I just got a used Associated 15 engine, previous owner said it overheated. I cleaned it, replaced all gaskets and oiled it and it still ran pretty good. I bought a temp gun, but I dont know the exact temperature to watch. Can somebody tell me what is the normal operating temp of a nitro engine (this engine specifically). How much it too hot?

Thanks,
AL

about 100Deg C off the side of the block just under the head and about 125 off the top of the head.

Tune for performance, not temperature. Some engines run perfect, but can be near 300 degrees F, while others run cool and around 220.

Forget the temp gun and tune with your eyes and ears. Crisp and clean with no bogging or sagging.

you will know when its too hot it will stall and you can risk wearing the engine .. you should look at temps its absolutely crutial. what your engine likes to run at is a different story..

NO, too hot will not wear an engine, too lean will. If you make it too lean, yes it will get too hot and the cylinder will expand to be larger than the piston, causing it to fade or sag or stall and be really difficult to restart till it cools down. Since you are too lean, you are not getting enough oil either so thats where the damage comes from, not the heat.
If you tune an engine so that it does not fade or sag on a full throttle run, you will not get too lean and therefore you will continue to supply enough oil and it will not have a problem.
If engine "X" is perfectly happy running a normal car fuel at 350F, is that too hot??? If tuning to some magical number and somebody says its too hot, then yes. The correct answer is: NO, it is not too hot if the engine is not exhibiting any signs of being lean (not sagging or fading, no detonation sounds, and it's running crisp and clean)
If I take the same engine, same day, track etc.... and switch fuels to one with the same nitro but more oil, like a plane or heli fuel, even with richining up the mixture so it runs correctly, it will run considerably warmer, likely 30 to 50 degrees warmer. Is that engine now too hot? Again, if somebody thinks it hotter than some mystical number then yes it is..... But, The correct answer is: NO, it is not too hot if the engine is not exhibiting any signs of being lean (not sagging or fading, no detonation sounds, and it's running crisp and clean)

I do this for a living. I demonstrate to hobby shop owners and their customers and teach classes on how to break in and tune car engines. I have three company cars with stock engines that have over 10 documented gallons each through them without a rebuild or even being taken apart, they all run flawlessly and have outstanding pinch.
I have tought my three sons how to tune by sight and sound, they each have engines that they actively race and practice with that have over ten gallons through, one has almost 20 gallons, all still going strong. Do they use a temp gun? No, at least not to tune with, they'll come grab mine and check engines out of curiosity just because they have racing buddies that are constantly trying to hunt for some mystical number and are getting be-littled because they do'nt tune by temp (my sons do'nt blow engines like the temp tuners either).

Bigger heat sink heads do not fix anything either, they just mask the visual signs of a lean run and engines can easily be killed by running them too lean and the racer never realizes it because he's been tought to tune by some magic temp, not with his eyes, and ears.

Heat makes horsepower. Lean runs cause oil starvation which wears out engines.

What is the facination with temp guns for the car guys? I have been around to quite a few competitions and have never seen an aircraft pylon racer, pattern flyer, 3D heli pilot, control line speed racer, boat racer or any other serious competitor (or even the the sport folks) ever worry (or even care) what temp their engine was running at, as long as it was reliably running and properly tuned. And, no, these guys were not getting free engines from sponsors (like some car racers), they ran what they bought and had to get the maximum life and performance out of everything. Oh, these engines last for years with literally dozens and dozens of gallons run through them. Bottom line is, Tuning by temp was designed to sell parts, not promote longevity of engines or win races.

Very well said.

What is the facination with temp guns for the car guys? I have been around to quite a few competitions and have never seen an aircraft pylon racer, pattern flyer, 3D heli pilot, control line speed racer, boat racer or any other serious competitor (or even the the sport folks) ever worry (or even care) what temp their engine was running at, as long as it was reliably running and properly tuned. And, no, these guys were not getting free engines from sponsors (like some car racers), they ran what they bought and had to get the maximum life and performance out of everything. Oh, these engines last for years with literally dozens and dozens of gallons run through them. Bottom line is, Tuning by temp was designed to sell parts, not promote longevity of engines or win races.


Ok why would you ever have an over heating problem with a plane that has its head exposed to cold fast air... Same with boats , they have water cooling.. Temp guns arent needed,... Get close to the ground and the temps are almost double.. ( we are talking buggys and trucks here) So temp guns are extremly useful tools.. Over heating will wear an engine. Over heating is not always caused by leaning the engine either.. so you can have an engine that seems to be running fine, decent smoke out of the pipe but the bugger still over heats and wears the engine pre maturely. And in a lot of ways i agree with you , temp guns are a bit of a gimmic. I spent the first 3 years or my racing carreer without a temp gun. And i did well without it. mind you i fried a few more motors than i do now. in the last 4 years i havent fried one motor, and its because i monitor the engine with a temp gun. If you have a bearing falire in the engine you wont be able to tell till its too late.. the engine will run happily till the bearing pops and lodges somewhere between your sleeve and piston , with a temp gun you can monitor whats happening inside the motor, the temp will tell you if something is wrong well before you ever pick up on it..

: )

And i think with over heating you will find the Sleeve is designed to expand at a lower temp than the piston. that is why the engine gets loose when its up to temp, Whan it over heats it means the sleeve has expanded to its maximum and is then governed by the crank case, this is when the piston starts to expand and wears the liner at a much greater rate..

I have been wanting to say this for so long except didn't know how to say it without offending all of you temp gun lovers. Finally MassiveMods has opened the door with boldness to ya all. Honestly Im relativly new to the hobby (only had 2 ntro engines so far) but I have been tuning dirtbike engines for some time which are essentially the same concept. You never will find a mechanic in the pits at a race; even in the pros, with his temp gun checking temps on the engine. That would just be silly. Yes car/ truck/ land engines run hotter. Thats obvious. However they are desinged to PERFORM and operate at those conditions. It drives me up a wall with everyone on these forums posting temps and needle settings. To me adjusting the engine to where it looks, sounds, performs it's best is very easy. There is no sense in relying on sometimes very inaccurate tools to tune an engine that is so variable. When the engine sounds CRISP, Runs goods, and performs well why ever pick up the gun?

Massive,
The line of thought you describe is not correct.
Even with a huge prop blast of cold air, measuring the temp at the base of the glow plug on most airplane engines will still give you readings of 280F all the way to 375F on a properly tuned engine, So what kind of damage is that doing?
Boats, If you do not keep enough heat in them (restrict cooling water), boat engines have a hard time coming on the pipe first of all and second- the piston and sleeves last only a couple runs when they are too cold.
Lets talk helicopters- very limited cooling and not a very large heat sink, and sometimes they are still overcooled even with the little fan. Using a temp gun is worthless in a heli, because it tells you nothing. You must use your ears and listen for the sagging or fading during full power maneuvers and the tell tale detonation rattle or frying egg sound. It could be only running at 250F but detonating like mad, still ruining an engine.
Keep in mind that the cooling fin size is appropriate for the environment, airplane engines have a lot less fin surface area because of the prop blast, heli's a bit more, and cars have even more so that they can radiate heat with little to no airflow over the heat sink.

Other than a pressure leak or the exhaust perssure line comes off, the only other ways I can think of to experience overheating when the engine is correctly tuned to the air fuel mixture ratio is to increase the load on the engine causing compression loading without making the necessary adjustments (richining) to the air fuel mixture ratio. OR- using the same example of a correctly tuned engine, then block off some of the radient cooling capacity (cover the head with metal tape), again without adjusting the air fuel mixture ratio. In those above cases you are subjecting a correctly tuned engine to a new environment and then not tuning it to run correctly in that environment. In any case, it is still too lean.
Forget the smoke trail, smoke trail is a function of the oil characteristics and content of the particular fuel you run. You can still have a good smoke trail and be too lean.
If an engine overheats and causes wear, that is a functon of being too lean unless you are increasing the load or restricting the cooling without adjusting the mixture, is still too lean which will cause the engine to overheat and will starve the engine of oil and potentially causing damage.
So what else can cause a correctly tuned engine to overheat if its not too lean?
Simply put- if an engine is tuned correctly to where the air fuel mixture ratio is correct for the conditions, the engine will seek its own tempreture. When those conditions are met, it does not matter what the temp gun reads, it is running perfect. If the temp gun happens to indicate 250F, 350F, 415F, or whatever, it does not matter. the engine will decide when its too hot by sagging or fading on a wide open run, in those cases it must be richened so it's happy again.

Sounds like experience and not the temp gun kept you from frying engines.
Locally, I see airplane guys buying cars and trucks, I have yet to see any of them have a problem tuning and engine, yet to see any of them blow an engine and have yet to see any of them use a temp gun. I have seen the opposite, car guys that are learning to fly rc planes. They always have the temp gun out and are always twisting the needles because its too hot and they are usually ruining a perfectly good plane engine before they even have a chance to crash it. Running it too cold. Worst part is, you can't tell them anything, they already know it all.

Just how exactly are you going to pick up on a bearing failure with a temp gun? Ears yes, temp not likely.
Bearings do not care how lean it is or how hot it is. Even the worst quality ball bearings used in model engine only require one half of one percent (0.5%) of lubricant in the glow fuel in order to continue operating at full performance levels that the bearing is designed for. Usually bearings go because of a bad quality issue like the pin rivits coming out and the cage comes apart or a little rust acts like an abrasive, when over time they get lose and start getting real noisey before they come apart. Dirt will also kill a bearing real fast, but if you ingested enough dirt to destroy the bearing, then the piston , sleeve and rod and possibly the crank pin is destroyed as well.

Completly incorrect. The coeficient of expansion of brass (sleeve) is much greater than that of the high silica aluminum the piston is made of . The brass will continue to expand faster than the high silica aluminum, the higher the temp, the greater the difference. The hotter an engine gets, the more the top of the sleeve expands, when it gets to a point where the sleeve gets bigger than the piston the engine will start sagging or fading out because it is losing compression, that is when it is too hot because it is too lean. Numerious design factors influence where that point is, it is not a hard fast point that can be measured with a temp gun on any engine. When it reaches that point, all you have to do is richen the needles slightly and it will resume. Continued operating at over lean settings is what causes problems.
Pistons do not wear the liner without a contributing factor, wear is caused by a lack of lubricant or foreign matter (dirt). Excluding dirt, the wear that is occuring when an engine is too hot is from a lack of lubricant because it is too lean. When you get to that point, the sleeve expansion allows the piston to slap around a little too much and the oil film is not thick or abundant enough to keep it from damaging each other. The other damage that occurs during these lean runs is the conecting rod at both ends gets starved for oil which causes egg shaping and excess heat buildup (due to lubricant starvation), and sometimes a catastrophic rod failure occurs.


There are so many variables to the engine temp, that twisting the needle to try to obtain some magical number that does not exist, is flawed logic. Operating tempreture of an engine is influenced by: nitro content, glow plug, oil type, oil quantity, methanol quality, barametric pressure, air temp, humidity, altitude, cooling fin surface area, header length and tuned pipe set up, and on and on and on.... Change any one of these and those magic numbers change too.

Well said Trapper. I think that Massive got a bit over the top here too. What most folks do not realize is that Fuelman is one of the most knowledgable glow engine people in the country. He is right there in the same category with Dave Gierke, Clarance Lee and Peter Chinn.
I'm gonna sit back and watch this as it looks like it will get quite informative.
By the way, Fuelman is righ on the money.

This thread did get way off topic, but its interesting.

I never once stated you should tune to temp, i think that was an assumption on your part. and is apparent in your response.. I too work with glow engines extensively and professionally every day and a temp gun for me is a must to help me monitor engines.. Its a monitoring tool thats all..
And originally all i did was to offer an average acceptable operating range. Which was what this forum was originally opened for. And i maintain that temp guns are essential to monitoring engine behaviour.
I think you may have let peoples misunderstanding of temp gun usage get to you and is now become a sore point. you may need to take a break from the sport as it seems to have made you a little upset ...
And granted if we were all blessed with your knowledge on Glo engines we wouldnt need a temp gun, Just eyes and ears.. But people beginning in this sport dont have this experience and need to have somehting to go by.. What we need to do is not bark at each other but educate Noobs on what to do.. Carrying on trying to prove your personal preference over mine is moot and not helping any one.

In answer to your question, bearing faliure or wear cuses engines to over heat, You cant always hear when a bearing is on its way out, no amount of tuning will help you there, Ever tried to tune a Traxxas 2.5 ? No matter what fuel, tuning, etc about 50% of these engines will over heat out of the box. this is because of 2 things. They put them in Monster trucks which is over load on such a small motor and their exhaust port blow down is some 35 deg. way concervative, in order for this engine to operate at normal temps IE not sagging stc is to increase blow down and extend the exhaust timing.. So tuning by ear and eyes is useless.. Engines will heat up by some 5 to 12 deg when a bearing is close to popping.. How you gonna tell this with eyes and ears.. you have no frame of refrence from when the engine is at normal operatinng temps (whatever that may be) to when it increases slightly..

EG if an engine is tuned and performing well and you temp it at say 127deg C then great ! If you notice a change in the same day in same conditions for no other reason then there is a chance a bearing is on the way out.. Now are you going to wait till you can hear the bearing rattle or do you go to your spare motor and open the original up and have a look ?

And as far as other motor sports are concerned i think that that they should all lose their temp monitoring too .. Its useless , it dosent tell you anything so Ferrari F1 just puts a temp monitoring system in their cars for kicks ?

Temp monitoring is essential its just not always used correctly.

Peace

Massive,
Point well taken. I do get a bit over zealous with the temp gun thing because I see so many of my customers get a brand new glow engine car, truck or buggy and the hobby shop sells them a fancy temp gun to go with it. Thats not the bad part, the hobby shop owners are there telling the new guys that they have to run this engine at no more than XXX degrees or catastrophic failures will result. The end result is that these guys (and gals) get so focused on a some number that is meaningless to what they are trying to accomplish (which is break - in and run the engine), that the engine pinch gets ruined in very short order due to running it too cold. The hobby shop owner is right there to sell him a new piston , sleeve and rod and then charge the new guy another fee for installing it. Very discouraging to say the least.
I've had a couple hobby shops allow me to teach new engine break in and running classes, at first the owners were not too crazy about me being in there teaching people how to get 10 gallons of life out of a car engine, but they warmed up to it. I always tought folks to watch and listen for certain indicators and not rely on the temp gun or focus on a number that means something to somebody else.
Yes, temp guns have there place for a seasoned person using them to monitor, they certainly are not for the new guy that will tend to focus on it too much and use it in a way that it's not intended for.
I agree, the Traxxas 2.5 is a comprimise to say the least, especially in the big trucks. I personally like the Fantom 18 in the TMaxx but that is a different story.

I have a model engine electronic fuel pump and metering device (mixture control) that uses an exhaust gas temp probe as one of its sensors, it works but that is beyond the scope of this.

Truce

Absolutely My friend ! I will keep an eye on your posts as you definitely know what you are talking about, im always on the hunt for knowledge ...

And i completely agree with you on the hobby shops misleading people ..Im against it , i gues thats why i dont sell much in my shop... lol Im always telling people how to do it right as opposed to geting it wrong because it means more money.. Disgusting behaviour ! Shame on you Hobby shop owners ! We will get you in the end ! lol

This had been a good discussion

Thank you ! : )

Hey ya all,

I agree, Yes this has been a VERY good discussion, I am learning a lot. This is what my LHS is missing, people with experience and know-how.

Thank you all for sharing what you know. Wish me good luck with this engine, my parts have arrived, I am replacing the sleeve, piston, con-rod, crankase and crankcase bearings.
I will need advice on breaking-in this rebuilt engine but that would be another topic to discuss.

Thanks!

Hey associated , good man ! there is numerous discussions on break in.. have a look around for advise.. dont run rich for 27 tanks its not goot ..