flyrotary@lancaironline.net Mailing List Archive

Yes, the bolts loosened and backed out; however, if I read Lynn’s and other’s analysis correctly, it is likely caused by over-tensioning the belt which elongated the mounting holes.

So, more bolts are better but an over-tensioned belt will still damage the pulley.

Live and learn … that’s why it’s so important to contribute to this list … hopefully my mistake won’t be repeated by myself or anyone else.

I really appreciated the feedback on this one.

Jeff

From:	bktrub@aol.com
Subject:	Re: [FlyRotary] Re: Water pump pulley departed in-flight
Date:	Thu, 04 Aug 2011 18:52:58 -0400
To:	flyrotary@lancaironline.net

So the bolts backed out? I am using SS allen heads bolts and they are safetly wired. I also have a serpentine belt, and the pulley, instead of being cantilevered, is more like the wheel of a modern car, and the pulley is run off of the smooth side of the serpentine belt. But, I only have one belt running the alternator and water pump.

Brian Trubee

From:	"Al Wick" <alwick@juno.com>
Subject:	Re: [FlyRotary] Re: Water pump pulley departed in-flight
Date:	Thu, 4 Aug 2011 16:46:51 -0700
To:	"Rotary motors in aircraft" <flyrotary@lancaironline.net>

Excellent analysis Lynn. Very strange design for a pulley to have the load so far from the bolts. Tremendous moment on that thin sheet metal. Easy to over tighten the belt and then you are screwed.

More fasteners, fine. But I'd sure focus on measuring belt tension.

-al wick

----- Original Message -----

From: Lehanover@aol.com

To: Rotary motors in aircraft

Sent: Thursday, August 04, 2011 7:35 AM

Subject: [FlyRotary] Re: Water pump pulley departed in-flight

Notice the offset of the pulley vice the flange centerline. The bolts are in shear for driving forces (very light) and in bending for belt tension (slightly higher load) so the little guys are working hard, and more bolts is a better answer. Racers run the single belt with the stock alternator location, and just about 30% of the water pump pulley engaged with no problems at all, so loads are light. I use bolts in all 8 holes with Locktite. If your pumps have only 4 holes, add 4 more and tap. And actually measure belt tension. There are stock two sheave water pump pulleys, where you run the alternator and, or, air conditioning with a two sheave crank pulley. And there is a belt length that you can run the water pump from the Mazda Competition pulley (smaller diameter) with no idler at all and perfect belt tension.

No pulley failures since that first one in 1980, (with 4 bolts).

Lynn E. Hanover

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