In-line triple 45cc

Discussion in 'General Engine Discussion' started by johnlaudano, Aug 9, 2018.

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  1. Aug 9, 2018 #1

    johnlaudano

    johnlaudano

    johnlaudano

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    I'm working on a self-designed in-line triple. it uses a few parts from airplane engines but most are my design. the cylinder heads, sleeves, cams, and pistons are from Magnum 91's. The rest I've designed. it's water/air cooled and will have glow ignition. the intent is that it would power a large model boat similar to others in my prior posts. the water cooled system would be a recirculating system this time as the pump is centrifugal and not self-priming; a raw water system needs to have a gear pump to be reliable and consistent. my plan is that the exhaust pipes will not be water-cooled this time; just short stacks.
    Thus far I've made no effort to balance the crankshaft/ connecting rod/ piston assembly. anybody have thoughts on this? will the rocking effect, fore-to-aft, be excessive at this scale at perhaps 2500 rpm? could adding weight to the flywheel and timing gear end of the crankshaft suffice?
    john
     

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    minh-thanh and michael-au like this.
  2. Aug 9, 2018 #2

    kuhncw

    kuhncw

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    John,

    It is nice to see another one of your engine projects. Nice work. I would like to see more detail on your crankshaft design.

    I can't comment on the rocking effect, but adding weight (inertia) to the flywheel is always a good idea to help the engine at low rpm.

    Please keep us up to date on your progress.

    Chuck
     
  3. Aug 10, 2018 #3

    johnlaudano

    johnlaudano

    johnlaudano

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    Chuck,
    the crank is made in pieces with the shafts pressed into the discs with 1/8 pins and loctite holding them. there are four ball bearings; one on each end of the crank (one is in the photo) there will be two others, one each on the center discs (only one is installed in the photo).
    The small brass slugs between the center discs are counterweights for the center portion of the crank; the center conn rod shaft is longer than the other two and has two brass spacers that need to be compensated for.
    I realize that using four ball bearings is an expensive way to go about it and in fact it may be that only one center bearing is needed to prevent the crank from deflecting. I also considered that, at this scale, center bearings of any sort may not be needed.
    The reason that the conn rod shaft lengths are not the same is due to design compromises related to accommodating the center to center spacing of the cylinders related to my use of model airplane engine heads. the cylinders are uniformly spaced apart.
     

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  4. Aug 13, 2018 at 12:00 AM #4

    kuhncw

    kuhncw

    kuhncw

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    John,

    Thanks for the crankshaft design details.

    I see your crankcase has endplates. I suspect the front and rear crank bearings mount in the end plates? How are the second and third crank bearings mounted within the crankcase?

    Chuck
     
  5. Aug 13, 2018 at 12:05 PM #5

    natalefr

    natalefr

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  6. Aug 13, 2018 at 1:47 PM #6

    johnlaudano

    johnlaudano

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  7. Aug 13, 2018 at 1:49 PM #7

    johnlaudano

    johnlaudano

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    Chuck
    You are correct. End bearings are in the end plates. The center bearings fit in bores inside the crankcase and will be held in place with loctite 680.
    John
     
  8. Aug 13, 2018 at 5:10 PM #8

    kuhncw

    kuhncw

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    John,

    Is your crankcase open at the bottom, then closed with a plate or is it one piece bored through for the main bearings and opened out if needed for crank and rod clearance. It looks like your camshaft housing is a separate piece and bolted to the block. You always come up with unique designs. A few more photos would be great. I'm just trying to understand your crankcase design.

    Thanks.

    Chuck
     
  9. Aug 13, 2018 at 11:59 PM #9

    johnlaudano

    johnlaudano

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    Chuck,
    yes the bottom is open and will have a simple cover plate. the photos attached all show the bottom. in the other photos you'll see the bearing bores; they are slightly smaller than the rest of the bore in the crankcase.
    As in most things in life there are endless compromises. Home engine design too. The cam housing is separate and is screwed to the main crankcase for ease of machining. both crankcase parts started as round stock. There are oil passage holes between the two for splash lubrication of the cam. My next design is going to have an oil pump that will direct oil onto the cam.
    DSC_1644.JPG DSC_1645.JPG DSC_1646.JPG DSC_1647.JPG DSC_1648.JPG
     
  10. Aug 14, 2018 at 4:23 AM #10

    kuhncw

    kuhncw

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    John,

    Thanks for the photos. That is an interesting design. I like it.

    Chuck
     

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