Camshaft

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Camshaft

This topic has 11 replies, 7 voices, and was last updated 25 June 2020 at 12:15 by Jeff Dayman.

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23 June 2020 at 16:42 #481749
SteveW
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@stevew54046
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?

picture in album

Edited By SteveW on 23/06/2020 16:45:21
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23 June 2020 at 16:42 #31647
SteveW
Participant
@stevew54046
24 June 2020 at 10:02 #481850
Kiwi Bloke
Participant
@kiwibloke62605
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…
24 June 2020 at 11:22 #481871
not done it yet
Participant
@notdoneityet
Does it have lightweight plastic valves and piston? 🙂
24 June 2020 at 11:36 #481875
Hopper
Participant
@hopper
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.
24 June 2020 at 12:14 #481880
Jeff Dayman
Participant
@jeffdayman43397
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.
24 June 2020 at 12:29 #481883
Martin Connelly
Participant
@martinconnelly55370
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
24 June 2020 at 12:37 #481885
Hopper
Participant
@hopper
Posted by not done it yet on 24/06/2020 11:22:12:

Does it have lightweight plastic valves and piston? 🙂

Ford built an all plastic car engine some years ago but never went into production.
24 June 2020 at 12:54 #481887
Neil Wyatt
Moderator
@neilwyatt
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
25 June 2020 at 11:06 #482068
SteveW
Participant
@stevew54046
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
25 June 2020 at 11:30 #482072
Hopper
Participant
@hopper
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???
25 June 2020 at 12:15 #482084
Jeff Dayman
Participant
@jeffdayman43397
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……..
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