Plastic Selection

I'm going to have an online machine shop build a part for me using a CAD drawing that I specify.

Typically, these parts are made of Aluminum, but this manufacturer also mills parts out of these plastic materials:

  • Polypropylene (PP)
  • Polystyrene (PS)
  • High impact polystyrene (HIPS)
  • Acrylonitrile butadiene styrene (ABS)
  • Polyethylene terephthalate (PET)
  • Polyester (PES)
  • Polyamides (PA) (Nylons)
  • Poly(vinyl chloride) (PVC)
  • Polyurethanes (PU)
  • Polycarbonate (PC)
  • Polyethylene (PE)

Polypropylene, I know, is the plastic used in Water Bottles, so I know that is not what I want.

This fabricated part will be used for the Clutch Cover on a motorcycle transmission and will have a raised section that needs to be tapped to allow attaching a gear shifter to, like in the Aluminum version below.

Clutch Cover with Shift Mount

I'd like something rigid and strong. Plexiglass comes to mind, but there could be a better alternative that I am unaware of, as long as I am not getting into something exotic that would cost more than Aluminum.

Is there a Chemical guy on here who could suggest a good plastic for me?

Naturally, the material would need to be oil resistant and withstand typical engine transmission temperatures.

Location on Transmission


Apparently, I never updated this thread.

What did I wind up doing? Instead of having something cut out of a polymer, I simply welded an aluminum tab to the aluminum derby cover.

Welded Tabs

Then, I hit them with some black engine paint:

Black Custom Covers

I've been running this setup for a couple of years now:

Custom Dirby Shifter

  • 1
    If you have a vague idea, it would probably be helpful to say what 'typical engine transmission temperatures' are. Most of these materials have melting points around 100-150 degrees Celsius but may soften before that. – Aesin Feb 22 '13 at 0:03
  • There is an oil temperature guage for the transmission. Theoretically, the oil can get hotter, but I've never seen it get over 210°F. I'm starting to lean towards a Vinyl. – jp2code Feb 22 '13 at 1:29
  • 1
    Most plastics melts too easy. The only you mentioned having a chance are polyuretanes and polyamides. And I will recommend aluminum anyway as it is much harder to screw things with aluminum. – permeakra Feb 22 '13 at 20:08
  • @permeakra: Maybe you could expand that into an answer by explaining why they "have a chance"? :) – ManishEarth Feb 24 '13 at 7:11
  • 1
    @permeakra: Ah. Again, you really could put all that into a short answer to the question. Comments aren't meant to be permanent. – ManishEarth Feb 24 '13 at 11:34
up vote 5 down vote accepted

Most plastics consist of linear molecules with little inter-molecular interactions, so most plastics melts too easy. The only ones you mentioned having a chance are polyuretanes and polyamides. They have (CO)(NH) fragments, that forms strong intermolecular hydrogen bonds. So, they are ones of the strongest polymeric materials

And I will recommend aluminum anyway as it is much harder to screw things with aluminum.

Glass filled nylon molds well, wears well and is most resistant to heat with regards to the plastics you mentioned

Your Answer


By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Not the answer you're looking for? Browse other questions tagged or ask your own question.