Cylinder head designs for the 80cc / 66cc 2-stroke Chinese bicycle engine

Discussion in 'Performance Mods' started by Fabian, Feb 21, 2014.

  1. Fabian

    Fabian Well-Known Member

    This thread has been replicated in the 2-stroke engines section of the forum because it lists various standard cylinder head designs that are fitted to the 80cc and 66cc 2-stroke Chinese bicycle engine.



     
    Last edited by a moderator: Dec 15, 2015
    FurryOnTheInside and mrbobbymelv like this.

  2. max350

    max350 Member

    A lot of talk about how the cylinder heads look like, nothing about what is really important! the combustion chamber looks - squishband- Worthless clips
     
  3. Fabian

    Fabian Well-Known Member

    Dear Mr max350, may i suggest that you invest in a set of prescription glasses, because the video clearly shows the cylinder head combustion chamber designs, furthermore, both of the manufacturers billet cylinder head designs in the video have squish bands that match the 47mm piston crown.

    May i suggest that you review your comments because they could be seen to be worthless.
     
  4. FurryOnTheInside

    FurryOnTheInside Active Member

    It sucks that my internet is so bad, I'd have been interested to see the video you posted.

    Do you think there is room to modify the Happy Time OEM slant head to include a compression release valve meant for chainsaws etc?

    EDIT: Never mind, I found jefuchs' thread. :)
     
    Last edited: Feb 21, 2014
  5. Fabian

    Fabian Well-Known Member

    You need to find someone with high speed internet access, and that will solve all of your problems.
     
  6. jaguar

    jaguar Well-Known Member

    I am waiting for someone to make a head without a squish band since that is what these engines need for these two reasons:
    1) a squish band is only truly effective in increasing engine power when the cranking pressure is above 150psi and the upper RPM is above 9000. These cylinders shouldn't have any more than 140psi because above that weakens the chrome lining which is temperature sensitive. US Chrome says that chrome liners can't withstand more than 400 degrees Celsius. Also a squish band decreases engine power if the piston to squish band clearance is more than .8mm.
    2) a squish band on a small engine leaves too little room for the central combustion dome and as a result all these heads create too much cranking pressure. One of them creates 185psi!!! High pressure creates high head temperatures which can damage the head.

    If you have a head with squish band then you need to buy a compression tester and make sure your pressure isn't over 140psi. Dremel away at the dome sides to lessen the pressure.
     
  7. FurryOnTheInside

    FurryOnTheInside Active Member

    I got through it eventually. :) I wouldn't say that solves all my problems though! But it does let me see a little better what will be coming in my HT kit and gives me an idea what to read and ask about. :)

    The after-market billet cylinder heads are expensive (and so is the shipping for me!) so what cheap/free "kitchen table" modifications can be done to improve the HappyTime heads?


    1. In the video Fabian focused a lot on the relative cooling efficiency of the different designs of cylinder heads.
    I read on MBc about attaching extra home-made cooling fins to the cylinder head; but I've never seen photos or diagram of how this is done. I'm assuming/expecting I would need to grind the edges of the cooling fins flat to allow a good contact area with the bolt-on fins, then drill the home-made fins and the original fins to accept bolts and somehow simply bolt to the original fins. Does anyone have experience of making this type of modification, and is it as simple as I'm thinking, and is it actually effective?

    2. In the video, Fabian told us that the most common HT straight head has very low compression; but MBc is full of threads about increasing compression so I'm not going to ask about that.
    I will have a slant head in the kit that is available here, and in the video Fabian tells us that this is a very high compression head. Bearing in mind what jaguar says in his post #6: Is there enough material (thickness) in the cylinder head to make significant changes to the slant head's combustion chamber? It appears to be mostly squish band and very little dome, with a tiny or nonexistent blending radius between squish band and dome. Could the dome be enlarged, reshaped, or the blending radius increased, or the squish angle increased to lower compression? If it is possible, would this be as advantageous as it appears to a layman like me?
     
  8. Fabian

    Fabian Well-Known Member

    The slant head's combustion chamber does not have a squish band. If you watch the video again, you will see that it only has a 4mm vertical wall coming off the combustion chamber dome.
     
  9. battery

    battery Member

    I have heard from a freind of mine, the motorcycle bum who rides year round even in the blizzards of ny. He has a freind who was experimenting with channels in an x or star shape running from the spark plug port to distribute the ignition faster throughout the cylinder. has anyone heard of or tried this?
     
  10. battery

    battery Member

    the cooling fin heat sink extention sounds like a good idea. Maybe someone should come out with a cylinder head with oversized cooling fins!
     
  11. Fabian

    Fabian Well-Known Member

    You will be waiting a long, long time.
    A squish band is useful when the engine is operating at low rpm with wide open throttle and especially when cylinder head temperatures get outside the optimal working range; which frequently happens at low road speed with the engine working it's guts out.
     
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  12. Fabian

    Fabian Well-Known Member

    It's already been done. Just order a CR Machine Manufacturing billet cylinder head.
     
  13. battery

    battery Member

    I could see how lower rpm's could cause oer heating as the gas oil mix also cools the engine and lower rpm increases burn time. I run my mix at 18:1 to help lubricate the engine more I ride through some steep hills here.
     
  14. battery

    battery Member

    Its a nice looking billet head. but I was thinking more along the lines of fins like mohawk's
     
  15. FurryOnTheInside

    FurryOnTheInside Active Member

    It is, it's also very expensive especially if you have to ship it across oceans. I was thinking along the lines of free. ;)
     
  16. Fabian

    Fabian Well-Known Member

    This concept has been tried but dyno results have not shown any power improvement.
    The below links show a variation on the theme.

    http://pesn.com/2005/10/13/9600187_Design_to_Improve_Turbulence_in_Combustion_Chambers/


    ProCheater-6.jpg


    ProCheater-3.jpg
     
  17. FurryOnTheInside

    FurryOnTheInside Active Member

    I've heard of it, since I just did a little reading and as I understand it, anything to increase turbulence within the cumbustion chamber will change performance.. perhaps only a significant change on significantly larger engines though? I thought that was what the squish band was for too.. another way to increase turbulence.
     
  18. Fabian

    Fabian Well-Known Member

    You get what you pay for and you have to pay reasonable money for a decent cylinder head.
    At the end of the day, a man has to do what a man has to do, in procurement of the finest billet cylinder head on the market.

    If finances are a problem, then you always have the option of standing on a street corner and offering your perfectly tanned and sculpted body at the roadside. I have heard that women these days are prepared to pay a man for the ride of a lifetime, so long as it comes with a "satisfaction delivered or money back guarantee".
     
  19. FurryOnTheInside

    FurryOnTheInside Active Member

    I really don't want to spend another 30 mins watching again and restarting my computer when Youtube crashes it, lol. I got a fairly good look at it the first time though so I'm not going to see any more. I just don't have that much idea what the cross sectional diagram would look like if there were one for this head. So there is a flattish-looking area but it's clearance (above the piston surface at TDC) is way too [thick] to be considered a squish band? There is or appears to be a dome in the centre and a flatter area outside so I don't know what else to call these different areas of the slant head combustion chamber. Names of things aside, I would still like to know what easy, free mods I can do to make a slant head (included in the HT kit) somewhat, even a little bit more like a terrifically expensive billet cylinder head from the other side of the world.
    I may well buy one one day, but it's hundreds of $$$ versus fun with a Dremel on something cheap and expendable and available to me this year.

    I REALLY don't understand why there aren't at least cross sectional diagrams provided by the manufacturers of the various after-market cylinder heads, for comparison.
     
  20. Fabian

    Fabian Well-Known Member

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