Lycoming Aircraft Engine Frequently Asked Questions

Lycoming exhaust valve face showing damage caused by operating the engine with a leaking exhaust valve. Notice where pieces of the valve are missing. These pieces don't go out the exhaust but drop down into the cylinder, do their damage, and then are sucked into the intake system when the engine is idling and then travel from cylinder to cylinder!

Maintenance Questions

How do I tell if I have sodium cooled exhaust valves in my Lycoming engine

The rocker arm pushes directly against the top of a solid stem valve.
The rocker arm pushes against a rotator cap that sits on top of the sodium cooled valve

Can't get dry tappet clearance? What push rod do I need

Download the program which is a copy of Lycoming Service Instruction 1060D "Push Rod Identification"

This program contains all the lengths and identification markings for Lycoming push rods and is very
helpful.

Note about this download:

Program is a viewer program that requires no installation. It does not put any other files onto your
disk except the program itself. Download the file and click on it to run.

How do I check or adjust dry tappet clearance on Lycoming engines

See my article:
Checking and adjusting dry tappet clearance on Lycoming engines

Which way does the connecting rod nut go?

Avco Lycoming Service Instruction (SI) No 1106D, issued 9-6­72, includes a Caution: "The connecting rod bolt cannot be tightened correctly if the nut is installed upside down. The raised edge, or lip on the end face of the nut must be on the free end of the bolt; the flat face must be in contact with the rod. See figure. . . . . " (as Fig 2). The SI also notes that the connecting rod bolt will loosen if under-torqued.

If the nut is installed with the raised lip on one end of the nut, rather than the flat face at the other end, bearing against the big end cap surface. It is possible for the lip to yield in service if the nut were installed upside down, resulting in loss of bolt preload.

How do I tell which starter ring gear is on my engine

Lycoming engines were manufactured with two different ring-gears. One type has 122 teeth ( 10/12 pitch) and the other has 149 teeth (12/14 pitch).
 

Why is this important?

The starter engagement gear (starter Bendix) must match the starter ring gear else you will grind down the teeth on the ring gear.

How do I know which oil pressure relief spring to use in my Lycoming engine

Use the ones listed in Lycoming's parts manual. To help identify which one is already installed use this handy chart.

The same Lycoming engine can be found with several different oil pressure relief valve springs. Sometimes this is done because of the way Lycoming engines remote mount the oil cooler. A different oil cooler mounting on one aircraft may result in different oil pressure amounts than another installation.

Note about this download

Program is a viewer program that requires no installation. It does not put any other files onto your
disk except the program itself. Download the file and click on it to run.

What is the difference between one Lycoming engine model and another

The "Same Engine" Myth

Questions that frequently are asked of Lycoming sales personnel, engineers, and technical representatives indicate that there is a myth regarding Lycoming piston engines. This myth seems to be prevalent among aircraft owners and aviation writers. In the minds of these individuals, each Lycoming engine series is essentially the same. For example, all 360 cubic inch displacement engines are inherently the same except for differences in fuel metering or turbocharging. The idea that these engines are the same is false. A few specific examples may help to put this myth to rest.

Lycoming builds 0-320 engines that produce 150 HP or 160 HP. The 150 HP O-320-E series engines operate at a compression ratio of 7.0:1. The 0-320-D series has high compression pistons which raise the compression ratio to 8.5:1, and increase rated output to 160 HP. Those who believe that the pistons are the only difference in these engines will be disappointed when they plan to upgrade their 0-320-E to the higher horsepower by simply changing pistons. Many models in the 0-320-E series were designed for the purpose of keeping the cost down. Thousands of these low compression engines were built with plain steel cylinder barrels instead of the Nitrided barrels used in the 0-320-D series engines. They also had two narrow bearings instead of one long front main bearing. The engines were certified at 150 HP and were not intended to withstand the additional stress of higher horsepower.

Because of the similarity in designation, it would be easy to believe that the 0-360-AlA and the I0-360-A1A are the same engine except that the first engine has a carburetor and the second a fuel injection system. Here are some features of each engine for comparison. The 0-360-AlA has a bottom mounted updraft carburetor, parallel valves, 8.5:1 compression ratio, and produces 180 HP. The IO-360-AlA features a horizontal front mounted fuel injector, angle valves, 8.7:1 compression ratio, and is rated at 200 HP. The I0-360-A1A also incorporates these design items which are not included in the 0-360: piston cooling nozzles, stronger crankshaft, tongue and groove connecting rods with stretch bolts, tuned intake system, and rotator type intake valves. There are actually few similarities except for the 360 cubic inch displacement.

There are individuals who have suggested that by putting 10:1 compression ratio pistons in an I0-360 engine, it could be the same as the HIO-360-D1A. These are some characteristics of the HI0-360-D1A helicopter engine that can be compared with the data on the I0-360 listed in the previous paragraph. To start, the HIO has conical rather than dynafocal mounts. The main bearing is a thick wall bearing instead of the thin wall, high crush bearing used in the I0-360. Other differences include: crankshaft designed for small crankpins, high speed camshaft, rear mounted RSA7AA1 fuel injector, large intake valves, and torsional vibration damper magneto drives.

Finally both the Navajo engines and the new turbocharged Lycoming used in the Mooney TLS are equipped with differential and density controllers that automatically set the maximum allowable horsepower when the throttle is advanced fully for takeoff. Some who have not taken the time to compare these engines have jumped to the conclusion that the TI0-540-AF1A which powers the Mooney TLS is simply a de-rated Navajo engine. This conclusion could hardly be more inaccurate. The most obvious difference, even to the complete novice can be seen by looking at the rocker box covers. The TI0-540-AF1A is rated at 270 HP and has parallel valve down exhaust cylinders. The Navajo series has three engines at 310 HP, 325 HP, and 350 HP. All have cylinders designed with up exhaust and angle valves. Other differences respectively in the 270 HP AF1A and the Navajo series engines are: small main bearing instead of large main bearing, 8.0:1 compression ratio rather than 7.3:1, intercooled and non-intercooled, pressurized Slick magnetos versus Bendix/TCM magnetos, and an RSA5AD1 fuel injector in place of the RSA10AD1 injector. There are some other differences, but those comparisons listed should convince even the most skeptical that these engines are vastly different.

By making comparisons of various parts and accessories used in engine models which some individuals have considered to be much the same, it is possible to illustrate the differences. Although some Lycoming models are closely related, this cannot be assumed. A review of the engineering parts list for each engine model by a knowledgeable individual is the only sure way of establishing similarities and differences. For those who may have been taken in by the myth that all Lycoming engines of a particular displacement are very much the same, you are now armed with a better knowledge of this subject.

How do I replace the spark plug helicoil?

The following article is from www.casa.gov.au AAC 6-58 Spark Plug Helicoil Repairs 6/95

Following a Major Defect Report investigation involving two in-flight incidents of blown spark plugs from the same cylinder position on the same aircraft, there is clear evidence a large number of approved workshops are not aware of the correct procedure for replacing spark plug helicoil inserts.

The Lycoming published procedure for replacing spark plug helicoils is detailed in Service Instruction No. 1043A. The Continental (TCM) procedure for replacing spark plug helicoil inserts is in the respective engine's overhaul manual. Lycoming in SI 1043A recommends all spark plug helicoil defects should be repaired by tapping oversize and fitting an 0.010" oversize helicoil, regardless of whether the defect is helicoil thread damage or the helicoil is loose, the TCM procedure only addresses a damaged spark plug helicoil. Thereby lies one of the problems; there is a difference between a damaged helicoil thread and a loose helicoil.

As with all aircraft defect rectification tasks, it is important to recognize the primary defect. Is it a damaged helicoil thread resulting from improper spark plug installation? Or, is it a loose helicoil resulting from erosion of the cylinder head material? Replacing a damaged spark plug helicoil with a standard size helicoil will fix the damaged helicoil. Repairing an eroded spark plug helicoil insert thread with a standard size helicoil will almost certainly result in a blown out spark plug (complete with the new helicoil).

The second issue is; not all commercially available helicoil repair kits, such as those produced by Heli-Coil, have oversize helicoil inserts. The kits may not contain the expanding and staking tool, as required by Lycoming Service Instruction 1043A and, in most cases, do not have the 0.010" oversize helicoil inserts or tap. Many maintenance organizations buy these kits from their local supplier and repair damaged or loose spark plug helicoils by simply replacing the helicoil. Again, what is the defect, what is the correct repair?

When carrying out a spark plug helicoil repair, specific care should be taken to prevent further damage to the cylinder head. Certain cylinders, such as high time cylinder heads with short reach spark plugs, are particularly susceptible to spark plug helicoil insert thread damage. Care should be taken when replacing the helicoil to reduce the possibility of further damage to the cylinder head material.

Where can I get some information about Lycoming oil pump gears

Click on the following for a copy of Lycoming Service Bulletin 456F "Replacement of Sintered Iron Oil Pump Gears"

Also see How can I get a copy of a RECENT Lycoming Service Bulletin

Service Bulletin 456F(327 KB)

The enclosed program is a viewer program in .exe format. Download it and run the program. There is no installation program required. There are no other programs or modifications to the computer registry. When you want to uninstall , just delete the file. This is a very simple program, that is why we use it.

Where do I hook up the Oil Cooler hose

Here are some drawings of a typical O-320Lycoming engine that shows the mounting points for various
accessories. Interesting, you won't find this drawing in the Lycoming parts catalog or overhaul manual.

This type of drawing is located in the Lycoming Operator's Manual. An obscure publication but well worth purchasing.

Note about this download

Program is a viewer program that requires no installation. It does not put any other files onto your
disk except the program itself. Download the file and click on it to run.

What does the color coding on Lycoming cylinders indicate

Lycoming uses the following color codes:
Orange - chrome barrel
Blue - nitride hardened steel barrel
White - rebarrel
Green - Plus .010 oversize barrel
Yellow -Plus .020 oversize barrel

Fin area between spark plug and rocker box

Yellow - Long reach spark plugs
Gray or Blue - Short reach spark plugs

What is a wide-deck and narrow-deck engine

For many Lycoming engines the same engine model may be a narrow deck or a wide deck. Each engine takes entirely different parts. How do you tell the difference. All wide deck engines have a engine serial number ending in A (except O-235 series engines). Lycoming serial numbers can be found on the engine data plate and also on the crankcase at the top parting surface.

Engine serial number stamping on Lycoming crankcase

Narrow deck engines also use internal hex style cylinder hold-down nuts and frequently use cylinder hold down plates. The cylinder flanges on wide deck engines are thicker and do not need cylinder hold-down plates.

When ordering engine parts be sure to specify narrow deck or wide deck.

Note: Narrow deck engines are older engines. Lycoming switched to the wide deck configuration in the late 1960's or 1970's
 

Service Publication & Specification

Where can I find engine specifications? compression, weight, etc?

The link below will open up a new window in your browser

Click here for model, weight, HP, etc

Lycoming phone number

717-327-7019

How can I get a copy of a RECENT Lycoming Service Bulletin

The link below will open up a new window in your browser. It has copies of the more recent Lycoming service bulletins.

Recent Lycoming Bulletins

Where do I find out more about operating and maintaining my Lycoming engine?

Check out the following link for articles from the Lycoming Flyer  Lycoming Flyer Articles

How do I purchase Lycoming Service Bulletins?

Service Bulletins, Instructions, and Letters are purchased direct from Lycoming on a subscription
bases. Contact Lycoming directly  phone 717-327-7019

Link to Lycoming Publication Info

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Disclaimer: sacskyranch.com contains abundant information relating to aircraft maintenance. The information provided  is not intended to supercede or supplement the F.A.A. approved  maintenance and/or operator’s manuals. Those F.A.A. approved manuals must be utilized when performing maintenance and/or operating aircraft.