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Skywagons >> Maintenance Tips

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duncan
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Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Camshaft, Lifter, Pushrod Removal and Inspection
      #1659 - 03/11/04 03:43 PM Attachment (151 downloads)

Although the ferrous PPM/Hr was low in my last oil change, I clean my ADC oil filter and send the debris to Aviation Laboratories at every annual inspection. Last month they replied that the material I sent in proved to spectroscopically match AMS#6371 - possible CAMSHAFT material. Since the original TCM re-man camshaft only lasted 500 hours, and TCM provided the replacement (at no charge) - I thought I better have a look-see.

This thread shows some of the tools and tricks that make this task easier, beginning with the attached photo of a home-built Pushrod Housing (Tube) Spring Compression device. You should have a licensed Powerplant Mechanic supervise your efforts.

First remove the lower set of sparkplugs and cylinder baffling. You can secure these on top the engine.

Next remove the Rocker Covers and their gaskets. If you don't have replacement gaskets, take care not to destroy the old ones, but they DO need to be removed from the cylinder to provide rocker shaft removal clearance.

Next, remove the targeted (exhaust or intake) rocker shaft hold-down bolt. Rotate propeller to ensure the cam lobe is not pressing on the rocker/valve. Generally you can remove the rocker shaft with finger pressure, but a soft mallet tap may be required to start it. The rocker shaft exits toward the side of the cylinder. You can leave the shaft in the cylinder housing once the rocker arm is removed. If you remove the shaft, be sure you return it and its associated rocker to the same cylinder location. Remove the two rocker arm thrust washers also.

Remove the pushrod, noting its location and up/down orientation. An easy way to do this is with a cardboard box, with 12 pushrod-sized holes in the top. Mark "forward" on the box too.

Although a large screwdriver can be used, the attached picture shows how an old flat bladed putty knife can be shaped to cup the pushrod cover radius, giving much more purchase, security, and less damage to the pushrod cover.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Pushrod Cover Removal Tool [Re: ]
      #1660 - 03/11/04 03:46 PM Attachment (138 downloads)

This picture shows how the tool is shaped to match the tube's outer circumference, and is applied to compress the spring. Note the spring has made characteristic wear marks on this pushrod housing tube.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: Pushrod Cover Removal Tool [Re: ]
      #1661 - 03/11/04 03:48 PM Attachment (120 downloads)

Engine-side view of applying pressure to compress the spring.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: Pushrod Cover Removal Tool [Re: ]
      #1662 - 03/11/04 03:49 PM Attachment (134 downloads)

It takes a lot of "push" to compress the spring. Note how narrow the tool must be to get betwen intake tube and cylinder.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: Pushrod Cover Removal Tool [Re: ]
      #1663 - 03/11/04 03:53 PM Attachment (119 downloads)

You need to push until you can see the (white) upper end pushrod housing packing and adjoining washers. Carefully remove these from the pushrod housing end. A second person is very helpful here, but don't slip on the tool and nip off the ends of their fingers!

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: Camshaft, Lifter, Pushrod Removal and Inspection [Re: ]
      #1664 - 03/11/04 03:56 PM Attachment (111 downloads)

Remove the pushrod housing (tube) and the washers and packing from the other end (engine block).

This picture actually show the packing just before re-installing the pushrod housing - repeated later with more explanation.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: Camshaft, Lifter, Pushrod Removal and Inspection [Re: ]
      #1665 - 03/11/04 04:01 PM Attachment (133 downloads)

Once you have remove the pushrod housing and packing, use a .030 safety wire, with a small 1/2 hooked end to extract the lifter. DO NOT use a magnet as it can magnetize the internal check valve. The hydraulic lifter should have a shiny surface with no pits. Lifters often fail before the camshaft does.

The picture shows the common "fishhook" wear pattern on the face of the lobe, just before and after the top of the lobe. This is caused by the angle cut on the cam lobe which forces the lifters to rotate during normal operation. No pits or corrosion should be seen.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Installing Lifters [Re: ]
      #1666 - 03/11/04 04:03 PM Attachment (117 downloads)

This picture shows how a 7/16 deep socket can be "padded" with black electrical tape to snug fit in the lifter and be used to insert into the lifter hole on the crankcase.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Pushrod Housing Installation Trick [Re: ]
      #1667 - 03/11/04 04:09 PM Attachment (115 downloads)

The idea here is to attach .020 safety wire to the pushrod housing springs, holding them in a compressed state. These are then slid onto the tube and makes reassembly a snap and easily done by one person.

First, place safety wires on opposite sides of spring, running though the last full loops. If you will be unable to cut and remove the safety wire when installed, due to clearance issues, add an additional "loop" as shown here towards the left side of the spring.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: Pushrod Housing Installation Trick [Re: ]
      #1668 - 03/11/04 04:14 PM Attachment (109 downloads)

Put the spring in a bench vise, compress it fully while applying tension to the safety wire. Once compressed, twist the safety wire ends. If using the "loop" method, give them good twists also. The loops will be snagged with another tool when installing the springs. You will tug on these loops and untwist the loose ends, so cut these rather short to assist in their unraveling.

If not using the "loop" method, it is best to cut the end twists rather long to assist your grabbing them once installed and the safety wire cut with traditional diagonal cutters. The small electronic ones work best.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: Pushrod Housing Installation Trick [Re: ]
      #1669 - 03/11/04 04:21 PM Attachment (89 downloads)

Install inner washer and packing ring to the crankcase. The soft packing ring will help guide and center during installation.

Place pushrod housing through upper hole in cylinder, go past cylinder wall cooling fins, slide on the spring (held compressed by two safety wires), then slide on the outer pushrod cover washer that goes against the packing.

In this picture there was sufficient room to get the diaganol cutters in, so the "loops" were not used. Note length of twist on safetywire ends to assist grabbing them.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: Pushrod Housing Installation Trick [Re: ]
      #1670 - 03/11/04 04:23 PM Attachment (96 downloads)

Now cut one safety wire and remove it using the twisted end. You can then rotate the pushrod cover to easily cut and remove the remaining safety wire.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
The "Loop" Method Installation Trick [Re: ]
      #1671 - 03/11/04 04:28 PM Attachment (83 downloads)

When you just can't get the diagonal cutters in, this "loop" method works great. Just make a loop "pulling tool" out of .040 safety wire that has a rotating hook. Slide the hook through the loop, rotate and pull hard enought to unravel the twisted ends of the safety wire.

This picture shows the hook engaged in the loop. Note the twisted ends of safety wire, with just a few twists. Pull hard.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: The "Loop" Method Installation Trick [Re: ]
      #1672 - 03/11/04 04:35 PM Attachment (89 downloads)

This is a close up of the .040 hook engaged in the .020 loop. Note the 1/2 twist on the hook to keep the hook from straightening out when pulling on the loop.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: The "Loop" Method Installation Trick [Re: ]
      #1673 - 03/11/04 04:37 PM Attachment (87 downloads)

When the safety wire ends unravel, you will suddenly have something like this in your hands. Be sure to note that both unravelled ends are attached, otherwise you may have some safety wire entangled in the pushrod housing spring. This must be removed if it happens.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: Pushrod Housing Installation Trick [Re: ]
      #1674 - 03/11/04 04:39 PM Attachment (93 downloads)

While the safety wires are holding the pushrod housing spring compressed, you can easily install the first washer before the packing.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: Pushrod Housing Installation Trick [Re: ]
      #1675 - 03/11/04 04:40 PM Attachment (83 downloads)

...then the packing.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Re: Pushrod Housing Installation Trick [Re: ]
      #1676 - 03/11/04 04:42 PM Attachment (83 downloads)

...then the final washer. At this point you will be ready to release the spring tension. Watch your fingers! You can pre-guide the cylinder end into its hole before releasing tension.

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duncan
Master Webmaster


Reged: 05/04/02
Posts: 249
Loc: Crawford, CO (99V)
Handy Valve Spring Compression Tool [Re: ]
      #1677 - 03/11/04 04:51 PM Attachment (129 downloads)

Here is a trick for compressing the valve springs. Place a 1/4-20 bolt into the hole where the rocker cover screw normally goes. Apply a claw hammer to the valve spring retainer. Be sure to observe that the valve spring retainer keys are not dislodged.

You might need to do this when reassembling the rocker arms. Note position of bevel in assembled rocker shaft. Be sure to fully align the rocker retainer bolt hole with NO side loads in order to properly torque this bolt.

Also note the wear pattern on the #5 cylinder's rocker shaft. I am told this is normal after just a few hours of running. The wear will be on the bottom (engine) side when properly asembled.

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The International 180-185 Club does not review, endorse, nor necessarily agree with anything posted on this Forum. No warranty is provided in regards to the legality of any aircraft modifications, nor for your personal pilot skills in performing any maneuver, including landings.