TRX250R.ORG
General => Lounge => Topic started by: rsss396 on July 21, 2013, 09:11:25 PM
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There is always so much confusion around timing with our motors that I would like to come up with a calculator to take can the diameter of the flywheel and produce a timing tape showing the degrees for that diameter flywheel.
here is some timing tapes from MSD but they do not have a calculator for other sizes
(http://forums.pelicanparts.com/uploads16/msd+8985_w1260132359.jpg)
I can find diameter to circumference calculators and I can find rulers and scales along with degree wheels but can not find a Calculator where you can input a flywheel diameter and print out a timing tape.
With this timing tape you now can take a typical timing light and look at how many degrees of advance the CDI is producing.
I have heard of people doing on a cad program but was hoping we could do it like a typical on line calculator.
I think this Calculator would generate some hits on our site and possible help our sponsors from the increase in traffic.
Thanks
Dave
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Dave I will look into this! I also think its a great idea...especially for those without a fancy timing light.
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Thanks, its really not hard to figuire out its really the circumference divided by 360 but I could not find a online ruler that I could scale and print
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You could get someone to write up a small and simple program in Visual Basic. I did something similar in college but it was to convert Celsius to Fahrenheit and vice-versa. I'll have to reach back in to that part of my brain
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I could Draw one up in AUTOcad....maybe write a little AutoLISP routine to calculate the length of strip and spacing based on the Perimeter of the flywheel....Pi x Diameter = Perimeter.....or (Setq Perimeter (* pi Diameter)) :) Lol The spacing is just the Perimeter divided by 360 degrees ? Right ?
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Yes, Perimeter divided by 360 to create the a mark for each degree.
A calculator would be awesome if it did different size flywheels but in reality if that is to much work then if we could come up with a printable timing tape for the stock trx250r,cr250 and cr500 flywheel that would be great also.
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A calculator would be awesome if it did different size flywheels but in reality if that is to much work then if we could come up with a printable timing tape for the stock trx250r,cr250 and cr500 flywheel that would be great also.
This is a great idea!! I could use one of those.
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This is a great idea!! I could use one of those.
honestly your thread inspired this idea along with others in the past I have tried to help.
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And your efforts are appreciated. Thanks.
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Dave and others, any progress creating a printable timing tape? I would like to be able to use one soon. :joyous:
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no but really it is something that can be done up with a digital caliper, pen and paper.
use this calculator to figure the circumference http://www.onlineconversion.com/circlesolve.htm
divide the circumference by 360 and lay out your lines on a narrow strip of paper.
after you are done you can tape it on to your flywheel with the 0 in line with a TDC mark.
To get the TDC mark on the flywheel it would be easiest to use a dial indicator since a degree wheel can get in the way.
There are machinist dial indicators and mounting bases that would require the head removed unless you have a long extension on it or there is dial indicators that can be threaded into the spark plug hole.
JJ&A sells a nice one
(http://www.jjandaracing.com/media/Indicator400.jpg)
(http://3.bp.blogspot.com/_WhVyxQqCTgE/R3fdwkqfRkI/AAAAAAAAAQM/7HGHBAkxXxA/s320/DSC00036.JPG)
(http://www.oldbritts.com/image/51_150101g.jpg)
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Easy Peasy! I'll give that a try. Thanks Dave.
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If you are running a CR250 ignition, we mounted a flat piece of alum off the 2 pickup coil screw holes used for the old 250r setup on the counterbalancer holder that extended out and was cut to a point right next to the flywheel.
We then rolled the crank around to TDC and marked the flywheel inline with this pointer this is now where you check timing from and its impossible for the crank and pointer to get out of phase with each other.
If you mount something off the stator plate it self or somehow mark the pickup coil you can throw off the phasing of your marks if you remove the stator and put it back on especially if you do not have the centering plates for the stator bolts
These marks are very important to have a accurate reading and there is not allot of difference from 1-2 degrees off
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That's a good idea about affixing a permanent indicator. First off, I really want to see where my timing was, when she ran last. Your so right about the importance of the readings.
For example, if the CR flywheel is 4" in diameter, that would translate to .035, for each degree. Not a lot to work with. I will have to make my index marks, much thinner. :pride:
(http://i532.photobucket.com/albums/ee328/RideRed187/250R%20Pics%20Parts/TimingMarksOffIdle.jpg) (http://s532.photobucket.com/user/RideRed187/media/250R%20Pics%20Parts/TimingMarksOffIdle.jpg.html)
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motion pro is $15 and free shipping on ebay. since the numbers go backward just put white out on there and write in the new numbers other wise you get confused
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That's a good idea about affixing a permanent indicator. First off, I really want to see where my timing was, when she ran last. Your so right about the importance of the readings.
For example, if the CR flywheel is 4" in diameter, that would translate to .035, for each degree. Not a lot to work with. I will have to make my index marks, much thinner. :pride:
(http://i532.photobucket.com/albums/ee328/RideRed187/250R%20Pics%20Parts/TimingMarksOffIdle.jpg) (http://s532.photobucket.com/user/RideRed187/media/250R%20Pics%20Parts/TimingMarksOffIdle.jpg.html)
yeah just use a flat piece of 1/8 alum wide enough to span the distance of the 2 old pickup coil threaded holes, drill the holes first and adjust the length so the plate is very close but not touching the flywheel.
Once mounted make a mark on your plate at the point where the flywheel is closest to the plate. Now make to angled cuts from that mark to create a pointer.
Once this is done take a dial indicator and put the piston at TDC, then without moving anything mark the flywheel inline with the pointer.
This now your new timing point that will indicate TDC or "0" , now with your new timing tape that you have made take some clear tape and apply it to the flywheel with the "0" on the tape inline with the "0" on the flywheel.
Now with a standard timing light you can check your timing, but now you should also have a tach of some sort so you can compare the timing/rpm relationship and plot it against my graph.
There may be issues with timing lights that have a advance feature, I am not sure it will be accurate or not, I think the simpler cheaper lights maybe the better choice on a 2 stroke motor
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I'd say use a string and wrap it around to figure out circumference. Then use an online tool like this: http://calcurator.org/circumference-calculator/ to figure out the diameter
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I prefer to paint the outside of the flywheel with Dykem layout die or you could spray the outside of the flywheel with paint. The tape will often come off at high RPMs and most printers will not print to scale. The are a lot of ways to find TDC. The positive stop method is more accurate than using a dial indicator. Measure the outside diameter of the flywheel, multiply the diameter by 3.412 and divide by 360 for 1 degree increments.
Example:
For an TRX250R OEM flywheel, the outside diameter is 111.5mm
111.5 x 3.142 / 360 = .97mm is the distance between marks when 1 degree increments are desired.
Your 1st mark @ .97mm, 2nd mark @ 1.95mm, 3rd mark @ 2.92mm ..............10th mark (10 degrees) @ 9.73mm, 20th mark (20 degrees) @19.46mm. As you can see the OEM flywheel mark spacings of 1 degree are spaced approximately one millementer apart.
1. Find TDC and scribe a mark on the outside of the flywheel
2. Wrap a 1/4 wide metric tape measure tightly around the outside of your flywheel.
3. Scratch you lines at the degree increments that you chose.
I would make your marks from TDC to no more than 25 degrees BTDC. All of the good running 250cc to 370cc engines I have had to create/optimize timing curves for, usually fall in the 10 degree to 25 degree range. Anytime the curve falls outside of that range, the pipe and or head is usually screwed up. The zero to 10 degreed range is only needed to monitor the timing at cranking RPMs.
I use 1 degree marks on the machined degree plate on my ignition dyno because the plate is approximately 7" in diameter which makes it about 1.5mm between marks of one degree. The RPMs are easier to control on the ignition dyno that a running engine in neutral. The engine RPMs are also much easier to control on a running engine if you have the bike on a rear wheel dyno and in 3rd or higher gears.
I usually place my marks every 2 degrees because one degree increments are difficult to read on a running engine with a flywheel of 100mm diameter or less. Some of the small rotor ignition may need 3 to 4 degree spacing between marks
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Post back from the dead. Great info
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It might actually be easier to make an adhesive timing wheel. The beauty of it is that you wouldn't need to know the actual circumference, and calculations like a timing tape around the outside of the flywheel. Timing and degree marks would extend outwards as far as needed.
With a printable design, you can buy a dozen shipping labels at Walmart for $3, and print as many as you need.
Forgive the crudeness of the image, I didn't feel like spending more than 4 minutes with Photoshop. You get the idea.