Timing a 2 stroke with no stator marks

[prawny1]

I have been asked to set the timing on a yz 125 (1994?) But it has had a new stator which has no timing marks on it, it would fire for a split second but not run so i tried adjusting both ways yesterday only to find the sparkplug insulator around the tip had broken and was resting on the firing prong so now I'm not really sure where to start from.

The flywheel and case have a line and arrow which I assume is tdc but the stator has nothing, am I going to have to get the bike running on a fresh plug then strobe/ adjust it to tdc then make my own mark on the stator to allow me to dial/ degree wheel it to the factory specs and reallign my new stator mark with the flywheel?

Or is the flywheel/ case mark already at the proper advance?

I have always used the factory marks or marked everything before disassembly when working on bike stators but this has been rebuilt elsewhere.

The guides online say to line the stator or to line the pick up and pulser, but where on the pickup should I be? The bike was set so that when the flywheel lines up the steel pickups trailing edge was just parralel with the pulsers lower edge ( just about to pass the edge of the pulser) .

On the flywheel side this engine turns anticlockwise, should I set it so the pickup block is just passed the pulser tip?
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hellkat wrote:

Some people are only alive cos its against the law to kill them.

[bikenut]

post some pics, of stator, flywheel and markings.

Stators are usually "keyed" ie they fit one way.

plug insulator broken, you sure no bits now in engine, post a pic of the plug as well, it was the correct plug, yes??

check that the flywheel mark and engine pointer are at tdc, just don't drop anything inside the engine thru the pug hole.
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nuts about bikes

[331X2]

I'd clock it to tdc, mark flywheel in line with case mark, mark the flywheel at point of static advance (using degree wheel) then get the strobe on and kick it over to see where you are in relation to the static timing mark.

As mentioned above, you need to be sure there's nothing rattling around in the bore first.

Edit: If it started but would not run I'd take a wild guess at it being retarded, if it was too advanced it would try to kick back at you.

[chris-red]

Have you got a strobe? Mark the stator at TDC normally there is some kind of mark on the casing mark tdc in line with that (or put your own mark).

Use a Protractor to mark however many degrees before TDC are required(make) it a different mark so it is easy to see. Then use the strobe to time it to the second mark.

Edit: What lee said!
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[MCN]

If you have the info for the 'static timing' ie Number of Deg before TDC it is possible to find TDC with a pencil.
(It is easier using fabricated tool from the nut of an old plug.)
You poke a rod through the plug nut and turn the engine over until you find TDC where the piston pushes the rod out the plug nut and then the piston moves back down the cyl.. You may need a couple of goes to get the 'feel'.
You then move the rod out the nut in the direction of the piston the measured amount ?º of engine rotation makes. ?mm

Then turn the engine around (in the direction of rotation for the engine. (Do not simply reverse direction as you loose a bit of degrees due to lash.)
Until the piston contacts the rod.
That should be the Static Timing.

You can probably google a better explanation for it and the detail of a fabricated tool. I'll have a shoofti.

My cat is sleeping on my lap and won't/refuses to allow me full range of the keyboard.

This is for a BSA but engine's are engines

https://www.wdbsa.nl/ignition_timing.htm
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[stinkwheel]

If you've got a degree wheel, finding precise TDC is easy and needs nothing so inaccurate as a pencil.

You need a piston stop tool. You can make one out of an old sparkplug. Essentially something solid sticking into the combustion chamber that the piston will hit. An old sparkplug with a nut and bolt through it will work, or you can buy a proper one quite cheaply.

https://www.jerrybramlett.net/images/pic_installation.jpg

So attach your wheel. Point your marker to wherever is a convenient fixed point. Insert the piston stop tool and rotate the engine one way until it hits the stop. Note the reading on the wheel and rotate it the other way until it hits the stop. You now have the number of degrees between the two stops. Half that figure and set the wheel to that reading with the piston on the stop. TDC is now at zero degrees.

If I read your initial post correctly though, your biggest problem is deciding exactly when the hall effect sensor is triggered. My uderstanding is it should trigger as soon as the sensor is totally covered. That should at least put you in the correct ballpark to fine tune it dynamically (which could arguably be better done by ear than by strobe anyway).

EDIT: You MAY be able to tell the exact trigger point on a hall effect sensor using a compass. The needle should swing the other way as it triggers

I have a horrible thingy for doing the timing on the enfield by mm BTDC. Essentially a pencil.
https://www.armoursltd.co.uk/wp-content/uploads/00411.jpg
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[prawny1]

I've been just picked up my dual guage, to set the timing, the plug hadn't lost any bits though so no worries there.

I can line the flywheel to the case im hoping those are tdc so i can strobe to that but the stator has no reference marks, so it looks like I will have to borrow a strobe to get the bike running at tdc to be able to make an accurate referance mark on the stator before I can dail gauge it for the correct advance.

I just wasn't sure without being with the the bike whether the case to flywheel mark was tdc or not I will double check first anyway.

It was a bit confusing when I read to line up the pulser with the trigger since the tried I'd probably the best part of an inch wide and the pulser tip is about 8mm, the adjustment slots dont allow nearly enough movement to get the two central to each other anyway.
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hellkat wrote:

Some people are only alive cos its against the law to kill them.

[prawny1]

The line on the flywheel is nowhere near the mark on the crankcase at tdc so I am buggered.

I am having to turn the stator fully anticlockwise to get the bije to fire but even then it won't run right, once it is started I can move the stator and it will stay running with the revs up. But I makes no real difference to the pitch of the engine
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hellkat wrote:

Some people are only alive cos its against the law to kill them.

[MCN]

[redeem ouzzer]

Dial gauge.
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Be a REAL MAN!

[stinkwheel]

Home printed timing wheel is cheapest timing wheel.

Trouble with a dial guage is they are seldom vertical and are acting on a domed or rebated piston crown. A timing wheel is better.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Pete.]

For finding TDC you don't need a timing wheel, just a positive stop.

Screw in the stop, turn the engine one way until the piston touches the stop, mark the flywheel. Now turn the engine backwards until the piston hits the stop the other way, mark the flywheel again.

TDC is mid-way between the marks. This is TDC or 'T' mark. If the two marks you put on the flywheel are a long way apart screw the stop out a bit and do it again - the mark will move closer together.

If it's points ignition and you know the static timing then putting a timing mark on the flywheel is easy. Take the diameter of the flywheel and multiply by 3.142. Divide the result by 360 and multiply by the static advance in degrees. The result is the number of mm around the circumference of the flywheel before TDC you put a mark for the static timing or 'F' timing mark.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[prawny1]

I know how to find tdc using a guage etc but is the arrow on the yz125 crankcase meant to line with the thin line on the flywheel for tdc or the ignition firing point? In my experience there are generally two marks, one for tdc one for spark but this bike only has one which neither tdc or pulser line up with on this bike.

the flywheel line with the piston set at tdc is nowhere near the crankcase arrow, neither is the pulser anywhere near the trigger tab with the piston at tdc or with the line and arrow aligned.

I could get it to run with the sator fully retarded / anticlockwise ( firing as close to tdc as I could) but it would not rev cleanly or tick over, anything more advanced would cause kickback to the extent that the kickstarter case has now cracked.

I ended up pulling the woodruff key out, setting the piston to tdc then setting the flywheel to where it looked right with the pulser and the bike fired up and revved cleanly.

I'm 95% convinced the crank keyway is not correct the flywheel part number is right but the bike had been rebuilt before my friend bought it and has never run right.

The cdi could be sparking at the wrong time but I can't see a part number on it to cross referance, but even after the guy buys a new crank I am going to be stuck for fine tuning the timing once it goes back together again without the stator timing mark.
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hellkat wrote:

Some people are only alive cos its against the law to kill them.

[Pete.]

Sounds like it has a crank from a different year then, or a different country. I would cut a new keyway for the woodruff key but that will require some decent engineering.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[331X2]

Sounds like a right ball ache.

Any chance the pickup coil could be bolted to the stator plate differently?

[Pete.]

[prawny1]

I suggested getting a new slot broach cut but he wants a new crank.

The stator can't go any other position relative to the three screws and there is only one place the pulser can mount to clear the flywheel.
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hellkat wrote:

Some people are only alive cos its against the law to kill them.

[Taught2BCauti...]

I came across a similar problem on another forum, where someone had swapped parts from different model years (Varadero 125). At first glance, the stators looked identical, but on closer inspection, the CPS was 20° out, compared to the original.

If someone has swapped the stator, and it's not the right one for the flywheel, then this could be the reason it's not running right.

If there is a part number on your stator, look it up and see if is the right one for the VIN number - there could be different part numbers for different years.
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[redeem ouzzer]

You don't need the woodruff key, it's purely for assembly purposes. Lap the taper in if it's at all rough but if you nip the flywheel up correctly it cannot slip (and a woodruff key wouldn't stop this anyway). I fitted a race ignition on my RD350B which had no keyway in the rotor, had to make a jig to lock the engine at the firing point, torqued rotor up, never looked at it again and neither did the next owner.
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Be a REAL MAN!

[Pete.]

Lapping a taper is an inherently difficult process. It's easy to ruin both parts and cause them to not grip together at all.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good