No announcement yet.

Question for the teckies

  • Filter
  • Time
  • Show
Clear All
new posts

  • Question for the teckies

    I needed a break so I started on the MLA diesel engine project. A few here have built them. I decided to get the plans. I read a user that stated he wanted to try it in aluminum for the crankcase I think. It is about weight, so I decided I would try aluminum. Not being a metallurgist I am not sure of expansion rates. Using aluminum for the cylinder I will have to sleeve it with steel. I was thinking on a press fit and then lap the piston and the sleeve.

    Would this be possible or am I wasting my time? I know they make nitro engines out of aluminum and a metal cyl sleeve. Not a diesel person so I do not know what to expect.

    Any suggestions would be appreciated.
    Life Is Grand

  • #2
    An Al block and a nickel cast iron sleeve should work just fine for a diesel. Keep in mind that a lot of engines use wet liners - the cylinder line itself is in contact with the coolant as the liner is strong enough to take combustion forces.

    Peak turbo diesel combustion pressures can exceed 2000 psi; this occurs at
    near TDC, so often the top few inches of liner will be solidly supported by the block; as pressures and temps drop as the piston descends the liner no longer
    needs support and coolant is allowed to flow around the liner. The block needs to be stiff enough to prevent the liner from expanding so far that it
    yields; remember that Al is one third the stifffness of steel/iron.

    My experience w/ VW diesels back in the 80s was that they ran forever until
    they overheaded; the Al head then promptly warped.
    Bart Smaalders


    • #3
      barts..thanks for the lesson. I should have stated that this small model engine is air cooled or air/fuel cooled. It is similar to a nitro model engine that uses the fuel for cooling, lubrication, and of course combustion.

      Having these facts do you still feel it would work?
      Life Is Grand


      • #4
        I don't think you will have a problem if you can make the liner with a shoulder at the top to clamp the liner down with the head. The only problem with a liner that shoulders on the bottom is it can get loose up and down and then get loose in the bore. Most liners are shouldered at the top in full size diesel engines.

        I am gathering up drawings for small engines. What site is your engine on?
        Last edited by Carld; 11-16-2007, 09:27 AM.
        It's only ink and paper


        • #5
          Use 12L

          On model diesels Most folks use 12L14 for the cylinders and a cast iron piston.
          James Kilroy


          • #6
            jk....the plans call for cast iron for the crankcase and aluminum for the piston and head. I do not have any cast plus I wanted to keep this light as I am thinking of trying it in an r/c plane. From what I have read this engine was made as a stand mounted engine but the designer said the thrust swinging a 12" prop was intense. This sounds to me like it would fly a .40 size model. Would be cool having a diesel powdered plane.

            Weight is a factor and it would have to be aluminum I feel to keep it flyable. A steel cyl. liner would be ok since it would not add that much weight. I am sure it can be pinned to keep it from moving.

            Just not sure of the expansion rates of these materials and am not sure about loss of compression if one expands much quicker than the other.
            Life Is Grand


            • #7
              Aluminum piston?

              Does the piston have a ring? Diesels need a very good piston to cylinder fit to get the required compression. Most of the time diesels with aluminum pistons are hard to start because you have to add clearance to compensate for the faster expansion of the aluminum piston vs the cylinder. This is why the iron piston / steel cyl is so popular. You use a lapped fit. There are plenty of diesels flying around out there with this combo. An aluminum block is required for sure.

              Is this the MLA you are talking about?


              Sure doesn't look like an iron crankcase to me.

              James Kilroy


              • #8
                Yes that is the one. The plans call for a cast iron crankcase. I asked the designer about that and he said as this was designed for a mounted display the weight was not a factor. He would not comment on using aluminum except to say it may be possible.

                The piston is a lapped fit with no ring. The rod is called out for stress proof steel. I will double check the piston to see what it calls for.

                Of course I can do whatever I wish so if an iron piston is the way to go I can do that.

                The added info supplied with the plans do have a section on some complaints about hard starting. The designer goes into much detail on how to use the compression needle to set it at the bare min. for running to make it easier starting. There were many complaints about hard starting and fluid lock.

                There is a user here that built this and it runs. I can check with him to see how it made it and what he ran into. He built it exactly as the plans called out.
                Life Is Grand


                • #9
                  Here is the email I got from the fella that built it. As you see he says the cyl is cast iron.

                  Once I have it running it has no trouble running the entire tank out without stumbling. It is a bit heavy for a model I think but have not done any calculations to verify. Personally I'm not very good at flying model airplanes without crashing them so I would be afraid of smashing the engine as well as the plane. I guess it might be good on a larger, slow flying control line model. The engine has no throttle control so it wouldn't do so well for RC. The plans specify a cast iron cylinder and the head is a pretty big chunk of aluminum. You could probably redesign the cylinder to be a cast iron sleeved type. This would definitely take some thinking and precision machining. With the tools I have now if I were going to build another I might try making the block out of square stock rather than round.
                  He mentions using aluminum and sleeving which is what I hope to do.
                  Life Is Grand


                  • #10
                    Klem,most model engines use a brass liner,which is chrome plated,running an aluminium piston.But on a homebuilt version,this might be a problem.Unless you know a place where you can get the plating done,
                    You can of course just use a brass liner as is,but I don't know how long it would last with a diesel.Their running characteristics are a bit different to glowplug engines.
                    Hence,for an engine I'm going to build,I'll be using aluminium for the crankcase,and cast iron for the separate cylinder barrel.An alloy piston will run well in a cast iron liner.Model diesels don't have rings as a rule,so the fit will need to be quite good.
                    Let us know how you get on,I'd love to see some pics of your build in
                    progress.Then I can steal any good ideas you may come across.


                    • #11
                      I have built the MLA-17. I posted pictures of it a little while back. I think you are confusing terminology. The piston is steel not aluminum and the crankcase is aluminum not cast iron. The cylinder is cast iron. I used dura-bar ductile iron for the cylinder. I may build another with all my design changes but the one I built to the plans ran pretty good and it looks wonderful mounted on wood sitting on my desk so I don't want to modify my existing one...especially since it was my first machining project it has a lot of value to me.

                      FINISHED ENGINE




                      • #12
                        Beautiful work

                        Jadecy, that is great work, made even more impressive in that it was your first project. You can be rightly proud of that accomplishment. Do you agree that 12L14 would suffice for the cylinder in place of durabar if availability was an issue? Have you managed to run your model and put a tach on it and see how see performs?
                        James Kilroy


                        • #13
                          here is a previous thread with more info.

                          Some might think it strange but I enjoy the journey more than the result. I do like the result just not as much as the doing.

                          I've moved onto my next project. I will make more posts about it as it progresses.


                          • #14
                            This is interesting. I went to the MLA-17 site and the engine is 4 3/4" tall and 5" long. It is a .20 cu. in. engine. From my experience with models that engine may not have enough power to fly a model of the size it would need. Diesels will turn a larger pitch and diameter prop than a glow engine so that would help. Diesels also vibrate a little more the glow engines so they tend to tear light airframes up. I have never used a diesel on a model but several of my friends have.

                            I think it's a cute engine and I think may buy the plans. To be honest, I don't think I would need plans to build one close to it, nor would many others. I have some old plans for model boat diesels that I can use to build the adj. comp head. It would be easy to make an exhaust throttle plate to control the engine rpm or even a ventura control.

                            Looking at the photo on the engine site it appears to me the crankcase and head is alum. and the cyl. is steel or cast iron. I would guess the cyl. has a sleeve on the end that slides into the stem of the crankcase. If not then I would modify it so it will do that. There may be ways to lighten the engine by contouring the outside of the crankcase or maybe the inside or both.
                            Last edited by Carld; 11-17-2007, 12:16 AM.
                            It's only ink and paper


                            • #15
                              Linear Thermal Expansion Rates

                              Originally posted by cybor462
                              I Not being a metallurgist I am not sure of expansion rates.
                              Linear Thermal Expansion Rates

                              Aluminum - 13.3

                              Iron - 6.5

                              The units are, micro-inches / (inch) (Degree Fahrenheit)

                              Aluminum expands twices as fast as iron. Hope this helps.


                              Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

                              Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.