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Discussion Nitrous Oxide

Discussion in 'The Pub' started by Frankster, Jun 3, 2021.

  1. Big Balls

    Big Balls Member Premium Member

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    back in the 80s they used a method called the squish method on 2 strokes when they were raced. Solder was placed down the spark plug hole, piston up to TDC, remove solder and measure the squashed solder to give clearance piston to cylinder head. Too small, no racing.
     
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  2. jmw76

    jmw76 Well-Known Member Premium Member

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    Yep solder wire works really well. I have used this on numerous occasions.
    It is a good way to confirm what you have before pulling an engine apart.
    It takes a bit of skill to feed the solder down the plug hole and manoeuvre the solder wire into the right location.
     
  3. Frankster

    Frankster "Play stupid games, win stupid prizes" Staff Member Premium Member Ride and Events Crew

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    It takes a bit of skill to feed the solder down the plug hole and maneuver the solder wire into the right location

    It would be almost impossible on the ZXR heads with their deep recess for the spark plugs. I'm going to pull the head off anyway (to deck the barrels), so I might as well do the plasticine method. It'll be a good experience for me. I did the solder squish test on the 2-stroke motor in the Nostalgia drag bike...it was 6mm, so that explains why it was running poorly.
     
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  4. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I wondered what the issue was that and if you got it resolved
     
  5. jmw76

    jmw76 Well-Known Member Premium Member

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    It is not as difficult as you might think. It works fine on GSXR engines and the plugs are in fairly deep on those.
     
  6. Frankster

    Frankster "Play stupid games, win stupid prizes" Staff Member Premium Member Ride and Events Crew

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    I might have a crack at doing the solder test before I pull the head off.
     
  7. Frankster

    Frankster "Play stupid games, win stupid prizes" Staff Member Premium Member Ride and Events Crew

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    @ruckusman the bigger issue was the (nostalgia) bike's instability. It was shaking from front to back (chain was smashing against the frame and chain guard) and the head was shaking just to complete the picture. The project is parked until further notice as there are zero chances to race a nostalgia bike at the moment.
     
  8. jmw76

    jmw76 Well-Known Member Premium Member

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    @Frankster choose some solder wire that is a little bigger than your expected squish clearance.
    You need to feed it down the plug hole and angle it over towards the main squish area of the combustion chamber.
    Make sure you are on the compression stroke for that cylinder with the piston just a bit before TDC. maybe 10mm down. This helps direct the solder into the right area. Carefully wind the engine past TDC. You will feel a little resistance as the solder gets compressed. Pull the solder out carefully and measure the thickness. That should be your current squish dimension. Subtracting your compressed head gasket away from this tells you how far below the deck you pistons sit.
    On older engines, you may get a little piston rock which can complicate things. 2 bits of solder either side of the piston might give a better reading.
    Some people just like to run zero deck height, leaving only the gasket thickness for clearance. Sometimes this works ok, but depends on your gasket. Single thickness metal shim gaskets will not provide enough clearance.
     
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  9. Frankster

    Frankster "Play stupid games, win stupid prizes" Staff Member Premium Member Ride and Events Crew

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  10. thebeefsalad

    thebeefsalad Well-Known Member Premium Member

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    I use soft solder (i.e. high lead content) to check squish (2t and 4t) and synthetic clay to check valve/piston clearance. Hadn't considered plasticine for piston/valve but I might change to that as it's less likely to deform.
     
  11. Frankster

    Frankster "Play stupid games, win stupid prizes" Staff Member Premium Member Ride and Events Crew

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    Lift the head again and cut the plasticine to see what your valve to piston clearance is.

    It's 3.98mm. Does that sound right?

    IMG_2127.JPG Squish.jpg
     
  12. jmw76

    jmw76 Well-Known Member Premium Member

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    @Frankster did you wind the engine through a full cycle? If yes, then that value should be the your valve to piston clearance. Looking at the images you have posted, you need to measure the minimum clearance value. This is likely to be at the extremities of the valve area. Using the same method, maybe with a bit more plasticine, you should also be able to get the minimum piston to head clearance (squish) also.
    My recommendations for intake clearance > 1.2mm & exhaust > 1.0mm. Others might say you can run less, but you will need really good valve springs and avoid over revving.
     
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  13. gregt

    gregt Well-Known Member Premium Member

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    That sounds about right for dead stock. Take a couple of cuts at different angles - you've got enough coverage for a good explore.

    JMW has his figures wrong, Those figures are for quite large valves - and you should run larger clearance on the exhaust side as that's the one most likely to be tagged by the piston.
    With very light and small valves as here, I've already said you can come as close as .030in without risk.
    There's a major weight difference between bucket and shim - and the lever type cam followers used on his GSXR engine.
    It's apples vs oranges.
     
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  14. inchoate

    inchoate Member Premium Member

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    Just curious, with these small displacement, high rpm motors does rod stretch become an issue?
     
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  15. gregt

    gregt Well-Known Member Premium Member

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    Not in my experience.
     
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  16. Gen

    Gen Well-Known Member

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  17. thebeefsalad

    thebeefsalad Well-Known Member Premium Member

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  18. Gen

    Gen Well-Known Member

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    Every time I hear a "new" 250/4 buzzing around town @ redline I think of this article , it's easy to get sucked in by the manufacture's claims of the era regarding redlines, inaccurate tach readings & peak HP, but how many of you have pulled a head & found valve sized "shiney" circles of carbon free valve cutouts on the tops of all 4 pistons ?
     
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  19. thebeefsalad

    thebeefsalad Well-Known Member Premium Member

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    sample size of 2. no such (bad) luck!
     
  20. Frankster

    Frankster "Play stupid games, win stupid prizes" Staff Member Premium Member Ride and Events Crew

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    That CBR250 article is interesting. I wonder if spinning an engine that fast without a head on it would make the rods stretch more since there's nothing (resistance) for the piston to push against. Even with the readings they got at 18,000rpm (23.5 thou) it's only stretching half a millimeter. So, as long as I allow for a small amount of rod stretch, then that should be okay.

    @gregt thanks for your post. I'll make a few cuts and report back with the figures. I did the squish test on all the cylinders, so I'll sample each one and note the results.
     
    Last edited: Jun 9, 2021

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