Paul Dye’s Notes from Lycoming Class


Ed. note: These notes are part of Paul Dye’s article about attending Lycoming’s engine assembly school.

For such “simple” engines, Lycoming type power plants, there are quite a few little tricks of the trade that should be used when taking one apart or putting it together that can make or break the chances of an engine going to full TBO without a problem. This is one good reason to go to the school, and here are our own notes taken at random during the three-day class.

Day 1 – Disassembly

  1. The class has six engines available for the students to take apart and put back together. Ideally, students work in pairs on a single engine to maximize learning and make an efficient use of time.
  2. Not all of the engines are alike – but they are close.
  3. Stripping the engine starts by removing all external accessories, such as Mags, filters, carbs, starter, alternator, etc. Intake tubes, oil return lines and anything else that isn’t part of the core motor come off next.
  4. Organization is a good idea – use boxes for parts, nuts and bolts. Keep cylinder assemblies’ together, and separate intake from exhaust.
  5. The two little plugs on the bottom of our sump were for sniffle valves.
  6. Removing the intercylinder baffles is done with a bent probe or special tool. It is not as hard as it looks.
  7. When removing rockers, make sure both valves in the cylinder are closed so there is no tension on the lifters.
  8. Use a curved brass rod to drive out the rocker shaft.
  9. It’s a good idea to have a box of the rocker shaft end caps on hand.
  10. Pulling out pushrod tubes is a knuckle buster – wear gloves.
  11. Roller tappets have different pushrod tube seals – easy way to tell that the engine is equipped with roller tappets.
  12. Make a hydraulic lifer removal tool from safety wire
  13. Never use a magnet to remove hydraulic lifters
  14. If the hydraulic lifter comes out in two pieces, use a pencil eraser to get the second half put.
  15. Removing sump and accessory case – make sure all the bolts are out!!
  16. There are two bolts that hide behind the right mag hole that will retain the accessory case.
  17. Sump comes off first, then accessory case because the rearmost fasteners for the sump are studs. On newer engines, this changes due to using bolts, as a result of the oil pump AD debacle.
  18.  When lifting off the accessory case, some loose parts can fall loose. Idler gears just lift off. Go slow if you want to keep everything in place.
  19. Tach drive lifts out of camshaft gear.
  20. Put engine on table to remove jugs and split case – take it off the engine stand.
  21. When removing jugs, loosen and remove small nuts first, then big ones.
  22. Don’t let rods hit cases openings, or you damage the case opening which is the seat for the cylinder base O-Ring.
  23. Remove cylinders across from each other – put the pistons at TDC for each pair – front two, then back two.
  24. Picture 8005 – “Let us pray to the god of internal combustion….”
  25. Use a slide hammer to remove through studs. There’s are made from a gear puller, with the right nuts welded on the end.
  26. You can tell which studs are free and which are screwed in by looking at the threads – they change dimension on the captive ones.
  27. Leave case edge bolts in place until through studs are removed!
  28. Remove all of the case edge bolts – and don’t forget the one behind the camshaft gear!!
  29. Don’t forget the bolt behind the camshaft gear! You can use a cylinder base wrench to get it.
  30. Use the slide hammer on the fixed studs to separate the case halves using momentum. Alternate front and rear (and top and bottom) to pull them apart evenly.
  31. Catch the crank so that it doesn’t fall, and put it in a wooden v-block support.
  32. Use alcohol to clean of the mating surfaces, clean the bearings, etc.
  33. Remove the tappets, and clean them off. If it’s a real rebuild, keep them in the correct spots.
  34. Cam is different for roller tappets!
  35. Front-mounted governor drive has a staked plug inside – have to remove the staking in order to remove it, then re-stake in another position on re-assembly, Can only do this so many times.
  36. Idler pulley shafts on back of engine are simple, and can stay in place unless case is going out for re-work.
  37. To remove rods, you need to grind down a long socket to fit, tapering the nose.

Day 2 – Assembly

  1. Most people use way too much antisieze when installing rod bearings – a thin film is all it takes.
  2. Rod cap bolts need a film of food-grade lubricant on the threads – just fill the threads with the white stuff.
  3. The tapered end of the rod cap nuts goes “in”
  4. Rods and caps get paired and numbers – for convention, all numbers go down when putting the crankshaft together.
  5. Lubricate the bearing surface with pre-lube (STP and Oil) before assembly.
  6. Rod end bearings are torqued to 40 ft.lbs using the tapered long socket.
  7. Many people like to assemble the case to the crankshaft on an engine stand. Lycoming prefers to do it on a bench rest (home-made). If you use rubber bands to hold the camshaft in pace, this makes it much less likely that a bearing will drop out of position.
  8. Paint the mating surfaces of case with POB, and then let it get tacky while you work with the bearings. Then apply the 00 silk thread. Two lines, inside the bolt holes.
  9. When lubing the bearings, don’t get oil on the mating surfaces – it will get trapped, then melt out and take the case bolt torque with it!
  10. Lubricate the tappets and insert them into the case. Make sure there are 8 of them! Flat tappets get a little moly grease on the face. Roller Tappets get a coating of oil on the roller.
  11. Coat the camshaft lobes with pre-lube before placing in the case. Over-lubing the bearing surfaces will just make a mess on the mating surfaces.
  12. Retain the camshaft in the case half with four rubber bands looped around the shaft and then out through the cylinder hole to a stud.
  13. Lubricate the thrust bearing surface with black grease on both case halves.
  14. Put the two liens of silk thread on the POB when it becomes a bit tacky.
  15. Test fit the main bearing into the nose journal, and draw sharpie lines to show you where it goes.
  16. Install the front bearing on the crankshaft with lots of pre-lube to adhere it in place.
  17. Install the second crank in the case, carefully lowering it in place. Play with the front bearing to line it up and get it seated.
  18. Flip the other half of the case and lower it into place letting the studs go through, and making sure it goes down level.
  19. It really takes three people to properly assemble the crank and case – two can do it, but things get heavy while ensuring proper alignment.
  20. Tap the cases together lightly with a soft-faced hammer.
  21. Install two upper and two lower case seam bolts just to keep the two halves from falling apart – just snug is OK.
  22. Now install torque plates or equivalent on the short studs on the cylinder openings. Next come the through-studs, and they get hammered in place using a special tool so you don’t drive them too deep.
  23. Thread cylinder hold-down nuts on to the through studs and torque them to 25 ft-lbs.
  24. Lower case bolts are installed above the sump with the holes lined up for safety wire. Cotter pins aren’t used in case they break off.
  25. Follow the SI for torque sequence of bolts – and make sure to use the right subsection for your engine.
  26. Don’t forget the nut on the stud behind the camshaft gear!!
  27. Doebler tip – the seal for pushrod tubes works better if you turn it inside out!
  28.  Safety wire the nut behind the camshaft gear.
  29.  Put the engine on the stand by attaching the stand to the engine -0 then tipping it onto the floor (hoist works best!)
  30.  Ring shave an up and down – make sure the match the wedge (sloped surface up).
  31.  Remove torque pates and install pistons, then use ring compressor to install cylinder.
  32.  Install cylinders from back to front because that is what the manual says.
  33. Torque sequence shown in SI.
  34. Oil pressure relief valve boss is relieved to fit cylinder base wrench.
  35. Install idler gears using alignment marks to set internal engine timing.
  36. Make sure to collapse hydraulic lifters before installing them!
  37. Put each cylinder at TDC in turn to install pushrods, tubes, and rockers.
  38. Check dry tappet clearance on all cylinders using feeler Go-NoGo gauge – between .028 and .080.
  39.  Install intercylinder baffles – you can pull up on the hook with a loop of safety wire!

Day 3 – Final assembly and dressing

  1. The hole on the left hole near the back for the baffle attachment is drilled into a boss that extends inside the accessory case cavity.
  2. The oil pump drive shaft is keyed to the drive gear with a flat.
  3. The oil pump housing floats on the mounting bolts, and needs to be adjusted so that the gears turn freely- then tightened down.
  4. Don’t forget the fuel pump drive plunger, and put it in with the drive flange facing up.
  5. The sump suction screen pulls il from underneath near the end.
  6. Oil is sucked up through a passage in the back of the sump and into the back of the accessory case. Make sure to keep the sump tight, or you’ll get an oil leak.
  7. Check the intake tubes on the sump for looseness – they can re-swaged.
  8. Orient the oil pump drive shaft so that the lugs are vertical, and make sure the crankshaft lugs are aligned the same way before putting on the case.
  9. Don’t safety wire the oil pump bolts across the drive gear!
  10.  Prelube the gears before installing the accessory case.
  11. If the accessory case doesn’t’ drop into place, re-align the oil pump shaft lugs.
  12. Watch the different bolt lengths when attaching the accessory case – the right lengths are obvious when you look at them.
  13.  Put the sump in place, then use a couple of nuts to hold it before putting the rest of the bolts in place.
  14. You have to retighten the sump bolts as the gasket shrinks (when the engine is in service).
  15. Make sure the Fuel pump drive plunger is “up” before installing the pump.
  16.  You have to start the fuel pump bolts before the pump is fully seated.
  17. The oil drain tubes are unique – they fit nicely when in the right positions.
  18. If the locating mark is missing on the ring gear support, set the crank at #1 TDC and align the timing mark on the back of the ring gear to the center case split as you install it.
  19. Put the pin in the correct hole in the mag, set the mag in place, then pull the pin before timing.
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Paul Dye
Paul Dye, KITPLANES® Editor at Large, retired as a Lead Flight Director for NASA’s Human Space Flight program, with 40 years of aerospace experience on everything from Cubs to the Space Shuttle. An avid homebuilder, he began flying and working on airplanes as a teen and has experience with a wide range of construction techniques and materials. He flies an RV-8 and SubSonex jet that he built, an RV-3 that he built with his pilot wife, as well as a Dream Tundra and an electric Xenos motorglider they completed. Currently, they are building an F1 Rocket. A commercially licensed pilot, he has logged over 6000 hours in many different types of aircraft and is an A&P, FAA DAR, EAA Tech Counselor and Flight Advisor; he was formerly a member of the Homebuilder’s Council. He consults and collaborates in aerospace operations and flight-testing projects across the country.


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