plastics material advice?

[928ram]

The background: A shifter part on my 928 needed replacing, but I being both cheap and up to a challenge decided to rebuild and improve the factory unit. I basically hand-made the plastic bushings from some 1/2" sheet I had around, which I believe to be nylon.

Step 2: I'm just about done making a cutter that will pop these out ready to use by simply cutting them from the sheet-stock using a drill press.

The question: What material should I use for the final unit? The material needs to be just slightly elastic (right word?), be able to accept standard automotive grease without breaking down, and be able to withstand standard underhood abuse and heat. Not sure how hot it will get yet, but the part is at the rear-top of the bellhousing on a front engine watercooler. I'm not even sure that the material I used for the "prototype" isn't adequate for the job, and don't know for sure that it's nylon (cut it out of a small plastic cutting board that's normally used around the kitchen).

[widebody911]

Cutting boards are usually polyethylene

I suggest going to http://mcmaster-carr.com under Raw Materials -> Plastics and take a look at what they have. They give a good description of the properties of each type of plastics.

[M.D. Holloway]

928RAM - Nylon may not be your best material option here. Nylon has its properties but it also has some disadvantages namely that it is not as abrasion resitant as some other polymers and it does absorb about 4-5% water. The dimensional stability can come into question for applications that are rather dependent on tigher tolerences. The machining isn't as forgiving compared to other polymers either. Some ideas would be:
1) Delrin: thats an acetal resin from du Pont, its a thermoset so once its cured thats it. You can get it in block form ready for cutting.
2) Polyurathane: many different to choose from. Some are very stable and resistant to oil and fuel and can be machined. These are considered a thermoset as well (but soemtimes they are considerd thermoplastic - long story). They can be cast into a mold or they can come in block form for machining.
3) Filled Polyetherimides: thermoplastic, these are used in everything from jet engines to food packaging. Not sure but I think you can get these in block form as well.
4) Elastollan: a polyester polyuretane from BASF. It is used in under the hood applications and is machinable. It will also have some good resistance to oils and grease. Call them at 800-892-3111. Try to get to tech service. when you get to the right person, see if they can send you a sample to test. You won't need much.

You may also want to give GE Polymer Shapes a call. They used to be Cadillac Plastics but GE bought them out. They can be reached at 866-437-7427.

Let me know what you find out.

[BGCarrera32]

UHMW, or "ultra high molecular weight" polyethelyene. Sort of a poor man's teflon. And the correct way to make bushings is with a lathe; you'll achieve far tighter tolerances and a superior surface finish which is usually critical in a bushing application.

Delrin is an excellent choice for prototype turned parts as it is very free machining, dimensionally stable, and very hard. But, it will have no give and it may not be especially slippery for a bushing application. Thom is right...try McMaster Carr first.

[M.D. Holloway]

agree with your statement about Delrin (to a point) but disagree with the McMaster Carr suggestion. They are distributors - very good, but just a warehouse. You wouldn't select you engine oil from a statement out of McMaster Carr would you? They know less than nothing about materials - call BASF or GE Polyemer Shapes. Get it from the techs that do this for a living. Plus you can get free stuff from them.

[BGCarrera32]

I now remember why I quit posting here.

[M.D. Holloway]

sorry dude, didn't relize it was that time of the month...

[BGCarrera32]

That's o.k., I wish you well through your time.

[928ram]

Thanks for all the replies, I've gotten quite an education on plastic today!

Lube, called the number you provided (thanks!) for GE, and the fellow I spoke with seemed to know exactly what I was talking about, and said a polyurethane would be the best. He must've been a car guy because he seem to have an idea of what temps I'd be facing in that location on the car. He refered me to a supplier upstate here who I can meet with in person.

Of course now plan "A" is on the shelf in favor of "B" which will be simpler and stronger; the idea being that it could be changed out in-car if need be.

[M.D. Holloway]

no problem - and I didn't mean to get BGCarrera32 upset. Sometimes the written word comes out harsher than the spoken. I will have to remember that.