. The "overhaul" of my accessory case didn't work out. Due to a combination of issues the shop could not accomplish the "weld & machine work" to my magnesium case that I had been assured they could & would. Good folks, and very good communication I'll quickly add & we remain friends!Moving on then and referred by the original shop to a quality "salvage" dealer, they had a low time/good condition accessory case (aluminum -- yay!), but it's for an 0200 "D" engine. That engine apparently came supporting only an electric tach, so for my C85-12 this "D" case would have to be modified/machined-- bored for the tach drive gear + mounting studs. I didn't have faith in the "guarantee" that the mod would be to exacting specs, so decided against that option, plus the case pt. # might require a "field approval"(?). Too, the ultimate cost would probably approach that of a new case.
The next step(s) included squeezing the piggy bank & trying to purchase new @ approx. $1,600.00+...or, to locate "serviceable". No new available...in the world, right now! I'm told that TCM had experienced an issue with their foundry molds at some point in recent history and had re-purchased every case from all of their distributors for building TCM's own factory engines. While they promised (and, continue to promise as of this date) to make more "spares" and ship, it hasn't happened. Spruce, Aircraft Specialties and all of the big names had none...and, can't promise when (if?) they will get any. On to finding "serviceable" & searching for ANY of the applicable part #s (there have been 8 superseded since the original #6726). Ebay, Trade-A-Plane, Barnstormers and other "normal" places turned up very few -- one in California, one in Argentina, and one in Georgia, off a 150. ...turns out that the Georgia owner and I have a mutual old friend plus he's been super helpful! His is low time & in good shape -- I now have that one. )
With all of my "experience" (owned/flown for this 140 37 years) and research to date I'm convinced that 99.9% of "total" loss-of-prime is due to worn pump cavities. That can come via an event(s) that allows metal to circulate & cause "grooves"/erosion, or just plain old use and time, or combo. As the cavities wear and allow for excessive gear movement, the shaft holes wear as does the pump cover, gears and gear shafts. The wear and ever-increasing space means that loss of prime is inevitable and will only get worse. One highly respected individual RE small Continentals, Harry Fenton, has been quoted as saying that "the old magnesium cases eventually may actually begin to rot"(?). One "approved" and, probably, temporary/stop-gap fix is bushing the gear shaft holes -- at least one of the major machine shops can/will do this...but, some say that the bushing material may wear even faster than the original casting did(?), 'though combining this with the installation of new gears/cover might help extend the inevitable(?). The use of single weight oil initially, and a willingness to "prime before each start" is certainly an option for those willing to put up with the inconvenience. ...an interesting side note -- the "new" Aeroshell "Plus" W100 oil supposedly has a special additive that helps "add" residual lubrication to those bearing areas that may get a bit hot when starting without initial/proper oil flow. Worth an extra buck or two for oil -- maybe so, maybe no? I still cannot answer why it seems that some seem to never have the issue -- maybe a better "metal mix" @ the foundry(?), luck at not ever having any particles make it to/through the oil pump(?), fastidious attention to regular oil changes(?), use of "premium" oil (whatever that may be -- opinions vary widely!)(?)...or, just plain old good fortune(??). There's some reasonable indication that the addition of a filter may cause a delay in pressure indicating but, again, the issue here is total loss of prime between flights.
The contrast 'twixt my old case and the replacement case is absolutely evident, visually and via measurements. Mine does yet meet minimum specs, however. Like my old case, this replacement is also made of magnesium (all of the early cases were), but it's significantly low(er) time and really hardly worn. The pump gears that came with it are also like new, 'though I'm using the new gears & cover "kit" that I already had. Cessna did have Continental include a threaded bore on the left/lower side for adding an air/oil separator on some of the 150s -- this one has that & my old one did not. That's not an issue & they're interchangeable, of course, but of interest (to me, at least
).As more and more of these old cases reach maximum wear to a point that a lot of folks are seeking solutions, let's hope that some new cases will be coming to the market. With today's worthless money, $1600.00 + tax/shipping is almost reasonable. I'm not saying that there aren't some good cases "out there" in "someone's" shop or hangar, but with a great deal of hard work and energy, I surely couldn't find them! I expect that there are still a lot of "major overhauls" with "serviceable" accessory cases & gears reinstalled that may or may not last. This could well become (even more of) a major issue, and expense for many with these little "old" Continentals. Please keep in mind, however, an admonition we see from John C. from time to time: "YMMV", and some (many) do make it to OH without facing the loss-of-prime issue.
We've now got'er all reassembled and flying. It's cold here now so we haven't done a lot of start-ups and flying but, so far/so good. Oil pressure is & has always been excellent at idle and at cruise and, now, there seems to be no "loss of prime" at start-up, even after several days between starts. Time will tell. Apologies for the long read!
Mac
Epoxies have come a long was over the years. Some were used judiciously in the NASA Apollo program - my company used it to repair large patch boards that interconnected all the booster system wiring. Most all consumables had shelf life requirements and were tossed when expired - so I obtained a tube, thus, and brought it with me when I left Canaveral.
), David Lowe was involved in a bit of related "research" back in the early 90s. He had completed a major on an Assoc. Prez's 140 engine and, soon after, it was losing prime 'twixt flights. Re-pulling the accessory case, inspecting the bores and gears revealed that all was still "within specs". ...head-scratcher. The instant fix (again, as I recall) was a switch from Aeroshell 15-50 semi-syn to 100AD. David then coincidentally mentioned a local (KY) machinist who was doing some experimenting with some sort of "epoxy build-up" to the pump case to tighten up the tolerances.....and, best I recall, that didn't proceed toward a practical "legal repair". Again, I think you're focused on what yet could well develop into a workable solution. And, as you indicate, David has accomplished a LOT in terms of practical STCs to enhance safety and airworthiness -- maybe this is still on his BIG "rountoit burner"(?). Too, and I know you'd agree, in addition to the several major repair facilities, we have a number of fellow members with the ability, expertise and experience to probably punch through experimenting with practical solutions...however the time, expense and anticipated regulatory hassle tends to temper any enthusiasm for making it a major focus. (Too bad this cloning deal hasn't worked out to produce several David Lowes "working for us" ! 
). So, as you suggest (and, if available?), oversize gears just might be the ticket for tightening up some "cases". Do you know if oversize pump gears may be available...or, if anyone out there might practically produce? Mac