Mephisto .21 ONH
 

So.....1st timer with nitro....I got this motor for my Inferno GT3. I didnt even try to start the motor yet. Motor out of car i tried to turn the driveshaft. The piston is getting stuck at the stop of the sleeve. When I take the underhead off, when the piston reaches the top, the sleeve would pop up too. Seems like the sleeve is too tight at the top. Any ideas?

Cylinder taper
 

When you get the engine started, heat will build up in the engine. This heat will cause the sleeve to change shape due to thermal expansion. In this case the part of the sleeve that is tight around the piston will expand and the piston will travel in and out of that area very freely. The engine was designed this way so you don't need a piston ring for all temperature compression. Properly breaking in this engine will result in adequate compression of the engine to support continued running till you stop the engine. That is when you have the proper mixture settings. Some times you need to pre-heat the engine to get it to turn over during the starting process. All that is doing is expanding the sleeve so the piston will pass through. Good luck.

Understood....but it wont turn at all when it reached the top when fully assembled. I used my started box and the thing started to smoke.

This is a case where the engine should have been preheated before starting so the piston would slide up and down in the sleeve. The smoke probably came from the motor(s) in your starter box. They don't handle high current very well when they are stalled by the nitro engine. I use either a heat gun or a hair dryer to heat the engine before starting when I am beginning the break-in process. That also eliminates some damage to the piston/sleeve assembly when they would be the tightest at TDC. There are also some engine heaters available that fit on the cooling fins of the head of the engine. They are battery powered and put heat in the engine the same as a tire warmer.

You must make sure the engine is not stuck at TDC when using the starter box to start the engine. And sometimes tools are required to move the flywheel over to an unstuck position so that it will rotate when the starter box engages.

Yes it came from the starter box....I did preheat the engine before starting. This happened right when I opened the box to the engine also. I could not turn it by hand right out of the box. The motor never started and the piston never made a full rev on the starter box. The starter box could not turn the wheel on the motor because it was so hard

i just heated the engine for 20 min with hair dryer....temps were around 220 at heat sink and 170 at body of motor. still could not turn past that point. Piston was at dead bottom during heating

Because these engine have no piston ring and there is no way to get the piston on the right dimension of the sleeve you will get an oversized piston you need to break in first.
As mentioned the sleeve is a tiny bit tapered but when the engine is running the sleeve is cooled on the lower part due the mixture and heated on the upper part taking the taper away to a straight shape.

Pre-heating will expand the sleeve more than the piston because there is no combustion heat making the piston hotter so it will start easy.

Important is to take the first liter with some care, do not over rev the engine

The heatsink is from aluminum, that will pick up the heat from the hair dryer and transfer it perfectly to the sleeve.

My newest engine is the Mephisto 21 onroad engine from NovaRossi. I had to heat the engine with a heat gun to get it to turn over for break-in. I ran it for 12 tanks (125c) in 4 three tank segments with 15min between segments. I run the engine full speed with an airplane propeller for load. I have now run about 2 hours on track and my engine still has the pinch at TDC. In fact, I still must use a heat source to get the engine to turn over for starting before each qualifying race and each main. This engine has never been over 225 degF during each run cycle. The point here is that you are not the only one that experiences this. I don't call it an issue, just the way it works.

I had one once that tight so I took it apart and put a nice coating of red high temp silicone greese it worked for me

Guys, you should always get your preheating up to 230*F or more on a new engine, or better yet send it to get modded and broken in for a small fee and no headaches...I always reach at least 220*F preheat before start on my already broken in engine...

I am buying a 8th scale RX8. And I have a novarossi engine. What Pipe and manifold combo for this application are people using?

It depends which model engine you have, but the 2015 pipe would work for all of them in onroad. The only difference would be the header. That is track dependent where you use the medium header for small, tight tracks and the short header for the long sweeping tracks where the engine stays at upper mid to high RPMS each lap. Some people use the standard headers for higher fuel economy and some use the conical headers for most all out power. Hope that helps. Now let the debate begin.