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Thread: Vertical hit and miss engine

  1. #181
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    Not going to happen Ringo, but if you want to see what happens I will gladly sell you a set of plans for $25. I have adjusted the valve and ignition timing a bit to slow this current engine down, and have it running at a much more sedate pace now.
    https://www.youtube.com/watch?v=9jjheq1pEPQ
    Brian Rupnow

  2. #182
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    Sparky--The metal piston rings had nothing to do with how quickly the engine started. My engines with Viton piston rings seal perfectly right from the time they are installed. I would love to be able to tell you with a straight face that it was because of my great skill at building these small engines that it started up so easily. Wouldn't be true though. I have learned what to do and what not to do to make these engines run, but that accounts for about 65% of it. The other 35% is just good luck. I have had other engines start just as readily as this one, but I've also had engines that fought me every step of the way and almost made me crazy before I got them to run.--Brian
    Brian Rupnow

  3. #183
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    Jun 2007
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    Anderson SC
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    Quote Originally Posted by brian Rupnow View Post
    Sparky--The metal piston rings had nothing to do with how quickly the engine started. My engines with Viton piston rings seal perfectly right from the time they are installed. I would love to be able to tell you with a straight face that it was because of my great skill at building these small engines that it started up so easily. Wouldn't be true though. I have learned what to do and what not to do to make these engines run, but that accounts for about 65% of it. The other 35% is just good luck. I have had other engines start just as readily as this one, but I've also had engines that fought me every step of the way and almost made me crazy before I got them to run.--Brian
    You missed the point of the post, it wasn't sealing, it was FRICTION. I remember some of the previous engines that on initial attempts would run while the starter was engaged but not quite sustain running own their own initially. These engines are not powerhouses, a lot of their output goes just to overcome the various frictions.

    Every see a commercial engine with viton rings? Suppose there are reasons for that?

  4. #184
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    The main reason you don't see commercial engines with Viton rings is that they have to run for more than 15 minutes at a time, and they never live out their lifetime setting on a shelf collecting dust. If builders could get away with building engines with Viton rings it would be happening right now. I have never built an engine that refused to run or remain running because of overly high friction from Viton rings.--That being said, I have half a dozen hit and miss engines that I have built, and none of them coast worth a damn and I 'think' that probably is because of too much friction from Viton rings.
    Brian Rupnow

  5. #185
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    Model size hit miss engines can coast very well with excellent hit/miss action. China proves it with some of their engines, here is one from Banggood. I have a feeling that hysteresis in the governor mechanism is one of the keys to good hit/miss/coast action.

    https://www.youtube.com/watch?v=K-oXuiOYBcM

  6. #186
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    Nov 2013
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    SF Bay Area
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    Here's a thought for your next engine, Brian. Ever seen Dykes rings? Fifty years ago my Bultaco Metralla used one as a compression ring.

    L-section ring with wide flat section wiping the cylinder wall, very thin lower part in a narrow ring groove. And very low ring tension.

    The idea was the ring tension didn't need to assure a seal with the wall because the combustion pressure would get in behind the vertical part of the L and force it outwards for a good seal.

    That little 250cc single was amazingly fast and nimble.

    -js
    There are no stupid questions. But there are lots of stupid answers. This is the internet.

  7. #187
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    We're finished. The engine hits and misses and runs excellently. Keep in mind that there are variables which can be tweaked to give even better hits and misses. The strength of the spring directly below the face cam, the height of the fixed collar below the ring supporting the counterweights. The ignition timing, and the needle valve on the carburetor. Even the size of the brass counterweights. I sell the complete drawing package as .pdf files for $25 Canadian funds, payed into my Paypal account to brupnow@rogers.com The solid models can be included as .step files or x_t Parasolid files, or even as native Solidworks 2015 files. This has been a fun build, and a relatively fast build. ---Brian Rupnow
    https://www.youtube.com/watch?v=X8pMtPM8HUI
    Brian Rupnow

  8. #188
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    What is my final opinion of the purchased cast iron rings? They work great. They are a damned snug fit into a piston groove cut with a 0.094" cut off tool, so I had to lay them on a flat sheet of glass with some 600 grit aluminum oxide lapping paste and lap then on both sides to get a proper fit into my piston grooves. They do go onto the piston with much breath holding and much 10W30 oil. I was really afraid that I was going to break them, but didn't. Before being installed on the piston I tried them for fit inside the cylinder. One ring had a gap of 0.004" so was fine. one has an end gap of about 0.002". so I worked the gap a little bit with a points file to widen the gap to 0.004". I couldn't get them to compress enough to go into the cylinder after they were installed on the piston, so I put the cylinder up on the lathe and cut a 20 or 25 degree lead in chamfer on the end closest to the crankshaft. That, along with more 10W30 oil made it possible to install the pistons. This engine rotates very freely with the sparkplug out. Considerably easier than an engine using Viton rings. would I buy these rings again?--Most definitely
    Brian Rupnow

  9. #189
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    Feb 2006
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    Phoenix
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    Quote Originally Posted by brian Rupnow View Post
    ... We're finished.
    Not quite. I want to see the little beauty hitting and missing under load.
    Allan Ostling

  10. #190
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    Aostling--Surely you jest. When this type of engine is under load, they don't hit and miss. They only hit. They don't start missing again until the load is removed. That means that to see the full spectrum of what the engine will do, I need a varying load. The only thing I have with a varying load is my sawmill, where the load varies between sawing a log and not sawing a log. Maybe tomorrow I'll think of something.
    Brian Rupnow

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