooling side of industry I would say plastic was not a good choice for engine gears and cams but it obviously works when engineered for the loads and temperatures it sees with the right type of plastic, the right lubrication, etc. Nothing wrong with it if done correctly, in my opinion.

I've got a Briggs and Stratton engine on my mower and I don't know how old it is but 20 years is probably the minimum. The engine still runs fine (it did have a new rubber gasket/joint/functional valve part for the carb a few years ago) but the sheet metal of the body has rusted through at least one place and the wheels are looking as though they are not going to last much longer.

Martin C

Ford built an all plastic car engine some years ago but never went into production.

My next Ed's Bench (already written) will feature a 3D printed differential for an RC car, not the same thing but I'm continualy discovering new practical applications for 3D prints.

Neil

Followers were flat and highly polished with lightweight pushrods. No signs of wear. The internals of the engine were quite high quality.

if something like it was available for a model size engine it would encourage me to have a go and I guess ,like most other model engineers, I’d be happy if it ran for 15 minutes every now and again.

Steve

It certainly would be interesting. I think it would have to be some pretty special plastic to withstand the rigours and the temperatures. Not sure if that would be available for 3D printing yet???

As far as I know, nobody yet offers a 3D printer and filament to make hi temp nylon alloys, polyphenylene sulfide, or polysulfone plastics. These are the big three candidate plastics for high heat high load applications. I think the pistons in the Ford plastic engine mentioned in an earlier post were polyphenylene sulfide with a ceramic insert on the hot side.

These plastics are available in rod and block form for machining parts out of, but they are expensive. Boedeker in USA is one supplier.

Stratasys in the USA is making 3D prints in Ultem polyetherimide, and has done for years, these are good to 200 deg C service. I just ordered some printed guard boxes for hot electrical components for a client in this material last week.

The major problem with plastics for engine cyls and pistons and valves is that they don't conduct heat well and they have high friction when running against each other.

A steel wet liner in a PPS block though, and a PS piston with PTFE faced ceramic side slippers and a ceramic top insert......maybe........