Hello

I am new to rctech but not new to 1:8 scale RC cars. I would like to share a project with you for which I need your experience.
I have seen a lot of threads about engine break in and dynos in this forum. And I hope you can help me here.

I am planning to build a break in bench for 3,5ccm race engines. Yes I know there are some to buy from the shelf, and I do have a hudy and used it several times. But I am not happy with this. Due to the construction and the prop which is almost touching the carburetor, it is impossible to use an air filter. And I want to use the air filter, or the ins box, or maybe something different not to clean the air but to reduce the noise, first of all not to disturb neighbors but also to make the process more convenient. In a next step i would also like to reduce the noise emissions from the exhaust, but this should not be part of this thread. I am also aware that there is this 1300$ break in bench, which I think is highly overpriced, however it goes in the direction how I would like to build my bench.

There are several reasons why I do not run in the engines on the track, first of all as I do not have the time to do so. And please do not recommend EBIS because I think it is not the optimal way to break in an engine. So I would highly appreciate if you do not start a discussion about how to break in an engine.

I have made some simple drawings to illustrate the set up of the bench. Unfortunately, as I am new to this platform I am not allowed to post pics in my first thread, so please see below this first one.

For my break in bench I would like to use a BLDC or a standard DC motor as a load. I am planing to use a part of a drive train of an old car, so there will be a clutch on the the engine and a gearbox. This is to reduce the rpm for the motor which simulates the driving resistance, and to have no load at idle rpm. Moreover I have made some calculations to have an idea what the load should be.

Unfortunately I am not an engineer, nor a technician... I have my doubts if a standard BLDC acting as a generator will “survive” in this set up. My concern is the running time. Breaking in takes 1-1,5 hours and I assume the load motor will heat up a lot, although I am planning to cool it with a fan. I saw many people here are playing around with dynos so there is some knowledge about electrical load, even if the running time of a dyno is very short, I hope you have some good tips for my project.

I think the picture of the bench is self explanatory. The table shows the results of my calculations based on my assumptions.

Column 1 includes the current speed, as an orientation for the rpm in the following columns. For the time being the plan is to connect the load engine with the gearbox shaft so the generator runs at rpm of the gearbox.

P resistance is the power in watt calculated based on air and roll resistance at certain speeds necessary to hold the current speed.

P generator is the calculated resistance of the generator connected to resistors at the relevant rpm of the nitro engine, I assumed that in generator mode the engine has only 70% efficiency. Which means that an engine with 1000 KV produces only 0.7 volt at 1000 rpm.

w/w gen shows the difference of the calculated resistance of air and roll compared with the load simulated by the generator. The box around 30 to 70 km/h should highlight the zone which I assume will be most used during break in. I know that w/w gen at low and high rpm show material deviations, but for the values within the box it’s fine. I know I could play around with different resistors to have different loads, but I don’t want to make it too complex right now.

R target load is the calculated resistance needed to reach certain load in watt at certain rpm.

Ugen KV 550 shows the voltage generated at several rpm levels and is just shown as an indicator but used in the calculations.

As you can see I really tried to get into this, but now I have my doubts how long an engine acting as generator will last. Or which one to use. First I wanted to use a RC car BLDC but I think those are made for short running times at least shorter what I need for the break in procedure.

Maybe there is an alternative to an engine. I was also thinking about a an aluminium flywheel and using solid magnets to create a magnetic break system.

I hope that was not too long and would really appreciate your support on this.

Second post, see pics in next one

One more

Ok this is pretty bad, I am not able to upload my pictures.... I always receive that prompt that I am not allowed to

1) you do need at least 10 usefull (!!!) postst before you can post pictures.

2) You think an oil bath is not the way but it is the best option in what you want. And really, if you have experienced the ease of it you do not want to go different.

3) a 1000kv motor is a motor that produses 1000rpm per volt, the KV has nothing to do with Kilo Volt. But yes, a decent BL motor will survive as long you use the right value resistors. A topic to several dyno benches using a BL motor and 3 resistors as a load:
Who makes a dyno for brushless motors

In other words a self count down to being able to post pic dont work.no 5.4.3.2.1..no it be 9...

An oil bath will wash debris out of the engine as soon as the debris is generated. This produces the smoothest possible surfaces inside the engine. If you're going to spend time and effort to build a break-in device for your engines, you might as well make it an oil bath.

Personally, I just run my engines super-rich for the first tank, then dump the oil out of the exhaust onto a paper towel so I can see the debris that was scraped off the moving parts. Then I open the engine and use cotton swabs to clean out any debris that might've gotten wedged into crevices, such as the space between the sleeve and the cylinder-head. Here's what came out of my most recent engine:



Before I ever ran the engine, I completely disassembled it, used a diamond file to de-burr the edges of the ports, washed all the components, and re-oiled the components before reassembling the engine. And there were still chrome flakes that escaped my careful attention! An oil-bath break-in would've washed them away immediately.

@ Roelof

1) ok I did not know that, but find it’s not useful. I cannot even use the quote function as this uses links.

3) I know what KV means in connection with BLDC motors. I have also read that thread before my post here. In fact I have read a lot of threads and other websites, but a Dyno is not a break in tool. On a Dyno you will accelerate the engine for a short time to stop and measure the power output. I have no doubts that a BLDC Motor or any other set up works fine there. My concern is that a BLDC used as a generator in break in bench will not survive a longer time, but that is what you need when breaking in an engine.
And yes you are right I have to use the right resistors in order to be able to adjust the load and compensate the power, but there is still the generator where I have my doubts.

1) it is to prevent spammers posting on these forums or other sites with picturs uploaded to this forum.

2) you did ignore this. I know you do not want the discussion but it is a well proved break in. And to be honest it is a 80% break in, the last 20% you still need to do on the track by starting easy with 2 or 3 tanks.

3) I was not talking about the dyno itself but how the load is made. With several dyyno's it is indeed done by a BL motor and 3 resistors. If you cake an 1/8 BL motor and give it a load of 10 to 20A per phase and add some cooling fans I think it will work fine.

Yes I ignored 2) however some thoughts...

With EBIS you will probably create a very nice surface, a perfect round shape, debris washed out. I have no doubts about that.

The temperature distribution with EBIS is the same everywhere, but when the engine runs on fuel you have different temperatures in different areas of the engine. The fuel is flowing into the engine and has an effect on the temperature of the crankshaft and surrounding parts and more important the flow channels and the sleeve. But this effect will not be the same on all areas in the same way. Especially the temperature at the exhaust port will be significantly higher than other parts of the sleeve. As a result the piston and the sleeve will not be 100% circular. But it will be circular when it comes out if the EBIS and this not ideal keeping in mind that it will wear differently once it is running on fuel.

I do also think that the sleeve will horizontally expand in a different way when it runs on fuel. You will have a relatively higher expansion at the top, compared to the middle and bottom section. Again using EBIS you have the same conditions everywhere so the expansion will be almost the same everywhere. As a result the piston and the sleeve using EBIS will have the perfect shape at the temperature of the oil bath but not when it’s running on fuel. Thus in my opinion the wear of the middle to top of the piston using EBIS is too high, and in a worst case scenario the piston may even tip over when it is running on fuel and will have a different wear.

I have some more thoughts on this. However please don’t let us start a discussion. There are different opinions which lead to different methods. I am not saying one is wrong or the other one is better in general. I just want to build a solution not to use this hudy bench anymore.

What you are saying is true and discussed a lot but is no issue when done in that way. What people do not see is that the piston will expand more and will have a grow when it will run on the track.
1) In the oil bath the piston will stay at 90 degrees celcius, the combustion heat will go far beyond that so the piston wil expand more.
2)Tthe piston will get a permanent grow when it gets combustion heat. The same when you make a shaft perfect fit in a bearing and you will harden the shaft. It will not fit anymore when cooled down. The molecule structure has changed and did gave some grow.
3) because the piston does not expand to the max because of no combustion temperature the fragile surface of the piston will be polished. If you look close to the surfave of the piston it looks like it has a very small screw thread made by the toolbit of the lathe. that screw thread with the tiny sharp tips will be damaged when doing a cold start and bring on combustion heat. In an oilbath because the less expansion and the 100% oil those tips are polished giving a much better surface.

Even after an oilbath you will hardly notice a difference of where the pinch begins but when try to start you will notice how smooth it goes. And with the expansion by combustion heat and the grow there is enough room to shape the piston to a not so equal rounded sleeve.
But hey, who am I? Many large names like Salven, Adam Drake, MAG Tuned, Rody Roem and many more have one or even more EBIS systems and many satisfied customers.