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Post by Thebatman on Dec 13, 2010 10:16:09 GMT -5
good morning guys..... well i'm playing with a degree wheel again... the manual says the timing is 15.5+-2 BTDC... now i assume my degree wheel should match this after i get it hooked up correctly???... the how to, thank you btw, doesnt say anything about the piston hitting the piston stop just beforee its completely to the top... there is approx. 2mm around the crown area that is exposed on the barrel but the piston is touching the stop......of course the oem piston is not a flat top piston... this may be nothing but tdc should be tdc.....having to fab a stop this a.m.... guess i should worry with my parts but i figure i may as well get a jist of it while i'm in here, then maybe i can get the measurements correct with my bbk... ;D....(i am not going to mess with the aero for a bit, i want to concentrate on my lil red devil... :drool: )
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Post by 90GTVert on Dec 13, 2010 10:58:42 GMT -5
Read over this section of the how-to I posted again. If done this way, you will be at true TDC when the wheel is setup properly. It doesn't matter if the piston is flat, domed, or dished.
"Then I rotated the crankshaft clockwise until the piston touched the piston stop. You only want to use gentle pressure, don't try to force the piston farther than just touching the stop. I made a note of the reading on the degree wheel. I then turned the crankshaft counter-clockwise until the piston was once again at the stop and made a note of the reading on the degree wheel. TDC is exactly in the middle of the 2 readings. Adjust the degree wheel accordingly. If properly adjusted, the piston should stop at the same reading on each side of 0/360 degrees. In my case, it was 345 degrees ATDC and 345 degrees BTDC. Once you get it dialed in, tighten the degree wheel so it doesn't move. Go through the steps again and make sure you haven't thrown anything out of adjustment when tightening the wheel. If it is only slightly off you may be able to bend/reposition your timing pointer instead of the wheel itself."
Another method of finding TDC would be to use a dial indicator. Position it so it's touching the piston near TDC and then turn the engine very slowly. When you get the highest reading, that's TDC.
If the timing is supposed to be 15.5 degrees +/- 2 BTDC, then you should see the pickup aligned with the reluctor on the flywheel somewhere bewtween 13.5 - 17.5 degrees BTDC. That measurement has no bearing on your degree wheel setup, just shows you when the pickup triggers a spark. Ideally if your degree wheel i setup properly it will be within those specs.
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Post by Thebatman on Dec 13, 2010 19:05:48 GMT -5
ok, can anybodyhelp me with some numbers...my oem cyl.. my first try with a degree wheel exhaust starts to open @ 111* full open @ 170* starts to close @ 196* full close @ 268* so if i am correct; then my exhaust duration is 138* ? boost port starts to open @ 174* starts to close @ 194* full close @ 240* so if i am correct; my boost port duration is 12* ?? the manual says i should be at 15.5*, but i tried several times and i came up with 22*.. when i took piston stop off she went to tdc when i rotated to 0. if i am anywhere correct on this, i guess i should do one for my bbk while i am installing it?..... my numbers may be whack cause my wheel isnt like brents, so i had to read backwards going in the CLOCKWISE direction, correct?
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Post by 90GTVert on Dec 13, 2010 20:35:59 GMT -5
The main numbers you are looking at are port beginning to open and port closed. So for the exhaust it's open from 111 degrees to 268 degrees. 268-111 = 157 degrees of exhaust duration. The part that seems a little odd to me is that your exhaust port just begins to open at 111 degrees ATDC and it closes at 92 degrees BTDC. From my experience, those numbers should be the same. Meaning, if it opens at 111 ATDC it should close at 111 BTDC. I would think you've either made an error with the wheel setup or noting the event. I spend a good bit of time with a flashlight moving the wheel around to be very precise on every measurement. If they don't match up, I check everything and readjust the wheel if necessary.
Not sure where you are getting 22 degrees for the boost port from those figures. Closed at 240 - opening at 174 = 66 degrees. This one you've measured to be opening at 174 degrees ATDC and closing at 120 degrees BTDC. Again, not symetrical.
I'm really thinking you should try this out again. Take your time.
Regardless of how the numbers are measured and if they're correct, the timing the manual refers to and what you are looking at are totally different. What the manual refers to is ignition timing. It is telling you that the spark plug should ignite somewhere around 15.5 degrees BTDC. So you should see the pickup near the flywheel lining up with the reluctor (bump) on the flywheel right around the time your degree wheel is at 15.5 degrees. What you are checking here is port timing, which is sort of like valve timing in a 4 stroke. Two totally different ideas.
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Post by Thebatman on Dec 13, 2010 21:03:39 GMT -5
hey man, thanks for the reply... well, i just thought i was going somewhere :no: ... i shall try this again...i may have to print out a wheel thats going the same direction as i am... ... the one i used goes in the counter clockwise direction.. seeing if i can get any sort of grip on this.. but now,how do you know what numbers you want.. more math i guess?? how do you know the numbers wont be crap? is it like the squish band?...you want certain numbers(.1) for that mod? or the exhaust port?..(you want 1mm)...(well, i assume 1mm works across the board before it really gets tricky)
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Post by 90GTVert on Dec 13, 2010 22:46:50 GMT -5
I use A. G. Bell's book, Two-Stroke Performance Tuning, which makes reference to certain port durations for certain RPM or if you are lucky you may find durations from others that have worked well on similar setups. If you plan to change anything, it's a good idea to know the RPM range your pipe is intended for. That book is absolutely a must have for folks like us.
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Post by Thebatman on Dec 13, 2010 23:11:09 GMT -5
yeah, i tried to print that book but never got anywhere.... hope santa brings me one. :tongue: .... dam, i have noooo clue what the lv zx pipe is intended for....(that should be here next week)....i dont even know what my pipe was rated for... only hit 7680 rpm, which i thought was terrible.. ;D
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Post by 90GTVert on Dec 13, 2010 23:57:54 GMT -5
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Post by 190mech on Dec 14, 2010 7:19:44 GMT -5
With the piston at BDC (bottom dead center) it should read 180*,if not your degree wheel setup is not right,I searched on you tube for a degree vid but had no luck.I like the biggest wheel I can find as my eyesight is not too good. Here is a PDF copy of Bells book; www.kreidler.nl/artikelen/performance-tuning-graham-bell/performance-tuning-graham-bell.pdfAs Brent says,the 15.5+-2 has NOTHING to do with port timing,so forget that number,work on getting the degree wheel reading correctly,then move the crank down till the exhaust just opens(doesnt matter which direction) and get that number(say 92*),then multiply 92x2=184,then subtract 184 from 360(360-184=176),That IS your exhaust port duration(176*).Repeat the same drill to get the transfer durations.. GOOD LUCK!
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Post by 190mech on Dec 14, 2010 9:37:50 GMT -5
The way I set up a degree wheel is turn the crank to hit the stop,reset the indicator pointer to "0",turn backwards till hitting stop,record degrees(say 42) Then take 42/2=21.With piston still on stop,reset pointer to 21*(dont reset wheel,only pointer),then turn crank back to stop in fwd direction,it should again read 21*,if not start all over again,it usually takes me 2-3 tries till I get it right..Hope this helps,kinda hard to write it,if I was there with you it would take only a few minutes!!
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Post by 90GTVert on Dec 14, 2010 10:40:01 GMT -5
Yeah, I do it the way John does now too. Resetting the wheel leaves more room for error retightening and all of that so it's much easier to move your pointer around instead. I use a paper clip as a pointer, so it's easy to move around and rebend. As he noted, bigger degree wheels are easier to read. They're more accurate too, because each mark is farther apart on a larger wheel. I have the same wheel as 190mech, from Summit Racing and I enjoy using it much more than my small printed degree wheel. It's $21, but if you plan to do a lot of work on engines I think it's well worth it. I know I've got my money's worth. www.summitracing.com/search/Part-Type/Degree-Wheels/?keyword=degree+wheel&kr=degree+wheel
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Post by Thebatman on Dec 14, 2010 13:30:52 GMT -5
hey guys, thanks for the replys this a.m....sorry i missed em.well i ended up with the maloosi 70cc cast kit along with a lv zx pipe..yeah brent thats the pipe i am waiting on....... never could get some info i wanted and seen on another forum where the malossi and zx would be good.......(over on s.i.)... i am trying to play with the wheel again... on bdc my wheel does read 180 so thats a plus... :thumb: ....i hope i just added wrong... remember this is the oem cyl not my bbk....trying to learn as i go, got a week before pipe comes in.. :lol: ...didnt figure there was any reason for pics at this point anyway...guess you know what i'm trying....imma go measure again........
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Post by Thebatman on Dec 14, 2010 13:41:11 GMT -5
ok i just got; starts to open @95* full open @167* starts to close @ 200* full closed @ 267* so that would make a 172 port duration?...... are these numbers any better?.... possibly closer? i'll go do the boost port also, wanted to get a feel if right track or not..... i see its still not the 186-188* that brent said was in the book......my math?...oem?.....gotta be taken to that # ...
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Post by Thebatman on Dec 14, 2010 13:49:19 GMT -5
on my boost port; i have starts to open @ 120* full open @ 175* starts to close @ 180* full closed @ 242* ...making a boost duration of 122*??... that # should be better....lmao... one thing tho, idk what the significent is but my boost port was never FULLY opened...the piston started the return stroke up before the whole port was exposed
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Post by 90GTVert on Dec 14, 2010 14:01:57 GMT -5
Thats better. That would give you 172* duration whether you average it ( 360- ( ( 95 + 93 ) / 2 ) x 2 ) = 172 ) or subtract open from close ( 267 - 95 = 172 ). 172 sounds about right. It's no real surprise that the stock cylinder isn't setup for high revs.
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