"Bumps" on the Way to 3,000 Engine Hours

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"Bumps" on the Way to 3,000 Engine Hours

Postby drdehave » Mon Aug 20, 2018 3:44 pm

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WILL MY 2007 STING’S ENGINE MAKE IT TO 3,000 HRS? I hope so; I’m currently planning some big fall trips over to the Burning Man playa in northwest Nevada, with it.

When the engine hit 2,000 hrs 2 years ago, I took my “condition checks” up a notch to include: (a) more frequent (MF) differential compression tests (DCTs); (b) MF spark plug examination; (c) MF magnetic drain plug inspection; (d) MF oil changes and related analyses (i.e., metals, either in the oil or oil-filter paper); and (e) inspections of the cylinders with a borescope. I also began eyeing my EIS numbers closer, pulling off the cowlings for more frequent inspections, and being alert to anything that could be considered anomalous.

Around 2,500 hrs, the increased diligence resulted in four “bumps in the road” to 3k. First, I started smelling dirty exhaust (only during climb-out). I feared the worst-–rings or valves “going south.” But the culprit was actually the #3 & #4 exhaust sockets leaking at the muffler; so we installed a whole new exhaust system TL Ultralight had provided (and I was saving for the inevitable new engine.) The dirty exhaust smell disappeared on the next take-off!

Second, I began finding NO oil on the dipstick, before first flight of the day, despite “burping” the engine after last flight the day before. What was going on? We soon found out: It was those new “green dot” oil filters (PN825-016) Rotax unleashed on us a couple years ago. Something was evidently changed inside them, and those new filters are no longer preventing oil back-flow in applications like the Sting's, which have an oil tank sitting higher than the engine. We confirmed this by finding a pair of the old, pre-green-dot filters (PN825-012) and testing them. Back-flow prevention resumed, just like during the previous 7 years when they were used! (If any of you have a supply of the old, 012 filters you’d like to unload, I’d pay double for them!)

Third, the #2 cylinder, which had been hovering around 80/87 psi in DCTs, suddenly dropped to 74 psi. My heart sank, fearing that this could become the new-engine trigger. But my mechanic was more optimistic: “Rich, I think I can do a valve (lapping) job on that cylinder and get it up by at least 5-7 psi.” So he did, and we got a miraculous result; #2 is now producing 86/87 psi, either hot or cold. That means I now have three 85/87 cylinders and the newly restored 86/87 one. Not bad at all, for a 2,500-hr engine!

A fourth recent scare came when two nasty-looking pieces of metal showed up on the magnetic drain plug. One exceeded 2 mm. Therefore, we had to pull the airplane from service until the source was found and resolved. The problem was a badly worn propeller shaft that had begun “making metal.” With a new shaft, and related gearbox issues restored to factory specs, my Sting is, right now, as smooth as it has ever been, even idling down to 1,600 rpm.

And there was more good news: after the valve-lapping (#2), gearbox overhaul, and new exhaust system (which likely relieved some back pressure, due to exhaust welds and soot), the Sting has gained a solid 100 rpm on WOT climb-out-–a very noticeable performance boost!

Nevertheless, she’s “on condition” and “one day at a time,” now. If she hits 3,000 hrs, I may call it a day and finally install a new engine; or I might decide to take it a notch farther. On the other hand, any “big-ticket” repairs that pop up before 3K will likely become the new-engine trigger.
Sting Flight (Flying the Sting LSA)

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Re: "Bumps" on the Way to 3,000 Engine Hours

Postby FastEddieB » Tue Aug 21, 2018 6:51 am

Fascinating. Will follow your experiment with bated breath!

Interesting about the new style oil filter. I suspect I’ve used them, but not 100% sure. Need to check, since my oil tank is slightly above my engine.

Please keep us apprised.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA

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