R/C Airplane MTD (Ryobi) With Port and Polish

[@mazpr2025]

The piston may be small, but thats one rock solid rod, looks to be forged.

[@cap10moman]

The idea for reducing the crankcase volume is pretty awesome, so thanks for the concept!! I do have a few questions about the way you decided to execute the concept, though: 1) While looking at the side view of the packed-epoxy (i.e. 4:24 - 5:00), it seems there is sharp formations of epoxy. Wouldn't those formations be a possible point-of-failure? 2) Why did you not continue to mold the epoxy, in order to achieve a smoother surface? 3) Does the rough/jagged/lumpy molding of the epoxy effect the A/F mixture in such a way that reduces power/efficiency? 4) What is the thermal expansion of the epoxy, relative to the metal it is adhered to? And did you take that difference into account while applying the epoxy? Thanks for the video, and thanks for your future response! -Adam

[@4395R]

Adam, I appreciate the questions. Sorry about the late response, I do not get into social media much. 1) The sharp formations formed with the back-plate, I needed to leave room to get the rod in and out. 2) The only place the epoxy isn't very smooth with the back-plate on is around the extreme edges of the crank, where I literally turned the crank while the putty was still malleable to ensure it was interference free. The edges of the rod scored and made the final form on around the edges. 3) A/F Mixture is a function of the carb, I have very good results in my opinion. 4) Epoxy putty while very strong can bend, expand, and contract. Adheres very well to clean metal, and the crank case of a two stroke engine is a very cool area. I just want to note, I have used epoxy putty in R/C aircraft engines for probably 20 years. I have built everything from velocity stacks, volutes, modified exhaust pipes, transfer ports, and even built rear engine mounts with it. Get some, use your imagination, form it up, drill, sand, mill, file, tap and bolt together. It is really good stuff. Brian

[@4395R]

Hello, I just added a video of the engine with a Redcat tuned pipe.

[@christopherknee5756]

Did you test the engine before the mods? What engine speed and propeller did you get eventually? Is there a flying video? Did you increase the carburetor size? Did you adjust the reed valve for more flow? If you raised the exhaust port, you lowered the compression ratio a bit. You could recover some power by lowering the cylinder a little and then raise the ports to compensate. Have you read combatpilot's thread on his attempts to modify the Ryobi? I have a summary of it in one file if you are interested. Were you able to use the same piston? Have you seen the Wiseco hole drilling trick to aid lubrication to narrow port bridges? Rounding / angling the edges usually helps. Is that what you did? What tuned pipe or muffler did you build? What is failing on that? Well done on a good video.

[@4395R]

I did run it in Utah at about 4300 msl. If I remember correctly it was around 6500-6600 RPM. I did taper and curved the ports slightly to tuck in the rings. I'm not familiar with the drilling technique you mentioned, please send me something on that as I plan to change the piston and rings on my Supersportser which has the engine in this video for about 6-7 years and hope to recover the 800 RPM drop I had. The wear from this video hasn't seamed to propagate since this was broken in.

[@christopherknee5756]

@@4395R Some engines with a bridged exhaust port suffer from high wear on the piston. The solution is to drill a small hole (1/16" for a 250 cc bike, so I'd use much smaller for a 30 cc) through the piston wall at the spot of the wear. This allows some oil from the raw fuel mixture below the piston to lubricate this area of the piston.

[@4395R]

@@christopherknee5756 that's a great idea. If I can find the right piston to replace it I'm going to do that on the wear areas. Thank you for the idea

[@4395R]

I finally added the tuned pipe by Redcat and uploaded a short video of it running

[@normaascur9520]

Hello, good day, I have an engine the same as the one you showed in the video, but I am missing the carburetor and the ignition coil. Could you tell me where I can buy it and how many cc has the engine, thank you.

[@4395R]

I'd look online for MTD engine parts. You can pick up power and reduce weight if you use a electronic ignition conversation. I'm not sure if anyone makes EI's anymore for these. Try Google C&H ignition for Ryobi

[@4395R]

Two things, check Redcat parts for a carburetor and I just uploaded a new video of the engine with a Redcat tuned pipe.

[@ionhunter]

You had time to Rc in the sandbox? Lucky

[@4395R]

I had time a shop and tools. I'd been there a few times so I brought a project with me. I built a jet engine out of a turbo there in 2010. I should post something on that someday.

[@tonyemory3618]

The first time that engine heats up to normal operating temp i see that epoxy destroying your engine and even if it does survive the initial testing and makes it installed on an aircraft i wouldnt trust it to last very long before the epoxy comes apart locking up your engine at best or at worse causing your engine to explode.

[@4395R]

Four years of flawless operation on a Super Sportster says differently. The biggest problem I have is keeping an exhaust pipe on it.

[@4395R]

The engine is cowled also, it's run pretty hot and hard.

[@captainsledge7554]

Some people have no idea what epoxy is. They think its glue. Its a composite. Composites are stronger then metal. The new ge genx turbojet engine on airplanes are made with composite turbine blades on the hot compressor. Which withstands 2600 degrees easily. The internet is a wealth of information and people like this use it to insult other people's work. Smh

[@FlyMIfYouGotM]

@@4395R To get the exhaust pipe to stay on have you tried first cleaning the both halves with brake cleaner. Once both halves are thoroughly clean, put a thin, even coating of Red RTV Silicon gasket sealer on both halves. DO NOT PUT THEM TOGETHER yet. Wait 24 hours for the RTV to thoroughly cure. After the RTV on both halves have thoroughly cured, put a very thin coat on one of the halves and then assemble by using some additional RTV on the bolt threads. (It's a bit like high temp Locktite.) Allow sufficient time for this RTV to cure before running. Years ago I had this same problem with a nitro heli engine. This method solved it. The problem with putting the halves together before the RTV has cured is that virtually all of the RTV is squeezed out as soon as you tighten the bolts. A few thermal cycles later and everything is loose and leaks. By letting the RTV set up on both halves first, you create a high temp rubber gasket that won't squeeze out and will flex slightly with thermal cycling.

[@FlyMIfYouGotM]

@@captainsledge7554 Over 30 years ago I asked a retired NASA guidance system engineer friend why no one was working on a ceramic composite replacement for jet turbine blades. No machining, just mold, fire and use. My reasoning for a composite was that it would overcome brittleness and the tendency to crack and shatter of a pure ceramic. In addition, ceramics could take higher temps than any known metal alloy. He insisted it wouldn't work! Imagine my surprise a few years ago when I saw GE was doing this. I just wish he was still around to see it. I am not sure but isn't Rolls Royce the ones actually making the blades for this engine? I seem to remember that only they had a proprietary magic process that finally solved the manufacturing problems.