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Press Fit Pulley - Steel or Aluminum?

Given a power steering pulley that is press fit onto the end of the pump shaft and retained only by the press fit. Given that a power steering pulley would need to be removed for when/if the pump has to be replaced or for other types of repairs. I.e. maybe

3 or 4 times during the life of the vehicle.

Can someone expect the same length of service from a aluminum pulley as they might from a factory steel pulley?

The main concern being that a couple cycles of removing and reinstalling an aluminum pulley would lead to excess clearance in the pulley where a similar set of cycles would not cause the same in a steel pulley.

The aluminum pulley would be machined from a block of aluminum. The steel pulley would have a forged center hub with the pulley itself welded onto the forged hub.

Is there any validity to the concern? Are there steps you can take when making the aluminum pulley to reduce or eliminate the effect?

Reply to
Mike H
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A taper fit hub with a pull up nut, or a keyed hub, tapered or straight would serve

Brian Whatcott Altus OK

Reply to
Brian Whatcott

...

Thanks for the response.

In this application, the shaft is straight and is not keyed, thus due to the aftermarket use of the p/s pump, the shaft can't be keyed. Thus the aluminum pulley hub has to be pressed onto the shaft using a common automotive tool. Here is a good link to an explination on how the steel units are removed, reinstalled and the tool used. The pictures may be helpful.

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The main concern is that it may not be possible to design a aluminum version of the pulley as a direct replacement due to the press fit on the steel shaft, thus the effort used to remove and install will over a couple cycles of on/off will cause the aluminum pulley to no longer fit properly.

Since the concern is coming from people that just have a gut feel, and no real engineering knowlege of steel vs aluminum it's hard to know if the concern is valid.

Reply to
Mike H

If budget and space allow, with these devices you can have an interference fit with no press or special tools...

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You may be able to take advantage of the difference in thermal expansion between steel and aluminum to effect a shrink fit. A 300F temp rise will yield about .002" differential expansion.

Ned Simmons

Reply to
Ned Simmons

Keyless expanding bushes, that's the approach I should have mentioned.

Shrink fit is wonderful going on - but not so wonderful coming off.....

Brian Whatcott Altus OK

Reply to
Brian Whatcott

But it may be practical in this case due to the considerable differential between the steel shaft and aluminum pulley. A .001 interference at room temp becomes .001 clearance at 300F.

On the other hand, how hot does the pulley get in use under the hood?

Ned Simmons

Reply to
Ned Simmons

Ned Simmons wrote: ...

The shaft of the pump is likely to be around 180F give or take due to the fluid running throught the pump and ambient air temps, not ot mention the proximity of the exhaust manifold.

The biggest place for concern is that removing and reinstalling an aluminum pulley a few times is going to result in excess clearance and defeat the press fit. Using the tool linked to in the previous post, there is a fairly significant amount of force required to remove and reinstall a p/s pulley. They don't see as much load, as say a crankshaft damper (which is press fit with a keyed shaft)

The item above looks decent enough.

Reply to
Mike H

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