N254MR

The comments function has been broken for a bit, but is now fixed. As always, your comments are welcome. To control SPAM submissions, all comments are moderated, so they may not show up on the site for a few hours. Thanks for your patience.

The first step in building the lower nose bowl rear edge shape stiffener was to transfer the approximate curve onto the back of a piece of foam core board.

The curve drawn on the foam core board was then further trimmed until it sat snugly into the inside of the nose bowl. As seen below, the foam core was cut down to a narrow strip about 3/4" high, then briefly taped in place so it could be "tack welded" with JB Weld quick setting epoxy.

The next photo shows the finished fiberglass layup. Two coats of mold release were brushed onto the blue tape before laying down four layers of fiberglass.

The next photo shows the stiffener about 3 hours after it was first glassed in... already dry to touch and quite solid, enough that the nose bowl has been released from the shaping frame. The blue tape rectangle shown above was carefully pulled out from under the edges of the fiberglass so as not to disturb continuing curing and adhesion of the approx. 5/8" wide fiberglass base flanges on each side of the stiffener. After it's fully cured, I'll sand off the 1/4" or so of fiberglass that had overlapped the blue tape.

A hairline crack had developed in the tight curve just right of the oil cooler intake "snout". The crack was visible as a thin line of light when viewed from the inside. You had to look very closely to see it on the outside. Although it's possible that contact from the oil cooler's silicone rubber baffle seal caused this crack, there was no evidence of chafing on the inside surface. The crack was probably just caused by fairly normal vibration.

The last photo is a closeup of the new fiberglass layers applied to the sides and bottom of the oil cooler intake "snout" to fix the hairline crack on the right side, and reinforce the tight, small radius compound curves there and on the left and bottom sides of this structure.

The left wing is on the operating table, ready for tank repairs. Before drilling and cutting metal, it needs to be well aired out. While waiting for several hours of tank ventilation, I got to work on another problem that was recently discovered or, more accurately, remembered, during the ongoing cowl rebuild. The problem was that the lower nose bowl's rear edge was not well shaped, not a symmetrical curvature. I forgot to get a good picture before beginning the modification outlined here, but the black line drawn in the photo below is an only slightly exaggerated representation of how it was shaped. I'm not sure exactly how it got that way, but do recall that when the cowl was originally built, Mike and I noticed the factory-supplied part's shape was a bit off when left to freely take its own natural "set", or shape. As I recall, it didn't seem bad enough to bother adding a shaping rib/stiffener at the time. Now, the lopsided shape seems to have gotten worse, at least enough to cause a change of opinion.

To reset the shape of the nose bowl's rear edge curves, a new low profile fiberglass rib/stiffener will be needed, similar to the stiffener added to the top nose bowl section. To get going on this project, the first step was to build a wood frame in which the part can be manipulated to the desired shape and held there securely during a multi-day fiberglass application.

As seen in the next photo, the procedure was to set the top, aft edges at the same height on both sides, and to level the fore-and-aft top edge horzontal lines. Trial and error and careful measurement showed that the center nutplate is actually left of the true center line. The true center point was set to the actual middle of the frame, and held there by a small nail driven down through the center nutplate, now properly offset to the left of center. That helped to slightly push out and lower the lower left corner. Shims were used under the right nutplate to push it up a bit and eliminate the unwanted bulge at that point of the curve. The new low profile fiberglass rib will go around part of the bottom curve, in the sanded area.

The corrected shape, which will be permanently stabilized and held by the new rib/stiffener, is shown below. Not perfect, but much better than it was.

With final installation of the bottom port covers today, the right wing tank repair is finally done. The first photo shows the top skin, where even the outside rivet lines were prepped so sealant under the rivet heads would be more likely to adhere properly.

The second photo looks up at the bottom port covers. This job alone, from start of the final cleaning prep through minimal tool cleanup, took eight hours. Working from the bottom up (overhead) was not fun. Will have to find a more ergonomically correct way to do that on the left wing tank. As planned, I started with the inboard bay cover, and after it was closed, I was able to check sealant coverage of the rivets from the middle bay port. Using an inspection mirror, I found two rivets where the sealant coverage wasn't optimal. Although access to them around the anti-slosh baffles was difficult, I was able to reach a hand in to squish a little more sealant around them for 360 deg. coverage around each rivet. Were the bottom ports worth the trouble, and additional possible leak points? I think so, if only for the access they provided to see and perfect the top skin sealant coverage.

After another week or more of curing time, I'll do a pressure test. At this point, it's just a relief to have this done.

Working 10AM to 10PM with time off only to eat, the right wing tank top skin was installed on this long day. Morning was devoted to final clean (power Scotchbrite) of all mating and sealing surfaces, including flange and stringer inside portions where the shop end of the rivets end up. Then all was primed with the PR-148 adhesion promoter. While that was drying, finally tool & material assembly took place. As seen below, we're ready to go with cups of various rivets, a bunch of new, acetone-sloshed clecos, gauze pads, etc., and clecos placed in strategic locations of the top skin to help line up the holes in ribs, stringers & bulkheads.

The first step was to coat all the undersides of spar, stringer, rib & bulkhead flanges with sealant -- so the dipped rivet tails would have a squishy home to meld into -- then all the top surfaces. Last but not least was coating the underside of the forward edge of the top skin that rests on top of the main spar. Not much to show of the long process, but it was good to have an awl handy to help line up stringer and rib flange holes through all the goop. I used the minimum air pressure necessary for the rivet gun to pull the rivets -- about 55 PSI.

When all the tank rivets were installed, the wing was flipped upside down, so the still viscous sealant could "sag" downward onto the top skin sealant joints, as seen in the next photo. It was very useful to have the bottom ports through which I could see all the top skin junctions (good squish coverage) and reach in to add sealant to complete a full coat all around the shops ends of the rivets.

The remaining photos look down on various parts of the top skin. First, looking at the rib between the inboard bay and center bays, along the aft bulkhead (to the right).

The next two photos are of joints in the third bay along the junction between the top skin and the outer rib.

The second tank, on the left wing, should go much more quickly.

Good progress on the cowl rebuild today, with completion of mods to the side beams, which now are shorter and sit higher on the firewall. Three new #8 countersunk nutplates on the end of each beam were reinstalled. The nosebowl is nicely centered side-to-side on the prop shaft, and is a smidge low. That's fine, because when the engine cranks up for the first time on the new shock mounts, it will probably settle a bit, and certainly will settle over time.

Next step on the cowl rebuild will be to modify the existing top beam, at which point the cowl structure will be solid once again.

Preparations for resealing the bottom "tub" of the right tank have seemed endless. Lots of steps, including the initial sanding, multiple vacuum, brush, and airgun blow sequences, roughening the original Pro-Seal with a small stainless wire brush, drilling out the 5-6 "suspect" rivets, finding them surrounded by areas of Pro-Seal with zero adhesion, rising flaps, etc. The tops of these rib flanges did not appear to have been scuffed in preparation for the sealant, which may explain the lack of adhesion in these areas.

This area, near the most troublesome junction, has been sanded in prep for resealing, and the sanding has exposed multiple pockets or voids in the original sealant.

Sanding & prepping those areas, and test probing for others was followed by another vacuum, blow gun & vacuum sequence, final power scuffing of the fresh metal adjacent to the old sealant, using the medium, maroon Roloc surface prep (Scotchbrite) discs, another vacuum, blow, vacuum, a comprehensive acetone scrub of the old sealant with a small nylon brush, cleaning up with gauze pads, a final acetone/gauze wipe over the sealant-metal junctions, then wiping the metal alone... Finally, late yesterday everything was clean, all oxidation gone, and I covered it up overnight -- knowing it must be primed and sealed within hours, before the metal surface oxdizes again.

This morning, I proceeded to apply the PPG/PRG-148 adhesion promoter (a.k.a. primer) with tiny gauze pads. (The primer base solvent is nasty, high VOC stuff, and a snug half mask with organic filters is essential, along with constant ventilation.) Primer is poured onto clean pads once and only once, so as not to contaminate the primer, and the pad is daubed and squeezed onto the surface. It has to be squished in behind each rivet tail or two, then pressed like a sponge. Each gauze pad is good for only about four inches, then it's thrown away for a newly soaked one. That took an hour and a half, and after allowing it to dry for 30 minutes, the new sealant must be applied within a few hours. The next photo shows the results in the outer bay.

The next photo is a closeup of the most difficult area, the stringers, where, using a tongue depressor as the applicator, the sealant has to be "stippled" multiple times all around each of the rivets to assure there are no air pockets and a fully "wetted" interface between sealant and substrate. The sealant is ultra gooey, of course, but still has enough of a glue-like consistency (especially near the end of the two hour work life before it sets up) that it seemed to need multiple presses even on the bare metal to fully adhere. The concept was to cover the existing, primed sealant and feather out to bright clear primed metal on either side as well. So yes, it took a lot of goo -- about 3/4 of a quart for this tub -- quite a bit more than would be required for a new installation.

It's not perfect. When all was done, I could see perhaps a dozen small spots where I'd not achieved full coverage. After the fumes clear out, I'll add more bright light for a full inspection, and catalog those places to cover when I do the top, if not before. Long day.

Work has continuied on the rebuild of the cowl to fit the new engine mount. As in the original build, the process starts by centerin the top of the nose bowl on the propeller shaft. Initially, the orientation isn't correct because the rear of the nose bowl is too low.

Hoping to reuse the existing side beams with some trimming, they're set up to check for proper sideways orientation of the nose bowl. This is a rather loose assessment, because the side beams are "sprung" wide to the outside of the firewall (FW). As expected, both side beams will be shorter. The left just enough to cut off the existing nutplate holes; the right takes more, but not enough to hit the existing rear Camlocs. Yay! The vertical position of the beams on the firewall is the tricky part. After a lot of trial and error, I determined I can raise both such that the two top original firewall flange holes can still be used, with new holes in the ends of the trimmed side beams, of course.

Trimming the beams is done a nibble at a time. Because of the FW angle, each small trim affects both the length and height of the beam.

All the while, I had to keep an eye on the angle of the front of the nose bowl to the prop shaft. To make sure everything will be in the right place, the bottom half of the nose bowl was installed at which point I found that the original bottom beam will work as is!  Yay!

While waiting for all the parts and pieces necessary to complete the tank repairs, I've been continuing to reinstall the engine on the new mount. There are lot of little details to attend to. For example, I discovered that the cap screws which mount the ignition coils have over-sized washers which easily rotate to contact the nearby engine frame. This is, shall we say, an unauthorised <g> route to ground, and may contribute to some static that's still in the radio reception. Resetting the coil gap while holding these washers off the frame and torquing down the cap screws was a little tricky.

Another example is that I've also finally gotten around to installing a new thermostatic oil cooler adapter (TOCA). Although I've so far never had problems with high oil temps -- even taking off in Montana with ambient outside air temps (OAT) of 90+F -- keeping the oil warm enough in our cool climate has been a little problematic. The procedure has been to block off varying amounts of the oil cooler using silicone baffle material. However, that's tricky to get right, and what's right changes from day to day. The new TOCA will begin to open the plumbing circuit to the oil cooler when oil temp reaches 170 F, and reach a full open state at 180 F. It wil also support larger, AN-8 size hoses so that when the oil cooler is really needed -- say, in the desert -- oil flow should be even better.

Unfortunately, the new TOCA is also about 5mm thicker than the stock OCA, so it's necessary to trim a couple cylinder head fins a smidge to facilitate getting filters on and off. I wouldn't normally be keen to trim cooling fins, but these are on the cooler, intake side of cylinder #2, where high CHT's have never been a problem, and several others have made this small mod without ill effects.