17prospective buyer

...why hasn't anyone developed a polyurethane motor mount? To me it seems an ideal material, and is stiffer on the durometer than rubber, so while it would translate to be probably less smooth than new rubber mounts, it would be a good compromise between the solid aluminum mounts (which people have said can be problematic because they allow no lateral driveline movement, putting additional stresses on the driveline) and plain rubber.

Couldn't one of the companies that specialize in automotive polyurethane products do a motor mount for our cars as a group buy thing?

I know there has been alot of talk regarding every motor mount that is currently available to us, this includes the solid mounts, the Volvo mounts, the Ford mounts, and the stock mounts.

Ducman82

good question. i know the early mounts would be easy...

Speedtoys

Are the rubber mounts somehow too soft?

tmpusfugit

polyurethane motor mount? I don't have any thoughts directly related to 928's, but I have some other cars where originial rubber based motor mounts have been replaced with polyxxxxxxxx compounds. Very poor results, I destroyed about 3 sets of the before I went back to rubber, and I have stayed with rubber, no failures for several years now. The polyurethane mounts do not tolorate oil, heat, or higher HP very well in this other engine mount....when hot, they get soft and rip apart quickly, while the rubber mounts tolerate it well....

928porschepatrick

Polyurethane is a unique material that offers the elasticity of rubber combined with the toughness and durability of metal. Because urethane is available in a very broad hardness range (eraser-soft to bowling-ball-hard), it allows the engineer to replace rubber, plastic and metal with the ultimate in abrasion resistance and physical properties. Polyurethane can reduce plant maintenance and OEM product cost. Many applications using this ultra-tough material have cut down-time, maintenance time and cost of parts to a fraction of the previous figures.

Urethanes have better abrasion and tear resistance than rubbers, while offering higher load bearing capacity.

Compared to plastics, urethanes offer superior impact resistance, while offering excellent wear properties and elastic memory.

Urethanes have replaced metals in sleeve bearings, wear plates, sprockets, rollers and various other parts, with benefits such as weight reduction, noise abatement and wear improvements being realized.

ADVANTAGES TO POLYURETHANE


Abrasion resistant
Parts made of polyurethane will often outwear other materials by a margin of 5 to 50/one when severe abrasion is a factor. It has been proven to be vastly superior to rubber plastics and metal in many applications.


Oil and solvent resistant
Polyurethane has excellent resistance to oils, solvents, fats, greases and gasoline.

Load bearing capacity
Polyurethane has a higher load-bearing capacity than any conventional rubber. Because of this characteristic, it is an ideal material for load wheels, heavy duty couplings, metal-forming pads, shock pads, expansion joints and machine mounts.

Tear resistant
Tear-strength ranges between 500-100 Ibs./linear inch, which is far superior to rubbers. As a result, urethane is often used as drive belts, diaphragms, roll covers, cutting pads, gaskets and chute liners.

Weather resistant
Polyurethane has outstanding resistance to oxygen, ozone, sunlight and general weather conditions.

Excellent noise abatement properties
The hard urethanes are now being used as gears in products where engineers desire sound reduction. The soft urethanes are used to replace rubbers for improved sound/vibration dampening.

Flex-Life
Most formulations offer extremely high flex-life and can be expected to outlast other elastomer materials where this feature is an important requirement. Dust boots, bellows, diaphragms, belts, couplings and similar products are made from urethane for this reason.

Electrical properties
Polyurethane has excellent electrical insulating properties and is used successfully in many moulded wire and cable harness assemblies.

Heat and cold resistant
Continuous use above 225°F is not recommended nor is urethane recommended in hot water over 175°F. At low temperatures, polyurethane will remain flexible down to -90°F. A gradual stiffening will occur at 0°F, but will not become pronounced until much lower temperatures are obtained.

That sounds good.

Speedtoys

Many of those benefits are for products not applicable to a urethane mount material.

AO

Given the proximity of the mounts to the exhaust headers, I'm not sure how well they would hold up given the heat. But if properly shielded, they might work.

The one thing I can think of is that urethane is poured whereas rubber is heat molded. So urethane is better suited for low-volume production and rubber is better suited for higher-volume. Given the availability of low-cost substitute motor mounts and the relatively low-volumes such a product would generate, I see little incentive to go through the development cost of a urethane-based mount.

backnblack

This material may work for something like that. We made a oil defector for a valve cover for GM that was ran on the car and held up. It is als very high impact resistant.

17prospective buyer

The above material a couple of you have posted regarding the qualities of poly are all ones which i am aware of, which is precisely why i wondered there was still nothing available for 928's. There are ones for Mustangs but "AO" you are probably right regarding the unfeasability of going through the process of R&D and product samples and still being able to sell them at a reasonable price point that is competitive with the alternative mounts and deffinitely competitive with the OEM mounts.

They did only make approx. 61 000 928's, and that's over what, 18 years just about? Ford makes/made that many Mustangs in a single year, i think they actually make/made about 150 000/year!

That's what i hate about these cars, very limited aftermarket support. ESPECIALLY compared to the Camaro/Firebird/SBC 350/Mustang crowd. Yes i do know it is a Porsche and this is the reason why, but it still bugs me.

Another reason i thought a group buy could make it feasable is that some transmission place made a bunch of 3.06 R&P's for a handful of 928 guys here, so i thought hell, poly motor mounts should be easy compared to that!

destructo_low

I'll design something and have a prototype in two weeks.

17prospective buyer

I like the way you think!

destructo_low

It's 90% complete in Solidworks right now. I need to get under my car with my caliper and get accurate dimensions of the engine mounting area for the mount. I'll upload some screen shots tonight.

dr bob

Invest some similar time in replacement transmission mounts, please, where there is no reasonable alternative to the $$$ Porsche pieces. Yet.

destructo_low

Here is the design.

It uses a universal Prothane bushing. It is a two piece bushing which will ride inside a piece of tubing on the mount. It also has a metal sleeve.

Tube Length: 2-1/2"
Bushing O.D.: 1-1/2"
Sleeve Length: 3"
Bolt Size: 9-16" (~14mm)



Any qualms? It mounts right to the engine and to the cross member. It is the same height as our original mounts. It is made from 7 gauge (0.179") carbon steel. They can also be made from stainless steel. They could be powder coated your choice of color. I could probably make these for $75 to $100 dollars a pair. That is in line with the rubber mounts and vastly cheaper than the solid mounts.

17prospective buyer

Looks solid to me, of course i'm no engineer so who am i to judge. But maybe another bolt to secure it to the crossmember? There would be alot of leverage and strain on that bolt with the weight and torque of sudden throttle opening.