It's annual inspection season again. I guess it like death and taxes...sure to come around. Lots of folks have asked "what all should I have done to my engine during the annual?" I would like to suggest what I'll call the "minimal requirements" for an effective 100 hr. inspection on R1340 and R985 engines:
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Oil change with sump and screen check.
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Valve adjustment - Positive or compression.
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Ignition timing check - Spark plug servicing.
Compression check - differential.
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Air filter and carb - heat system check.
Oil changes should be done 25-50 hr. intervals, or at 90 day intervals. If you only flew 25-30 hr. a year, once a year oil change wouldn't be frequent enough. You will cause engine damage due to acids and moisture accumulation in the oil. It is absolutely essential to drain both sumps and check the screen at every oil change. If you have a spin-on or sock type filter, it should be cut open and checked for metal contamination.
Let me explain something about the 2 filter systems, both original and after market types. The engine's oil "screen" is a pressure side screen and it filters the oil just before it goes throughout the engine. The after market filters are all outlet oil filters. They filter the scavenge oil just before it makes it to the cooler. This is good, because it keeps the cooler and tank cleaner, thus keeping the entire oil system clean. However, because it is an outlet filter, it will mask the engine oil screen, which is the traditional location for checking metal contamination. Unless you cut this filter open, you have no way of checking for contamination. The press side valve located just above it. This valve prevents reverse oil flow through the screen after shut down. It also helps prevent oil from draining into the engine past the pump during periods of storage. I like to remove and clean it during an oil change, largely to prevent it from falling out when I'm not looking.
The only other avenue for oil to get in to the engine during storage is to reverse flow through the oil press relief return passage. Removing and lapping the plunger to seat is the usual "fix" for this problem. The Scavenge system has a "finger screen" in the sump that is designed to prevent large pieces of metal from being sucked into the pump, resulting in pump and pump drive failure. This screen is an effort to keep the engine running as long as possible during a failure, and is not a maintenance check item.
Covington Aircraft recommends the use of mineral oil during break-in, or the first 100 hrs. At this time we don't have enough experience with multigrade oils to make and firm recommendations. However, we are experimenting with the 25W 60XC oil. As a mechanic, I understand the reasoning behind a multigrade oil is sound. The only problems reported from the field have been a few instances of customers telling of slightly lowered oil pressure and one instance of erratic oil pressure on multigrade. The one engine we have run so far (a R1340-AN2) exhibited slightly higher oil pressure. Two of our customers have reported slightly higher oil consumption on multigrade. Oil additives are not approved for use in these engines. My problem with Teflon-type oil additives stems from some design features of this engine. The 1340 has many "roller" type components, roller cam followers, tracks, roller rocker bearing, roller main bearings, etc. These parts require some friction to function. An additive that produces very slick parts could induce a slide where there should be a roll and result in component failure. Besides, in the event of a wreck or failure, I don't think I would want it known that I was using an unapproved engine oil additive in my aircraft engine.
Valve adjustments provide you with an excellent opportunity to check the hottest side of your engine for unusual wear. You should see the most amount of required adjustment at the first 100 hr. valve check. If more than 1 turn on an adjusting screw (either way) is required to obtain a good clearance, I would suspect problems such as bent/broken pushrod, recessed valve seat, stretched valve, worn or failing rocker bearing, etc. I prefer the compression method of adjustment on an installed engine to the "positive" method. If you set them one way and double-checked it the other, you would be hard pressed to find any differences. I normally set each valve at .010" clearance (using a fairly free .010") then check for at least .010 and no more than .017 (book says .025"). Each valve should be checked at least 4 times, as the cam has 4 sets of lobes. Lock nuts should be torqued to 375 in./lbs.
Engine timing check: Since this engine has no external timing position indicators, you have to establish timing position with some type of mechanical indicator like a Time-Rite type of mechanical indicator that attaches to the propeller. You will also need a probe (screwdriver) to feel for the #1 piston's limit of travel. The mags time to 25 deg. BTC #1. If your timing is off more than 1-1/2 deg., the timing should be adjusted. This can be done by removing the mag attach screws (bolts) and lifting the mag up and back while keeping the drive grommet against the mag gear. While keeping the mag gear from turning, rotate the rubber drive grommet right to retard, left to advance. One (1) tooth equals approximately 1 deg. Reinstall the mag and safety bolts. Torque to 300 in./lbs. If timing is off more than three degrees the mag should be removed and bench checked for bearing slack, point follower wear, etc., and reinstalled. It is important that the rubber drive grommet on the Bendix mags have some slack after being installed. This prevents preloading the rear rotor shaft bearing, which causes premature failure. Point follower wear is much more of a problem on the Bosch mag that the Bendix. Point gap is also much less on the Bosch (.008: to .010" overhaul). A physical point gap check should be made on the Bosch mags every time timing is checked. It helps to put a few drops of 30 wt. on the felt lubricator around the cam.
Let me say a word or two on spark plugs. Massive electrode spark plugs should be serviced every hundred hrs. or so, cleaned, gapped to around .016" and fresh anti-seized applied.
Caution: Nothing kills a spark plug quicker than excessive or sloppily applied anti-seize. 3-4 threads up from the gasket is sufficient. If you can't screw a plug in all the way by hand, the hole should be cleaned or chased out. Thread chase taps are available for this. A regular thread tap will lock up in a helicoiled hose, so avoid using them in any thing other than original brass threads. Remember to apply air pressure to the other plug hole to blow chips out of the cylinder during chasing/tapping. If air isn't available, use a coating of grease on the chase tap.
Compression checks: These checks are valuable tools in determining the health of an engine or cylinder. However, a mechanic needs to be familiar with larger displacement engines in order to get the most out of it. For example, a reading of 65/80 in an 0-200 may be cause for concern, but in a 1340 the reading should be noted the cylinder rechecked at the next opportunity (if engine is performing normally). I have seen many 65/80 cylinders give 76/80 after a 20 minute run-up. If, however, the cylinder continues a downward trend or has an audible exhaust leak that "staking" doesn't help, removal and repair is necessary. R1340 cylinders very rarely give 80/80 reading.
Carb heat: The carb heat system on your aircraft is more important than most people give credit. This is not because the engine is ice prone, because it's not. The reason is that most systems have notoriously leaky valve bodies at best, and substantial amount of performance can be lost through a valve that is open just 1/2" due to worn or loose linkage. This is especially true in a worn condition. The carb heat box is also a good source for unfiltered air. Dirt ingested through a sloppy or slightly open carb heat valve isn't likely to cause "Engine failure," but can result in completely worn out rings in as little as 300 hrs of operating time.
I know a good annual isn't going to be cheap. But you know an aircraft down for serious engine work during your season is even more expensive.
God Bless ya'll and fly safe!
