Degree tool?

danlandberg

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Apr 25, 2009
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569
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 .
 


HeadSmess

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May 17, 2010
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3,049
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.
 

danlandberg

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Joined
Apr 25, 2009
Messages
569
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.
Thanks, I have a bad magnet I can attach the degree wheel to.
 

HeadSmess

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May 17, 2010
Messages
3,049
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...
 

danlandberg

Member
Joined
Apr 25, 2009
Messages
569
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.
Thanks, I have a bad magnet I can attach the degree wheel to.
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...
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.
 

HeadSmess

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May 17, 2010
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3,049
through the spark plug hole to find TDC. Then add an extension for BDC.

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.
 

danlandberg

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Apr 25, 2009
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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.
Dan
 
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HeadSmess

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May 17, 2010
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3,049
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.
 

danlandberg

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Joined
Apr 25, 2009
Messages
569
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.
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
 

HeadSmess

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May 17, 2010
Messages
3,049
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.
 
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