Airplane Owner Maintenance

A Maintenance Oriented Podcast For Airplane Owners, Pilots, and Mechanics

Tag: compression

222 – How an Engine Cylinder Went From 25/80 to 75/80!

May 13, 2023 /

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I inspected another A36 Bonanza recently, and one of the cylinder compressions was too low… lower than the minimum prescribed by Continental using the master orifice tool.

I had two options:

Option One: Remove the cylinder for repair or replacement.

Option Two: Make the exhaust valve seal better and improve the compression result in hopes of saving the cylinder from premature amputation.

I chose Option Two.

It was at least worth a try…

… and the result was stunning!

After lapping the valve in place and installing a new rotocoil, I ran the engine again and rechecked the compression.

It was 75/80!

The lowest cylinder on the engine was now the highest cylinder.

I also lapped the exhaust valve in cylinder #2, and that one improved from 49/80 to 63/80.

If you’d like more info about valve lapping, click here for episode 109.

Another surprise during the inspection was a cracked / leaking exhaust riser.

Here’s a close-up view of the bad area:

Also in this episode, I talked about some other squawks that were repaired during the inspection. Be sure to listen to the audio for all the details.

In Part Two of this episode, I talked about our most recent trip in the King Air. It was quite an adventure navigating some weather situations!

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172 – A Perplexing Low Cylinder Compression on a Piper Saratoga

March 26, 2021 / / 0 Comments

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12/80! That’s a terrible compression test result. And unlike some cylinders, this one did not show any obvious reasons for the low compression… take a look at the valves after the cylinder was removed:

Unless I’m missing something, I don’t see anything that would explain such a low compression number. The cylinder has been shipped to Tim Barnes at Skyline Cylinders for repair, so I’m hoping he will be able to give me more information about it. You can listen to the audio for more thoughts about this whole experience, and maybe I’ll give an update on it in a future episode.

I also mentioned in this episode my latest project in the shop at Classic Aviation – an annual inspection on a nice E33A Bonanza:

It’s a great airplane, with a great owner – now that’s a good combination!

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170 – Eddie’s Jabiru Cylinder Compression: From 0/80 to 70/80!

March 5, 2021 / / 3 Comments

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I had a surprise call this morning… my friend Eddie called and wondered if he could borrow a borescope. One of the cylinders in his Sonex’s Jabiru engine had zero compression, and he wanted to take a look inside the cylinder, especially at the exhaust valve.

Since I’m always looking for a good story, it didn’t take me long to say, “This sounds interesting… I’ll grab my borescope and drive right over to the airport.”

We got the borescope set up and quickly noticed the exhaust valve appeared to be open a tiny bit when it should have been fully closed. There was just enough leakage past the valve to keep the compression at zero.

We’re still not totally sure about that area at about the 8 o’clock position, but we didn’t see anything alarming when we looked at the valve edge with it open.

Thankfully, Eddie had done some research online and quickly got some feedback about the importance of regularly adjusting the valves in the Jabiru engine.

Sure enough, the exhaust valve had no clearance between the valve stem and the rocker arm (it should be .010)

After adjusting both valves on that cylinder, Eddie did another compression test, and we were pleasantly surprised… 70/80! And it was even a cold compression test!

It’s always great when there’s a simple solution!

Well done Eddie! And thanks for the good story we can all learn from!

In this week’s episode, we also talk about Lycoming SI 1418, a rarely used procedure for cleaning cylinders on the engine using some special equipment and ground up walnut shells.

Listen to this concept and let me know your thoughts… hit that button over to the right and tell me if you think it’s a crazy idea, or a great idea… I’m curious about it.

Reminder: I offer a service to evaluate your borescope photos. If you are not sure what your pictures mean, send them to me and I’ll evaluate them and send you a report within two days.

Rates:

  • 4 cylinder engine: $50
  • 6 cylinder engine: $70
  • Twin engine: $100

Click here to make your payment.

Then email me your borescope photos, and I’ll send you a report.

dean{at}airplaneownermaintenance{dot}com

Thanks everyone, and have a great week!

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