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  1. #21
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    Aw c'mon NC, why can't PoWaKiD42 suffer like we did? After all, I'm sure he has enough time to waste to say he is learning from his experience (aka failures) and still recover!!

    PoWaKi, NC in his wisdom has a good point or two. Before you decide firmly to design from scratch, you might consider combining existing components to produce your target engine.

    I see situations where very succesful Sports Car Club of America (SCCA) class C & D Sport race cars are made of combined engine components. For example, a custom do-it-yourself (DIY) engine builder made his own crankcase. He attached (6) cylinders [from (3) 2-cyl. engines] to his crank & crankcase. He also used the pistons & connecting rods from the above cylinders. This combination was (and might still be ) the US points champion in SCCA C & D Sports Racer class.

    I myself made such wierdo engines for snowmobile and outboard motor boat racing (thats why I got kicked out of APBA sanctioned STOCK racing and was told to move to NOA where they allowed modifying) Many years ago.

    But if you want to suffer like NC & I keep on trying.
    DZASTR

  2. #22
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    Why should a budding tinkerer have to reinvent the wheel and/or re-experience an unmittigated disaster if they don't have to?

    Yes, we learn from our mistakes but, BUT if you know that it is a mistake to jump off a bridge, do you still let someone do it to see if they might, just might see a different result from the same bad judgement/decision?

    I think not.

    Part of the benefit of a free form message board is to share information and knowledge - both good and bad experiences are here to be shared and learned from. Should the member wish to jump off the bridge in spite of admonitions to the contrary, they are free to go ahead and do so - I would tend NOT to however.

    THere is one thing worse than being a dreamer. That is to be a dreamer who, in spite of admontions to not do something, they go ahead and do it anyway to "I'll show you" - especiallly something that really shouldn't be attempted by a rank rookie.

    I've done that and occasionally have shown that the common thinking may need to be adjusted, just a bit. I've also had the "what the hill were you thinking" realization hit me because I didn't listen to the seasoned veteran. On occasion, however, with the support of sound research and engineering, I've confounded some veterans and moved on at a faster rate.

    Dreaming is cool - I did my share. However, I also created some nightmares by NOT buying when I should have and tried to make too much on my own.

    Ultimately, caveat emptor. You heard it here first.

  3. #23
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    I thought I covered that pretty much in #17 above. I think PoWaKiD42 can find his level then ask the right questions. Then the rest of us old farts can help him with our in (un) valuable information gathered over years of experience (self inflicted failures). As above and above that, try Blairs and others books.
    DZASTR

  4. #24
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    PoWaKiD42, It might help us to help you if we would have some idea of your experience / education / knowledge base relative to 2-stroke engines.

    Understand that most enthusiastic users of these simple?? machines have a very limited understanding of how they function. This is not an attempt to embarrass or humiliate anybody (myself included).

    There are many "racing speed secrets" out there that are clever improvements in engine design. Many have been included in commercially produced products. Examples: 3-port transfers, 5-port transfers, P (power) ports, expansion chamber (tuned) exhaust and intake systems and many more.

    When you started this thread, you mentioned starting with a small displacement single cylinder motor. Maybe we should go back to your start point.
    DZASTR

  5. #25
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    Hi, i have some news, i started the design of the engine. I took for basis a rc engine, a OS v spec.. my engine is a 119cc with 54 bore and 52 stroke, it has rotary valve intake. What clearance should it have?

    Is there anyway to calculate the power that it will have? the engine has a height of 250mm, i think it is very small for a 119 engine, i wonder, if i make a v4 it will be very small, and powerfull i think...

    I made the water cooling system, with two 'tanks' inside de cilinder


    Richard, my experience in two stroke engines, i always loved motorcycles and always tried to know everything about it, i raced, i like radiocontrol cars too, so i know a little bit of rc cars and engines, i am studying mechanical Engineering, first year. I am sorry if i ask you silly questions, but i need to know everything, the ignition, the water cooling system, etc so i can design the engine. Another question is , what spark plug should i use?

    In this design the fuel mix is forced up by the crankshat by the centrifugal force, on a v4 or in lin 4 i cant have this type of crank because it has more than one rod , what is the best sistem? i am thinking about a rotary axle linked to the crank, opening at the right timing.

    The pics are atached, i dont know how to make a video on solidworks, i will see how to do it then i will post a video so you can see it work =D

    Thanks for all the help
    Attached Thumbnails Attached Thumbnails cambota.jpg   cilindro.jpg   cilindro2.jpg   Metore.jpg   metor2.jpg  

    motor.jpg   bloco.jpg   motor_.jpg   motor___.jpg   motor2.jpg  


  6. #26
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    Your best bet is to get Gordon Blairs book on 2 stroke design, it is the bible.
    Much too complicated a subject for a one line repy.
    Read the book.

  7. #27
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    PoWaKiD42, Normally, it is not centrifugal force that sends the charge through the transfers. The fresh incoming air/fuel mixture is compressed in the crankcase and forced through the transfers.

    The higher the crankcase pressure, the higher the velocity, density
    and volume of the transferred charge. That is why I mentioned in posting above that you will need to know the basic engine ratios, one of which is the crankcase to swept volume (basic) compression ratio.

    I see in your attachments the crank is not full-circle but similar to typical 4-stroke balanced crank. This allows more volume in the crankcase, reducing the basic compression ratio. You might consider having clearance in your piston skirts to clear full circle crank outside diameters. This allows the bottom of the piston skirts to move below the od of the crank at bottom dead center.

    Another ratio you may keep in mind: connecting rod crank bore center to wrist pin bore center ratio 1.5 X stroke. in your example, 52mm X 1.5 = 78mm connecting rod cc distance.

    More later if I can be of assistance. Good luck

    add: more info www.iwt.com.au/MOTA.HTM
    DZASTR

  8. #28
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    There was a nice series on 2-stroke design in http://www.strictlyic.com/ magazine. They have been discontinued, but you can get back issues. This particular series, I believe, was about $40 for all of the issues. It will probably save you more than $40 in material, unless your only objective is to start a few fires inside a cylinder, and get those fires to push the piston a few times.

  9. #29
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    Hi Richard, thanks for the help. I made a V2, pics atached, but i have no idea how to make the intake, if it was a inline 2, its not dificult, but a v2, how do i make the intake? when the right piston is up, the other is down, if i make the intake to the block i think it will not work, i prefer rotary valve but i dont know how to put it on a v2, or v4... do you know any book or site with information about the 500gp? i cant find it, i searched a lot and i cant find it..

    The simulation programs are great!!! what is the best programs to simulate engines? calculate the power, etc... and exhausts too? that program calculates, but there is a better one?

    Thank you
    Attached Thumbnails Attached Thumbnails v2.jpg   v2_2.jpg  

  10. #30
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    I atached a pics of my carburator too...

    Tks
    Attached Thumbnails Attached Thumbnails cab2.jpg   carb3.jpg   carb4.jpg   carb5.jpg   carb6.jpg  


  11. #31
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    PoWaKiD42, A 2-stroke V-2 can be a problem. I can not see on you graphic, but you need seperated crankases in order to have crankcase compression to force the incoming fuel/air mixture thru the transfers.

    Also, The V-2 configuration will require un-even timing. This will induce vibration unless some clever counterbalancing is done. In-line 3 cylinder 2-strokes are naturally balanced similar to 6 cylinder in line 4-stroke engines. (like BMW's).

    Jeff Miller built an opposed firing flat 6 cylinder using Kohler cylinders, pistons, connecting rods etc.

    He didn't have to re-invent the wheel, just improved on what was available. If the crankcase to cylinder dimensions are maintained, stock parts can be used. Stock crank dimensions can be used to make up the new crank etc.

    Same could be done with Yamaha, Kawasaki or ?

    In the opposed cylinder configuration, 2 opposing cylinders can use the same crankcase chamber for primary compression.

    My experience with rotary valves is on Rotax in-line twins. (fine little engines) They have one rotary valve, a thin plate, serving 2 cylinders. This plate can be easily modified for whatever intake (not transfer) timing you want to try. I've seen these doubled up into in-line 4's.

    I do think reed valve intake(s) might be a better choice for first engine experience.

    Just to keep up the aggravation, try again to find Blairs book. There was a program with the book to calculate all the spec.'s for designing engines.

    Good luck
    DZASTR

  12. #32
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    PoWaKiD42, I must confess an error. The connecting rod c.c. distance should be 1.8-1.9 : 1 (52 mm X 1.8 = 93.6 or 94mm)

    If this helps you, use it. I have some specs for a rotary valve engine.
    bore 67.5 mm
    stroke 61.0 mm
    con.-rod 120.0 mm
    swept volume 218.3 cc
    min.crankcase vol. 404 cc
    primary c/r 1.54:1 (swept vol.+ min. crankcase vol. / min. crankcase vol.)
    cyl. compression ratio 13.3:1 (corrected 6.9:1)
    combustion chamber volume @ TDC 17.8 cc
    combust. chamb. volume @ exhaust closing 105 cc
    exhaust duration 198.4 deg.
    transfer duration 130 deg.
    boost port duration 133.8 deg.
    rotary intake valve open @ 136 deg. BTDC
    rotary intake valve close @ 75 deg. ATDC
    intake duration 211 deg.

    This produced 79kw (107hp) @ 9,500 rpm (max rpm was 10,250 rpm)
    These are data for a stock 2 cyl. in-line Rotax Super Stock snowmobile engine used in 1979 with 110 octane racing fuel.

    The limiting factor for rpm on twin 2-strokes is harmonics in the 12,000 rpm area. Once the engine passes thru that range, the harmonics come back again later (24,000?)

    In snowmobile racing you have a clutch balance problem above 10-12,000 rpm as well.

    FYI these engines had 1 44mm Mikuni carburetor on each cylinder, isolated by a soft rubber intake tube. The rubber tube prevented fuel foaming in the float bowl from engine vibration (harmonics). I believe fuel injection would prevent this.

    The harmonics occur in the 5,500 - 6,000 rpm area on 3-cyl. engines. Since that is relatively low for a 2-stroke small engine, we tuned the 3-cyl. engines for 10,000 rpm to stay above 6,000 rpm and below the 11 - 12,000 rpm range. These were piston ported and reed valve intake triples.

    HTH
    DZASTR

  13. #33
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    PoWaKiD42,
    The above specs apply to a race tuned engine. This means the exhaust system is tuned to 10,250 rpm. Snowmobiles have constant velocity transmissions (CVT) which keep the engine at a near constant rpm while the CVT changes ratios to respond to vehicle speed / power requirements.

    The same belt driven CVT is used on Polaris all terrain vehicles (ATV's).

    This type of transmission is being re-introduced to many automobile lately as well. The object is to keep the engines operating at their most efficient rpm.
    DZASTR

  14. #34
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    PoWaKiD42, What happened? Did you find Blairs book and get lost in the middle? How about a progress report.
    DZASTR

  15. #35
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    Richard..1979? that really dates us..that was 28 years ago !
    (just had to say something!)

    Adobe (older than dirt)

  16. #36
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    I havent found the Blair book yet... i will go to a bookshop that i was told that should have it... i started the design of the v4...

    i atached some pics... the admission is on the cylinder... i saw some engines with this intake system but i dont know how the engine sucks the fuel mixture... but it should work, i will put reed valves and injectors, i have to make the alternator and water pump mounts and the cylinder heads. what water pump and alternator should i put in this engine?

    Thank you

    Nuno
    Attached Thumbnails Attached Thumbnails motorv4_2.jpg   v4_2.jpg   v4_3.jpg   v4_4.jpg   v4_7.jpg  

    v4_8.jpg   v4_cut.jpg   v4_cut_2.jpg  

  17. #37
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    You may want to reconsider the port timings...And use a "stuffed" crank instead of the 4T design you have...Nice pictures though I seem to remember seeing an online calculator for expansion chambers in the distant past. Is it possible to Mill the barrel? I can see how to cast one easy enough but they are a pretty complex shape with internal passages which I think are inaccessible to machine tools :shrug: Either way good luck :cheers:
    Keith

  18. #38
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    What do you mean in milling the barrel?

    Thanks

    Nuno

  19. #39
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    Quote Originally Posted by PoWaKiD42 View Post
    ... but i dont know how the engine sucks the fuel mixture... ...
    Four strokes draw air/fuel into the cylinders with the vacuum created when the piston goes down.

    Two strokes ram the air/fuel mixture into the cylinder with pressure, not vacuum... the fuel/air is in drawn into the crankcase when the piston goes up (vacuum for that), and then when the piston goes back down, the crankcase becomes pressurized, so when the transfer ports are open, that mixture is blown into the cylinder.

    That's why a v-4 with "shared" crankcase chambers will not work (i.e. your design), unless you time the crank so that the pistons go down at the same time. The way you have it, the crankcase will almost always have the same pressure. There's very little time for a vacuum to draw in the air/fuel, and not nearly enough pressure to force it into the cylinder. For a multi-cylinder two stroke to work, you must do one of two things... either time the pistons so they cycle in unison, or give each piston its own crankcase chamber. (And you can do a combination of both for your v engine, but getting the airflow consistent between cylinders will be a bear.)

  20. #40
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    Yes, i understand that... my one cylinder engine has that type of intake... crankcase intake... but i saw that some two stroke engines have intake directly in the cylinder... because it is a v4 i canot separate 4 crankcases... i can only separate 2, thats the case... the lubrification is done by the bypasses on the cylinder, that takes the fuel with oil to the carter, lubricating the engine.

    I atached a pic of a inline 2 engine with intake directly in the cylinder...

    Thanks

    Nuno
    Attached Thumbnails Attached Thumbnails thumbnails.jpg  

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