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aircraft engine overhaul
What we do do when overhauling aircraft engines
I prefer to remove and reinstall the engines ourselves as many problems can be detected during removal and thus be prevented during installation. A good installation is just as important as a good overhaul. Some aircraft engine overhaul shops are not located on an Airport and cannot remove and reinstall your engine. Many people will ship me their engine to be rebuilt. If this is what you choose, please include the baffles and seals for replacement. We will run your motor on our test stand after the overhaul and ship it back to you for installation. To get an engine to run smoothly all the cylinders need to be the same compression and the Engine / Propeller combination balanced together at cruise RPM. This is done by dynamic balancing, running the engine and propeller at full rpm and then measuring the vibrations in inches per second, then installing weights to balance it out. similar to a car tire balancing, you cannot balance a car tire and wheel separately and achieve good results. some shops balance the crankshaft separately in the shop.
If it was significantly out of balance to start with you will realize some results, but without running the engine and propeller together and adjusting for the measured vibration it will not run smoothly as it will with dynamic balancing. We do this after an overhaul of your engine if we have the propeller. The balancer does not lie. most engines run with a vibration of .15 inch per second about the thickness of a nickel bouncing up and down, even after overhaul with a balanced crankshaft. Usually, I can get the vibration down to .05 inch per second. That is like a piece of paper.
"To be a good mechanic you have to keep your hands moving and your lips still" Bob Vondersaar
We are a distributor for electronic international engine monitors, they are one of the greatest recent aviation innovations. We do the install for free if you buy one during your engine overhaul. We also have great prices for units from the manufacturer. You will not find a lower price on EI equipment than ours
This photo is the normal sludge buildup inside a crankshaft, the power pulses of the pistons cause the buildup to be in an oval shape causing an imbalance of the weight inside the crankshaft and creating vibration, I can usually eliminate vibration by adding a few small washers but the imbalance here caused by the sludge buildup is considerably more than that.
We are a small shop, we do not overhaul 40 engines per month like some large repair stations do. We also do not have millions of dollars of liability insurance. On the other hand if you are looking for someone who is personally responsible for how your engine is put together you have come to the right place.
Repair stations are not required to hire licensed A&P mechanics and some repair stations hire ASE automotive certified mechanics and try to pass them off as Aircraft A&P.
Repair Stations have FAA-approved procedures written in their repair station manual and cannot deviate from those guidelines. Anyone off the street can be hired to follow their manual, but if you require repairs not listed in the manual they will not be able to do those types of repairs. Once a customer of A&E used a large repair station for an exchange engine and the crankshaft had a service bulletin against it. SB is not mandatory, but the repair station manager told him it is their policy to require the SB compliance so they ended up charging him $5,000 for a new crankshaft and destroyed his old one before he got it back. Repair stations are doing a field overhaul the same as we do. All engine overhauls that are not completed in the factory are called field overhauls. The factory is the only one who can rebuild an engine making it zero time. Our field overhaul requires the same parts and procedures as anyone else.
Many repair stations do not take the time required to custom fit parts or perform extra services to make the engines perform at their best. It is because they are not allowed to by the repair station manual. When new piston rings come out of the box many fast build shops do not check the end gap or try to adjust it. Our rings are adjusted to the minimum gap allowed by the overhaul manual this gives better compression, more power, and longer life. At Annual inspection the engine compression is tested with an Orifice differential tester, there are 2 sizes of orifice used. For cylinders over 5 inches in diameter a .060 orifice is used and smaller engines .040 as marked on the image to the left. If your ring gap is worn to .040 the compression test will fail and you will usually replace the cylinder. Our ring gaps are .007 new cylinders I have seen ring gaps of .015 I have seen overhauled cylinders with ring gaps of .030 as the rings wear the gap keeps getting bigger. Some engines have very low oil consumption, which means there is not much oil left on the cylinder wall to lubricate the ring and it is going to wear faster. Chrome-plated rings wear the best but the cylinder wall can get rusty, cast iron rings are used on a chrome-plated cylinder and do not make it until overhaul because they are softer, but since they are not being used as much will last longer. New Nickel Silicon Carbide (NiC3) plated cylinders scratch easily and cannot be repaired, they have a very hard surface but if dirt scratches them you have to throw away the cylinder and are also very sensitive to overheating, you can destroy a set of new cylinders by leaning improperly, great for the engine manufactures. Steel Nitrided cylinders and chrome rings wear the best. Piston rings have a small surface area and the most movement, thus the piston rings need the hard chrome coating for wear. Combining the corrosion-resistant surface of wear-resistant nitrided steel cylinders and chrome rings will consistently give good compression all the way past TBO. I have had flight schools run them to 4000 hours and still have high compression.
Overhauling your engine is not an FAA requirement unless you are using it to transport passengers or freight for hire. The manufactures' recommendations are not mandatory, although they are good guidelines to follow. We suggest an overhaul when the oil sample shows excessive metal or if the oil pressure drops and or it is making noise. It may be time for an overhaul if you are just not confident in its reliability or If metal is found in the filter at an oil change (cutting open your filter after an oil change is your best defense against premature failure). Doing an oil analysis at least once a year will allow you to track the rate that the engine is wearing by detecting microscopic metal particles that pass right through the filter.
You do not want to be forced to land in a field while you have several unopened oil filters back at the hangar full of metal that you have not looked at. Your second choice is Oil analysis, I have seen engines that do not show any problem on oil analysis and the filter is full of metal chips. The metal is too big to pass through the filter and does not get sent into the Laboratory in the sample. Still, it can help tell who when it is time to overhaul the engine as well as warn you of an impending failure. If you show high lead it can mean your bearings are starting to wear and it is time for an overhaul. If then the high lead stabilizes and you have high steel now it will be time for a new crankshaft. I have seen high silicone and the intake tube was torn pulling in sand and dust. Oil analysis is microscopic, all the materials they are looking for pass right through the filter, I have seen camshafts worn to a nub and they show high iron on analysis but find nothing in the filter, Oil analysis looks at the rate of increase of many particular metals, so the more times you take a sample, the better picture you have of what is going on. It is not a perfect system but it is the only one we have.
Engine overhauls can be completed to new limits or service limits. The manufacturer has established serviceable limits for parts that are worn but do not require replacement, the manufacturer offers a service limit overhaul themselves. The Manufacturer is the only one who can offer a (zero time) overhaul. Everyone else can only be a 0 SMOH but total time on that engine will continue. Service limits usually allow 1 to 3 thousandth of an inch wear beyond new limits. A $1,800 shaft may be worn .001 over the new limit but it is still a perfectly good part. For engines that meet new limits, we will sign off the engine as "overhauled engine to factory new limits" otherwise it is "overhauled IAW manufactures overhaul manual". Both are 0 SMOH, Both Continental and Lycoming now have a long list of mandatory replacement Items so most of the time the part has to be replaced no matter what condition it is in.
There is only one more option, IRAN and that is Inspect And Repair As Necessary, This engine overhaul is not able to be logged as an Overhaul. We call it refurbished. TSMOH continues. If money is an issue, It is better to have a good strong high time running engine than a weak leaky power-plant.
Aircraft engines were originally designed for frequent disassembly and inspection to ensure reliability. Not a complete rebuilding of all components to new limits every 2000 hours. Someone figured out if they put mandatory replacement parts at overhaul in a Service bulletin they will sell a lot more parts even if there is nothing wrong with the old ones. If the engine is not overheated and the oil is changed regularly if it is run often and everything is perfect. it will make it to TBO still looking brand new inside as far as the lower end is concerned. Cylinders have a hard life and occasionally reach TBO if not overheated.
Even A brand new engine often will not make it to the recommended overhaul time, most of the time the cylinders will fail, or on Lycoming, the camshaft will fail, it will start making metal, the cylinders can get overheated and burn up the oil. The case will Leak, or crack. The point is even if you overhaul your engine to Factory new limits that don't mean you will make it to the recommended TBO. Still, there is no better value for your money than a factory rebuilt engine, it is a zero-time engine with all new parts and a 2-year warranty, it just cost twice as much as our overhauled engine. I have seen overhauled engines that cost more than a zero time factory rebuilt engine, and they claim it gives you more value than a factory remanufactured one and that is ridiculous.
Lycoming engine camshafts are located at the top of the engine, they do not have any provision for providing oil to the camshaft or the lifters until the crankshaft throws some oil up to it. So if you start your engine after sitting a long time the Camshaft will be running dry. Especially if you use thin multi-grade oil. Multi-grade oil starts out as 20 Weight oil and they use additives to make it thicker as it warms up, these additives break down as you use it and it remains 20 weight when you need 50. If you put a drop of Aeroshell 100W on the wall and a drop of 20W50 next to it, you will find the !00W remains in place much longer. I have found a high incidence of wear on the multi-grades, I do not know if it is because the additive broke down or because of lack of protection at startup. I have also found oil additives provide no additional protection against wear, I have seen new cams destroyed at 700 hours using additives as well as ones that do not, But mostly more using multi-grades. One large flight school I serviced switched to multi-grade to save some money and lost 7 camshafts that winter. I have had problems getting Superior piston rings to seat or wear into the cylinder, and started using multigrade for breaking in the rings because it does not provide as much lubrication as Aeroshell 100 mineral oil.
The Lycoming regional Tech rep. came to visit me once and I asked, what can I do about the cam wear problem? He said, "they do not have a problem". So I asked, why did they come out with roller lifters then? Roller Lifters are only available on the newer engines. They are mandatory replacement at overhaul and cost $250 each. But they have solved the cam wear problem, older engines can be modified to use roller lifters, it is expensive and you may be better of getting a case that has to be machined to fit them Roller Lifters. Chuck Ney had a great fix for that. He installs a spray nozzle in the top of the case to spray oil on the camshaft as soon as the engine starts up, they are called Ney nozzles, Chuck has passed now, rest in peace. ECI had a similar nozzle that uses pressure regulated nozzle, They are gone also. Lycoming came out with Hyperbolic Lifters as standard replacement. they are a pear shape and allow the lifter body to oscillate in the bore. This reduces the load on the camshaft by 40% The tip of the camshaft has the highest load in the entire engine.
Also, I believe the increased oil coming off of this lifter body gets on the camshaft inadvertently and provides better lubrication. I have been using these in all my engines and have not had any wear problems. Although many customers complain about low oil pressure at Idle, Lycoming says this is normal at Idle and it is OK to drop to 10 PSI. I once installed Ney nozzles and Hyperbolic ones in the same engine but the Oil pressure was so low I had to remove the Ney nozzle.
I like mineral oil. If you feel it between your fingers it is the best for lubrication. Alas, it is not ashless and that means it leaves some black ash deposits when overheated, and it does not have dispersants that help hold contaminants in the oil to be separated by the filters, any metal particles in the oil collect in the bottom of the pan and not in the filter. That is why it is used as a break in oil. To make the mineral oil cleaner they have additives that make it ashless, and add dispersant to retain the dirt in the oil. Then put a W in front of the viscosity rating that stands for winter, making it, W100. Aeroshell also includes more additives for anti-wear and is W100+ and I believe it is the best aircraft engine oil available. Several additive manufacturers produce products to do this also. I overhauled all the engines for American Flyers for 5 years and they used 1 pint of additive every oil change, we never had an engine failure, but I also did not notice any difference in camshaft wear, although when the engines come in for overhaul they were spotless inside so that product must be an excellent dispersant.
No engine can exceed TBO if it is overheated. Oil will start to oxidize and coke up at 315 degrees F. If CHT's exceed 400F, oil dripping on the hot exhaust valve stem will burn, causing valve guide wear, sticking, as well as glaze the cylinder walls causing piston ring wear. The way that a piston cools is by transmitting its heat through the rings to the cylinder wall. When the piston overheats the rings stick in the piston ring groove, then can no longer transfer heat to the cylinder. The burnt oil starts to form an insulating layer on top of the ring that looks like burnt oil on a frying pan. The rings then stick in the groove and will break scratching the cylinder wall and allowing hot exhaust gasses to blow by the piston, contaminating the oil with black carbon residue, and increasing oil temperature. This hot gas will melt the side of the piston causing it to seize up.
dont line bore
lycoming test cellhttps://www.youtube.com/watch?v=pKjQ3dYHyhw
Corrosive Acids form in the oil from combustion:
Have you ever noticed water dripping from the tailpipe of a car? Water is one of the by-products of combustion and it is leaked into the engine case during "blow-by" contaminating the oil. Often when the engine has a bad oil leak the belly of the aircraft will be corroded from the acidic oil contacting it. The best way to prevent this is to keep the oil from turning black and maintaining good ring seal (compression) and keep the oil changed. Oil has to be warmed up to 215 degrees for a reasonable time to eliminate moisture from forming.
Valve springs are uniquely manufactured and hardened, stresses occur during the coiling process that makes them the most likely item in the engine to rust, a small pit from rust can cause them to break from flexing in as little as ten hours.
Also, water builds up inside the engine from condensation, if left sitting too long. On a cool night the engine cools down, then as the day warms up the inside of the engine remains cooler than the outside temperature and moisture forms on the surface of the crankshaft and other components, the same as it does on a glass of iced tea in the summer. The moisture is trapped inside the engine and collects there. The best environment to develop rust is a hot humid one, so starting your engine and running it for a short time only heats up the oil and does not burn off the moisture trapped inside. You need to fly it for about 30 minutes or more to do that. You can also buy Desiccant plugs that absorb moisture to help with that.
If you use an engine heater in cold weather without a temperature regulator on it the heater it will prevent condensation inside the engine, but it gets so hot if there is any moisture inside it turns into a steam bath for your steel parts.
There are approved processes that can be added to improve your engine's longevity, reliability and to help control your costs. Although some other repair shop procedures are created just to promote a product or service, there are many that have value. We have several of our own that mainly deal with high temperatures such as removing flashing or mold marks as seen above allowing the cylinder cooling fins to have better airflow through the cylinder. Camshaft oil spray nozzles to keep it lubricated, ceramic coatings help or prevent heat transfer, good tight baffle seals and engine monitors to watch temperatures. Also balancing the propeller and crankshaft together with a dynamic balancer at rated RPM This can help reduce vibration on avionics, airframe, and passengers. Port and polish intake ports to help the engine breathe better. Power flow headers are bolt-on power.
We coat the Overhauled cylinders, the oil pan and the oil cooler with ceracoat' A ceramic coating to help transfer heat from the engine. CERAKOTE
We coat the Overhauled cylinders, the oil pan and the oil cooler with ceracoat' A ceramic coating to help transfer heat from the engine. CERAKOTE
Exhaust systems can be coated with a Header coat to help prolong life and reduce heat transfer into the cowling area, by preventing heat from escaping through the header and insulating it from the rest of the engine.
Coating your exhaust with ceramic can reduce the cowling heat dramatically. Click on the blue links in this Paragraph to see how a header works to help scavenge exhaust from your cylinders and free up more horsepower.
We can paint your engine any color you like. cylinders are usually black if we overhaul them because we use a black high temp heat transfer coating. New cylinders come Lycoming Grey from the factory, we would void the warranty to change that. But ours cool better! We can have valve covers powder coated, also available in metal flake to match your plane or your preference.
We prefer to replace all cylinders with new ones using OEM (Original Equipment Manufacturer) parts. New cylinders do not cost much more than many of the overhauled ones. Manufacturers do not support or recognize engines that use aftermarket parts. Warranty and insurance claims could be ignored when aftermarket parts are used. Lycoming representatives have told us that engines with other than Lycoming pistons are no longer a Lycoming engine.
Steel Nitrite, hardened cylinders, and chrome rings wear the best. Piston rings have a small surface area and the most movement, thus the piston rings need the hard chrome coating to prevent wear. Combining the hardened surface of wear-resistant steel cylinders and chrome rings will consistently give good compression all the way past TBO. Unfortunately, if you do not run the engine Once a week, the steel cylinders will rust and cause you problems, the best solution is to Channel chrome the cylinder so it will not rust, Other methods such as New Chrome and Nickel carbide are damaged easily by Dirt and Heat.
This piston is showing abnormal wear on the skirt. Lycoming pistons do not wear like this in this area that is shown.
Advantages of using new cylinders:
Good warranty, no metal fatigue, and less downtime during overhaul.
Advantages for us to overhaul your cylinders are as follows:
No new cylinder purchase required, proven reliability, fins can be blended for better cooling, rings can be gaped tighter for better compression, the head can be stripped bare and painted with heat transfer ceramics, barrel exterior can be coated for better corrosion resistance, cylinder wall depressions can be honed out for better ring sealing, valves can be lapped for tighter fit, and mold marks/ flashing can be blended for better cooling
If you feel the need to coat your cylinders in chrome, ceremonial or nickel in order to keep them from rusting, you should also be aware that there are many other parts that can rust as well, like in the camshaft, lifters, gears, and springs.
During an engine overhaul we NDT the case to detect any cracks, we alone and prime it with corrosion-resistant primer before reassembly, then again after assembly, & repaint the entire engine sealing out moisture with a ceramic heat transfer coating or heat resistant enamel. All hardware is thoroughly cleaned and inspected, all plated steel washers that contact aluminum are replaced with new to prevent dissimilar metal corrosion. We magnaflux all steel parts, assemble the main bearings and double-check clearances by using plastigage. We replace the camshaft with new, regrinding the camshaft is approved but the thin hardened layer is reduced so I prefer new. The propeller is dynamically balanced to the engine using a Chadwick Helmuth balancer. We run the engine on the ground for at least two hours with EGT and CHT monitoring, then drain the oil, check the oil screen & cut open the filter. Rubber hoses are fabricated with new or replaced with Teflon Hoses, accessories can all be overhauled if desired. We use sealant on all gaskets, clean the oil cooler, replace all baffle seals to provide optimum cooling, tie up all wiring to prevent chaffing and breakage, change magneto points and inspect Magneto, this should be done every 500 hours new mags or not. And if you really want to do it upright, install a complete engine EGT and CHT monitoring system. You get 25% off retail listed prices on new engine monitors when purchased through us.
You must maintain positive deck pressure (ram air pressure on top of the engine) to force air through the cooling vanes. This is done with good tight baffle seals. Baffle seals do not just deflect air through the engine, they have to seal in ram air pressure and force it to go in between the thin cooling vanes, this is done by sealing any leaks larger than a pencil. Your engine cowling air inlet has a limited size opening to decrease drag, this limited air supply has to sufficiently pressurize the top of the entire engine in order to keep CHT's low, leaks in the baffle seals deplete this pressure. Additional cooling can also be provided by using a rich fuel mixture, thus running at 100F richer than peak Exhaust Gas Temperature. This brings up the question: do you want to cool your cylinders with good tight baffle seals or extra fuel? Also, see this Link about Cowlsaver Baffle seals.
Spark Plugs : use the coldest plug you can and not have the plugs foul. On taxi you cannot damage the engine by leaning at low power, lean it out until it about to die. The only time you should be full rich is takeoff power, the reason for that is it prevents detonation. This link is a good one about fine wire plugs they cost a lot more but have other advantages and can last 4 times longer.
LOP or lean of peak. Is when you keep leaning the fuel mixture after reaching peak EGT, you lose a little power due to the leaner fuel mixture (approximately 300 rpm), you also lose the added cooling effect that the extra fuel provides. Monitoring all the cylinder temperatures closely is important because they have to be closer together than when on the rich side of Peak. All cylinders need to peak at the same time to realize many benefits from LOP, if one cylinder starts to peak 50 degrees before the others you will have to stop leaning early. For an engine that uses a carburetor, it is harder provide this balance, although with injected engines we can adjust peak EGT to be within 30 degrees of each other by using Gami injectors or sometimes repositioning your current injectors to raise the temperature on a richer cylinder and lower it on a leaner one. When operating LOP you are only using air to cool the cylinders not fuel, requiring constant CHT monitoring. You should not operate most engines over 85% power lean of peak, but you can save 30% on fuel using this procedure. This engine operating guide is excellent From Electronics international click here LEANING GUIDE
The FAA mandates the manufactures to keep engines from operating near the detonation range. The most dangerous area for detonation is peak EGT. Detonation is the auto-ignition of fuel due to high heat or pressure, it can slam 4 or 5 tons of additional force on top of the piston and blow holes in it. The pinging sound you hear in a car when using low octane gas is detonation, you cannot hear it in your aircraft due to the propeller noise. An indication of aircraft detonation is a reduction in EGT and power with an increase in CHT. The highest risk of detonation is at peak EGT, you do not want to operate closer than 50 degrees of peak EGT without an engine monitor, individual cylinders can drift into this danger zone if they are not all monitored. That is why the FAA designates 100 degrees ROP as a standard leaning point on most un-monitored engines. Operating 100 degrees ROP provides this margin and best power. With a good engine monitor, you can operate closer to peak EGT without an un-monitored cylinder drifting into the dangerous detonation zone. Additionally, if you have fuel injectors they can become restricted from a small piece of rubber or dirt and create a leaner mixture in that one cylinder, this can burn up your piston in a matter of minutes, you can spot this early by the peaked bar graph, and preset alarm provided on your sophisticated engine monitoring equipment such as the UBG 16.
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PMA CERTIFIED VOLTAGE REGULATORS
PMA certified solid-state Voltage Regulators with protection, field short (overcurrent) protection, reverse battery protection, precision load sharing and support either 14 or 28-volt applications with the simple change of two jumpers.
PMA certified Voltage Regulator, Replaces many (Ford), Electrodelta, Prestolite, Interav, Wico, and VFR voltage regulators.
PMA certified solid-state Voltage Regulator, Replaces voltage regulators on twin Cessnas, Beechcraft, and Vulcanair.
Voltage on a twin-engine aircraft is hard to control. There is always an in-balance between the two alternators: if the voltage on one is slightly higher it can dominate and cause the other to drop offline. This can cause a field short and burn up the regulator. Installing engine monitors like the MVP 50 allows you to monitor the amperage of both engines and the battery, many times you do not know the outputs of either. All you have are the two fail lights, one Alternator may be putting out 35 amps and the other only 2 while the fail light remains out or intermittently flickers. Installing the Plane-Power voltage regulators with load sharing ties the two voltage regulators together extending the life of the regulator and the alternator, and costs under $500. for both. We can Install them free with your next twin-engine overhaul. Or for a minimal charge at Annual.
FYI Do not run up your engine on the grass, there are rocks hiding in there. They may and may not be a problem at idle, but if you power up it is going to eat one, This one cost me 10K and only took 5 seconds. Have your plane towed to the clear taxiway.
Photos of Engine Overhauls
Below are a few links to the Lightroom photo album, that you receive access to, so you can monitor and verify the progress on your engine.