According to Paradise Wheels, the turning torque of an SN series blower should be 20-25 in.lbs. That caused me to check the unit on my early Avanti since I replaced all the drive parts approx. 3000 miles back. I got 40 in.lbs. Checking the parts books, the early Avantis used load spring 1542958 and plain shim washer 1558157. Later Avantis used 1563153 and no washer. The Hawk/Lark book (green section) lists load spring 1559183 and no washer. Does anyone have the specs. for these springs, or the reason for the differences? Removing the .064" plate washers from my ball load assembly dropped the torque to approx. 30 in.lbs. This is still above the recommended range.
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"SN series blower" could include later SN type superchargers with a belleville spring washer, instead of the race load assembly with coil springs. I think the spec for rotating torque was used to make the adjustment on these, (SN93 and up?). I doubt if rotating torque is the same for all SN's. On an SN60, it would be interesting to see how it changed over time, as an indication of wear.
Although the "R2" Stude supercharger is an SN60 type, serial #'s started with MS for Avanti, or ML for Larks & Hawks. I don't know if the spring change was only on these Stude superchargers, or something incorporated on all Paxton's. Stude service letter K-1964-1, from Nov. 1963, is about the new springs. There is little information, except that they were painted red for easy identification. I put a copy up at: .
I checked my Dec '63 Avanti parts book, and the 1563153 spring is the only one listed. The 1542958 spring was listed as for a '57/'58 Golden Hawk, (VS57S), in the '61 revision of the chassis parts catalog for '55 to '58. No shim washer is listed for either the Avanti or Golden Hawk, in those parts books. Both use fourteen springs.
Mike M. -
Thanks for the post, Mike. The 1542958 spring and 1558167 washer are listed in the July '62 Avanti parts book. Since my Avanti was built in Sept. '62, it would have had the earlier springs and it does have the washers. When I got the car, there was evidence of black paint and not orange. This is generally considered "rebuild color" but on an early car,is it? There is no paint on the springs other than a hint of black. They may have been changed and the washers left in place, since the bulletin made no mention of them. I rebuilt the unit 2 years back with all new drive parts but didn't touch the spring pack. The resulting 40 in.lb. torque under operational load was causing the impeller to scuff both the scroll cover and base housing probably due to cocking of the front race carrier of the spring pack. The impeller had been properly set at .015" off the scroll cover. Removing the .064" washers dropped the torque to 30 in.lb. so I'll go with that for the time being. I recently set up a SN92 to 30 in.lbs. for a friend for drag purposes. Since the drive parts are essentially the same, apart from the method of loading the balls, I suspect the same torque specs would apply. Older drive parts would definitely raise the torque and make it difficut to get a steady reading. I'm using a 0-80 in.lb. beam torque wrench for measuring rotating torque.Comment
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I misread the date on the bulletin as 1962. Obviously most Avanti blowers would have had the earlier spring and washer setup. Incidentally, the serial no. on the Avanti blower is M121. It is specifically drilled for the Avanti mount. A spare Hawk blower I have is ML705. The Avanti blower must have preceeded the differentiation between Hawk/Lark and Avanti SN60's. On reassembling the spring pack, I set all springs "end out" rather than alternating them as specified in the bulletin. I'll have to revisit that. ThanksComment
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