Break In Need some advice!

Discussion in '2-Stroke Engines' started by justin.fiveash, Jul 26, 2014.

  1. justin.fiveash

    justin.fiveash New Member

    I ordered a pre assembled mongoose mountain bike kit with a 66/80cc motor. I haven't received it yet but I want to be ready for when I do. I don't have much experience with 2 stroke engines. I've read that u wanna run 16-1 gas ratio on your first tank but is there anything else I need to oil/grease or anything like that?

  2. butre

    butre Well-Known Member

    don't worry too much about break in, the rings seat the first time you run it. Just don't peg it wide open straight away, and feed it a fuel oil mix no leaner than 32:1.

    on a 4 stroke, the break in period is just changing the oil at 500 miles instead of 2000. in a 2 stroke, it's getting fresh oil every cycle.

    the only reason break in periods exist is because in a 4 stroke where it keeps the same oil until you replace it a new engine will make a buttload of metal dust that needs to be drained out before it does some damage. since a 2 stroke never has the same oil for very long I don't believe it's really necessary to have a break in period.
  3. justin.fiveash

    justin.fiveash New Member

    I read somewhere to put a little bit of oil in the carb before running it for the first time. Is this something I should do?
  4. justin.fiveash

    justin.fiveash New Member

    Oh and butre your reply makes a lot of since. Thank you!
  5. HeadSmess

    HeadSmess Well-Known Member

    NO NO NO!

    the break in period is getting the rings bedded into the cylinder walls, something that happens on the first ride, in the first five minutes.

    cylinders are honed. that typical cross hatch pattern. creates lots of lil sharp edges.

    the rings slide up and down, and when first installed, are never a perfect fit.

    the points on the cylinder wall grind away at the rings...thats called bedding in.

    rings seal from combustion pressure forcing them into the cylinder wall. it is NOT the springiness of the rings that seal.

    so, you need to give all engines full throttle, with a heavy load...once warm of course. doing that from cold will kill them. idle them til warm.

    then the honing is worn down slightly, to rounded edges, no longer "grind" and the rings are well sealed.

    max sealing = max power :)

    and its the main reason why you always rehone a cylinder and install fresh rings when you pull the cylinder off.

    oh, sure, it will keep running if you dont...dont worry about that... it just wont ever realise its full potential!

    50:1 oil mix has never given me any grief. ever.

    i agree with the four strokes and filings inside...change the oil about five times in the first few hours until it no longer glitters...amazing what comes out from a brand new engine!
  6. butre

    butre Well-Known Member

    While you certainly shouldn't baby it, I don't think full throttle is right. as long as it's got a heavy load on it I don't see full throttle being any better than reasonable throttle for break ins.
  7. HeadSmess

    HeadSmess Well-Known Member

    because, regardless of the speed one is doing...full throttle will give the maximum pressure in the cylinder. full throttle does not necessarily equal full speed...

    and what is needed is pressure, to force the rings out and into the cylinder walls. they have to conform, wear into the cylinder, and they only have a very brief chance of doing so. the first few minutes. after that...the cylinder honing simply doesnt "cut" the same.

    i always hit a steep hill, brakes on. load it right down and just WOT it :) i cant do that with a push mower, dang nammit! but id do the same if i could!
  8. Anhevius

    Anhevius New Member

    Okay, here's what I was taught by a master mechanic with over fifty years of experience:

    There are two 'proven' ways to break in a new engine or to seat new rings.

    The first, and most common method:

    Run the motor in short cycles (30min-1hr) at a time, never going above half throttle. During this break-in period, you will want to run a 30-50% higher mix of oil:fuel. (IE, if it calls for 20:1, you're best bet is between 14:1 and 16:1)

    This method has quite a few benefits. The main one is that with a smooth break-in, you promote the longest lifespan possible out of all of the components. You also aren't ripping excessive amounts of material from the rings. For a daily operated motor that won't be 'raced' and just used in a normal manner, this is the absolutely best method, tested over time.

    The second method:

    Start the motor, allowing it to idle for a few minutes to warm it up. Then, with a load on it (NEVER break in a motor without a load against it), dial it up to 50% throttle for two minutes. Allow it to drop to idle and rest for two minutes. Then dial to 75% throttle for two minutes, and allow to idle for two. Dial to WOT for two minutes, and idle for two minutes. Run at 75% throttle for five minutes, idle for two. Run at 50% idle for five minutes, idle for two. Allow to cool completely before running again. DO NOT force cool the engine with water or compressed gas. Natural cooling only (if in winter, have a space heater nearby so that the motor doesn't cool too fast. I would also use it to warm the incoming air if it's below 40F, so that the oil isn't condensing and creating 'pockets' in the mixture.)

    During this process, you will want to run a oil:fuel mix with 50-75% more oil. Also, before initial run-in, remove the spark plug and put four drops of oil in a NSEW (ninety-degree spacing basically) around the rim of the piston. Allow a few minutes for the oil to soak in and spread. If you do not do this, you will end up dry-running the engine (little or no oil being transmitted to needed areas) and burn off the rings.

    This is what is commonly referred to as a 'racing' break-in, or a hot break-in. The benefits to this is that the motor has about a 20% chance to gain in the top end, and can handle heavy loading (fast cranking of the throttle) or being operated at WOT for longer periods. One of the down sides though is that it will wear more material from the rings. This means they will need to be replaced faster than rings set in with the more conventional method.


    When running a motor in, you are using the compression generated to 'push' the rings into position, the hashing to smooth the ring surfaces, and the heat from the motor to cook them into permanent shape. All of these things must be factored in if you wish to set the rings properly and have a motor that will last you.

    Utilizing the first method, I have run-in two cycle engines that have seen tens of thousands of hours of operation with only basic maintenance required. Spark plugs, a coil or two, things like that. The second has also produced great-running engines, though generally they have needed tear-down faster.

    It's all about what you want, and what you feel comfortable with doing.

    Also, talk to a local small-engine shop mechanic about your choices. They will always have little tid-bits and tricks to help you get the most from your engine as you break it in to get exactly what you want from it.

    And remember, no two engines are perfectly alike. What works for one motor might not be the best option for another. Some engines will run best with a slow run-in, others with a hot one.
    Last edited: Aug 4, 2014
  9. LewieBike

    LewieBike New Member

    These break-in techniques would apply if these HT engines have iron cylinders, but they do not. They're Chromium or Nikasil plating directly on the aluminum casting and should have a fairly good seal to start with. I would think just moderate running for short periods of time with frequent stops and cooling off periods for the first tank full. Then run it like you own it.