Bess Heat-Cycling Break-In Questions

Whenever i break in an engine i just run 4 tanks of gas really really rich, then start giving it gas on the fifth tank but not reaching max speed. use after run oil.
Damon

Damon, that's the traditional break-ing method. This one is new and recommended by a lot of top racers.

Here is our original heat cycle thread:

https://www.rcnitrotalk.com/forum/showthread.php?s=&threadid=7218

Yeah, Bess is a little vauge on some points.

The needle settings aren't the same from engine to engine. 1 half turn on my engine may be equivilent to 3/4 of a turn on your engine.

I BELIEVE that Stephen Bess wants the RC as rich as possible without causing it to stall or to under shoot the target tempurature.

I recently did Stephen Bess's heat cycle on a rebuilt engine of mine. I basically kept taking temp readings over and over. If I was too cold or if the RC wouldn't move (give it gas and it dies), I would slowly adjust my needles until the RC moved and the engine target temp range.

So far so good for me, but I have to reiterate that this my interpretation of the quote you have there. In other words, It's possible I did it wrong.

Good Luck and welcome to RCNT.

-Rob

Thanks for the welcome! What you said is probably the best way, I'll let it idle then get a temp reading to see if it's getting hot enough, then lean it out from there..

Thanks Again!

No problem. I didn't see that you had already posted on the original heat cycle thread. I guess you didn't need that link after all. LOL

it sounds like you have a pretty good handle on the hobby, but if you have any more questions (or answers for that matter) feel free to share.

-Rob

An engien break in method I found

I Plan to do this on my new RC10GT when it comes but i think it may be a really good heat cycling break in. this may be a repost but i think its the first time

Engine break-in has always been debated with many theories and ideas of what is trying to be accomplished. Which has led to a lot of confusion. One common first mistake is to assume that the nitro engine functions like a ringed 2 stroke -- or 4 stroke for that matter. Small nitro engines get compression seal by using a tapered cylinder wall. The higher the piston goes up to compress the fuel/air mixture the tighter the fit between piston and sleeve. Sounds simple, but the sleeve is made of brass and the piston is aluminum, which leads to a heat expansion rate that is different between the two materials. For this reason the piston O.D is actually a bit larger than the sleeve I.D at top dead center, when the materials are at room temp. However once the engine is running up to temp (220-300`F depending on manufacturer) the materials have the proper tolerances and clearance required. The brass expands more than the aluminum. Break in is more of a heat expansion cycling than a "wearing-in" like with rings. This is why it is not good to compare the break-in of a ringed engine (which requires time and lubrication to properly let the rings mate into the crosshatch pattern of a bore) to the break in of a nitro engine. Because the cylinder is tapered, because aluminum and brass expand at different rates, because at different temps the expansion rate will differ and so will the tolerances between the piston and sleeve, manufacturers have recommended nitro content, oil content and glow plug heat range for a reason. Each one of these factors will affect temp, which will then affect tolerance, which will then affect performance and engine life. Proper break-in requires the use of a temp gun.


Each time an engine is shut off, it immediately begins to cool. Knowing that the piston in a fresh engine is larger than the sleeve when cold, each time you shut off your engine during break-in and in its future runs, the piston should be brought to bottom dead center (BDC). Doing this allows the sleeve to return to its normal size. Otherwise if the piston were at the top of its stroke the sleeve would cool on the piston and never get to its normal size. This leads to pre-mature over sizing of the sleeve.


A new nitro engine, as we all know, should not be raced right out of the box. But it should not be run cold either. If an engine normally runs at 240F, that is when the piston/cylinder fit is optimum. If this engine is broken in at 160F the piston will be scrubbing the cylinder walls because the sleeve is not at the temp it needs to be. As a general rule .12 and .15 engines run 20% nitro and .21 engines run 30% nitro (Please refer to your manufacturers recommendations). The following is only a guideline. We will assume the engine is in the vehicle. You can follow it word for word or you could shorten or lengthen it by one or two cycles. Before you begin, remove your glow plug and turn the flywheel until the piston is at the bottom of its travel (bottom dead center). Then mark the flywheel so you can bring it to BDC by just looking at it. Replace the glow plug and fill the fuel tank.


1. Check your radio and all connections/linkages. Get the engine started. Set the idle so the engine will not quit. Monitor the temp. After about 60 seconds if the temp is not over 150F turn the main needle in1/8 to 1/4 turn in (lean). The goal is to reach 200F before the first tank runs out. It is OK to blip the throttle to keep it running. A blip is not a full throttle rev session. Just before the fuel runs out, tap the flywheel to shut off engine and bring the engine to bottom dead center. Let the temp drop to below 120F

2. During tank #2 run your vehicle in a calm oval just using the lower half of the RPM range. Bring the engine to over 200F shut down and put piston to BDC. Do this 2 or 3 time during tank #2.

3. Tank #3 repeat steps#2

4. Tank #4 Start tuning for performance but still bring up to temp, shut down, pull to BDC and cool 2-3 times

5. Tank #5 Use common sense, your engine will still progress with the next few tanks. After each tank pull the piston to BDC.

wait..does that mean if do 'my' break in method its bad for the engine? so with my new sirio I'm gonna get i should do the one you guys are talking about? whats the average engine life of a sirio running on 25% nitro fuel, after run oil and a good break in?

thanks for the info Ajeauxdn
I'm about to get a new engine thanks for the info i will break it in that way

Ajeauxdn, :clap: that was some good information. That method is very similar to Bess's break in, but this one is running full tanks of gas through (not just 3 minute sessions). The BDC thing makes total sense now. I wish had known to do this with my previous engines.

I think I'll stick with Bess's break-in, but that article gives a wealth of great info.

-Rob

Fine and dandy but unless I'm missing something here you would have to do basically the following the determine BDC and know you are there:

1. Remove the plug and get a depth measurement through the plug hole to find BDC.
2. Mark the flywheel so you know where the BDC location is (this assuming that the flywheel never moves or is removed after you mark it).
3. Check and manually turn the flywheel after every running to position your mark.

Not for me. I'll just continue to shut down and leave it at that.

so then i break my engine if i do it my way? how many tanks of gas does an engine normally take bfore it loses compresion..i heard 4, is that right?

damon

How do you pull the piston BDC? I'm fairly new to the forum and to nitro as well. Can you explain, so I can do this as well? Also, I'm not going to run my Savage for a few days, should I remove the glove plug and pull the fuel line to the carb off?

When you are finished running allow the engine to cool first.
1. Clean area around the glow plug to get all dirt out of the head.
2. Dain the fuel tank.
3. Remover the glow plug and put a few drops of after run oil in the plug hole.
4. Replace the plug and spin the engine a few times to distribute the oil.

Leave te fuel line, air filter, and plug in place.

why do you guys ingnore me...i feel left out

damon

Damon: If your engine loses compression after only four tanks of fuel you really screwed up. At least a couple gallons unless your running real lean for racing and don't care about engine life.

I meant gallons...my bad, 4 gallons.

damon

opps i mena 4 gallons, my bad

damon

Finding BDC is quite simple. Turn the flywheel by hand until you reach max compression. You should encounter a ton of resistance here. When you pop it over, you have just passed TDC (Top Dead Center). Rotate the flywheel 180 degrees and there you have BDC.

Until 2 weeks ago I followed the cold running/very rich method of break in, still recommended by engine instructions, including my new hyper 8-port. Then I got the book Ultimate nitro engine guide by Air Age media (rc car action, rc nitro).

It has detailed info about the heat cycle method. It describes 2 ways, in car and on the bench. With either method, you never allow blubbery rich 4-cycling and always heat it up with a hair dryer or heat gun before starting to loosen the inital piston clearange.

The bench method is very different: Use a small airplane prop (7" dia x 4 pitch), pin it wide open, adjust needle for slightly rich 2-cycling with 200-230 F, run 1 minute, cool down completely, repeat with increasing run times for at least 30 minutes total.

I'm shocked by it, but it makes sense. They say that if you run it too cold, the cylinder doesn't expand enough and excess material will be worn off, resulting in shorter life before compression drops off. My hyper still runs well, but is getting harder to start. I'm going to try the heat cycle method when I need a new sleeve kit.

i am about to break in my new .25 engine and i will use the bdc way i hope ot works