RECIPROCATING ENGINE OVERHAUL PROCEDURES

01. What is a over haul and why engine overhaul is necessary?
02. overhaul shop
03. Tools and equipment
04. Shop safety and preparation for overhaul
05. Disassembly
06. Visual Inspection
07. Structural inspection
08. Repair and replacement
09. Connecting rods bushing replacement
10. Crankcases and accessory cases
11. Replacement of Studs
12. Reassembly
13. Use of safety wire
14. Assembly
15. Installation
16. Engine testing and run in
17. Engine Staring procedure
18. Preparation of overhaul records

Preparation of overhaul records

OVERHAUL LIST.

The operator is required to develop procedures for recording the time since the last overhaul of all items installed on the aircraft that are required to be overhauled or inspected on a specified time basis.

OVERHAUL/REPAIR RECORDS

Records must be made of every component overhaul/repair and must include the following:

1. A description of the work performed or reference to data

2. A positive identification of the person performing the work and the person approving the work

CURRENT AIRCRAFT INSPECTION STATUS.

A record, identifying the current inspection status of each aircraft must be maintained, detailing:

The time in service since the last inspection

Records must be maintained for periods as listed in a states regulations

MAJOR MODIFICATION AND MAJOR REPAIR.

operators are required to retain records of major repairs and major modifications

Major modifications

record should include:

x the date of modification

x a brief description of the work accomplished

MAJOR REPAIRS.

Operators are required to retain records of major repairs

Engine Staring procedure

Start the engine in accordance with the following procedures.

· Place mixture control in full rich position

· Turn fuel valve to on position

· Set throttle at 1/10 open position

· Turn magneto switch to left and engage starter

ü Turn combination magneto starter switch to start.

· When engine fires moves magneto switch to right.

ü Combination spring loaded switches will return to both.

Operate engine at approximately 1000 RPM until minimum oil in temperature of 140oF is obtained. Check magneto drop off and general operation of the engine. Check the engine for oil leak. Any malfunction or oil leak should be remedied before continuing the run.

Oil consumption run

An oil consumption run should be made at the end of the run-in schedule. Oil consumption can be determined by the use of a scale tank through which the oil line pass and the scale reading

taken at the beginning and end of the oil consumption run. Or it can be determined by draining and weighing the oil supply before and after the oil consumption run.

Engine testing and run in

After getting everything put back together and clean it is a bit scary to turn the key for the first time. What if I screwed up during assembly? The engine could not run, or worse loud nasty noises could occur and bits of metal might fly off.
You start with pre-oiling the engine to ensure that it has lubrication before the oil pump starts drawing oil for the first time and fills up all the oil passages. Then fill with oil and any other fluids (such as hydraulic fluid). Then a final inspection and assurance from your mechanic.

I had to charge up my battery after several months of inactivity in order to crank, but once it cranked the engine caught after the first few blades. It took about 35 seconds to register initial oil pressure, which is ok, the magnetos were grounding safely, and the engine ran steady. It wouldn't idle slowly enough, though, which called for more investigation.

Turns out that the rubber intake manifold connector hoses were loose. Assembly to engine start took about a month. During that time the rubber connector hoses took a set and squeezed out around the clamps. This let outside air bleed in, effectively adding throttle to the engine and leaning the mixture downstream of the carburetor. The fix was simple - tighten up the clamps on the hoses. After that of course we had to readjust the idle speed and mixture on the carburetor.

This made for more ground running than is ideal with a fresh engine, but not an excessive amount. The first flight itself consisted of a normal taxi, run-up, and a somewhat shallow takeoff and high-power cruise. The Oil and cylinder temperatures were monitored and recorded to see the spike and decrease in temperatures that is expected with a successful break-in.

Two issues were noted: the oil pressure was on the low-end of normal, sitting at 30 psi. This is within the Continental acceptable range but it is better to see about 55 psi on a stable basis. The second issue was that the R.P.M. was running about 50 R.P.M. low at the full-increase propeller setting.
I flew around for about 40 minutes making a large circle north over a local lake, heading south towards Enumclaw, and then continuing on to Eatonville before getting ready to turn around north back to Renton. Performance overall was good. I was about 5 miles west of Eatonville at full cruise when a loud bang and buzz occurred!
Oh crap. The buzz is very loud, but the engine is running, and the airplane is flying without any buffet or other strange behavior. A quick scan of the instruments reveals nothing out of place - oil pressure, oil temp, R.P.M., manifold pressure, and CHT. I zoom upwards to gain some altitude, and turn towards the Eatonville airport. The buzz noise continues. Since nothing appears to be wrong with the engine, I throttle back a little to slow down and the noise diminishes slightly.

The panic is off, but the buzzing noise is loud enough that I don't want to continue the flight, so I head to Eatonville at the slowed-down speed, lower the gear right over the airport, and make a circling approach from high altitude in case the engine decided to quit during the descent. The landing was a little hot but not bad considering. I rolled out to the end and shut down to inspect, fearing a large oil spew down the side of the airplane.

Fortunately the engine had no problems. A very careful engine inspection reveals no leaks, no missing parts, and a full oil pan with no obvious metal chunks. Upon checking the airframe I discover that a piece of fabric finishing tape covering the windshield-to-fuselage seam on the left side (right by the pilot's seat) had peeled up on the leading edge. Airflow was getting under the tape and was making it vibrate. Fortunately the tape hadn't pulled up any other fabric and was still on the airplane.
After some cellphone consultation with my mechanic, who by this time was starting to get worried that I hadn't returned to home base on schedule, we decided that it was ok to make a temporary repair with some tape. I scrounged some duct tape from one of the airport locals, and applied it to the offending finish tape fabric, then started up and took off again.
The duct tape worked like a charm, although I kept the speed down on the return trip. Upon returning to Renton I put the plane away for the day, having had plenty of excitement!

Repairing the fabric tape that had peeled wasn't very difficult, although getting the finish paint to look good is harder.
Fixing the engine squawks proved more annoying. My engine is old enough that it has the old-style non-adjustable oil pressure relief valve which uses a fixed spring and plunger. The only adjustment for the pressure is to put washers under the spring. I decided to call up a junkyard and get a workable adjustable oil pressure relief plunger. That took a few days to arrive.

Unfortunately on the Bellanca there's not enough room between the back of the engine, where the oil pressure relief valve assembly is located, and the engine firewall. It is impossible to reach in from the side unless your hand is about 1/2" thin, so I had to get at it from below. This entails removing the carburetor and Y-pipe that connects the carburetor to the intake manifold runners on both sides of the engine.

After initially removing the relief valve spring and plunger to make sure there was no junk on the valve seat holding the valve open, the new valve was installed. Now it was a question of adjustment, which is a trial-and-error process.
I got good at taking the Y-pipe and carburetor controls on and off, since it took 5 tries to get the oil pressure plug adjusted just right at about 55 psi. The first time was too low, then too high, then too low, etc. About 3 hours after getting going, the pressure was set and the intake was back together for the last time.
Fixing the propeller R.P.M. problem was also annoying. After verifying that the problem wasn't the tachometer, using a visual propeller tachometer device, the problem turned out to be the propeller governor linkage. Upon inspection, the propeller control, which moves an arm attached to the governor via a complex bracket and bellcrank assembly, was not reaching full travel, so the governor control was not on the full-R.P.M. stop.

Prop governors are designed to have an adjustable control arm that can be moved to different radial positions to accommodate different installations. In my case, during the governor overhaul it looked like the arm was put back on at a slight different angle from the original angle. The fix was to remove the governor, take it back to the overhaul shop, and have them re-index the governor arm back a few notches to enable the bracket/control to reach full travel.
That part was easy, the downer is that to remove the governor on a Bellanca you have to remove the nose bowl, which means removing the propeller since the Bellanca nose bowls aren't split. Removing all of this is easy, re-installation is very time consuming. Re-installation of the propeller bolts, torquing them, and safety-wiring them is a "use the force, Luke" kind of job where the nose bowl must be installed before the propeller goes on, which means that you can't directly see what you're doing and you need about 3 extra elbows in your arm. After 3 hours of swearing, and a few puncture wounds from sharp safety wire ends punching into fingertips, the job was done. Someday I'm going to get around to splitting the nose bowl cowling so this job will be easier!

Overall getting the engine broken in and initially debugged was pretty painless. The next 5 flights were uneventful, and I recorded engine parameters and temperatures to monitor trends. The CHT readings did come down slightly and stabilize, indicating an initial breakin. Twenty flight hours later the first oil change had no metal in the filter, the spark plugs looked good, and a quick compression check yielded good readings all around.

Installation

Here's the engine being painted. The Superior cylinders came from the factory with black paint on the barrels, so I left that as-is and just painted the core engine case. This took quite a bit of masking. If you have a Lycoming, or if you're using overhauled cylinders without paint, I'd recommend just painting everything one color and save yourself the masking effort.



The baffles and air scoops got repaired, acid-etched, Alodined, epoxy primed, and then topcoated with grey Imron for maximum corrosion protection and shine. I have a fetish about corrosion protection so I gave them the full treatment. It is debatable whether this is worth it given that baffles are effectively consumable. Here's the priming step for one load of pieces.




After all the engine work, there's the re-installation on the airplane. This process is a lot cleaner after overhaul, but takes a lot of time due to the many fiddledy brackets, clamps, wires, hoses, and controls to route and secure.



Once the prop is reinstalled you need to set up the engine's internal timing by measuring angles from top-dead center piston stroke on the #1 cylinder. A timing disk attached to the spinner and a piston stopper plug is the most accurate way to perform this task on an O-470. The magnetos are then installed and timed to the engine and to each other so that they fire at the right position for the engine to make power.
Lastly there's finishing details such as the spark plugs, spark leads, P-leads for controlling the ignition, exhaust manifold, baffle sealing strips, carb heat and intake air hoses, and the engine cowling.

Assembly

Connecting rod.

Assemble two new connecting rod bolts in each connecting rod . Install new bearing inserts in the connecting rod and cap , making sure the tang of each bearing insert enters the locating slot. Assemble each connecting rod and cap, tighten the nuts moderately. Measure the inside diameter of each bearing and check for clearance against the measurements taken previously on the diameter of the crankpin journals. Do not take measurements of connecting rod bearing across the parting of the rod and cap. Take all measurements at 60° from the parting of connecting rod and cap. 7-54. Place the crankshaft on a suitable support on the bench so that all crankpins are free for installation of connecting rods. Disassemble connecting rods after checking bearing ID, thoroughly coat both inserts and the crankpin journals with preservative oil and assemble rods on their respective crankpins. The order of assembly should be such that the numbers stamped on the caps and rods will be down (toward the sump).

NOTE

Connecting rods are marked at manufacture with the part number followed by a letter (A through E) designating weight groups. It is recommended that replacement sets of rods be of the same weight classification. Individual rods may be replaced by a service rod bearing the letter "S". 7-55. The connecting rod bolts are tightened to a specified torque of 480 inch pounds (40 foot pounds).

Crank case.

Place both crankcase halves on a suitable support with the interior of each half facing upward. new bearing inserts in the crankcase making centre that the tang of each insert is fitted into the recess provided in the crankcase.

Place the left crankcase half on a suitable sup the bench with the cylinder pads down. This should be so constructed as to give approximately ches clearance between the crankcase and bench.

Lay the right crankcase half on the bench with the cylinder pads down. Install the governor drive shaft gear where applicable.

A counter bored recess is provided for an oil seal ring at each bolt and stud location. Install a new oil seal ring at the base of each stud.

Piston and cylinders.

See that all preservative oil accumulation on cylinders and piston assemblies is washed off with solvent and thoroughly dried with compressed air. Immediately prior to assembly of piston and cylinder to the engine, space the ring gap and apply a generous coating of oil mixture as described in paragraph 3-39. Apply to inside of cylinder barrel and to piston and rings working the oil mixture around the rings and into groove. Starting with no. 1 cylinder proceed to install as follows:

Rotate crankshaft so that no. 1 piston, when installgroove. ed. will be approximately at top dead center on the firing stroke: this is determined by both tappets of no. 1 cylinder being on the base circle of the cam lobes. Before any attempt is made to rotate the crankshaft support the connecting rods.

Assemble piston on connecting rod with piston number, which is stamped on bottom of piston

head, toward the front of the engine. The piston pin should be palm or hand push fit. If the original piston pin is tighter than a palm push fit, it is probably caused by nicks or slight carbon in the piston pin bore of the piston. If a new piston pin or piston is to be installed, select the pin to give a palm push fit at room temperature of 15 to 20 C. (60 to 70 F.). After piston pin is in place and central-ly located, insert a piston pin plug at each end of the piston pin.

Place a rubber cylinder base oil seal ring around the cylinder base assemble the application piston ring compressor over the top piston rings and install the cylinder over the piston, pushing the piston ring compressor ahead with the cylinder barrel. As the cylinder barrel approaches the crankcase, catch the piston ring compressor as it drops off the piston skirt. When the base of cylinder is seated on crankcase pad, secure the cylinder with 3/8 inch and 1/2 inch cylinder base nuts, tightening the nuts finger tight only.

To assure proper assembly of the crankcase halves and to eliminate the possibility of subsequent loosening of cylinder base nuts, a definite and specific sequence of tightening all crankcase and cylinder base nuts must be followed. Be certain that crankcase halves have been brought together, and fastenings secured as directed in Section 7 before installing cylinders. The cylinder base hold-down nuts are installed as described in the following paragraphs.

When all cylinders have been initially installed on the crankcase as described in paragraph 5-81, begin

tightening all cylinder base nuts as described below, using the proper cylinder base nut wrenches and handle in conjunction with a suitable torque indicator. Torque wrenches should employ the flexible beam design hydraulic principle or a dial indicator with rack and pinion.

NOTE

Before installing cylinder hold-down nuts, lubricate crankcase through stud threads with any one of the following lubricants, or combination of lubricants.

1. 90% SAE 50W engine oil and 10% STP.

2. SAE 30 oil.

3. Fel-Pro Food Grade AA Anti-Seize Lube.

a. Tighten 1/2 inch hold down nuts to 300 inch pounds (25 foot pounds) torque.

b. Using the same sequence, tighten the 1/2 inch nuts to 600 inch pounds (50 foot pounds).

c. Tighten the 3/8 inch hold down nuts to 300 inch pounds (25 foot pounds) torque. Sequence is optional.

d. As a final check hold the wrench at the correct torque, tapon each nut for about five seconds. If the nut does not turn, it may be presumed to be tightened to correct tor-que.

After all cylinder base nuts have been tightened, remove any nicks in the cylinder fins by filing or burring.

Install some type of vented plug in each spark plug hole after assembly of cylinder to prevent entrance of foreign matter and at the same time to permit the engine to be turned easily by hand.

Install hydraulic lifter in crankcase.

Assemble new shroud tube seal on both ends of shroud tubes.

Parallel Cylinder.

Install each shroud tube through its hole in the rocker box and press to firmly seat the seals in their respective position in the cylinder head and crankcase. Install shroud tube spring , lockplate , and 1/4-20 plain nut over stud provided in the rocker box. Tighten nut to proper torque and secure by bending the lockplate up around the nut.

Use of safety wire

self-locking nuts-

Self-locking nuts provide tight connections that will not loosen under vibrations. Self-locking nuts approved for use on aircraft meet critical specifications as to strength, corrosion resistance, and heat-resistant temperatures. New self-locking nuts must be used each time components are installed in critical areas throughout the entire aircraft.Self-locking nuts are found on all flight, engine, and fuel control linkage and attachments. There are two general types of self-locking nuts. They are the all-metal nuts and the metal nuts with a nonmetallic insert to provide the locking action. The Boots aircraft nut and the Flexloc nut are examples of the all-metal type. See figure 5-7. The elastic stop and the nonmetallic insert lock nut are examples of the nonmetallic insert type. All-metal self-locking nuts are constructed either of two ways. The threads in the load-carrying portion of the nut that is out of phase with the threads in the locking portion is one way. The second way is with a saw-cut top portion with a pinched-in thread. The locking action of these types depends upon the resiliency of the metal.



Washers-

Finally, a hardware item that is simple. You are likely to encounter only a couple of different types of washers AN960 and AN970. The main purposes of a washer in aircraft installation are to provide a shim when needed, act as a smooth load bearing surface, and to adjust the position of castle nuts in relation to the drilled hole in a bolt. Also, remember that plain washers are used under a lockwasher to prevent damage to a surface.
AN960 washers are the most common. They are manufactured in a regular thickness and a thinner thickness (one half the thickness of regular). The dash number following the AN960 indicates the size bolt for which they are used. The system is different from others we have encountered. As an example, an AN960-616 is used with a 3/8" bolt. Yet another numbering system. If you see "L" after the dash number, that means it is a thin or "light" washer. An AN960C would be - yes, a stainless washer. I can tell you are getting more familiar with the system so I will throw another wrench into the equation - an AN970 washer has a totally different dash number system. I am not even going to tell you what it is. I will tell you that an AN970 is a larger area flat washer used mainly for wood applications. The wider surface area protects the wood.
There are other types of washers. I mentioned lockwashers that are made several different ways. They are often split ring, they are sometimes internal tooth and even external tooth (see Figure 5). You will also find nylon washers and finishing washers that usually have a countersunk head. So, as you can see, washers are not quite as confusing as other hardware even though we can make ft difficult if we wish.

Reassembly

Now for the fun stuff, reassembling. Before doing that, you measure to check limits. Even if the parts are new you measure to make sure the parts are within limits. To measure the case you have to put it together with specified torque but without anything in it. Keep a record of the measurements for later reference
Corrosion-Prevention.
Prior to assembly of subassemblies, all parts should be cleaned to remove all traces of preservative oil and accumulated foreign matter. During assembly, cover all steel parts with a heavy coat of preservative oil. This mixture should be used on all machined surfaces, especially on bearing surfaces, cylinder bores and piston rings. The practive of using plain lubricating oil during assembly is not recommended.

Pre-Lubrication of Parts Prior to Assembly.
Many premature failure of parts have been traced directly to improper pre-lubrication of engine assembly. If parts are not properly lubricated, or an inferior lubricant is used, many of the engine parts will become scored before the engine oil goes through its first cycle and has had a change to lubricate the engine. This, of course, will lead to premature parts failure prior to normal service life, and in some cases, lead to engine failure before normal service hours have been accumulated. It is of utmost importance, therefore, that the following recommendations be adhered to a engine assembly. Consult the latest edition of Service Instruction No. 1059.

Coat the camshaft lobes, face of tappet bodies and rocker tips with lubri-bond (A) or equivalent.
Coat the valve stems and the interior of the valve guides with Texaco Molytex "0" or equivalent.

All other parts should be coated with a mixture of 15% pre-lubricant (STP or equivalent) and 85% SAE No. 50 mineral base aviation grade lubricating oil.

Olite Bushings.
During overhaul cleaning operations it is possible to wash the oil from these bushings; also, if a bushing has been replaced and either reamed or broached, its porosity may be affected. Therefore, before the
bushings are reassembled into the engine they must be impregnated by immersing then for at least fifteen minutes in engine oil that has been heated to 140°F.

It is strongly recommended that all overhaul facilities adapt a firm policy of checking pitch alignment
of bevel gears at the same time backlash is adjusted during engine overhaul.

Oil Seals and Gaskets.
When building up an engine during major overhaul, replace all oil seals and gaskets throughout the engine. For complete replacement sets of seals and gaskets available for these engines, consult applicable parts catalog.

Arbitrary Replacement of Parts.
It is recommended that certain parts throughout the engine be replaced at normal overhaul regardless of their apparent condition. Consult the latest edition of Service Bulletin No. 240 for information on the replacing of parts at overhaul. Included among these are the following:-


All engine oil hose
All oil seals
All gaskets
All circlips, lockplates and retaining rings
Piston rings
All exhaust valves (except Inconel alloy
All exhaust valve retaining keys
Crankshaft sludge tubes (where applicable)
Cylinder fin stabilizers
All bearing inserts (main and connecting
Magneto drive cushions
Stressed bolts and fastenings
Camshaft gear attaching bolts
Connecting rod bolts and nuts
Crankshaft flange bolts
Damaged ignition cable
All laminated shims
Crankshaft counterweight bushings
Piston pin plugs
A.C. diaphragm fuel pumps

Replacement of Studs.

Any studs which are bent,broken, damaged or loose, must be replaced.

The methodof removing studs depends on the type of stud and manner in which it is broken. The procedure for removing and replacing studs is as follows:

a. If there is sufficient thread area available on stud, use a collet grip tool consisting of a tapered collet that threads onto stud and a housing that slips over the collet. Tighten bolt on top of the housing and draw collet into housing to lock puller on the stud with a tight grip.

b. If the collet type tool cannot be used, drill a small hole into the stud. Employ a pilot bushing to guide drill into center of stud when stud is broken beneath the surface of the crankcase. Redrill the hole to enlarge it to accommodate the proper size extractor. Using the extractor, remove the stud.

c. After studs have been removed, check for size and condition of threads in stud holes to determine whether oversize studs must be used for replacement. Coat threads of studs with thread lubricant. Specification JAN-A-669, and drive stud to correct depth by using a suitable stud driver.

Crankcases and accessory cases

Crankcase.

The crankcase consists of two reinforced aluminum alloy castings with the accessory housing as an integral part, fastened together by means of thru bolts, studs and nuts. The mating surfaces are joined without use of gaskets and the main bearing bores are machined for use of precision type bearing inserts.

The crankcase is the foundation of the engine. it is around the crankcase that the engine is built. it has to support both itself and a variety of internal and external mechanisms .it performs a verity of functions. it:

1. Contains the bearings in which the crankshaft(and sometimes the camshaft) rotates

2. Provides an oil-tight enclosure for the lubricant

3. Provides mounting points to attach the engine to the airframe

4. Provides support for the attachment of the cylinders

5. Prevents misalignment to the crankshaft and its bearings

The crankcase may be of one or multi-piece construction, but generally crankcase can be divide into three groups:

1. In-line or vee-type crankcases.

2. Opposed engine crankcases.

3. Radial engine crankcases.

Accessory cases.

The section of an aeroengine that contains the devices to operate such accessories as fuel pump(s), hydraulic and air pumps, and generators. An accessory gearbox is driven by a driveshaft from a bevel bearing connected to a compressor shaft in some gas turbine engines

Connecting rods bushing replacement

Connecting Rod Bushings.

If the bushing in the small end of the connecting rod is worn beyond service limits, it can be removed and replaced by accomplishing the following procedure;

1. Clamp the connecting rod on the connecting rod replacement block (P/N 64597) in such a manner that the small bushing in the rod is in alignment with the hole stamped "Remove Bushing". Use the connecting rod bushing removal drift (P/N 64535) and drive the bushing out of the rod. Move the connecting rod to the "Install and Burnish" position and clamp it securely in place. Using the replacement drift (P/N 64536) drive a new bushing in place in the rod. Be sure the split in the bushing is located so that it is toward the piston end of rod and 45 off the centerline.

2. Use a suitable arbor press and the connecting rod bushing burnisher (P/N 64580) to burnish bushing in place. Pass the burnisher completely through the bushing. Remove the rod from the holding block and finish bore the bushing to diameter shown in Table of Limits, reference 510. Check the bushing ID with finish ID gage (P/N 64767). Check alignment of the hole in the bushing with connecting rod parallelism and squareness gage (P/N 64530) as described in paragraphs 7-29 and 7-30. If the assembly does not meet the requirements shown in references 566 and 567, Table of Limits, the entire assembly must be replaced.

Repair and replacement

Damaged Parts.

Abnormal damage such as burrs,nicks, scratches, scoring, or galling should be removed with a fine oil stone, crocus cloth, or any similiar abrasive substance. Following any repairs of this type, the part should be carefully cleaned in order to be certain that all abrasive has been removed and then checked with its

mating part to assure that the clearances are not ex-cessive. Flanged surfaces that are bent, warped, or nicked may be repaired by lapping to a true surface on a surface plate. Again the part should be cleaned to be certain that all abrasive has been removed. Defective threads can sometimes be repaired with a suitable die or tap. Small nicks can be removed satisfactorily with Swiss pattern files or small, edged stones, pipe tapped threads should not be tapped deeper in order to clean them up, because this practice will invariably result in an oversized tapped hole. If scratches or galling are removed from a bearing surface of a journal it should be buffed to a high finish. Generally it is impossible to repair cracks; however, welding operations may be performed in some parts of housings, providing the area is not a stressed section of the part. For example, almost any area of a rocker box may be welded, but no part of the cylinder head except the fins may be welded.

Painted Parts.

Parts requiring use of paint for protection or appearance should be painted in accordance with the following recommendations using material from the following list of approved material. Thinner –Toluene or equivalent (AMS3180 or equivalent Federal Spec. TTT- 548). Primer - Zinc chromate (AMS3110 or equivalent MIL-P-8585). Enamel - Phthalate resin type (AMS315C or equivalent MIL-E-7729).

NOTE

All machines bosses should be masked before painting. Do

not paint areas under hold down nuts where torque is required.

Aluminum and Steel Parts.

Parts shall be cleaned and degreased prior to painting. Apply one coat zinc chromate primer, thinned with approximately two parts toluene, and air dry. Apply one coat of enamel and bake at 250°F., to 300°F., for one-half hour. Enamel may be allowed to air dry but an inferior finish will result. Parts from which paint has not been removed may be repainted omitting the primer coat. 3-30. Magnesium Parts. Magnesium parts should be cleaned thoroughly with a dichromate treatment prior to painting. This treatment consists of cleaning all traces of oil and grease from the part by using a neutral, non-corrosive

degreasing medium followed by a rinse. After which the part is immersed for 45 minutes in a hot dichromate solution (3/4 lbs. of sodium dichromate to one gallon of water at 180°F. to 200°F., quantity as required). The part should then be washed thoroughly in cold running water, dipped in hot water and dried in an air blast. Immediately thereafter the part should be painted with a prime coat

and engine enamel in the same manner as prescribed for aluminum parts. 3-31. Shroud Tubes. Shroud tube should be thoroughly cleaned and dipped in zinc chromate primer thinned to spraying consistency. After the primer is dried the shroud tube should be painted on the outside with engine enamel. 3-32. All paint applied in the foregoing operations should preferably be sprayed; however, if it is necessary to use a brush, care should be exercised to avoid an accumulation of pockets of paint. 3-33. Replacement of Studs. Any studs which are bent,broken, damaged or loose, must be replaced. The method of removing studs depends on the type of stud and manner in which it is broken. The procedure for removing and

replacing studs is as follows:

a. If there is sufficient thread area available on stud, use a collet grip tool consisting of a tapered collet that threads onto stud and a housing that slips over the collet. Tighten bolt on top of the housing and draw collet into housing to lock puller on the stud with a tight

grip.

b. If the collet type tool cannot be used, drill a small hole into the stud. Employ a pilot bushing to guide drill into center of stud when stud is broken beneath the surface of the crankcase. Redrill the hole to enlarge it to accommodate the proper size extractor. Using the extractor, remove the stud.

c. After studs have been removed, check for size and condition of threads in stud holes to determine whether oversize studs must be used for replacement. Coat threads of studs with thread lubricant. Specification JAN-A-669, and drive stud to correct depth by using a suitable stud driver. 3-34. Corrosion Prevention. At the conclusion of all repair operations and subsequent inspection, coat all steel parts

with preservative oil.

Structural inspection

Structural failures can be determined by several different methods depending on the part involved. The following are a few of the methods employed:

magnetic particle,

dye penetrant,

penetrate,

x-ray and various electronic methods,

Visual Inspection

IGNITION SYSTEM

Ignition Harness. Unless the harness assembly is in obviously new condition and is known to have been recently installed, it is recommended that the harness be replaced at overhaul.

CYLINDERS, PISTONS AND VALVE TRAIN

Inspect all cylinder, piston and valve train parts.

Cylinder Head (Visual Inspection).

Examine the cylinder head thoroughly, checking for the following

possible defects.

a. Loose, scored, pitted or otherwise damaged valve seats. (Mark for replacement).

b. Loose or damaged studs. (Replace with 0.003, 0.007 or 0.012 oversize studs).

c. Loose or damaged spark plug heli-coil inserts. (Mark for replacement with oversize insert.

d. Loose, cracked or scored valve guides. (Mark for replacement).

e. Nicked, scored or dented mounting pads. (Intake and exhaust ports, rocker box covers.)

f. Cooling fins. The following standards shall prevail insofar as acceptance or rejection of cylinder heads are concerned.

Physically damaged, broken or bent fins.

(a) The blended area for any one fin shall not exceed 3/8 square inches, nor 3/8 inch in depth.

(b) No more than two blended areas on any one fin.

(c) No more than four blended fins on the push rod side of the head. No more than six blended fins on

the anti-push rod side of the head.

(d) In addition to the above, it is recommended that a fluorescent penetrant inspection of the cylinder be made. Pay particular attention to the following areas.

(1) Between the 15th and 20th cylinder fin (counting from the top) on exhaust port side of cylinder.

(2) The area around the lower spark plug

Cylinder Head (Dimensional Inspection).

Check the ID of each intake valve guide (it is recommended that exhaust valve guides be replaced at overhaul) with the flat plug rejection gage (ST-81). Check the diameter and outof- roundness of the guide bore by checking with the gage at a minimum of two position 900 apart. If the gage enters the guide at any of the positions tested, mark the guide for replacement.

Cylinder Barrel (Visual Inspection).

In addition to a thorough inspection of the cylinder barrel to ascertain its general condition, make the following specific checks.

a. Cooling Fins. It is recommended that notches or nicks be profiled with a hand grinder or file. A cracked cylinder barrel is cause for rejection of the cylinder.

b. Cylinder Skirt. Replace any cylinder having a bent, cracked, broken or corroded skirt,

c. Check mounting flange for cracks, nicks, warping, or corrosion.

d. Inspect interior of barrel for scoring or corrosion. Minor damage can be repaired by regrinding or honing; deep scoring or pitting, however, is cause for rejection of the cylinder.

e. Inspect interior of nitrided barrel for barrel glaze and a possible ring wear step at the point where the piston reverses travel at the top of the stroke.

Cylinder Barrel (Dimensional Inspection).

Dimen-sional inspection of the barrel consists of the following measurements (the numbers in parenthesis refer to the ap-plicable reference numbers in the Table of Limits):

a. Fit between piston skirt and cylinder (519).

b. Maximum taper of cylinder walls (520).

c. Maximum out-of roundness (521). c. Maximum out-of-roundness (521).

d. Bore diameter (522).

Piston (Visual Inspection).

Examine the top of the piston for excessive pitting, cavaties or surface distortion. The latter may be evidence of detonation, particularly if the piston has been in service for a relatively short time. Other critical points which must receive thorough visual examination are the piston ring lands and grooves, piston pin holes, and piston pin holes bosses.

Piston (Dimensional Inspection).

Make the following dimensional checks on each piston (the numbers in paren- thesis refer to the applicable reference numbers in the Table of Limits).

Table of Limits

a. Side clearance between piston ring and piston (514,515 and 516). Pistons for Lycoming opposed engines are ground with a slight taper from the skirt to ground with the exception of the lands between the the head, with the exception of the lands between the top compression and oil control rings, which are ground parallel.

b. Inside diameter of piston pin hole (512).

c. Clearance between piston skirt and cylinder and piston diameter at top and bottom (519).

Piston Pin and Piston Pin Plugs.

Check OD of piston pin against ID of hole in piston (reference 512, Table of Limits). Measure fit between piston and plugs and check OD of plugs (reference 513, Table of Limits). Examine interior

surfaces of piston pin for corrosion or pitting. Valve Rockers. Damaged, badly worn, pitted or

scored top and push rod sockets warrant replacement of the rocker. Rockers that are scored at the point of contact with the fulcrum must be replaced.

Push Rods.

Inspect push rods for wear or looseness of ball ends. If ball ends are loose, replace the rod. Rod must be straight within .010 inch.

Valves.

Remove the valves from the cylinder and clean to remove soft carbon and examine visually for physical damage, damage due to burning or corrosion. Valves that indicate damage of this nature must not be reused.

OIL SUMP AND FUEL INDUCTION

Oil Suction Screen.

Before cleaning the screen, inspect for evidence of metal particles, which could serve as an aid to locate deterioration in some section of the engine. Inspect the screen for distortion or openings of the mesh.

Carburetors.

Inspection of carburetors must determine parts serviceability and repair and replacement requirements. Check applicable manufacturer's publications for limits to be used when conducting inspection.

CRANKCASE, CRANKSHAFT & RECIPROCATING PARTS

Inspect all crankcase, Specific instructions follow.

Bearings (Precision Type).

AU precision type bearing inserts used for main crankshaft bearings and connecting rod bearings should be replaced with new bearing inserts at overhaul.

Crankcase (Visual Inspection).

Check carefully for burrs, nicks and cracks around the bearing support webs. Check bearing bores and inspect tang slots for any roughness that might case improper seating of bearing inserts. Check all drilled holes.

Fretting on the contacting surfaces of the hearingsaddle supports in the crankcase occurs on some engines. This condition is caused by slight motion between the contacting surfaces and results in erosion of the metal surface.The affected areas have tiny pit holes and a frosted appearance. as contrasted to adjacent shiny unaffected surfaces. This condition can be misleading because of its trivial appearance: nevertheless it can be the cause of severe engine damage.

Fretting, by inself in this area. does not appreciably damage the structure of the metal. but the metal removed by the fretting action does change the size of the bearing saddles sufficiently to cause loose thru-studs and undersize main bearing bares. If not detected during overhaul.

excessively tight crankshaft bearing fits will result with eventual engine failure.

Crankshaft (Visual Inspection).

Carefully inspect all surfaces of the shaft for cracks. checking the baring surfaces with particular care for scoring, galling, corrosion, pitting or other damage.

Crankshaft (Dimensional Inspection).

Place the crankshaft in Vee blocks supported at the locations called out in Table of Limits and using a surface plate and dial indicator measure the run-out at center main bearings. If this total indicator reading exceeds the dimensions given in reference 556 the shaft must not be reused. The crankshaft flange run-out may be checked at this time and if the total indicator reading exceeds the run-out given in Table of Limits (reference 607) the shaft must be rejected.

Using new inserts at all main bearing locations,assemble crankcase halves together, temporarily torque all thru-bolts to 300 inch pounds and measure the ID of the bearings. Measure the OD of the crankshaft main bearing journals and compare the resulting clearances

with the Table of Limits (reference 501). Assemble the connecting rods temporarily (using new bearing inserts)and check the crankpin journal clearances in the same manner, see Table of Limits. If clearances

do not fall within prescribed limits, the shaft must be brought undersize. See Repair and Replacement section for instructions for regrinding.

Camshaft (Visual Inspection).

Carefully inspect all surfaces of the camshaft for cracks, scoring, galling, cor-rosion, pitting or other damage; be particularly careful when inspecting bearing surfaces. If a hydraulic lifter has been rejected for spalling, inspect the corresponding cam lobe. Any indication of distress, surface irregularity or feathering at the edge of the cam lobe is cause for rejec-tion of the camshaft.

Camshaft (Dimensional Inspection).

Support the camshaft in Vee blocks at its front and rear bearing jour-nals and check the run-out at the center bearing location.

See Table of Limits Slight bending opera-tions are permissible on the camshaft providing careful magnetic inspection follows such procedures. Measure the diameter of the camshaft bearing journals and check them against the bearings formed by the crankcase. Table of Limits.

Connecting Rods (Dimensional Inspection).

Discard all connecting rod bolts and nuts; new bolts and nuts are to be used on assembly.Check condition of bore in large end for seating of the bearing inserts. Check bore in small end of bushing with connecting rod bushing plug gage (P/N 64537). If the gage enters the bushing, bushing must be replaced.

Connecting Rod Parallelism Check.

Using connecting rod parallelism and squareness gage(P/N 64530), insert tapered sleeves (1 and 2) in bearing holes in connecting rod. Be sure that bearing cap is assembled properly and securely tightened. Place arbors (3 and 4) through sleeves (1 and 2 respectively) and place gage arm to exact distance between arbors and lock the adjusting screw with nut . Then remove gage arm, place

it on other end of arbor, and check distance between ar- bors. For exact parallelism or alignment, the distances checked on both sides will be the same. See reference 566, Table of Limits.

Connecting Rod Squareness Check.

Using the same gage that was used in the parallelism check described above, place parallel blocks (1) on surface plate and, with sleeves and arbors still in place in connecting rod, place ends of arbor on parallel blocks. Check clearance at points (2) where arbors rest on parallel blocks, using a feeler gage. For exact squareness or zero twist, no clearance will exist at the designated points.

Counterweight Bushing

Wear in the counterweight bushing is usually evident as out-of-round on the inside diameter. Check each bushing with the bore gage P/N ST-73. The diameter should be between .7485 and .7505inch. Out of-round should not exceed .0005 inch. The ST-73 gage is specially made so that it can be set with a micrometer. If the diameter of any bushing is oversize, or excessively out-of-round all the bushing in the counterweight must be replaced.

Crankshaft Counterweight Bushing. Wear or damage to the crankshaft counterweight bushing ,

located in the crankshaft counterweight lobes is almost impossible to detect by normal inspection procedures. Because of this situation and as damage to the counterweight bushing could cause failure to the counterweight and/or the crankshaft, it is mandatory that these bushings be replaced at overhaul.