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My DIY oil dipstick repair instructions

johnhefley

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My Cub has an A-75 engine, and recently my oil dipstick cap felt a bit wobbly after checking the oil. On inspection, one of the little ears, or tabs that keep it snugly in place was starting to fail. So I snapped it off to prevent it falling into the kidney tank, and decided I'd have to buy a new one.

Well, as others have discovered, finding an OEM dipstick for one of these little engines isn't that easy. My Cub Whisperer and principal in Biplane Investments (Cub wing tanks), Scot Prescott advised that Wag Aero has the go-to replacement dipstick. For information, my dipstick measures 13" from tip to inside the cap. Wag Aero's LONG dipstick would have been the appropriate replacement, measuring 13.25" from tip to "top of the cap", according to their customer service. The reviews of the quality of that dipstick aren't 100% awesome, so I kept thinking about repairing mine.

Bob Turner mentioned something on another thread about a couple of repair options - one involving some .040" thick steel he cannibalized from a household appliance, and another involving a screw, presumably through the cap. I didn't ask Bob to elaborate, but his hint that these things were repairable became a brain worm that threatened to keep wriggling around until I investigated what he might be talking about.

It turns out that I recently replaced all of my fluorescent hangar lighting with LED lighting, and had various "throw-away" bits of those fixtures. I retained one piece of sheet metal on the off chance that it'd prove useful. And it did. I quickly measured the thickness, and got .040" on one measuring, and .050" on another. I didn't bother picking the fly poo out of the pepper. It was close enough! Plus, it was painted.

Bear in mind, I'm not an engineer, a machinist, or a manufacturer of anything. I'm just an idiot with a Cub who DESPISES downtime. And I was singularly motivated to get my plane operational again. If I had tons of time (and the interest) to fiddle with a tiny project, I suppose I could have spent a few days with my digital calipers, scribes, and maybe I could even have purchased some quality tools! But wanting the plane flying ASAP, I relied on the tools at hand, my eyeballs, and a bit of hand-fitment. So this won't be one of those glorious tutorials that produces a magnificent, artful airplane part. This is Yankee engineering. Now that I know what's involved, I'd approach the project a little differently, and would make a more beautiful part. But I'll bet this is my first, and last one of these. I had no expectation of success, nor of posting a tutorial. Accordingly, I only took pictures afterward. But I think there's enough here for anyone with even feeble skills to figure it out.

Enough of the intro. Let's make a part!

1. The dipstick only has a few parts: The cap, a flat rubber seal, the locking tab disc, a spring, and the dipstick. That's it. To disassemble, hold the cap in one hand, upside down in your palm. Grasp the end of the dipstick closest to the cap, press down to compress the spring, and rotate 1/4 turn to release the dipstick base from the tabs inside the cap. Remove the flat rubber seal, the tab disc and spring. Clean all parts. For the cap, I just flushed it with avgas, and wiped it out. It was rusty, but I didn't bother trying to make it perfect. It'll just rust some more. Basically, I cleaned it sufficiently that no rust will separate from the cap and enter the oil tank. For the dipstick itself, I just hit it with a crappy wire wheel on my bench grinder that I inherited with my hangar purchase. (Note to self: replace the wire wheel and grinding wheel. They suck. Better yet, just buy a whole new one!!).

2. With the tab disc removed, you can get an idea of the likely dimensions. If your is like mine, eaten up with rust, I'd submit that the dimensions are likely smaller than you'll want for your new one. So I oversized all dimensions, and just hand-fit everything. Pro Tip: To save yourself time, measure the space between the bent ears on the cap that retain the dipstick base, and use THAT as a guide for MAXIMUM diameter of your new tab disc. The tab disc MUST insert between those tabs, whether as a drop-in, or with a bit of wiggling. The maximum length from the end of one tab to the other on the tab disc is equal to (or slightly smaller than) the diameter of the INSIDE of the cap.

3. I marked out the oversized dimensions of my tab disc with a sharpie, using the old one as a guide. I used a dremel tool with a cutoff wheel to rough cut it, and shaped it on the grinder, finishing it with the wire wheel.

4. Note that the original tab disc has a depression in it. I needed to duplicate this depression without the use of a press (hydraulic, or otherwise). Also, I figured that forming this depression would "shrink" the diameter of the finished part. Another reason to oversize it. In the absence of proper tools, I decided to bash the new part into the shape I needed. I watch a few car building shows (my favorite is Bitchin' Rides), and am always amazed at the magic of metal working. But this ain't that!!! This is caveman metal bashing! I selected a socket that duplicated the diameter of the shallow end of the cone, or depression in the old part. And I selected a socket of diameter just smaller than the outer diameter of the new part. I set the new part on the large socket, placed the small socket (approximately) in the center of the new part, and bashed the small socket with a hammer to make the depression. I overlaid the old part into the new part to judge the efficacy of my bashing, and repeated until a satisfactory facsimile of the OEM depression was bashed into my new part.

5. From here, it was all fitment. Grinding the new tab disc to size, and shape, by eye, and wire wheeling it to remove the burrs.

6. Reassemble the parts the way you found them.

7. Try it out.

Mine isn't fancy, it's not symmetrical, and it's not beautiful (but it's PERFECT to me!!). And boy, does it work!!! And my cap is more snug and secure than ever before. It took me less than an hour. If I had to make another one, there are things I'd change. Here's what I'd change:

1. I'd start with a circular template, like a socket, or the bottom of a Red Solo Cup. Something about the diameter of the outside of the oil dipstick cap.

2. I'd mark up the disc, finding the center, and would mark the disc into symmetric quarters, marking an "X". I'd ignore one full leg of the "X", and use the other full leg of the "X" as the center point of my tabs. This would aid in creating symmetry. I would also mark it up so the tabs were of equal (or nearly equal) lengths.

3. I'd figure out how to stabilize the part, and my "dies" while bashing it with a hammer. Using my original method, everything moves when bashed. I'd like the "cone" or depression to be more perfectly formed, and perfectly centered.

Questions? Email me at my username (no spaces, dots, dashes, capital letters, etc. )@comcast.net

Because I didn't take pictures with an eye toward writing a tutorial, what you're seeing below is for the most part "in progress."


jh
 
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