Max_Power

After being around RC quite a few years I am always hearing from one person or another about running engines lean and instantly destroying them. Specifically piston/liner.

I know with many mechanical items I have worked on failures are not always as common, or easily achieved as many folks state. When you run a automobile engine out of oil failure is almost always at the cam lobes or crank/rod bearings, almost never the cylinders or pistons...which have almost no lubrication anyway(think about a race engine with a crank wiper?).

I've run many engines lean (not on purpose of course) and been in situations where they could not immediately be shut down,etc. Yet in my own experience I've never seen any of these engines damaged or failed to have them run again...barring bad glow plugs,etc. In fact almost all of the failed engines I have had have been broken crankpins or rods(and many of those diesel conversions run too hard,etc) So I guess what I'm after here is experiences, (or especially PHOTOS!!) of engines and parts that were destroyed by running too lean. Am I just lucky, or is this simply one of those things people over-emphasise because they have constantly been told about it...and not necessarily from having it happen? Thanks in advance, Todd

Mr Cox

In ABC, ABL and AAC engines the cylinder can/will get irreversibly enlarged from the heat and the engine then looses compression. There is not much to see apart from some discoloration of the liner and the loss of compression.

djlyon

I have on a couple of occasions sever galling occur on the piston and liner on both model airplane engines and motor cycles. Just need to get them hot enough and the lubrication to break down. That's destruction.

Denis

j.duncker

My Feedback: (2)

If you are running an engine in a situation where the last 3 or 4 % of rpm is not critical then the damage done by a lean run might not be noticeable.

Running pylon race engines you DO NOTICE the effects of a lean run.

Max_Power

I've definitely seen galling on motorcycle and auto engine skirts too, but it wasn't the reason most of them were torn down. I know the engines can be damaged, I guess what I'm wondering could be compared more to how people say if you put a car at full throttle it will sling a rod instantly, But in experience I've run 4-5 old cars with a brick on the gas pedal before sending them to scrap and at least twice I've ran out of beer before the thing blew up. Same with lawnmowers with governor disabled.

I'm curious as to how likely a glow engine is to damage itself before just "flaming out"? Especially when there is castor involved. I know it seems like every 4-stroke I see at the field run on 10-15% has that "smokin hot" smell. I bet the car guys have some carnage pics...but I think I'm more curious about a situation like a airplane engine where there is a higher oil content and more reasonable RPM. Maybe I should just experiment with a old broken lug engine.

freakingfast

My Feedback: (3)

Max
Sometimes there is no visible piston or liner damage, yet there is some to major power loss. With a lean run, what can happen is the piston can get so hot and soft that it can extrude, re-form or burnish to a smaller size, then when it cools down to normal operating temps there is too much piston/liner clearance and power loss. That type of damage may show no visible damage like galling, smearing, tearing or liner peeling.

MetallicaJunkie

ive had situations my self were im doing wide open passes continiousl, and as soon as i detect a slight increase in rpm/performance i throttle back and take it easy on the motor and land.... i then let it cool off a bit and richen the high end 2-3 clicks and the engine resumes normal operation.... i have yet to burn up and engine to the point it's worthless...

i think burning up an engine only applies to those who fail to read the symptoms of a lean over heating engine

blw

My Feedback: (3)

The engine is supposedly a bored YS 120 that ran on 80% nitro. I think the piston is from top fuel.

fizzwater2

My Feedback: (61)

I've seen similar melted pistons back when Formula 1 racing was mini-pipes and 65-70% nitro..

Max_Power

But that isnt a model engine piston?....Interesting damage on the YS....the rod still looks straight. I wonder what happened. I'm curious what EGT on a glow engine on 25% is? I know that a gasoline engine pulling hard is like 1500f. , But I'd have to bet from holding my hand behind a rc muffler glow is WAY cooler. These pictures arent exactly the question or my curiousity...But thanks for the carnage pictures...ALWAYS fun to look at! Todd

fizzwater2

My Feedback: (61)

By Formula 1 I meant radio control Formula 1 plane racing - and yes, I've seen melted pistons from the .40's when using that much nitro.

Max_Power

Thanks Fizz...I knew you were talking models, it was the melted piston in the picture above I was commenting on.

djlyon

In F3D Pylon they melt pistons with no nitro.

Denis

vicman

My Feedback: (10)

I have burned a few piston/sleeves up as well as had bearings CATO and go thru the engine.
The first engine I had go sour was a LA.40. It turned out the air bleed hole had crud in it causing it to go lean. I fought that engine for weeks till I figured out what it was.

I haven't had one melt down in a few years now but some of my race motors are not up to race tune and I only use them for practice.

blw

My Feedback: (3)

I could be wrong, but I think exhaust gas temps (egt) is measured only on turbines. Same as tot.

Max_Power

Many general aviation piston planes have a EGT gauge...as well as most automotive Dynomometers. I guess this is why I am so curious about this stuff. I know a glow engine exhaust is nowhere near this hot. It also amazes me that a glow 2 stroke with 600 degree exhaust needs 20% oil but that a weedwacker engine with twice that can be run on 100:1 oil?

NM2K

My Feedback: (14)

Not that I enjoy seeing engines abused, but I wish I could have seen that YS 1.20 run its last time.


Ed Cregger

earlwb

I remember destroying several engines many years ago, when 100% synthetic oils first came out in glow fuel. I was flying pattern and using tuned pipes which is a good recipe for damaging engines. Anyway, with a weather change, it caused one engine to lean out too much in the air and it siezed up good before I could chop the throttle. A couple of other engines died on the ground adjusting the needle valve. With synthetic oils, you have maybe a split second to catch it before it goes lean and destroys the engine. Some guy from a fuel company was touting their new 100% synthetic oil fuel as the greatest thing to use and he gave me a gallon to try out. I gave the rest of the fuel away to someone else. A ringed piston engine is more adversely affected by a lean run than a ABC type of engine. The ABC cylinder tends to expand more causing a compression loss and reducing power, and if the lean run isn't too harsh, it will likely recover after it cools off. But not always. Nowadays many companies are using nickle plating instead of chrome and the nickle isn't as rugged in this case.

I think control line probably has the best examples where the engine leans out too much in the air but not enough to die, all you can do is hang on until the engine quits one way or the other. Sometimes the engine still works OK, but usually it now has a power loss and doesn't run as strong as before. When I was a kid doing control line flying I trashed a couple of engines by running them too lean too. But I had a well used beat up Fox .35 stunt that seemed to go through those nasty lean runs and survive Ok with no difference in power afterwards. But a couple of McCoy .35's were trashed afterwards though.

As mentioned already with the higher temperatures from a lean run, cause the cylinder and or piston to expand too much and stay enlarged and not shrink back down. The magic temperature point is a little over 500 degrees F too. At 565 degrees F the aluminum alloys become damaged. You can simulate it by heating up a crankcase over 500 degrees to remove the bearings and you'll discover that the new bearings are a loose fit afterwards as the aluminum won't shrink back down like before after it cools off.

Mr Cox

A blocked airbleed hole would make it go rich, so that couldn't be it either...

Sport_Pilot

The oil has nothing to do with engine exhust temp. It is for lubricating the engine, and at much lower temp than the exhaust temp. Glow engines need more oil because the alcohol has a very low viscosity and lubricity compared to gasoline so more oil is needed to bring it up to the required amount. Also most glow engines do not have needle bearings in the rod end requiring more oil.

earlwb

Mr Duke Fox years ago did a great magazine article (August 1989 MAN) about glow fuel oil percentages and the engine displacement. it is a lubricating area to displacement ratio that governs the oil percentage needed. The larger the engine the less there is of the surface area that needs lubrication.
He found that small engines like 1/2a engines needed more oil and the larger the engine the less oil it needed up to a point.
So you might have 20% to 25% or more oil in the fuel for a small engine whereas in a big 30cc or larger glow engine you only needed 10% to 12% and even 8% may work OK in some cases. I think he had worked out the optimum oil percentages needed by engine displacement too.
Dave Gierke and Clarence Lee pretty much agreed with it as well as they used to quote his article as a reference in their articles too.
You can see examples of this today with the big Supertigre 2,000, 2300, 3000, 3250 and 4500 engines where they suggest using 12% oil content fuel after the engine is broken in good.

now then the old timey lapped piston, bushed crankshaft engines needed more oil in them as the oil also served as a sealant to improve compression too. More oil is needed as the common glow engine does not have needle bearings on the rod, so it is harder to get oil in there to lubricate it. The ringed piston engines can generally use less oil than a ABC engine too. Some engines do not use bronze bushed ends on the rods either, so they require more oil too. Oil itself doesn't have as much cooling effect on a engine as does the methanol in the fuel. The methanol sucks a lot of heat out of the engine when it is running by its nature of evaporative cooling.

Here is Dave Gierke's article from MAN in the January 2010 article.
http://www.modelairplanenews-digital...001?pg=51#pg47

here is another article about glow engine oils http://www.rcmodelreviews.com/goodoil.shtml

we actually had a engine that was manufactured years ago, a twin cylinder engine no less, that needed little to no oil for it to run OK. At first they said it needed no oil, but eventually they said maybe 5% oil was better though. I think it was a Daimo twin 1.20, if I remember correctly. They had ball bearings and needle bearings all throughout the engine.

Max_Power

I understand the oil is there to lubricate. It sounds as if you are thinking I'm saying oil controls exhaust temp....I'm saying the oil needs to have some ability to survive the combustion temp, which is WAY higher on a gasoline engine. I still think a twenty-fold difference is oil requirement (100:1 versus 20%) is very significant and amazes me. ED...interesting article....seems to support that there is a lot of over-oiling in modern fuels...which may go along with a inflated fear of lean runs(or maybe not)

downunder

Ideally no oil should be involved in the combustion process itself because all oil should be deposited between/on the piston/liner which is the only place it can do its job in the hot part of the engine. The only temp it has to survive in is the temp of the piston/liner itself. With synthetics this means a temp lower than what causes the oil to revert back to the chemicals it was made from (unzippering) which is somewhere around the 450F mark. Ordinarily no liner will reach those kinds of temps unless there's a problem like a muffler pressure line falling off or whatever.

All engines have their own particular oil requirements and the part needing the most oil can vary between engines. As a for instance, the old cast iron piston OS Max-S35 could run quite happily on 20% oil but the lower end of the rod needs at least 25% to survive for any length of time. While it may seem amazing that so much oil is used in glow engines it has to be remembered that these quantities haven't really been plucked out of the air. Sixty odd years of trial and error gathers a lot of information about what's needed . The reasons behind why so much is necessary is less important than the empirical fact although petrol being a lubricant and methanol being a solvent is part of it.

blw

My Feedback: (3)

Clarence Lee must have had more than one article because I recently read one where he was recapping previous information. He did have the calculations and I'll go back and try to find them. He said the same things the MAN article did. All was very interesting.

acdii

Diesels have EGT gauges too. In fact if you tune a diesel and DONT put an EGT gauge on, you are tempting fate BIG time.   I have an F350 7.3 Powerstroke with an 80HP tune, and my EGT's can reach 1600* if I am not careful.  This is PRE turbo temps, so you can imagine what the temps are at the pistons.  If you mount the probe post turbo you are also tempting fate.  To get an idea how much power my 7.3 puts out, somewhere I have pictures of the shattered rear end.  The Dana 80 went BOOM while doing a a power pull.  Blew out the spider gears and put a hole in the cover.  The EGT's were at 1400* at the time.   I would say it was well over 500HP at the crank at that moment.