Ask Paul: The seal of approval

questionable seal

Q: We’re building an RV-6A using an O-360 narrow deck engine. There are six studs that hold this engine together. The center studs are wider at the base than the outer four studs. The case has an indentation where the seals fit. All six are counterbored. The size of the center studs at the base is slightly larger but the seal fits over the stud and rests into the counterbore OK. Should my gasket set have contained a slightly larger seal for these center studs or does this look OK?


questionable sealA: Thanks for your inquiry regarding the use of “O” ring seals on your O-360 narrow deck engine. After looking at the photos, it appears your crankcase is in compliance with Lycoming Service Instruction 1123D, which covers the “Installation of Dowels and Rubber O-Ring Seals at the Crankcase Thru-Stud Locations.”

While it was difficult to actually determine from your photos, the information you provided would lead me to believe your crankcase does incorporate the counterbores. I’d suggest you review a copy of the Service Instruction in order to actually confirm it. You should find this SI in your Avantext library. Also, any FAA approved repair station should have a copy of this publication if it maintains Lycoming engines. I think you’ll find after reviewing this publication the seal fit you spoke of is correct and no larger seals are required.

The RV6A is a very nice aircraft and I know you’ll enjoy owning and flying it.

Paul McBride, an expert on engines, retired after almost 40 years with Lycoming. Send your questions to:

Ask Paul: Use it or lose it

Q: I am considering buying a plane with a Lycoming 540 factory rebuilt engine. TSOH is 50 hours. The problem is the engine was installed five years ago with a new turbo and the owner has not flown it much since, although it has flown a few hours recently.

There is a lot of chatter about unflown engines rusting inside and not making it to TBO. I don’t need to make it to TBO, but I don’t want it to go south within the first year or two after purchase. How much of this chatter is exaggerated? Is an engine that sat like that such a huge problem that it should be avoided? Is is possible that a low-time factory rebuilt can be rendered useless that easily?

R. GASTON, via email

A: Here we go with one of those deals that look good up front, but may not turn out so good in the end. I admire you for being sharp enough to ask questions before taking the leap, but just in case you already put your money on the table, let’s look at a few things that may help save the bacon.

The “chatter” you hear regarding engines rusting inside and not reaching TBO is closer to fact than fiction. [Read more…]

Ask Paul: More on hot engine starts

Q: I’d like to offer my response to a hot engine start (What is the procedure for a hot engine start?). If I know I’m going to have a quick turnaround after engine shutdown, this is what I do: I throttle up to about 1,500 rpm, then I turn the fuel selector to off. By doing this, you use the fuel in the line and, when that is gone, the engine will shut off. This basically eliminates any vapor lock on restart, the typical cause for hot start issues.

Hot start procedures using this shutdown method should proceed as if the engine was cold. It’s worked for me countless times. Have you ever tried this method?

ANDY REINACH, via e-mail

A: Thanks for sending in your comments regarding hot engine starts. It’s always nice to get ideas from folks who have had success with things like this particular issue.

While you didn’t say, I assume you have a fuel-injected engine, which would make sense. Usually the problem of getting a hot engine to start is a result of the fuel boiling in the lines and evaporating while the engine is shut down following the flight.

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Ask Paul: Why are Piper and Cessna mag checks different?

Q: During a checkout in a Piper Cherokee, (I had only Cessna experience), I asked the CFI why Piper has me check the mags at 2,000 rpm and Cessna at 1,700 rpm on what is, essentially, the same engine?

My opinion is that it is not a deal breaker to not have exactly the rpm in question, just close, and that it is the percentage of change during the mag check that is what is really important. Can you help us understand this?

DAVE RICE, via e-mail

A: This is a question that may have crossed many a pilot’s mind as they transition from one aircraft type to another. First of all, the most important place to check for the proper procedure for the specific aircraft you are going to fly is to review the airframe manufacturers Pilot’s Operating Handbook (POH).

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Will my engine benefit from new technology?

Q: The O233 LSA engine uses the new E-mag electronic ignition that they say advances the timing to 38° BTDC, much like other systems. Does this much spark advance also have Lycoming’s blessing for the O320 and O360? I realize that the spark advance is rpm and manifold pressure controlled.

LYLE FORSGREN, via e-mail

A: Lycoming is putting forth an all-out effort to focus on new technology and the electronic ignition system is probably one of the first results of its efforts. I’m certain we can look forward to several new exciting things like this to enter the marketplace in the not-to-distant future. While we all understand the market is a bit down, it’s quite evident more concentrated efforts are being put on research and development during these slow times. While it may be difficult to justify the expense during difficult financial times, the rewards will come for all of us as the industry rebounds and this new technology is incorporated into the products of the future. Hopefully, the engines currently in operation will be the recipient of some of this new technology as retrofittable options.

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What is the procedure for a hot engine start?

Q: I have a Grumman Yankee Model AA-1 with a Lycoming O-235L 108-hp engine. What is the procedure for a “hot engine” start? When I shut down the engine, I run it lean at 1,800 rpm for about 10 seconds before I pull the mixture. Then, when the engine is cold, it starts right away. However, if I stop to refuel on my way to the hangar, it is very difficult to start and I don’t like cranking for a long time for obvious reasons. Would you be kind enough to advise me as to the proper procedure?

CARY MATHIS, via e-mail

A: Cary, this subject usually causes me to ask more questions about specific situations before I even attempt to provide an answer. I’m somewhat at a loss because you didn’t provide your engine age or history, which may provide a few clues, but let me throw out a few thoughts on the subject to see if they might help.

First of all, I’d recommend you review the airframe manufacturer’s Pilot Operating Handbook (POH) for specific “hot start” procedures. These, as well as normal starting procedures, may vary from aircraft to aircraft, making the POH the best source of information for any specific aircraft. However, some of the POHs may not explain why certain procedures are used in the starting process.

Your shut down procedure is fine and should cause no problem in restarting the engine.

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Ask Paul: Narrow deck cylinders, the Twin Comanche and a Lycoming milestone

Geez, it’s really beginning to look like I’m losing it when it comes to misstating things in my columns. The most recent concerned the “Wide Deck” vs “Narrow Deck” cylinder column in my last column.

I thought I’d explained the difference between the two and used an example of the Piper Twin Comanche PA-30 as being the first to use nothing but the Wide Deck configuration. Boy was I wrong, and thanks to my “old” friend Charlie Melot, who happens to own PA-30 serial number 410 so he would know, I was informed of the error of my ways and, with his enlightenment, returned to the straight and narrow path.

Thank you Charlie! Other than the mention of the PA-30 never being produced with Narrow Deck cylinders, the rest of the information was correct, to my knowledge.

So there isn’t any confusion, the Piper Twin Comanche was built with engines using the Narrow Deck cylinders and, as Lycoming did a rolling production into the Wide Deck cylinders, they were eventually used on the PA-30.

Let me try to explain how I came to throw out the 1963 date about the cylinders. For you old-timers like Charlie and me, the the Twin Comanche sets an important milestone as far as Lycoming history is concerned and the impact this important change had on Lycoming engine TBO times.

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Ask Paul: Wide deck vs. narrow deck engines

I recently received a question from a friend of a friend in Texas regarding the difference between a “Narrow Deck” and a “Wide Deck” Lycoming engine. This has been confusing to many, so let’s see if I can shed some light on the subject.

The difference between a Narrow Deck (ND) and a Wide Deck (WD) configured engine is easily determined by checking the specific engine serial number. The WD serial numbers end with the suffix “A,” such as L-0000-36A on an O-360 series WD compared to L-0000-36 on a ND.

There are a few exceptions to this, such as the O-320-H series and O-360-E series, neither of which have the suffix “A” but still contain WD cylinders. [Read more…]

Which cylinder is where?

Q: Over the last three years of annuals I have had three different mechanics. The mechanic does the compression check, calls out the cylinder number and I record the values. It appears to me that the mechanics might be confusing the cylinder numbers and I can’t find anything online that tells me in what sequence they are numbered.

My questions: What is the sequential numbers of the cylinders on my Lycoming O320E2D? What may be the primary cause of compression loss? What repair is required to correct the problem?

STEVE SARCHETT, via e-mail

A: This is one of those questions that more people would like to ask, but are hesitant to do so because they may get a few chuckles from their friends for asking such a basic question. Steve, I’m proud of you for bringing up the subject and I can guarantee that many pilots out there are also confused as to which cylinder is located where on their engines.

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Tips to reduce spark plug fouling

Q: In my pilot club meeting last month, a pilot complained of spark plug fouling before takeoff in our Grumman Cheetah with 150-hp Lycoming. I suggested that after starting the engine, and before taxiing, she lean the mixture, keep it lean while taxiing and put on full rich for run-up. However, if there is a delay — say she’s fourth in a line of four airplanes for takeoff — she should lean until cleared for takeoff.

Another member cautioned that leaning while taxiing can burn up a cylinder. I say that while taxiing the engine rpm is too low for a lean mixture to burn a cylinder. My brother says not leaning may, in addition to fouling plugs, cause a valve to burn or other damage.

What say you?


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