Off set key

Discussion in 'Performance Mods' started by 45u, Feb 18, 2016.

  1. 45u

    45u Active Member

    Has any one tried a off set key to adjust the timing? If so input please.
    Thanks
    Jeff
     

  2. butre

    butre Well-Known Member

    they exist and people have done it, but this is a better product

    http://www.pistonbikes.com/product-p/mmatm.htm

    combined with an aftermarket CDI like a Jaguar CDI can make for easily adjustable timing and a proper timing curve
     
  3. 45u

    45u Active Member

    Thanks for the input. What do you know about squish? Been working on combustible engines none stop for over 45 years. Did a lot to my 1/5 scale gas buggy. Work on motorcycles just about daily including but not limited to all machine work. I had all ready plainded on getting a better CDI (capacitor discharge ignition)
    Thanks
    Jeff
     
  4. sbest

    sbest Active Member

    Timing advance is a crutch to get over slow combustion. If you can speed up the combustion, you don't need so much advance. Pressure, heat and turbulence tend to speed up the combustion. RPM and increased throttle opening tend to increase these and help to pick up the pace, so less advance is needed. A tuned exhaust pipe increases the pressure substantially so often some sort of timing retard mechanism is needed once you go tuned exhaust. Improved squish will also necessitate less timing advance.

    An offset key will do the job and has been used for years as a timing tool. Many of the CDI coil conversions for older engines come with a stepped key for the flywheel right from the engine manufacturer. Timing advance is normally conservative on a stock engine so a few more degrees advance will liven a stock engine. Raise the compression or otherwise modify it and you risk detonation.
    Steve

    Where detonation starts on a Happy Time motor:
    [​IMG]
     
    45u likes this.
  5. 45u

    45u Active Member

    Thanks for the input. On the rotor in the link above they say to go the hole width of the key slot if I am not mistake a offset key only advance it about half that much. Being parts for these little engines are fairly cheap going to try one just to see.
     
  6. sbest

    sbest Active Member

    Jeff,
    Typical advertising stuff. More is always better.
    The good news is detonation is very audible on these motors.
    I am assuming you are using the key to advance the timing?

    You know that rpm advance works opposite on 2 stroke engines from 4 strokes?
    The efficiency increases immensely with rpm, so will pressure and burn speed, so less advance is needed at rpm.

    Note in that drawing above there are little pockets in the squish out near the cylinder wall?
    That is accurate on the stock head. The squish area does not go out to the cylinder wall.
    Cut the squish out to the edge of the cylinder walls and you will have MUCH less detonation.
    This is from my own experience with these engines.
    You want it to look like this on the right (stock on the left):
    [​IMG]
    I mention this because the increased burn speed caused from the squish turbulence acts the same as timing advance.
    An offset key would still be a good tuning tool.

    Steve
     
    45u likes this.
  7. 45u

    45u Active Member

    Before I do anything I will check the timing with a degree wheel. I know on the many fixed timing motors I have messed with the timing is normally off at least some. Steve do you have any idea how many degrees before TDC the timing is suppose to be?
    Thanks
    Jeff
     
  8. Bufu racing#1

    Bufu racing#1 New Member


    Yes they work if you file them down right first.. depending on wat gas and compression you got ... it's only going to be little gain unless it's used in conjunction with other methods of tunning... mine is set very close to stock and we get the stock ignition over 14k rpm , what I'm trying to say is you stock ignition is beautiful China work lol
     
  9. 45u

    45u Active Member

    Does anyone know what the stock timing is suppose to be? If I new this I could check it with a degree wheel. How many degrees before TDC? I have seen too many fixed timed motors that where not very close. I am going to run the motor stock then do upgrades to see just how much I can get out of one of these little motors. When doing a perfrmace up grade a little here and a litte there ads up.
    Thanks
    Jeff
     
    Last edited: Feb 23, 2016
  10. Bufu racing#1

    Bufu racing#1 New Member

    If I'm not mistaken it's somewhere in the ballpark of 30
     
  11. sbest

    sbest Active Member

    Gonna be hard to check, there are no points to check it with. All you can do is run it and use a plug fired timing light. Most automotive lights won't work. I have a xenon spark fired light I save for these motors. Dim, but it works when nothing else will.

    Steve
     
  12. 45u

    45u Active Member

    I have over 25K worth of tools not counting my machines like boring bar, valve machine, lath, Sunnen honing machine and more. I have worked on MANY CDI bikes. I all so have MANY degree wheels. Much off my living has been working on motorcycles. I think I will be able to figure it out.
    One of my babies and my instruments. I have build many a crank as well. My bike will never be started till I check the true of the crank. I will all so be putting much better crank bearings in the case.
    Thanks
    Jeff
     

    Attached Files:

  13. HeadSmess

    HeadSmess Well-Known Member

    *waits to see what becomes of this expertly hand crafted engine*

    2rs or zz bearings?

    what tolerance class? what abec ratings? p2, abec 9?

    and what clearance designation? c1? cn? or maybe a c5?

    not many people stock anything but CN...

    maybe some 7XXX series would be more suitable? a, b, c, or a5?

    not sure how one would keep the preload on them... :D

    ahhhh, choices, choices, choices...

    all them funny letters actually mean something? :eek:
     
  14. sbest

    sbest Active Member

    My experience was that the stock motor/head was easily prone to detonation under heavy load (hillclimbing) even in Canadian winter temperatures. The last thing I'd want to do is advance the timing with this going on. I needed to solve the detonation. That is what my long-winded illustrated lecture above was all about. Now with chamber shape improved and no signs of detonation you'd think I might be tempted to increase advance?

    Timing advance is worth playing with, but I know from other engine experience experience that improved squish reduces the need for advance.

    Steve
     
  15. 45u

    45u Active Member

    Time will tell as I will try one to see. The key could be used to retard the timing as well. I will be trying many things. I am going see how the stock engine performs first. Before I ever start the stock motor I am going to check it out well including checking crankshaft true and cylinder bore.
    Thanks
    Jeff
     
  16. Bufu racing#1

    Bufu racing#1 New Member

    None of you need to change the timing ... we are doing way over 70mph with e85 with this China motor ... 65+ on gas all day guys

    Britt vanegas on fb
     

    Attached Files:

  17. 45u

    45u Active Member

    Would like to see a video of your bike being clocked running what you say until then that is all it is talk.
     
  18. sbest

    sbest Active Member

    215 lbs of me is getting 60kph (37mph) on an almost stock Grubee Skyhawk on a heavy fat tired mountain bike. The only mods are what you cold do with sandpaper and a file.

    A skinny rider on a sleek roadbike with a tall sprocket in a tuck would have no problem getting 10 kph faster with this motor. I have no problem believing Bufu racing#1's comments that 40mph is easy with a stockish motor and that much higher speeds are possible in purpose built bikes, especially if these bikes capitalize on speed over anything else. The earlier generation of Happy Time motors seem have been limited to about 6000rpm. This 2015 Grubee can rev to 8000 without problem, which seems to explain some of the differing views from older members.

    The most important point to take is that huge timing changes have not been needed. An offset key is perhaps all you need to experiment to find out if this is true.

    Steve
     
  19. 45u

    45u Active Member

    Off set key is a VERY SMALL change far from huge. This is by far not my first with timing changes just was wonder what others experience with these little motors are? 65MPH all day is totally ridicules with these little motors unless the displacement was increased a LOT and you have a 35 pound driver! I did notice he has gone from 70mph to 65mph.

    I am not building a race motor but those that do it is not one thing you do to get more performance but a bunch of small things that added up.
     
    Last edited: Mar 6, 2016
  20. skyash

    skyash Active Member

    77.1 kmh I got I don't see it getting much better unless you want a piston in the face.