80/66cc bike build

Discussion in 'Photos & Bicycle Builds' started by wagel, Oct 5, 2016.

  1. wagel

    wagel New Member

    Hi guys. This is my first attempt with these Chinese engines. The goal of this build is to explore the world of tuning 2 stroke engines and enjoy doing something interesting on my free time. I have two different 66cc engines. The plan is to have one running reliably and then tune the other one until it blows up and go one step backwards from there:D. The No1 engine is mounted on a frame and running. It has slant head with slightly increased compression, cleaned and matched transfers, upgraded 4x6202 c3 bearings, DIY ignition which retards the timing a bit and a expansion chamber made with using Jaguars design but adjusted a bit as the material that I had for the header and stinger was a bit off. Running quite OK for now, will post pictures soon.
    The second engine is going to be tuned until it blows up or runs great. It's probably going to be a case reed with VM18 carb, Jag pipe and custom ignition.

    Anyway, started measuring the ports today and the first thing that started messing with my head is the transfers. On that jug the transfers are weird. Didn't have a caliper at home so all measurements are not 100% accurate but here they are. All taken from top surface of the jug. Exhaust 29mm, Transfer on exhaust side 35mm and intake side 31mm, intake 44mm. So the transfer roof is 4mm higher on intake side. If I calculate the duration should I use this measurement or take the average or something else? Maybe I should just dremel the roof flat so it is 31mm on both ends and then start working from there?

    Engine No2 has straight plug low comp head and deck height approx 2mm. Tried it on the frame once but runs like sh*t compared to No1. 4strokes a lot with same carb.

  2. wagel

    wagel New Member

    Rat style
    Steve Best and zippinaround like this.
  3. zippinaround

    zippinaround Active Member

    whats that coil off? and do you have it running straight from magneto wires?
    Steve Best likes this.
  4. wagel

    wagel New Member

    zippinaround likes this.
  5. wagel

    wagel New Member

    Changed crankshaft seals on the black engine as the originals were leaking quite nicely, had some goo behind magneto. Also trued the crank, as I could have guessed it was pinched together on the opposite side from crank pin. Also drilled 9.5mm holes for balance which was a huge mistake. Before it was vibrating a little at 6.5krmp but now it is unbearable, I'll try to fill those holes with something. Location was same as the upper hole here http://www.dragonfly75.com/motorbike/images/mycrank.jpg