The Cessna 120-140 Association Forum

...just curious if anyone has installed this "oil pump overhaul kit" in their accessory case as an (only) "fix" for loss of oil prime at start-up? I'd sure like to solve the pesky problem without a lot of expense/down time, so just grasping at this as a possible fix. Mac

From what I hear most of the problem is a worn accessory case either from the gears rotation on the wall or worn shaft holes? Thought Don's dream machine did a repair on them? or a call to aircraft specialty.

6898 wrote: ↑Tue Nov 17, 2020 6:49 pm From what I hear most of the problem is a worn accessory case either from the gears rotation on the wall or worn shaft holes? Thought Don's dream machine did a repair on them? or a call to aircraft specialty.

Yep, that's normally at least part of the issue. I think Don Swords actually sent his out to either DIVCO or another case refurb. facility (Drake or Aircraft Specialties?). DIVCO did mine & bushed the case shaft holes...still look good. I've just now discovered actually that the new pump cover that was installed on mine @ major OH (less than 400 hours) has a casting flaw (pic, below) that may be causing some (all?) of the problem. The cavity measures in specs as do the old gears...but, I'm going to replace both the cover and gears to bring all back at least close to new specs. Time will tell. Thanks for the response! Mac

What is the source of those parts?

a64pilot wrote: ↑Sun Nov 22, 2020 9:19 pm What is the source of those parts?

The pump "overhaul kit"? Spruce, Aircraft Specialty Services, Fresno Airparts among others -- Fresno seems to have the best price @ $515.00. They're TCM parts. Mac

In this Forum under Neal Wright technical articles there is one that talks about loss of prime of the oil pump.

Check it out.

Rick

8342 wrote: ↑Mon Nov 23, 2020 5:47 am In this Forum under Neal Wright technical articles there is one that talks about loss of prime of the oil pump.

Check it out.

Rick

Yes, indeed -- that is the all time ultimate piece on loss-of-prime. I had the privilege and pleasure of talking to Neal several times as he was doing the research. We lost an incredible contributor and great friend when Neal flew West. Our own Director of Maintenance, David Lowe, and others here have a great deal of experience and knowledge in this area, too, as might be expected. In any event, my current question centered on any success anyone may have had with "just" replacing the oil pump gears/cover & it seems that none may have that experience. Meanwhile, while I have the "overhaul kit" in hand and my acc'y case appears/measures as "serviceable", I've decided to look at options for new or new(er) cases before putting things back together. Case R & R as well as "priming the pump" is no biggie, but I'm focused on solving the problem so as not to face doing either again in the near future. Mac

I can’t speak to this particular pump. but cover plate wear is a very large contributor to impeller pumps in general losing prime.
Just as a for instance it happens pretty frequently with boat motor raw water pumps, there the cover is simply a flat piece of steel and the “Fix” is to turn the cover over.
Boat pumps are a single rubber impeller, but the mechanics are similar, it’s amazing to see just how little wear it takes for a boat pump to lose prime.
Obviously air is much less dense so even a tiny air leak will prevent priming, and oil is of course much more dense than water, especially cold oil.
Seeing as how it’s a TCM part, it’s likely they manufacture it for a reason. I’d do it, I don’t see a downside?

On mine it takes about a good 5 sec or so for oil pressure to come up at a 700 ish idle speed on a cold motor, other motors I’ve had its pretty much instantaneous. Big Conti’s and Lycomings.
So is 5 sec or so normal for our little motors, or am I at the beginning of an issue?

Jody wrote: "...or am I at the beginning of an issue?"

Appreciated insight and advice...so, no, you're right on time. Thanks. This engine had historical loss-of-prime issues prior to a major overhaul less than 400 hours ago. The acc'y case pump shaft bores were "bushed" (photo) then & new cover installed over the serviceable pump gears. It's worked fine...up until the last 30 hours or so. And, while the shaft bores and pump cavity all look OK (bushings noticeably grooved, however) & measure good, I'm a bit gun-shy about trusting the new gears & pump to solve the issue...long term. I'm looking at some used cases...but, of course, I already have a used case . Exploring having this one re-bushed. Also, considering new from TCM...pricey, of course. Again, 'preciate the shared insights and thoughts, Jody!

Interim update: The accessory case is with a repair facility in Tulsa who has a method of "adding metal" (welding) and machining the oil pump back to new specs. Not everyone is capable of nor wants to "mess" with these old magnesium cases, of course, so I was happy to find a respected shop who can/will (a referral from a fellow member here, incidentally -- what a great value this 120-140 family is ). Time will tell if this + new pump gears & cover is the answer -- I'll report back. Mac