I have the 3-blade McCauley Top Prop conversion on my Sierra. The spinner sits much closer to the cowl opening; probably a good half-inch closer. This may be great from a drag standpoint. But it is murder trying to get the lower cowl reinstalled without scraping something on the LH side of the spinner or cowl. What’s the secret?
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Technical Editor:
You might wish to consider shaving the forward lower edge of the LH engine baffle metal. The spinner on the McCauley is indeed positioned about a half-inch closer to the cowl nose opening. The lower (bottom) cowling is very difficult to slide into place behind the LH aft side of the spinner, without scratching both the spinner and the cowl nose, unless something is done to increase the clearance. If you view the RH baffle, you will see that its forward edge is much further aft than on the LH side.
The modification is very simple. On the forward edge of the LH lower baffle metal there is a strip of soft baffle material, held in place by a narrow retainer strip of metal. The retainer strip sandwiches the soft material to the main baffle metal. Your shop just needs to draw a line down the aft side of the existing retainer. Then remove the retainer and baffle material, and trim off the leading edge of the main baffle metal, along the marked line. This can be done in a number of ways. You can use a hand-held metal hacksaw blade; air-driven cutoff tools; a body saw; or whatever works for you. Just make sure that the resulting edge ends up straight and smooth, without a lot of tool marks.
This usually results in the removal of about a 5/8” wide metal strip. The original soft material and retainer are riveted back in place, unless you need to replace them due to poor condition. The original cowl clearance is so excessively tight in that location that the soft strip has often been cut by abrasion. The normal method for reattaching the seal and retainer is by the use of soft A-Type universal (round-head) rivets. These soft rivets can easily be set with a smooth-jaw, parallel-jaw plier-wrench, such as the Knipex brand. These standard non-structural aviation rivets provide a professional appearance to the finished job. They are also easily removed when all the engine soft baffle materiel is eventually replaced. Since this is a non-structural application, you can also use common (but quality branded such as the ‘POP’ brand) “pop rivets’. Do NOT use structural CherryMAX blind rivets, or someone will regret it when the day comes for new seals. Not to mention the very high cost of these structural blind rivets. If you do use the common pop rivets (and some shops do), you should probably use an aluminum back-up washer under the shop head, beneath the baffle metal. These rivets have a lower-strength aluminum than A-type universal rivets. They also will not deform during setting, to fill misshapen holes, and may pull out from vibration if the backup washer isn’t used. Do NOT use a steel backup washer, nor rivets with a steel body or steel stem; only all-aluminum rivets.
You will find that the resulting new seal ‘fit’ is still ‘tighter’ than on the RH side, and the cowl will seal perfectly well. More importantly, you will then be able to R&R the lower cowl with ease.