Crankshaft rods cams

Discussion in 'General Engine Discussion' started by cumminspower665, Feb 13, 2020.

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  1. Feb 13, 2020 #1

    cumminspower665

    cumminspower665

    cumminspower665

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    So I've never built a small scale engine before. I'm working on a inline 6 with a supercharger. Have questions about crank rod cam sizes if I'm going to big to small?? Hoping someone my have some input on this subject for me. Maybe help with a plunger haha! Here's a picture of what I've been working off of.
    Bore 1.4in
    Stroke 1.5 in
    Rod length is 2.6in
    Crank counter weights and all 2.6in
    Block is 10.15 long
    4.75 wide
    Cant seem to add any photos...
     
  2. Feb 13, 2020 #2

    cumminspower665

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  3. Feb 13, 2020 #3

    Longboy

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    Not sure what you are asking here looking at the drawing......What will you be operating on the engine at the end of the plunger from a "crank rod cam"?
     
  4. Feb 13, 2020 #4

    cumminspower665

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    Haha. The plunger is for getting the head out of a$$!
    But what I'm asking is..
    Am I over sized or undersized. Feel like I go to far on some things not enough on others. Looking for a little insite what someone has found for ratios between these sizes that works good or best.
    -Crank journals. 7in
    -Piston pin location
    (this drawling is older but still used. Pin is closer to center but not all the way)
    -Cam .5in diameter
    Rods 2.6in
     
  5. Feb 13, 2020 #5

    Longboy

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    Your guide here is your engine block and cyl length and will determine the rotating diameters and lengths of the moving con rod assembly. Lets go to clearances instead of under / oversize. The engine is not going to care much about ratios of its components. They do run built as long stroke, small bore, deep skirt piston or....... short stroke, big bore, short skirt piston design. Your parameters begin with the crank center line position and end at the deck height of the block. Your piston rise has to end somewhere below the deck as per your illustration. Tell me some more about the cam stock diameter!
     
    Last edited: Feb 13, 2020
  6. Feb 13, 2020 #6

    cumminspower665

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    Stock diameter I set to .75in
    Will work from that point.
    And yes that's how I got to where I am now.

    I guess what I'm looking for is this ok and it will be able withstand the forces
    I should just cross that bridge once there.
     
  7. Feb 14, 2020 #7

    Longboy

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    Not knowing your back round, you should think this over some more Cummins. A red flag in your first post: "Never built a scale model engine before"......... Heading out 1st. with a multi cylinder, you may shelve early or just drop out all together. This thought is backed up by the veteran machinists here. However if you know some design work and machine tools....I would say here that your cam stock, .75 in. diameter.... seems like a large dia. piece of metal for a camshaft on a sub foot long model! Also, you can in the search window find out how to "post photos" on this forum. :)
     
  8. Feb 14, 2020 #8

    awake

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    I too am a newbie to model engines (though not to machining), and I took the advice that Longboy suggests - starting with a simple single-cylinder model that is freely available (the Webster). I must say, I am glad I did - the number of small, fiddly parts even for a single-cylinder model is quite astonishing; even though I read through the plans carefully before starting, I have been surprised. Likewise daunting is the number of uncertainties - have I got good sealing in the valves, good compression in the cylinder, etc. - I *think* I have the cylinder and piston sorted, but just getting to the point of seeing whether my valves will seal (and working on them if - maybe more likely when - they don't).
     
  9. Feb 15, 2020 #9

    cumminspower665

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    I actually work on engines generators digital boards etc. Tiny bit of machine work. At this small of scale things are different. I'll figure it out tho.
    Thanks for your help.
    I dont plan to shelve it.
     
  10. Feb 15, 2020 #10

    cumminspower665

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    That is great advice but knowing myself I'd never stop what I'm currently working on unless some major happen.
    Well I look forward to checking it out once you do.
    Valves are a bridge I haven't yet crossed. I've mocked up everything. Assembling everything now and setting the tolerance to see if I get the engine to bind.

    Knowing myself dont think I'll be able to stop working with current project. I tend to not let things go easy and the harder it is to figure out the more I want to do it. Haha!

    Making sure I have that seal is a concern of mine as well. What i've done in my engine is adding of more head studs 6 per cylinder. Also im making this a dry deck block. Cylinder head will get coolant from the backside of the block directly from main galo. Feeding to the front and meeting cylinder coolant before heading out to radiator. Same for the oil. Dry decks are great for turbos chargers compression. Gasket should be easier to make as well.
    Fire ring the cylinder .025 protrude from steel liners. Use of the copper gasket here will make for a great spacer with Hope's of bringing that to .002. Should be enough clamping force to hold it down. Well see tho.
     
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  11. Feb 15, 2020 #11

    awake

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    Likewise, I look forward to seeing what you come up with. Onward!
     
  12. Feb 15, 2020 #12

    kuhncw

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    Hi Cumminspower,

    Please tell us more about your engine configuration. You mentioned supercharged/turbocharged. Spark ignited or compression? Two or four valves per cylinder? Overhead cam or cam in block? The dry deck is a good choice.


    Regards,

    Chuck
     

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