Lower Crank Pulley Bushings: Polyurethane or Silicone?

[wurd2]

As part of my Mach1 rebuild project with a terminator engine, we're rebuilding the lower crank pulley component. Since this component's rubber bushings are no longer available from Ford (lame), we decided to get some material from McMaster-Carr and cut our own bushings.

I found two ideal tubes with the right diameters, one being polyurethane (part 87235K12) and the other being extreme-temperature silicone rubber (part 5546T56).

Both of these tubes have a durometer hardness of 60A (medium hard).

Taken from McMaster-Carr's site, here's some relevant information about their polyurethane:

Temperature Range: -20° to 185°F
Tensile Strength: 40A tubes are 850 psi; 60A tubes are 4000 psi; 80A and 95A tubes are 6500 psi; 90A tubes are 5500 psi; 75D tubes are 7500 psi
Use indoors

And here's some information for the extreme-temperature silicone rubber:

Temperature Range: -60° to 500° F
Tensile Strength: 700 psi

I'm leaning towards the polyurethane, but I'm somewhat concerned about the indoor use and lower temperature rating.

Anyone have any opinions or recommendations?

 

[cj428mach]

I'm going with silicone on mine. I have bought a Poly and Silicone from McMaster-Carr and I don't believe the sizes people list are correct as they all list US standard size and they're probably actually Metric. I cut some and pushed them into my lower and they fit tight and the tribar fits really tight into the bushings after they're installed. I think it'll last for a long while.

 

[oldmodman]

Just going by the fact that both materials are listed as the same 'hardness" but one is stable at four times the temperature of the other I would go with the silicone too.

Do you think that you could have access to the assembly while it's on your car? So if you needed to you could do a swap out while the part is in service?

Post up some pics during your replacement process. It would be interesting to see how tough a job it is to do.

 

[wurd2]

Just going by the fact that both materials are listed as the same 'hardness" but one is stable at four times the temperature of the other I would go with the silicone too.

That's 2 votes for silicone and 0 for polyurethane.

Do you think that you could have access to the assembly while it's on your car? So if you needed to you could do a swap out while the part is in service?

I'll have to get back to you on this, but I'm pretty sure you cannot swap out the bushings while the component is assembled and attached to the timing cover.

Post up some pics during your replacement process. It would be interesting to see how tough a job it is to do.

I will definitely do this. I can tell you right now that we used 3/4" drive tools, along with a cheater pipe, to break the tri-bar piece loose. And if you're looking to replace the bearing, which we've done, you'll be grinding some burrs off to get the old bearing out.

 

[hotcobra03]

When I did mine I just used rubber hosing..

mine however needed new post which I had to custom make 3 the same.

its been a couple years now and its still holding tight..

good luck getting unit apart. .tri-bar is as tight as removing from car..

caution when using heat..it might take threads with it and it also is reverse thread