Thorp Air Command - T18.net

Still had to spend a lot of time on business stuff this week, but some things that I got done include:

* Bought a couple cheap exhaust hangers at AutoZone to compare to the disintegrating original rubber straps. One forum member earlier in this thread said that, in his experience, his hanger from the auto parts store didn't last long. I can see why. These hangers are going back and I'll make my own.

* Degreased and cleaned the engine. The engine turned out beautiful, but the outcome is that I'll end up loosening all the jugs so that I can replace all the pushrod tube (shroud) seals. My engine must have had leaky seals on the right side's two inner pushrod tubes, and a mechanic used some black goop to presumably seal the leaks. Well, that black goop didn't fare too well when the engine degreaser liquid came into contact with it. I've decided this is a blessing in disguise and I'll replace all the seals now while I'm doing the other work. My EAA Chapter 45 buddies have work sessions every Monday night, and we will replace these seals when the plane goes back to the airport in August. I'm told there is a whole procedure to follow to loosen the heads and tighten them back up after the seals are replaced, so I'll need some experienced folks around me to advise on this.

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John Twigg N12055 SN.79 Pittsburgh, PA (KFWQ)

Rich - thanks for the rod end greaser suggestion. I'll order one tomorrow. The link I found is http://www.aircraftspruce.com/catalog/a ... reaser.php

Jeff J - thanks for finding this substitute MS21150 rod end bearing. It does look awful close.

I'll try going the grease route first because these rod end bearings aren't cheap! If that doesn't work, I can always make a new tube that isn't reamed on the MS21150 end. Awesome!

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John Twigg N12055 SN.79 Pittsburgh, PA (KFWQ)

On a Lycoming to replace the pushrod seals, the valve cover is removed, then the rocker arm shaft is removed at top dead center of the piston, remove the rocker arms and pushrods (mark both the rocker arms and pushrods of where you removed them, they must go back into the same position) there is a keeper between the two pushrods tubes held in place with one nut with a bent lock tab holding it in place, straiten the lock tab remove the lock tab nut, lock tab and the hold down plate (be mindful of the direction you remove it) you can wiggle the pushrod tubes out of the cylinder, remove the old seals, clean the areas where the seals are, install the new seals and reassemble using the correct torque on both the hold down nut between the push rods and the valve cover screws. Other tips are to bleed the lifters of oil while you have the tubes out, this allows easy install of the rocker shaft. when bleeding the lifters remove them using a piece of safety wire with the very tip (1/4") bent 90 degree's into a hook, they just pull out of the lifter body(again make sure they go back into the lifter body you removed them from) using only a wooden tooth pick in the end of the lifter with the small tube compress the lifter in a bath of solvent this will allow the oil in the lifter to be expelled, allowing the lifter to be compressed during installation of the rocker arms, only use very light oiling for re assembly as it will end up inside the lifter causing problems installing the rocker shaft.

Phil
118 BC

For exhaust hangers I used a 3" x 4" piece of .020" stainless shim stock as a 'flexure' on each pipe. Stainless is low-conductive, heat resistant, and won't deteriorate. Wish I had a better picture, but this one also shows the 'backward' air box for updraft carb. Air from rear baffle, it eliminates the bottom scoop.

Les.

I tried to find a pic of my hangars , but no luck . I used a stainless adel clamp on the gear frame (don't use the aluminum ones) , then attached my conveyor belt material to it . Used the stainless steel band that came with my Custom Exhaust and attached that end to the free end on the conveyor belt . So far everyone is happy .

RB

I used 1/8" SS cable, made a 5" diameter circle using a nicopress, twisted it in a figure 8 and clamped it with SS hose clamps. Might have to adjust the circle to fit your needs!

Phil, boy if I don't need to loosen the cylinders to remove the pushrod tubes, that would be fantastic. I wasn't aware of your method, but I hadn't looked into how to take them off much - just figured the cylinders had to be pulled a little. If I understand your method, that means that it's way less involved and I can do it myself in my basement. Sweet!

Les, Bill & Rich - good to know that it doesn't need to be rubber! In my case, my exhaust pipes have no slider or ball joints anywhere. 1974. Just solid pipes. Any idea if rubber is the best support in my case (since rubber was what was used)?

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John Twigg N12055 SN.79 Pittsburgh, PA (KFWQ)

I think you probably need something with a little "give" since you don't have a ball joint . Engine moving in the mounts and twerking while operating . Something like Bill used would work .

RB

Yes, it's pretty simple to remove pushrod tubes and replace seals. No need to loosen cylinders. Like it was said, be careful to track where each of the moving parts came from and get them back in the same place. Before you put the covers on you could check the rocker arm gap to the pushrods. Lycoming has a spec for that. I pre-oiled my pushrods before installation, just stick each in a bottle of oil ahead of time. I used plastic tube on opposite end and learned to 'suck it up'. They can hold quite a bit - I remember how much I dripped everywhere when first pulling them!

Les K.
Albuquerque

John,
replacing the pushrod seals is fairly simple. It will take you about a hour for the first one, then about 45 min's for each of the three remaining. It is best to only work on one cylinder at a time so not to get things mixed up.

Phil
118BC

Guys that's an 0-290 .. he unfortunately does have to loosen the cyls to replace the push-rod seals ..

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

Hi Guys, Lee is correct - O-290-something. I peeked inside the valve cover and I don't have the retainer clip holding the pushrod tubes in place. I'm reading the Lycoming O-290 Operators Manual as I type this and it covers the cylinder removal (loosening in my case) and reassembly and nut tightening procedures.

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John Twigg N12055 SN.79 Pittsburgh, PA (KFWQ)

"Sometimes you get the bear and sometimes the bear gets you !"

RB

I did not realize you had a 0290, sorry. At least you will not have to deal with the hydraulic lifters.
Phil
118BC

Phil, no problem! Your suggestion was great but my plane didn't cooperate with your suggestion. Please keep 'em coming! This education is supposed to be what experimental aviation is all about and I'm learning a lot.

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John Twigg N12055 SN.79 Pittsburgh, PA (KFWQ)