378

My Feedback: (4)

TBJ, excessively overheating an RC engine can damage it. It won't destroy it, which you've found out yourself overheating several of them, but it will make it an absolute -beep- to get the sleeve out when it does come time to rebuild. You may end up having to scrap the engine because the sleeve just won't come out. It can also cause detonation because our ignition timing is heat controlled. Too much heat in the combustion chamber may set the fuel off at the wrong time or cause it to explode instead of smoothly burn, and that can destroy pistons.

The reason our engines are so tolerant to heat, IMO, is because they don't use rings. If they did, an overheat would cause the ring to lose it's tension, and when that happens it loses any hope of sealing everything. That's why car engines are so easily screwed over if you overheat them.
It's simple to gauge the performance of the engine. From slow idle jam the throttle wide open. Note how the properly tuned engine will smoothly and instantly react to your input and scream up to top speed, often with all four wheels spinning helplessly looking for grip that isn't there. An out of tune engine will not do that.

Sound is just an indicator of the tune, it is not what one should tune for. You want to tune the engine for crisp throttle response, as much power as you can get, and to be very smooth. Sound, smoke and temps are just indicators of whether or not the tune you've settled on is good. I use the same principles when I tune the carb in my pickup truck.

Well, except for temp. That thing has never overheated in the 75,000 miles I've put on it. But that's for another thread entirely.

Anthoop

I always grimace when people quote temperatures...so your engine was still ok after 300x but you knew it was getting close to the limit?
If you are talking fahrenheit then 400 will not bother any of those materials, however those materials will not enjoy rubbing against each other at any temperature without lubrication.

Of course we use many ways to determine correct tune but for me the sound of an engine will tell me far more than trying to guess whether it went faster before or after that 1/8 turn.
Try watching a youtube video with the sound off and then listen to another without watching....if you can not tune by sound then maybe we are talking a different game here?

CEN GST 7.7

  
     Argess
           What is your opinion on the best way to break in the motor on a new truck I'm going to buy. Go through a few tanks of gas letting the motor idle or use the Heat Cycle method ?  I think Cen recomends to just let the truck idle through the first two tanks. For the third tank No more than a quarter throttle. After that I dont think that there is any restrictions on the throttle. I'm not sure how the heat cycle method works so I thought I would stick with the idle method. What do ya think ? 

378

My Feedback: (4)

I don't like idling around. What I did when I broke in my OS is I set the carb as per the manual, fired it up, and within thirty seconds it was driving around at partial throttle. I didn't beat on it but I make damn sure it got up to at least 200 degrees and I held it there for a while. I shut it down when the tank was nearly empty by plugging the exhaust, then when it cooled I refilled the tank and fired it back up. This repeated until I had finished off five tanks, then I tuned it and that was that.

ThunderbirdJunkie

My Feedback: (3)

This makes sense...ThunderbirdJunkie has not overheated most of his engines that he knows of, but he also doesn't check temps. If it's running good, it's good to go. He has confirmed one engine running about 360 degrees after running in a low speed/high load/high throttle/high rpm situation with very little airfllow. That engine is still running great in a buddy's truck.

The truck was running fine. It could've even been leaned out a bit; the performance was there. Lubrication doesn't go away just because of temps. If you were able to provide realistic reasoning for an engine to dislike high temps, that'd be one thing. You clearly don't fully comprehend the forces at work here.

Argess

I don't think it's a big deal. Even if you never do a break-in procedure, the engine will break in through use. It just takes longer. The danger is working the engine too hard before break-in is complete could cause something to break, like the conrod, crank pin, etc.

I know I have broken in engines incorrectly, but they seem to last as well as ones I've followed to the letter.

Basically, I use a combination of break-in procedures. I do idle the first tank. During that time, I get the LSN adjusted so it keeps running, and get the HSN adjusted for a rich mixture, yet lean enough it won't quit when I rev it a bit. There's lots of heat cycling going on because it stalls so often during this first tank and prelimianry adjustment procedure.

Once I'm through a tank, I then basically do what 378 does, and drive it around for the next 6 or 7 tanks. I give it lots of little burst of throttle, and shut it down every few mintues for heat cycling. I become more agressive with the throttle as more and more tanks of fuel get used up.

Even after I consider break-in complete, it isn't really done dependant on the engine. I try not to be too hard on it until more fuel is used, and that means I don't hold it at WOT very long. But I drive it more or less normally other than that.

On heat, I've had engines accidently get up to 400degF and no damage resulted. But it wasn't held there very long either. I had one engine that was touchy to tune and when it was run too lean, it would detonate. I could hear it...weird sound too. And detonation for any length of time can cause damage. This usually occurred at about 325degF, so I try to keep things under 300degF. But as I said earlier, the terrain and driving style will dictate the temp more so than a slight tuning change.

Anthoop

When an oil is heated the vicosity is reduced, meaning our metal parts are now closer together?

ThunderbirdJunkie

My Feedback: (3)

Closer together is not the same as no lubrication.

Anthoop

Ah but now we are more susceptible. Reducing the film thickness will increase wear and at minimal thickness failure is far more likely...no?

ThunderbirdJunkie

My Feedback: (3)

No...if there's a film of oil actually separating the piston and sleeve, then there is no contact, therefore no wear. You've blown a hole in your own argument [&:]

378

My Feedback: (4)

The pressures in the combustion chamber are astronomical. Five, six figures even for some engines(Though probably not for ours, but hold on with me here). A thin film of oil combined with the insane pressures exerted on the parts means the parts can punch through that oil film. Then there's the G-forces alone. The piston in a typical engine revving at about 2 grand will experience anywhere from 200 to 5,000 Gs as it goes up and down. This puts a ton of stress on several oiled joints. Crank, rod, wrist pin bearings, they all take a beating. Usually when an engine throws a rod this is the force that does the trick. At the ~30,000 RPM our engines run at, they too are subject to forces that high. This alone can break through a thin oil film without combustion pressures also factoring in.

All engines are designed with certain tolerances that expect a certain thickness of oil film while they're running, and if that film is too thin they won't last very long.


It'd be like if I put a change of 0W20 in my old Ford truck. Sure it'd run, but the oil is so damn thin that I might make it 50 miles before the rod bearings commit suicide, and that's assuming the oil didn't blast right past the rings and get burnt. Which it probably would. But if I feed it the 10W30 it calls for it will run happily mile after mile.

ThunderbirdJunkie

My Feedback: (3)

378...Anthoop wanted to talk theory, so ThunderbirdJunkie talked theory[&:]

He is aware of the actual practice and reality

Anthoop

We had a nice little discussion going....and now all of the eggs have been spilled out of the basket.

supertib

You cant tune by smoke..all fuels have different smoke characteristics...some fuels will hardly smoke under a perfect tune, and others will be fog machines under a perfect tune.... so tuning by smoke is useless unless you know exactly how much smoke to be looking for when tuned properly......... tune by sound and performance ! forget smoke and temperature....... Also not weather conditions will affect how much smoke trail an engine leaves as well...some days they can smoke lots, and others they will hardly smoke.......