A puzzling compression problem

Paul McBride, an expert on engines, retired after almost 40 years with Lycoming.

Q: My engine, which now has 300 hours on it, is an O-290-D2B which had a new-limits field overhaul. It has settled-in as a nice smooth-running, economical and reliable powerplant with plenty of power. It gets about 7-8 hours per qt. (Aeroshell 100) at 6.5 gph. All EGTs and CHTs are normal and it always has a clean oil filter element (it is cut and checked at each oil change, 50 hours or six months), and has a healthy oil analysis report (no anomalies or unusual artifacts). However, I’ve noticed the compression going down at each annual on all cylinders and a recent pre-annual check-up has them in the low 60s (over 80) with a static compression test. It also takes a bit of “prop-rocking” to get it to settle in. I can hear some blow-by in the dip-stick tube. It seems uncanny that all cylinders would have this problem, so I’m a bit puzzled.

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Ask Paul: Are these spark plugs approved for my plane?

Q: Could you please help my pretty blonde wife and myself with our spark plug problem? We are desperate! Our mechanic is going to put the new fine wire plugs we just bought into our 1976 Cessna Cardinal RG, but we have conflicting information on the proper plug.

We bought some SR83P plugs from a dealer at Sun ‘n Fun, who assured us that the plugs were the same as the Champion fine wire plugs that fit our Lycoming IO-360-A1B6 engine, and that they cross-referenced just fine.

JIMMY & SANDY HONEYCUTT

A: After doing some research of Lycoming Service Instruction 1042Y dated Sept. 1, 2009, which covers all “Approved Spark Plugs” for all Lycoming engines, I was afraid you may have a problem because there is no SR83P listed. I had a strange feeling about this, so I did some further checking with an old friend from the industry, Frank Gurko, who spent nearly a lifetime with Champion Spark Plug Co., then started his own company, PlugGuy.com, after retiring. He confirmed the SR83P spark plugs you bought are approved for your IO-360-A1B6 in your Cessna Cardinal RG and will work fine to replace your present REM38S plugs.

It would appear that there was an oversight by Lycoming during its last revision to SI 1042Y from earlier versions. As a matter of fact, the SR83P was shown as approved for your engine in SI 1042X, which I believe was dated in 2002. I discussed this with Lycoming and they will address this oversight when SI 1042 is next revised. So Jimmy, it looks like you’re good to go with the SR83P spark plugs for your engine.

I really appreciate you sending in your question because it reminded me of something I’ve been meaning to address. I’d like to make certain all readers understand that the outcome for Jimmy could have been much different had these spark plugs been the incorrect type for his engine. If incorrect plugs had been installed, there is the possibility that several nasty things could have happened and none you’d like very much. [Read more…]

Ask Paul: Can this be correct?

Q: My Tri-Pacer has an O-320 with a narrow deck (A) engine. It has SL32000N-A1 Millennium cylinders, which are are installed with no plates and splined nuts. Can this be correct? I have no wide deck cylinders to compare them to.

BLAIR MOHR, via e-mail

A: Let me see if I understand what you’re telling me: You have an old Lycoming O-320 Narrow Deck engine that has Millennium cylinders installed using the spline type cylinder hold-down nuts? Yes, it could be possible that these cylinders would be installed without cylinder base hold-down plates, which was done on the early low compression engines.

The spline type nuts have been long gone but, as you mentioned, apparently still in use. Should you wish at some point to convert to the more recent Cylinder Base Allen Head Nuts, this may be accomplished by complying with Lycoming Service Bulletin 213A, dated way back in 1957, but I’m not certain I’d go through the work. I think what you’ve got should work just fine.

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

Is new technology worth the investment?

Q: I am about to change my Alfa Romeo boxer engine to a Lycoming O-360A1F1 on my experimental Glastar aircraft. I read your answer recently to a question if LASAR is really useful (Will my engine benefit from new technology? Jan. 12 issue). Its actual price is $2,500. Do you think that it is really worth this high sum?

My mechanic has doubts, saying he is not confident in electronics — that if the electronics don’t work, the engine will stop. He also says that standard magnetos usually always work.

G. FRANK, Italy

A: I appreciate the fact that you read my article on the LASAR system. One thing I overlooked when explaining the system is that any interruption of the three data sensors — manifold pressure, cylinder head temperature, or rpm — and the system automatically reverts to the fixed timing on the engine just like the LASAR system was not there. Therefore, the engine would not stop as a result of the LASAR system experiencing an electronic failure.

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Ask Paul: Why do my serial numbers differ?

A: I have a narrow deck configuration in my 1964 PA 30-270. The first entry in the aircraft logbook, made on Jan. 3, 1964, shows radio installation and LE serial #S or L 606-55 and the RE L 640-55. However the engine log books show LE L 938-55 and RE L 909-55 and the first oil change at 55 hours. Both are IO-320-BIA. I have not yet confirmed the numbers on the installed units — too many screws — and I don’t know the exact place of the info plate.Also, the N number was changed from N7373Y to N4009Y in 1966, but I have no idea why. Please help! I am baffled.

KARL ROESCH, Arlene, Montana

A: Karl, the difference in your logbooks is interesting and confusing, to say the least. The only thing I can think of is that the original engines were replaced at some point with the higher serial number engines. I am surprised, however, that this isn’t reflected in the aircraft log. [Read more…]

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?

BARRY DiSIMONE, Tucson

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: AskPaul@GeneralAviationNews.com.

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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