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Thread: mac engine


  1. #1

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    mac engine

    I have a mac engine but not sure what cc anyway to tell by the looks? I'm looking for a gasket set for this engine could someone give me a link to a site that sell's them? I am having no luck finding one!!! Here ar some pic's of the engine in question.
    Thanks for the help
    Greg
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  2. #2

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    RE: mac engine

    Kahn,
    Just go to your local auto parts store and buy some 10 to 20 thousands gasket material. Use a hobby knife to cut it out on a hard wooden surface. For the cylinder base, I usually cut a hole to fit the cylinder base flange. Slip it on the cylinder, then press lightly around the edges of the transfer ports and mounting holes. Trace the impression with a pen and cut it out. Make sure that you allow for the pulse port. I have this engine. It will run on EI or glow/gas fuel and power my GB Ultimate. I cut the center of the flywheel out with my drill press and turned it down in it also. This allows me to use a standard prop hun. The thread is 8x1.25mm metric. The tail shaft was cut off with a Dremel cut off disk. I used the 9.5mm Walbro carb from a 28cc Mac trimmer. Here are some pictures of my 21cc Mac.

    Dave
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    Every day above ground is a good day.

  3. #3

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    RE: mac engine

    Dave
    What kind of performance are you getting out of this engine? How heavy is the plane that this engine is hauling? Prop size and RPM would be very helpful. I have to make sure this engine will be a good match for a 13 pound corsair what do you think? I'm flying it now with a OS 1.20 fs . Is this 21cc more powerful?
    Greg

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    RE: mac engine

    Kahn,
    I just got it this far recently. I haven't run it yet. It had very mild port timing. I lowered the intake port 1/16" to give it 120 degrees duration and I raised the exhust ports to get 140 duration. Mine has a floating ring, so the ports are narrow to prevent catching on the ports. I modifed the piston also to improve flow. I think that you will be happier with a Homelite 25 or a Toro 25 in your 13# corsair. I am looking at a ten pound plane. Thats why I got rid of the heavy flywheel etc. Here are some pictures. You can see the enlarged intake port in the picture on the right.

    Dave
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    Every day above ground is a good day.

  5. #5

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    RE: mac engine

    I guess I'll look for a 25-30 cc engine but I will still convert this engine for latter down the road!

  6. #6

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    RE: mac engine

    Kahn,
    Mine weights 40 oz. as shown. Add 7.5 oz. for the EI with battery, 47.5 oz. or 3 pounds. It should swing a 15x8 at 8,000 rpm. How much lead do you have in the nose? This engine with mag will weigh about 3.5 pounds. Does the OS 120 fly it well? If you are replacing lead with engine, the balance should remain the same. If the Mac will get the RPM you need without porting you will be ok. I would use a bigger carb though. Test it on the bench and see how well it does.

    Dave
    Every day above ground is a good day.

  7. #7

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    RE: mac engine

    I have an easy pound of lead in the nose of the corsair. It wont be flying for a little while just crashed it today. It will be running in a week I guess, If I can figure out how to get the con rod off the crank pin....... The 1.20 flies it well just want more power for reserve. I fly that plane at full with a 15/8 mas prop... More power would be nice.
    Greg

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    RE: mac engine

    It sounds like you need something that will swing a 16x8 at about 8,000rpm. What is the rpm with the 1.20?

    Dave
    Every day above ground is a good day.

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    RE: mac engine

    On my 1.20 I am turning a 15/8 at around 9-9.3 RPM What is your opinion on this matter? What would you do?

  10. #10

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    RE: mac engine

    I'd like to see a little more reserve power. When you run the mac it may get what you need. It will be an easy conversion. The engine will weigh about 3 and a half pounds. No lead needed. A 16 or 18 inch prop will make a world od difference in handling. Just follow the rules for a gas install.

    Dave
    Every day above ground is a good day.

  11. #11

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    RE: mac engine

    I had some time on my hands today and went to a few small engine repair shops, found a boat load of used toro weed eaters 21-31cc for 20 bucks. There is a place not to far from me that has a repair shop on his farm with all makes and model weedies you can imagine. Your choice 15.00 Could you point me towards another weedie that would be reliable with good power? brillelli engines says go with a toro, cant be beat!

    Any thought's
    Greg

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    RE: mac engine

    Homelites are my favorite. Most are 25's. Here's a thumbnail of my 30 from my gallery
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    RE: mac engine

    kahn41: Jenison MI is only about 45 min form Here in Hesperia. Are the Toro engines in pretty good shape? What cc diplacement are they? Thanks Capt,n
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    RE: mac engine

    I dont know how big they are, I have never done a gas conversion before ,. the guy said they were the bigger ones. I'm assuming the 25-31 my mac is a 21? and the head on the toro are much bigger
    Compression sounded good and felt good.
    Greg

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    RE: mac engine

    Kahn,
    The Toros are a great choice. Read my forum on "who is converting Toro trimmers?"

    Dave
    Every day above ground is a good day.

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    RE: mac engine

    Dave
    I will read your thread on the toro's But I think I'M going to offer 30.00 for both of them he said he had them a while I dont see why he won't take the offer!

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    RE: mac engine

    Kahn,
    I'd offer ten each and go higher if necessary.

    Dave
    Every day above ground is a good day.

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    RE: mac engine

    Capt: i am only 15 min from you in a F-16
    Ken
    Ken
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    RE: mac engine

    I've been reading the post pretty interresting, but I did'nt understand how you tell the difference from a sngl barrel from a 2 barrel when it's still in a trimmer form? cant see much!
    Greg

  20. #20

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    RE: mac engine

    Kahn,
    The 25cc Toros currently for sale come in two versions, 1bbl and 2bbl. The 2bbl carb has two venturi's, stacked verically. The top intake flows air only. The bottom is fuel mixture. The top barrel feeds reed valves in the transfers. The carb is usually replaced with a standard butterfly carb. The reeds are removed and blocked off.

    Dave
    Every day above ground is a good day.

  21. #21

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    RE: mac engine

    So I guess when I buy this toro it is just the luck of the draw and see what you get? The toros he has for sale are two different 4 digit number models, like for instance a 1020 and a 1040 and I beleive he said the higher number, the newer model, but dont quote me on that!
    thank you all the valuable help and advice I am learning a lot, but still need more knowledge on this conversion thing.
    Greg

  22. #22

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    RE: mac engine

    So I guess when I buy this toro it is just the luck of the draw and see what you get? The toros he has for sale are two different 4 digit number models, like for instance a 1020 and a 1040 and I beleive he said the higher number, the newer model, but dont quote me on that!
    thank you all the valuable help and advice I am learning a lot, but still need more knowledge on this conversion thing.
    Greg


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