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IndustryArena Forum > Hobby Projects > I.C. Engines > 2-stroke ported OPOC engine (125cc x 2)
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  1. #25
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    Quote Originally Posted by packrat View Post
    If you mean me, I was responding to the OPs engine. Don't think a 125cc cylinder would count as a RC engine. And it has been stated that it has rings.
    Wanna bet?

    TowerHobbies.com | DLEDLE-170 DLE-170 DLE Engines DLE-170cc Twin Gas Engine

    TowerHobbies.com | DLEDLE-222 DLE-222 DLE Engines DLE-222cc 4-Cylinder Gas Engine



    Mark

  2. #26
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    The replacement parts list for the 170 lists piston rings. I didn't see a replacement parts list for the 220.

    Dick Z
    DZASTR

  3. #27
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    Yep, it has rings. I was responding to your statement that you didn't think a 125 cc cylinder would count as an RC engine. ;-)

    Mark

  4. #28
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    That was packrat, not me.LOL

    Dick Z
    DZASTR

  5. #29
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    Crap. I need to keep my reply-to's under a little closer observation.

    Mark

  6. #30
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    And the examples aren't the same. The OP is making a 250cc motor - 125cc per cylinder. Thats dirt bike territory! Definitely needs rings for the compression he wants too.

  7. #31
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    Quote Originally Posted by UUU View Post
    Glands where a piston rod passes through the end of a cylider are not common in IC engine designs - but they are well used in steam engines. If you can look up pictures for designs for these you'll see they often have an o-ring seal or some twists of graphited yarn as the packing.

    Thor detail of piston road and gland | Flickr - Photo Sharing!

    http://www.co2.pwp.blueyonder.co.uk/...ics/glands.jpg

    Pump Packing Installation
    oo, that's really valuable advice, saves me some searching and research for options. thank you.

    You'll see in the picures there's a clamp to tighten up the packing. Some designs have a threaded ring to do the job. Your pressures are quite low so you may get away with the shaft just passing through a cloesly fitting tube.
    sleeve bearing. yes. although, i heard recently that up until 20 years ago jaguar were still using oil-impregnated leather as bearings (just like bourke did). in this case you actually _want_ a drip-feed of oil through the bearing.

    Although you're really inviting suggestions for making your design, and not on the design itself, I'd have to say that the cam arrangement is not going to be at all easy. Perhaps you could look at this side rod steam engine, and imagine an extra cylinder on the right.

    'SIDE ROD' TABLE ENGINE - Brunell Steam Model Engineering

    The two cylinders would be connected by a common piston rod, and the side-rods take the back-and-forth motion off to a crank and flywheels. This would be a lot easier to make.
    yees, but although the cam itself is tricky as hell and will need very accurate CNC machining, the cam arrangement is essential to the simplicity of the _rest_ of the design, as well as the long life, etc. etc. and the cams *are* the flywheel. cranks have been done before: i want to try something that hasn't!

    thanks uuu.

  8. #32
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    Quote Originally Posted by packrat View Post
    And the examples aren't the same. The OP is making a 250cc motor - 125cc per cylinder. Thats dirt bike territory! Definitely needs rings for the compression he wants too.
    allo mr packrat,

    apologies first, to you (and all!) - i didn't realise this was an ongoing discussion, cnczone hadn't sent me a message in a while!

    ok, i've been doing a bit more research and a bit more thinking: i'm still going to go with the 250cc total, but.... as a 6-cylinder arrangement (!) in 3 double-opposed pairs, each offset at 60 degrees, all on the same cams. i will however start with only two! the reason for 6 is because a) they'll fit b) 3 sets are perrrfectly counter-balanced: absolutely zero vibration.

    so ho hum, 250 divided by 6 is 42 (ish), that comes out at about a 37mm bore (or so) and a 40mm stroke (or so). approximately this, in fact: TowerHobbies.com | DLEDLE-55 DLE-55 DLE Engines DLE-55cc Gas Engine

    hmm, that's aluminium. i wonnderrrrr... if i could get away with re-using those cylinder heads - and pistons, save me some machining, hmmmm....

    and hell yes definitely rings. higher compression, much *much* leaner mixture to compensate.

  9. #33
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    oo good find, mark. that lead me to some 55cc DLE engines which are close to what i need, i could consider buying those off-the-shelf instead and their pistons, save me making them. do you - or anyone else for that matter - happen to know of any other model RC engines, preferably 2-stroke with glow-plugs, in the 30 to 55 cc range, that use rings? using ready-machined matching parts like these would make the remainder of the engine a much easier proposition that i would be much more comfortable with.

    /peace.

    l.

  10. #34
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    Quote Originally Posted by wendtmk View Post
    If you're talking ringed pistons, the bore is straight. Non-ringed 2 stroke engines, like the R/C engines mentioned above, do have tapered cylinders.

    Mark
    i'd heard about piston rings that are angled so that when it all goes "bang" the pressures push them harder against the side-wall. the tapered cylinders (no rings) had me pause for a second though. don't believe i need that (whew).

    l.

  11. #35
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    ikcl, you might "google" Dykes rings. They have an "L" cross section and do an excellent job of sealing. They are placed near the top of the piston reducing the area of "blow by".

    Dykes rings were regularly used in the rotary valved Rotax engines. Some use a single 1mm ring for higher rpm, less ring "flutter".

    Dick Z
    DZASTR

  12. #36
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    Quote Originally Posted by RICHARD ZASTROW View Post
    ikcl, you might "google" Dykes rings. They have an "L" cross section and do an excellent job of sealing. They are placed near the top of the piston reducing the area of "blow by".
    Dick Z
    star, richard. really appreciate the pointer.

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