Another 100-Hour Letdown, Comparing GA With Autos

[MadseasoN]

So the airplane goes in for a 100-hour yesterday and the mechanic calls me to tell me number 2 cylinder has very low compression. It's the exhaust valve. A couple hundred hours ago the same thing happened with number 1 cylinder. These are semi-recent (~500 hr.) Superior Milleniums. The first time I had asked a few people in the know if Millenium was a good cylinder, and the answer was always yes. I know that the original TCM cylinders were not so good, and there is even an AD out on most of them calling for a retarding of ignition timing to reduce the likelihood of cylinder cracks developing. The engine is an O-200 in a 150L. Here are some facts with a few questions for those of you in the know: The O-200 has a specific output of only .50 hp/cubic inch. My automobile engine has a specific output of 1.32 hp/cubic inch. The O-200 turns a max rpm of 2750, my car's engine has a redline of 6800. The O-200 has 4 exhaust valves, my car's engine has 12(more of 'em to have trouble with). My car's engine now has about 3500 hours on it (140,000 miles) with absolutely no problems whatsoever, and I would fully expect it to go another 140,000 trouble-free miles. My O-200 has about 1100SMOH and about 500STOH. Why does an seemingly understressed engine have such issues with burned exhaust valves? It would be even worse with the OEM cylinders and their "cracking". I fully understand that an O-200 spends more time at wide open throttle but given the fact that the displacement is so large in comparison to the power output, and that at cruise the engine is producing aroud 60-70 horsepower, loafing along at around 2200-2300 rpm, why the unreliability? There are quite a few times that my car is at wide open throttle, and at highway speeds it's constantly making a large percentage of what the O-200 is at cruise. Even given the fact that a lot of the time my car engine is not producing a lot of power, I don't understand the disparity, after all, I'd rather have the more reliable engine in something that puts me thousands of feet above the ground. Any thoughts?

Lots of valid points, however ... even at wide-open throttle on the highway I doubt you regularly reach redline. If you do then you need to upshift

The HP rating of your engine does not include the 20-30% loss due to the transmission, wheels, etc. Put it on a dyno and you'll be suprised.

Your car needs 20-30HP to keep it at cruise speed. That's nowhere near 75% of rated power which is at least 5100RPM on your engine. If you ran your car at 5100RPM everytime you drove it I bet you it wouldn't outlast the O-200. Better yet, run it at 5100RPM pulling a trailer to simulate the drag and wind resistance that an airplane sees.

As for reliability I calculate 3500 hours in the 150L at ~260K miles.

 

[brcase]

Please explain the O-200 as it is applied in a Formula racer then?

simple, they sacrifice efficiency (small prop) and longevity (higher RPMs) to get a lot more horse power out of them. The extra horse power is greater than the losses due to the small prop.

Brian

 

[Geico266]

Lots of valid points, however ... even at wide-open throttle on the highway I doubt you regularly reach redline. If you do then you need to upshift

The HP rating of your engine does not include the 20-30% loss due to the transmission, wheels, etc. Put it on a dyno and you'll be suprised.

Your car needs 20-30HP to keep it at cruise speed. That's nowhere near 75% of rated power which is at least 5100RPM on your engine. If you ran your car at 5100RPM everytime you drove it I bet you it wouldn't outlast the O-200. Better yet, run it at 5100RPM pulling a trailer to simulate the drag and wind resistance that an airplane sees.

As for reliability I calculate 3500 hours in the 150L at ~260K miles.

Excellent post.

The experimental world is littered with auto conversion attempts trying to use auto engines in airplanes with minimal success. I have lost several aviator buddies to these engines and I don't want to see any more. I have seen dozens of airplanes stripped of their auto engines and a Lycoming installed.

It sounds easy, take a reliable car engine and bolt it to to airframe and live happily ever after. The problem is unchartered territory, mechanical skill level, and those pesky laws of physics.

Reliability of the old technology is unmatched by any thing on the market today. Improving that technology is where the focus should be. Advancing ignition, true fuel injection (not fuel flow) are just two of the areas ripe for improvement, but certification of these systems takes millions of dollars with an extremely limited market. This is where experimental shines. We have advancing ignition for improved performance and fuel economy today, from several different vendors. Very reliable now.

http://www.emagair.com/Intro.htm


A clean sheet design has produced the Rotax 912 series engines with these improvements, but currently the HP is limited to 115 due to market forces.

 

[Davis]

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[MBDiagMan]

On a related note, my parents owned a 1954 Volkswagen Beetle sunroof with the 36 horsepower flat four. That engine spent a large part of it's life at WOT, no problems.

The new cylinder/piston assembly is on order and is being Fedex'd overnight, the mechanic said it might be done by Monday

If that VW spent it's life with "no problems" that means that SOMEBODY spent a LOT of time underneath the back of it or squatting behind it with the hood up.

To keep one going reliably, it needed an oil change and SCREEN CLEANING every 1,000 miles or less with the oils of the day. It needed points and plugs about every 10,000 miles max, 7,000 was much better. It needed valve adjustements about every 1,000 miles.

It just kills me when I hear people talk about their "trouble free" Beetles. They don't remember all the work to keep them "trouble free."

 

[steingar]

Yeah, I think someone is looking at the past with rose colored glasses. In my youth I couldn't afford the services of a mechanic. The one poster was right, everyone was a mechanic, it was the only way I and my buddies could afford to keep our rides going. I remember sweating and cursing over the things all the time. They weren't as reliable as aircraft engines in the day, not by half. These days certainly, but not the cars of yesteryear.

 

[denverpilot]

Yeah, I think someone is looking at the past with rose colored glasses. In my youth I couldn't afford the services of a mechanic. The one poster was right, everyone was a mechanic, it was the only way I and my buddies could afford to keep our rides going. I remember sweating and cursing over the things all the time. They weren't as reliable as aircraft engines in the day, not by half. These days certainly, but not the cars of yesteryear.

All the way into 70s cars too.

I don't miss adjusting points and cleaning them, changing rotors and caps, oil changes every 3000 miles because the poor oil was already toast, adjusting/rebuilding carburetors, tires that never made 70,000 miles, etc etc etc.

We still have the functional equivalents of all of those fussy mechanical things to do in light aviation though.

 

[Henning]

Well, these are Milleniums, not TCM, I've been told the Milleniums are better. I actually have an EGT gauge, it's a single so it's fairly useless, one or more cylinders could be substantially richer or leaner than the one that's being monitored. And hey, I've got a 499 pound useful load!

My finding is it's a batch by batch crap shoot as to whether TCM, Superior, or ECI is going to give you better quality..., sigh.

 

[eMKay]

We recently replaced the engine in our race car, it's a Nissan SR20 2.0l DOHC 4 cylinder making somewhere north of 150hp at the wheels (figure 180 at the crank) It spent maybe 80% of it's time at WOT, the reason we had to replace it? A large rock got kicked up, puncturing the radiator, lost coolant and overheated, warping the head and cracking a bore. It had 54,000 race miles on it, this car was a race car the day it left the showroom (raced for yesrs in SCCA Showroom stock, then ITA, then Lemons and ChumpCar endurance races). How long would it have lasted if not for a catastrophic failure? Who knows. Forever? Proper fuel mapping and modern synthetic oil can do wonders. I have seen engines with 200,000 miles plus run on synthetic with no noticeable wear on anything.

If only airplane engines had modern fuel injection, modern oil (straight mineral oil? REEEALY?) and modern cooling systems. Just take the engine in my 2011 Forester, make a redundant ECU system, maybe even redundant cooling (one system for each side) and plop it in with a reduction gear. It will run forever.

 

[Henning]

simple, they sacrifice efficiency (small prop) and longevity (higher RPMs) to get a lot more horse power out of them. The extra horse power is greater than the losses due to the small prop.

Brian

Right, they still do it by turning 5600rpm is the point, and the engines don't do particularly bad at it, it's the props that are limiting. If they turned up a 3-5 bladed CS prop on a GO 300 case you could probably turn a solid 4200rpm high speed continuous.

 

[kimberlyanne546]

So the airplane goes in for a 100-hour yesterday and the mechanic calls me to tell me number 2 cylinder has very low compression. It's the exhaust valve. A couple hundred hours ago the same thing happened with number 1 cylinder. These are semi-recent (~500 hr.) Superior Milleniums. The first time I had asked a few people in the know if Millenium was a good cylinder, and the answer was always yes. I know that the original TCM cylinders were not so good, and there is even an AD out on most of them calling for a retarding of ignition timing to reduce the likelihood of cylinder cracks developing. The engine is an O-200 in a 150L. Here are some facts with a few questions for those of you in the know: The O-200 has a specific output of only .50 hp/cubic inch. My automobile engine has a specific output of 1.32 hp/cubic inch. The O-200 turns a max rpm of 2750, my car's engine has a redline of 6800. The O-200 has 4 exhaust valves, my car's engine has 12(more of 'em to have trouble with). My car's engine now has about 3500 hours on it (140,000 miles) with absolutely no problems whatsoever, and I would fully expect it to go another 140,000 trouble-free miles. My O-200 has about 1100SMOH and about 500STOH. Why does an seemingly understressed engine have such issues with burned exhaust valves? It would be even worse with the OEM cylinders and their "cracking". I fully understand that an O-200 spends more time at wide open throttle but given the fact that the displacement is so large in comparison to the power output, and that at cruise the engine is producing aroud 60-70 horsepower, loafing along at around 2200-2300 rpm, why the unreliability? There are quite a few times that my car is at wide open throttle, and at highway speeds it's constantly making a large percentage of what the O-200 is at cruise. Even given the fact that a lot of the time my car engine is not producing a lot of power, I don't understand the disparity, after all, I'd rather have the more reliable engine in something that puts me thousands of feet above the ground. Any thoughts?

Our coastal adventure tomorrow will make you forget all your troubles. This is the hottest it has been since last September which might mean no clouds, not even on the coast. We will see the hidden temple, the rocky cliffs, park the plane, then walk to town and then fly back. Oh and the Bay Tour. All in all the best day ever.

 

[Aeric]

Our coastal adventure tomorrow will make you forget all your troubles. This is the hottest it has been since last September which might mean no clouds, not even on the coast. We will see the hidden temple, the rocky cliffs, park the plane, then walk to town and then fly back. Oh and the Bay Tour. All in all the best day ever.

Sounds very cool. I guess I better do something better than Half Moon Bay next time. :wink2:

 

[Aeric]

We recently replaced the engine in our race car, it's a Nissan SR20 2.0l DOHC 4 cylinder making somewhere north of 150hp at the wheels (figure 180 at the crank) It spent maybe 80% of it's time at WOT, the reason we had to replace it? A large rock got kicked up, puncturing the radiator, lost coolant and overheated, warping the head and cracking a bore. It had 54,000 race miles on it, this car was a race car the day it left the showroom (raced for yesrs in SCCA Showroom stock, then ITA, then Lemons and ChumpCar endurance races). How long would it have lasted if not for a catastrophic failure? Who knows. Forever? Proper fuel mapping and modern synthetic oil can do wonders. I have seen engines with 200,000 miles plus run on synthetic with no noticeable wear on anything.

If only airplane engines had modern fuel injection, modern oil (straight mineral oil? REEEALY?) and modern cooling systems. Just take the engine in my 2011 Forester, make a redundant ECU system, maybe even redundant cooling (one system for each side) and plop it in with a reduction gear. It will run forever.

That's sort of my thinking, although I really do see the different missions involved. Not to mention the fact that air-cooled engines are designed with looser piston-cylinder tolerances due to the wider range of temperatures encountered, something that water-cooled engines don't experience as much.
Your post reminds me of a UAW protest in Michigan back in the late 70's. These guys had an old Toyota they were trying to blow up. They started the engine and jammed the throttle wide open with a stick. The car just sat there screaming and just wouldn't quit. After a long time they had to rupture the radiator with a hammer. Then the poor car just sat there screaming in a huge cloud of steam and finally seized up. Nice protest.

 

[dmac5356]

Much of the problem is due to air cooling. The engines run hot, and the temperatures are uneven across various parts. Uneven fuel distribution and leaded gas don't help either.

If a cylinder has low compression with a leak out the exhaust it does not necessarily require a new jug. You may have a piece of lead or carbon on the valve or seat... which may clear through staking, or a bit of lapping compound applied through a plug hole and turning the valve in-place. Or pull the jug and replace the seat and machine the valve to fit. You may have a valve sticking in the guide, which can be fixed in place by lowering the valve into the cylinder and cleaning the guide, or remove the cylinder and press in a new guide. If the valve is burned, then a new (or good used) valve and perhaps new seat. Most of these options can be completed in a day or less. If the jug is cracked, then I'd go with a replacement cylinder.

 

[Aeric]

Much of the problem is due to air cooling. The engines run hot, and the temperatures are uneven across various parts. Uneven fuel distribution and leaded gas don't help either.

If a cylinder has low compression with a leak out the exhaust it does not necessarily require a new jug. You may have a piece of lead or carbon on the valve or seat... which may clear through staking, or a bit of lapping compound applied through a plug hole and turning the valve in-place. Or pull the jug and replace the seat and machine the valve to fit. You may have a valve sticking in the guide, which can be fixed in place by lowering the valve into the cylinder and cleaning the guide, or remove the cylinder and press in a new guide. If the valve is burned, then a new (or good used) valve and perhaps new seat. Most of these options can be completed in a day or less. If the jug is cracked, then I'd go with a replacement cylinder.

I agree that it probably wouldn't require a new cylinder assembly. However, last time I had the same problem the cylinder was overhauled for about the same cost as purchasing a new one. The airplane was down for a week and a half whereas just buying a new cylinder would have had the airplane up and running in a few days. And if there were any cracks, I would have had to purchase the new one anyway.

 

[n20junkie]

On columbias we stopped changing spark plugs.

We replace all the jugs at annual.

 

[dell30rb]

Wow. 100 or so hours on a set of cylinders? At least clean the old plugs and re-use them Ha

 

[Aeric]

Wow. 100 or so hours on a set of cylinders? At least clean the old plugs and re-use them Ha

This wasn't the same cylinder. I wasn't too clear in my last post, what I meant was that last time I had the same exhaust valve problem in another cylinder, it was overhauled, this time I bought a new one at about the same cost.