Ask Paul: Should I worry about my #2 cylinder?


Q: I had my Lycoming 0-360-A1A rebuilt at Victor Aviation in 2001 — new crank, new cam, new pistons with new Millennium cylinders. The engine, which now has about 400 hours on it, has digital cylinder head gauge probes in each cylinder. My question: On a warm summer day in Alaska (75°F), with a load in the plane on floats, during climb out, the #2 cylinder head temperature hits 400°F. [Read more…]

Ask Paul: Solving a mystery

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

Q: Here is my mystery: I have a Geronimo Apache equipped with 0-360-A1As. The left engine is about 1,200 SMOH, the right engine is about 700 SMOH. They both had oil pressure of 85 psi in cruise and about 50 psi taxiing in after a flight. At about 1,150 SMOH, the LE began to show low oil pressure. It slowly, over about 20 hours, started dropping in cruise from about 85 psi to about 65 psi and down to 30-35 psi taxiing in. I thought bottom end bearings. [Read more…]

Tips to install an oil cooler

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

Q: We have a Citabria 7ECA with a Lycoming O-235-C1 engine. We live in East Texas, where summers are very long and very hot. Even with an external oil filter with a blast air tube, the oil temps push 220°+ on normal altitude flights, even when babying the air speed and climb rate (which means that we need to climb to pattern altitude to get from cruise to landing configuration. Not really, but the old joke does illustrate the point.) We think we need an oil cooler.

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Ask Paul: What’s up with my oil temperature?

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

Q: I’ve been having trouble with my Lycoming O-360-AIA engine for some time. The oil temperature is running about 200° on a cool day. The head temperature is in med green.

I have completed the following to determine the problem: A few months ago a new temperature control oil cooler by-pass unit was installed; and I checked the oil temperature probe by placing it in boiling water. The instrument in the aircraft read about 200°.

The oil cooler is a Positech with six tubes. The air source is an outside air inlet. I believe that the air flow is enough to cool the oil. I have no way to check. I have asked around the airport for help but this has not been fruitful.

GARY QUESTA, via e-mail

A: Gary, after reading your e-mail, I could hardly get the smile off my face. I don’t quite know how to tell you this, but most Lycoming engine operators would really like to have that kind of oil temperature on their engine.

Let’s look at some of the important things about oil temperature. [Read more…]

Ask Paul: Why are holes larger than dowel pins?

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

Q: I recently saw your article about Narrow Deck vs. Wide Deck and believe you are just the person to ask this question. A fellow AMT has been field overhauling his Lycoming O-360A1A engine. It is a “first run engine” out of an early Mooney. It is a Narrow Deck engine. (Yes, I know it is way past the 12 year time frame).

Here is the issue: The engine has small “stepped” dowel pins in the case half main bearing saddles (where the main bearings are installed). The removed bearings (original from factory) have small holes to match the small dowel pins. The new bearings (except for the forward {long} bearing) have much larger holes for the dowel pins. [Read more…]

Why mineral oil for break-in?

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

Q: I’ve seen this in Lycoming literature — “Keep in mind that all turbocharged Lycoming engines must be broken-in on ashless dispersant oil only” — but why is it true? My engine overhaul shop, Central Cylinder in Omaha, Neb., insists, in writing, that for its warranty to be valid, I must break my turbo’d IO-360 in on mineral oil.

PAUL MILLNER via e-mail

A: This requirement has caused some confusion for Paul and I bet he’s not alone. [Read more…]

Is 172 with H2AD engine a good buy?

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

Q: Hi, I am a Mexican looking for my first plane. I found a 1980 Cessna 172 with an H2AD engine that has just 100 hours since overhaul. The serial number ends in 76T; I had read about 76A. Is it OK? Is it the same as the 76A?


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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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Is it possible to convert my engine?

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

Q: I have a Lycoming O-360-A1F6D that was originally installed in a Cessna Cardinal. This engine has since been used in an Van’s RV-6 and I will be installing it into a Van’s RV-8. It does not have a magneto with it as the previous owner used electronic ignition. I have not settled on an ignition source but do not want to go back to the Bendix D4LN-2021 dual mag. I recently noted in a General Aviation News article that Teledyne (TCM), now the owner of the Bendix mags, has stopped support for the dual mag. Is it possible to remove the “D” on this engine configuration by changing accessory housing and gears? Maybe it’s possible but not economical?

DAVE PARADIS, Hubbard, Ore.

A: I really wish you had asked me a different question because I’m afraid my answer to this one is not going to make you a happy camper. [Read more…]

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.


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,, 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…]