Degree tool?

Discussion in 'Spare Parts, Tools & Product Developement' started by danlandberg, Feb 27, 2016.

  1. danlandberg

    danlandberg Member

    Looking for a degree tool that I can use on the magneto side of my GT5 Pro Racing 66cc. Anyone know a good place to get one? I thought I seen a post on this some time ago. Can't seem to find it now. Any good ideas for making one? I'm looking for ALL the specs for this engine. Everything, port timing, ignition timing, port durations, bore and stroke, rod length ect. Can anyone help with this information? Or post a link where to find a printable version of these China made engine specs. Any information would be greatly appreciated. Thanks in advance. Danlandberg .

  2. HeadSmess

    HeadSmess Well-Known Member

    138~140 exhaust,

    104~ from memory on the transfer...

    i forget what the intake was... 96 or something?

    plenty of degree wheels on fleabay... fitting them can be a challenge. hint, buy a small 3jaw drill chuck at the same time ;) works if you aint got a lathe handy.
    KenM likes this.
  3. danlandberg

    danlandberg Member

    Thanks, I have a bad magnet I can attach the degree wheel to.
  4. HeadSmess

    HeadSmess Well-Known Member

    and dont forget the pointer! no use using a degree wheel if you havent got a fixed pointer to measure from!

    lil piece of metal, hole drilled in it... poke a bolt through, wind on a locknut, screw bolt into handy threaded hole in engine case with another locknut so you can fine tune it and lock the whole thing in place... then zero away. i find a BP**Es ngk plug, anything with a long thread and projected tip helps for zeroing. turn one way til piston hits, turn other way til piston hits, zero is dead in the middle of both "stops".

    magnet is prone to slippage...
  5. danlandberg

    danlandberg Member

    Thanks, I have a bad magnet I can attach the degree wheel to.
    Ya, I noticed that the keyway between magnet and crank is a little sloppy. I've been an air-cooled Porsche and VW engine builder for 30+ years, so I've got a tool to check deck height that I can adapt to use through the spark plug hole to find TDC. Then add an extension for BDC.
    The magnet keyway goes on at the 1:00 position, so I assume that the 12:00 position would be a line from the center of the crank to the spark plug (center mount plug, not angle fire head). I didn't check for TDC when I changed the magnet. Should have, just for curiosity sake. I'll figure it out, it's just an engine.
  6. HeadSmess

    HeadSmess Well-Known Member

    nope...dont try and find tdc or bdc simply by measuring. the piston travel through the top 20/30 degrees is way too inaccurate.

    is ok for figuring stroke, but not much more.

    stop the piston a fair bit before TDC on either side, and zero to the halfway mark is virtually foolproof. then you get BDC at the same time. with a degree wheel, anyways.

    ie, zero the wheel at one stop, then when you spin it back the other way and it stops at 32, you know TDC is exactly at 16...

    some people try using rope stuffed down the cylinder but thats pretty inaccurate as well.
  7. danlandberg

    danlandberg Member

    I know what your saying. My tool screws down to touch the piston (in fine thread increments. One complete turn = .xx thousands). Turning the engine one direction till it touches the stop, then turn the other direction to stop, take the reading, ÷ by 2, That's TDC. Time to set pointer. Another question, exhaust port duration. Is this measured when top of piston reaches the bottom of the port to the top of the port? Or visa versa (top of Port to bottom, port is now open) either way, the duration would be the same. Just be a different location on the Degree wheel. BTDC and/or ATDC. Or it may be a reading on one side, (ex; ADT). I'm just trying to put all this on paper (kinda Blueprint) so I understand the workings of things more completely in the 2stroke world.
    Thanks for all your information.
    Last edited: Feb 29, 2016
  8. HeadSmess

    HeadSmess Well-Known Member

    duration is measured from port opening, all the way through BDC til port closing again... you can assume its normally twice the figure you get from port opening to bdc, unless its a desaxe type cylinder...offset from the crank center line. these particular engines are not.

    hardest bit to measure is the transfer timing... its a bit of a guesstimate unless you tear it down, measure conrod length and do some maths.

    i usually just remove head, replace two of the nuts with some packers underneath to keep the cylinder in place as if its assembled, and yeah...

    the whole things a slight guesstimate anyways, as theres a slight amount of leakage from top of piston to top of rings, unless you got a dykes ring which sits at the top edge of piston. once again, not on these particular engines. no harm in trying to modify a piston to take one if you got a lathe handy... havent ever heard of anyone doing such a thing to a china engine yet.

    if youre gunna port, get some dental drills off ebay. dremels/die grinders just wont get in there. you have no control, and its far too easy to slip and take a chunk out of somewhere you dont want to... plus you cant get the angles in the transfers.

    do a search for "gordon jennings 2 stroke tuning", the pdf is readily available online. or on here...linked it a few times.
  9. danlandberg

    danlandberg Member

    I kinda know what NOT to do when porting. Don't want to enlarge the port at top or bottom, that will change port timing. Enlarge side to side a bit and remove the casting flaws should be OK.
    I'm doing a little research on building an expansion chamber (just for the fun of it). I love to build as many thing from scratch as I can. That's one reason I ask for as many specs as I can.
    I figured the best way to figure transfer port specs would be to do it mathematically.
    Thanks for your input and help. I can build the heck out air cooled VWs, now I've got the 2stroke fever. NEED Input. LoL
  10. HeadSmess

    HeadSmess Well-Known Member

    that sorta sounds like a reference to short circuits, need input...

    mh-aerotools has a free java app for tuned pipes. not great but they work, for a freebie.
    be warned, you need a fairly old java to run it, unless you install it and run it that way...
    also has a very handy silencer calculator, you can punch in various figures, get an idea of what attenuates what, and it actually works very well :eek:

    sticking the stinger or outlet pipe virtually all the way into the pipe reduces a lot of the noise. just make sure it isnt sitting halfway into the "reversion" cone, it stuffs things up seriously.

    me myself use 2 stroke wizard pro..i preferred version 3 to 5, and cant really say anything about the "duel" add on program now supplied with it(only tried making one with the extension once, maybe if i had more patience to experiment with various mesh sizes?). pretty cheap, seems to work ok though.

    never had a justifiable reason to buy any expensive stuff like "MOTA"... all the forum blurbs elsewhere say it pops out dimensions fairly similar to the cheaper 2 stroke wizard anyways.
  11. danlandberg

    danlandberg Member

    I'm looking at one on Google Play, it asks a couple of specs, and a couple of targets. Want to put in factual readings, build one out of cardboard, see how it looks and then go from there.
  12. danlandberg

    danlandberg Member

    One of th
    One of the questions is exhaust port length, I assume that is the measurement from piston skirt to exhaust manifold flange. I know what height and width is all about. Don't know how good the calculator is, but if it has me build some crazy looking thing then I guess I'll know. Your right, "short circuit" I think I may have one at times. LoL
    Can't stop wanting to build stuff.
  13. HeadSmess

    HeadSmess Well-Known Member


    200 GSM paper, or very thin cardboard. the only "straight/untapered" sections on this template was the first piece, the belly, and the stinger..

    lay out the conical templates with some free software called cone layout... divide the pipe up into sections, i tend to work on round mm per segment, and tweak the pipe design to get nice workable, 270mm with an increase of 9mm divides into nine 30 mm sections increasing by 1mm very easily ;) who cares if the powerband is at 7,543 rather than just 7,500 rpm?

    found that aiming for anything over 8000 rpm is a waste of time. with these at least. another reason i gave up on porting, its too much effort laying up a new pipe to suit all these new dimensions each time.

    the best bet is to do as described in jennings book... use a stub exhaust, experiment with best intake length until the engine has plenty of grunt, then design the pipe for those dimensions.

    the more bends the better, except it gets hard to join them all. started a thread on hydroforming and thats about as far as ive gotten... still dont have a new tig or a pressure washer to pump the profiles up with. when i do, might start experimenting with the ports again ;) once a pipe takes twenty, thirty minutes rather than twenty, thirty hours!

    jag did make the effort to calculate the flat profile needed to make a 1.5" tube with 180 degree bend on a 5 inch radius. two curves, 10.3 and 12.8 inches from memory, marked at 78 degrees included angle... never been confirmed though. making a tapered section is slightly more awkward.

    my first pipe went underneath, with only about 3 sharp bends, then i flattened it to clear between tyre and pedals...dont do this! it stuffs up all your calculations! they work on changes of dimension. flattening is obviously a change of dimension.
  14. Archiwax

    Archiwax New Member

    I printed this and stuck it on a piece of plastic on a piece of plastic and drilled a hole in the middle.

    Attached Files:

    danlandberg likes this.
  15. danlandberg

    danlandberg Member

    I have a couple of 180° protractors I could use to make a degree wheel.
  16. 45u

    45u Active Member

    I have one I use on my radio control motors and big ones for motorcycles. I think I will adapt the small one to work. If you know of anywhere to get 1/5 scale parts should have them if not you can get one here.

    Never mind did not know they went up so much.
  17. danlandberg

    danlandberg Member

    Add the link please. Would like to see a pic.
  18. 45u

    45u Active Member

  19. danlandberg

    danlandberg Member