The Basics, Port & Polish and Port Matching

Discussion in 'Heads and Cylinders' started by BarelyAWake, Mar 20, 2010.

  1. Nitbbe

    Nitbbe New Member

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    I already have the springer forks ordered along with a cns carb (probably gonna regret it from the posts i read on here). The engine will be here tomorrow so it will get a good inspection and cleaning inside and out. I'd like to put a pipe on it but exhaust sytems are one of my week points, I know how these little motors love their back pressure. Im kinda shooting for a whizzer style bike so I still need to figure out the exhaust setup.
     
  2. KCvale

    KCvale Active Member

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    If you are using stock parts absolutely grind the flange hole to get the whole inside of the pipe, be it exhaust or intake pipe, as flush with the attaching plate as possible.

    But if you want more performance get an Expansion chamber exhaust first, (the SickBikes one is already port matched), that will instantly give you a boost you can actually feel with some 1 piece ones for ~$50.

    As gearnut mentions it's all about flow and nothing makes that better than an X.
     
  3. Nitbbe

    Nitbbe New Member

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    I like the idea of the expansion chamber but the physical appearance of it will throw off the look im shooting for. I need a straight pipe of some sort. Surprisingly my engine came today so it's time to clean it and port it when I get home at 7:00. I'll be starting a build thread if anyone is interested..wee.
     
  4. uniblab

    uniblab New Member

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    Sorry to resurrect this ancient thread but hopefully someone will find my suggestion helpful. In tight areas such as this you can use a special bolt which has a cylindrical body with a smaller "footprint" and either a hex head or a socket head. I don't know if these are available in the proper size for this situation but I suppose you could fab one if you really felt up to the task. Thread a piece of tube and install a screw in one end. You could either jam it in tight, JB Weld it or even zap a spot weld or 2.
     

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  5. kkalan

    kkalan New Member

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    Anyboby have a video on how to port a 2 stroke?
     
  6. rustycase

    rustycase Gutter Rider

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    Yah, sure!

    just go to youtube and try '2 stroke porting' !!!!!

    :)
    rc

    drn2
     
  7. rustycase

    rustycase Gutter Rider

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    The reason this doesn't work is because the chinagirl is a $%@! cheapo engine!
    http://motorbicycling.com/attachment.php?attachmentid=49912&stc=1&thumb=1&d=1342522928

    Just abt everything is right at the limits of tolerances.
    ..some.. porting can be done, but not really much that is useful.
    AND, the case studs are in a position that makes opening the port impossible.
    I had to grind off one side of the flat washers so there would be proper bearing against the surface. Of course, YMMV ! lol

    So this style of stand-off nut just wouldn't work for this application.
    Good idea, though!
    Best
    rc

    dnut
     
  8. Frogster

    Frogster New Member

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    Hey guys, I know this thread is from 2010, and im not sure how many of the original posters are even still using this forum, but I have a question.

    What about adding your own third transfer port right below the intake port as seen here : http://www.youtube.com/watch?v=DsIHtz0p-Pg&feature=youtu.be

    Would this be a good idea or will I hang a ring? Arrowcycles also sells a cylinder jug that has a third transfer port in it here : http://www.arrowmotorizedcycles.com/shop-now---high-performance-ported-cylinders.html

    What are people opinions on doing this? It would seem that most of the racing engines have a third transfer port added. All i can see this doing is helping lubricate the crank a bit more
     
  9. GearNut

    GearNut New Member

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    It will have no effect on crankshaft lubrication. All it is is another port to transfer the combustion charge from the crankcase chamber up into into the cylinder's combustion chamber. Done right it can significantly improve engine efficiency which in turn increases power output. Without a reed valve it is useless and will greatly reduce power.
     
    #89 GearNut, Feb 24, 2013
    Last edited: Feb 24, 2013
  10. Frogster

    Frogster New Member

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    Okay, can you explain to me what exactly a reed valve is, and why it is needed to add a third transfer port?
     
  11. k.mah

    k.mah New Member

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    reed valve is a 1-way valve. the 3rd transfer port allows for more fuel flow through the engine when paired with the reeds.
    a 3rd port without reed would allow all of your pressure to escape OUT the intake side, basically robbing you of your power.

    anyone feel free to correct me if that's off at all.
     
  12. GearNut

    GearNut New Member

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    k.mah, you are correct.
    Allow me to elaborate a little.

    All 2 strokes without a reed valve, rotary valve, ect. actually pass the intake charge backwards, back out of the intake port, a little bit until the piston has traveled down the cylinder enough to completely cover the intake port. (This is why the air filter is always oily when you check it for cleanliness.)
    A small portion of the intake charge actually passes through the carburetor backwards and an odd side effect to this is it sprays the air cleaner with the oily intake charge rendering the air cleaner to be "self oiling".

    This is not good at all when looking for performance. Each time air passes through the carburetor it picks up fuel from the fuel circuit. This is what a carburetor is supposed to do. It is working just fine.

    This whole backwards/ forwards episode ends up being a triple pass before it actually enters the engine.
    Once through the carb while the piston is traveling up. (normal direction)
    Once again through the carb as the piston is traveling down and the port is not closed yet (backwards direction).
    The double pass charge is now trapped in the air cleaner and inlet side of the carburetor. It will stay suspended there momentarily.
    And finally once again it passes through the carb as the piston travels upwards again (normal direction).
    Mind you this is only a small portion of the original intake charge, a now very rich small portion.
    The whole process repeats itself over and over with each power cycle of the engine.
    As you can imagine this can be tricky to account for while tuning the carburetor for some circumstances such as racing. The engines RPM's also affect the effects this triple "gulp" of fuel, making things even more tricky.

    Now a reed valve acts like a one way valve.
    As the intake charge enters the crankcase the force of it opens the reed valve.
    As the piston comes to a stop at the top of it's stroke the reed valve automatically closes due to the fact that there is no more vacuum being created by the piston rising and the intake charge comes to a rest.
    Now the piston travels down and the intake charge cannot pass backwards through the carb due to the fact that the reed valve is closed.

    This completely eliminates the triple gulp of fuel.
    This also increases the pressure obtainable inside the crankcase.

    Another downside of not having a reed valve is when this small portion of the intake charge is released back into the intake port it reduces the overall pressure potential that can build up inside the crankcase, not to mention the loss of intake charge volume.

    More pressure = a faster initial charge through the transfer ports into the combustion chamber and more fuel to burn. More burn = more power.

    Now that the intake port is sealed off by the reed valve when the piston it traveling down it can also be used as a transfer port too if the correct cylinder and piston modifications are made.
    Why not take advantage of this necessary void in the cylinder? Put it to use! It can do double duty!
     
    #92 GearNut, Feb 25, 2013
    Last edited: Feb 26, 2013
  13. k.mah

    k.mah New Member

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    Yeah! What GearNut said :)
     
  14. Frogster

    Frogster New Member

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    Sick! thanks guys. See this is why I love this forum. Nowhere outside of the internet could I go and get access to so many knowledgeable people who are willing to give me advice. If you hadnt have explained it so concisely Gear nut, I might have been dumb enough to go and make a third transfer port when I go to port out my engine and inspect all my internals before breaking the motor in.

    :)
     
  15. LAguyyy

    LAguyyy Super Skilled Master Newb

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    Not on the topic of porting, but when I popped my head off I added heli-coils for my studs while it was off. Nothing more reassuring then stainless steel threads. Drilling was not even required for the stock 8mm studs, just the included tap and insertion tool. Now I can torque to 15 ft/lbs without worry.
     
  16. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    I'll throw this into the mix... I've built several reed valve HT engines, & I've found that they all needed to be jetted up (more gas).

    Gearnuts 'triple gulp' explanation might just be the reason why HT reed engines need more fuel. ;)
     
  17. CarpsCustoms

    CarpsCustoms New Member

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    hey BarelyAWake thanks for all that info. Im a noob who has a bikeberry motor with a pro jetpipe chamber & jaguar CDI..this really cleared up alotta stuff for me...

    but Jw, after port matching, do you think I should trim my piston skirt myself??? Or am i better off buying the Cut On piston from jake's Custom's???. What do you think bro
     
  18. rogergendron1

    rogergendron1 New Member

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    i have a youtube vid posted of absoloutly perfectlyvport matched transfers on a stuffed grubee gt5 case .! its in the performance section under gt5 from the case up !
     
  19. Porting newb

    Porting newb New Member

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    Can you post pictures of the bits your talking about that are needed for this job
     

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