engine braking

Discussion in '2-Stroke Engines' started by blue 48, Nov 24, 2011.

  1. blue 48

    blue 48 Member

    hi folks just wondering what possible damage can be caused by using the engine as a brake (engine braking ) by turning ignition off and clutch out.

    all opinions appreciated :D
     

  2. geebt48cc

    geebt48cc Member

    :ee2k:Yeah, Blue, I do the same-thing to help slow down some of my weight. See, the bike is 29" at 60lbs, and I am 255lbs. So, at 315+, V-brakes really aren't the best to keep it 100% safe. (I cruise at 25ish, tops lower 30's)
     
  3. motorpsycho

    motorpsycho Active Member

    why would you want to do this, it's not good for the engine in my opinion.
    you'd be allowing the piston rings to scrape the cylinder walls with no oil, and the bearings to possibly run dry.
    since the engine would not be running, there would be fresh no gas/oil entering the crankcase.
    I understand that there would be residual oil on the rings and bearings, but it can't be all that much.
    I would think that doing this a lot over time would just prematurley wear out the rings and bearings due to short times of no oil.
    I wouldn't do it.
     
  4. geebt48cc

    geebt48cc Member

    Understand, but I personally am just talking about a very brief moment going into braking. That's the one thing that I really appreciate about using synthetic oil because the residual doesn't dissipate that quick.
     
  5. Old Bob

    Old Bob Member

    Just shutting off the ignition doesn't stop A/F mix from entering engine.As long as the engine is turning its still getting oil and gas but only a lean mix with the throttle shut.I wouldn't do it for long periods but briefly shouldn't be an issue.
     
  6. cloud_2901

    cloud_2901 Member

    I hold my throttle half-open while engine braking with the killswitch.

    That way it's not going to run out of fuel, it will in fact get too much fuel in there if you don't ease off the throttle after 30 seconds or so.
     
  7. motorpsycho

    motorpsycho Active Member

    I still wouldn't do it.
     
  8. geebt48cc

    geebt48cc Member

    Braking

    Well, I have done the kill-switch thing to help slow down, but I never have enough real speed to cause problems when going there.

    I've got it! I'll just ease this missle down, and then I wont have to worry about slowing down this beast.:cool2:
     
  9. Barnfresh

    Barnfresh Member

    Sounds like what you really need is a decompression valve (compression release) like the old 2-stroke flat track racing motorcycles used to slow down, back in the days when they weren't allowed to have brakes.

    The comp release normally threaded into the combustion chamber with a 14mm thread (like a 2nd sparkplug) and had a single valve controlled by way of a cable attached to small one fingered lever which hung under the clutch lever on the handlebars. Squeeze the lever and the valve would open allowing air to escape from the combustion chamber slowing the engine down, much like a jake brake on a diesel engine. They were effective to the point that if actuated while in too low of a gear the rear wheel could lock or skid.

    The only problem with installing one on the little HT is it's size in relation to the small combustion chamber. You would need to locate a compression release that is more in "scale" to a 50cc engine. Maybe start with a decomp valve off of an old moped (Sachs?) or small chainsaw. Figure a suitable location, cut fin, drill and tap head. Install comp release valve assy making sure there is adaquate clearance so valve can't contact piston crown at TDC when fully open. Run cable to a 2 finger BMX lever on handlebar.
     
  10. Cavi Mike

    Cavi Mike Member

    Just because the engine isn't firing doesn't mean fuel isn't still being drawn into the engine. These aren't fuel-injected engines. Carburetors work on vacuum so as long as the engine is spinning, it will be creating vacuum and fuel will be drawn in. It doesn't matter if the plug is igniting the mixture or not, the mixture will still be there lubricating the engine.
     
  11. blue 48

    blue 48 Member

    i agree with motorpsyco and also with other opinions here i dont do it when i can avoid it
    its just that i had a trailer on the other day and i was going down this steep hill and the trailer was loaded with a 40 kg tool box and brakes alone were struggling to pull me up so i hit the kill switch and had half throttle , it pulled up better. ..... but i feel that these engines are not very effective as brakes for obvious reasons.

    so after all that im going to build a brake setup for the trailer and use them.
    towing a trailer that heavy is regular thing for me. take off sux big time and involves a lot of peddaling but once its going its just loves it even with a 36 tooth rear.
     
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