You think stokers are retro-tech......

You should then try airplane engines - most of which were designed BEFORE our beloved stokers.

I have the misfortune of having to pull a cylinder off our 1946 Cessna 140. It flies behind a Continental C-85, which is approx. 200 cubic inches and develops 85 horses at 2575 rpm. This cylinder is about a dozen years old, but has only flown about 200 hours. We found during our annual inspection this particular cylinder had very poor compression. Compression is tested using a leakdown test, where you apply 80 psi air to the cylinder through the sparkplug hole through a calibrated orifice in the tester. The rate of cylinder leakage causes a compression reading, less than 80psi. "GOOD" would be anything above 70psi, notated as 70/80, or 73/80, etc. 50s and 60s are becoming troubling, and lower readings are cause for serious concern. 3 of the 4 measured 75/80 or better. This particular cylinder measured 35/70, and we could hear air leaking from the exhaust. NOT good. First thought was to fly it a bit and see if the compression would come up (sometimes the ring gaps become lined up, or a piece of carbon or lead residue will hang on a valve seat), but I suggested that we pull the valve cover and look, about a 10 minute job.

We got the valve cover off and noticed the rocker arm hit the valve about 3/32" off center - it was almost touching the spring keeper/washer with its edge. I was able to push down the valve a bit and found it wobbled significantly in the guide. Again, NOT good. My mechanic saw this and said that the jug had to come off the engine. Damn...that's a bummer, and $$$$. If this was a car, it would have the equivalent of about 10,000 miles on it.

As GregL suggested in the thread where this went off-topic, maybe the rocker is supposed to hit the valve off center to rotate the valve at each actuation. Maybe so, but this was REALLY off, even he noticed it more than usual. The rocker arm wasn't loose or anything like that, so it was put together that way. We didn't take any other valve covers off to see if it was normal or not, but none of the others were low on compression. Seeing as this engine was designed before WWII, I don't know if valve rotating was "in" then, and it's a low compression engine, certified on 73 octane fuel.

For more low-tech - it uses magnetos for ignition, a generator for 12V supply, and basically a John Deere tractor pull cable actuated starter. OK, it was built in 1946. The problem becomes that the engines made today use the EXACT SAME technology. Only very recently have aircraft engines started to use electronic ignitions, and even the fuel injected engines use a crude mechanically regulated constant flow injection system. Very recently, a few engines have been developed and certified with FADEC controls (Full Authority Digital Engine Controllers) where all you do is push the throttle which is nothing more than an electrical signal, and the engine computer does the rest to figure proper fueling and ignition. Gee, sounds like cars of 20 years ago already.....

But, things are starting to turn around - diesels are making in-roads in certified aircraft as they can burn Jet A, and also more fuel efficient. Some day 100LL fuel will go away as it won't be practical or feasible to have leaded fuels in the refinery stream any longer. Unleaded fuels are being developed along with engines to use them. Modern machining and materials are becoming common in aircraft engines.

Even still, with the antique technology they use, aircraft engines are some of the only engines that are designed to run at high power settings (75% or more) continuously. An automotive engine in that application would self destruct quickly. They are also highly reliable given proper maintenance. Some of the larger, turbocharged engines produce 350hp or more from 540cid at 2500 rpm, and do it reliably. Just don't make big power additions or reductions quickly to avoid "shock cooling" the engine. That can cause cracked heads which means $$$$.

OTOH, GregL flies an Airbus where he has to worry about none of this. Just push the levers and make noise. Overhaul times on a jet engine are measured in 10's of thousands of hours. I'm lucky to get 2000 hours. Turbines are a good thing..... He also doesn't have to pay the maintenance bill or the fuel bill.....

Have you tried or has your mech. suggested, "staking the valve"?

Staking the valve will not repair the worn out valve guide will it?? I think knurling a guide is an automotive process, not for aircraft?? .. Chris said, maybe not in this thread, but in the original one [VW TDI Jetta for sale] That the valve had very excessive wobble in the guide, enough to make me comment that I hope the guide hadn't got loose in the head, ruining the head. I know oversize-outside guides are available, but not sure for aircraft.

I'm sure Chris will take some good close up photos of what the wear and issues are... Right Chris??

Greg L

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Staking the valve won't correct a worn guide. The process is used only for carbon deposits on the seat. I'd say the guides are replaceable. The engines are very similar to an old Harley engine, which had replaceable guides. I've got a jug down stairs, don't know if a Continental or Lycoming, however it looks like the guides are replaceable.

I had a cylinder on a Lycoming TIO540, a 310 HP version, that had a guide get loose in the head, it wallowed out the bore in the head really bad.. The rebuilder had it welded up, rebored, new guide pressed in.. it wasn't cheap, but less than a new head..

Hopefully Chris won't have to spend too much on it.. and I hope the cam, lifters etc are OK,, it has very little time on the engine over a long period of time... lots of time for surfaces to loose the protective layer of oil and rust.

Greg L

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Don't you guys worry that the thing might break when flying? I mean, when the magneto on a tractor goes bad you hop off and leave it in the field, where do you go in a plane? Yes I know that flying is safer than driving...I flew once in a helicopter, once in a Cessna at a fair, and twice on commercial jets. That was enough for me, I'd rather walk before I get on another plane.

Dallas wrote:Have you tried or has your mech. suggested, "staking the valve"?

As soon as we pulled the cover and found the valve wobbling around, that was the end of it. Time for the jug to come off the engine. Guide is shot, and probably replace the seat as well.

e.alleg wrote:Don't you guys worry that the thing might break when flying? I mean, when the magneto on a tractor goes bad you hop off and leave it in the field, where do you go in a plane? Yes I know that flying is safer than driving...I flew once in a helicopter, once in a Cessna at a fair, and twice on commercial jets. That was enough for me, I'd rather walk before I get on another plane.

Well, planes are thoroughly inspected every year by a certified mechanic. The plane is darn near disassembled and everything tested or inspected. If the plane is used for training or any other sort of paid flying, it has to be inspected every 100 hours. Compression, timing, nuts, bolts, everything on the entire plane is checked, adjusted, and lubricated.

It had only been 16 tach hours since my last annual. That was enough time for the valve to go from perfect to crap. If it was a tractor, I would have run it until either that cylinder started missing or maybe failed entirely. In an airplane, you have the opportunity to find the issue before it becomes major.

Even so, if the big fan out front quits and I start sweating, it's pretty easy to find a place to land. Road, field, etc. It glides very well and lands slow. As long as you FLY THE PLANE and don't panic, you have a very good chance of walking away, maybe with a bent airplane, but that's better than dead.

e.alleg wrote: I mean, when the magneto on a tractor goes bad you hop off and leave it in the field, where do you go in a plane?

DOWN!

LsFarm wrote:I'm sure Chris will take some good close up photos of what the wear and issues are... Right Chris??

Greg L
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Unfortunately not - I didn't have a camera at annual time, and my mechanic pulled the cylinder and got it into the shop before I got out to the hangar yesterday.

Fortunately, it appears to just need a valve, guide, and maybe a seat. Only light pitting in the bore due to rust, and it will clean up with a light bottle brush hone. Probably can even resuse the rings.

I trust the old contis. I'd like a new, clean slate design, but those have not seemed to work out (Porsche PFM, Orenda, Rotax, etc). I have hopes for the german diesel, Thielert, but they too just had a full stop grounding AD this week for fuel line cracking. I'm comfortable with the old stuff; they tend to fade rather than break.

We have an A-65 in the Luscombe and I learned from it, by handpropping, the condition of the cylinders. If a valve 'tips', you'll get your 35psi "death sigh" when you pull the piston through. I check the 180 the same way (w/tail tied down, mag off, etc. Not going into the right way to prop...)

I trust them. Marsh Harbor, Abaco Island, Bahamas, couple weeks ago:

Greg, just to jog your memory. Those are what we call 'guages'. They tell us information about flight attitude, engine condition and nav/com. No typing, computers, flat screen TVs, bunks, attendants or head.

Charlie Z wrote:I trust the old contis. I'd like a new, clean slate design, but those have not seemed to work out (Porsche PFM, Orenda, Rotax, etc). I have hopes for the german diesel, Thielert, but they too just had a full stop grounding AD this week for fuel line cracking. I'm comfortable with the old stuff; they tend to fade rather than break.

Actually, the Rotax have proved to be very robust and reliable engines. They do have a few issues, but they are minor (voltage regulators, carb "rubbers", and the gearbox slipper clutch must be kept properly adjusted and maintained). But, the engine itself is extremely robust and reliable. Oh, the Rotax do NOT like lead, or regular aviation oil. The key is running premium unleaded and a high quality synthetic motorcycle oil - that keeps the gears and slipper clutch happy, just like a motorcycle gear box.

There are a few others out there that bear watching - the Gemini diesel out of the UK looks to be interesting - two stroke, three cylinder, opposed piston design. The Rotec radial looks really nice, also, for a different style of airplane. Bear in mind, these are "experimental" engines, not intended for certified aircraft at this point.

I like the Thielert - it's flying on that really nice Diamond Aircraft twin engine. Based on a Mercedes car diesel, so it should be pretty reliable.

I've hand propped the C-85 a few times due to a flat battery. With a shot of prime, she'll fire up at a dead idle on the first flip. It amazes everyone that has seen it. She has a Stromberg carb and the old Eisemann mags. With everything tuned up right, it runs like a watch. All I do to prop it is chock both main gear wheels, and verify 3 times that I'm at full idle. After it starts, I can pull all the chocks and get it without it rolling away.

Hey Charlie,,, lets see, I have about 11,000 hours looking at those round thingies... The rest of my ~19,000 hours looking a CRT tubes,, small TV screens...



Nice photo !!

Greg L

You know what they say, they select airline candidates today based not on the number of hours they have but the words per minute they can type.

My favorite is, "What other job can you get up in the morning, suit up like a South American dictator and part the crowds of awestruck passengers on the way to your command?" I have a couple of line captains as friends that feed me all this...

Chris, all those engines 'worked', they just never took over from the lycs and contis. I'd like to see the Theilert work out, too. They're looking about 3x the cost of a reman conti, though.

I'd miss the smell of 100, though. Nothing like an hot Friday afternoon as #14 on the taxiway to departing at Morristown or Teterboro behind all the corps, blowing jet-a all thru you. It's hard to get it out of your nose.

LsFarm wrote:I had a cylinder on a Lycoming TIO540, a 310 HP version
Greg L

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That reminds me of the time I was at the Glenn Curtiss museum. I don't fly but I like looking at the old airplane engines at air museums like Glenn Curtiss. This museum is not too far from coal country, a few hours, and lots of good wine to be had along the way!