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#854794 07/28/21 2:28 am
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Hello;
if is there other gap could be that the engine not fire up?


-Tissue paper seems too little for the 0.12 suggested by Hunt.

Thanks

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Point Gap is .012 to .015 set with a feeler gauge .

magneto timing is to ... points just opening ,
( the cig. paper , or cellophane cig pack cover ... just releasing from between the points trick )

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...of course feeler gauge; the doubt was if the gap is to say half of that could be no fire up? I have spark; fuel; not so incredible compression but have it.

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The proper gap gives the best spark generally. Too wide or too small changes the E-gap and you get weaker spark. Many Lucas mags tend to give the hottest spark at full advance on a Manual advance mag. So the trick is to find the spot where it is retarded enough to start without kicking you back but advanced enough to be making enough spark so it can start easily.

Point cam wear also affects E-gap. A wider point gap setting can offset this a little but the best solution is a unworn point cam..

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for a fixed advance
the piston is located at its full advance angle ( down hole piston depth ) or however you set full advance .
and the mageto is rotated in its ajustment slots ( counter clockwise ) till the "fag paper" will just release
( timing done )

any thing paper or plastic .. stiff and thin will work as a substitute for cigarette paper .

dont think your engine has any timing marks or crank stop does it ?

for extra credit .
with primary cover off ,
mark a line through the rotor onto the stator ... once piston full advance is located .
then you can use these marks to check strobe timing .
if the rotor has a mark , just add a mark on the stator .

Last edited by quinten; 07/28/21 5:02 am.
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After setting the timing, check the timing again.

Try starting on full advance. If it kicks back, retard it very slightly and try again.


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Originally Posted by reverb
-Tissue paper seems too little for the 0.12 suggested by Hunt.
0.12 mm = 0.005", which is getting close to being too thin for paper, and is definitely too small for a magneto. But, to be clear, the gap should be 0.012" (inches).

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A feeler gauge is used to gap the points at .012" to .015"
A feeler gauge is used to gap the spark plugs at .018"

"fag paper" is another gauge ... but used to judge when points first open
( but only after the .012" points gap is set )

Just measured the "cellophane" window on a piece of mail .
it measures 0.02mm , or 0.0010" ... or one thousandth of an inch .
a Perfect Replacement for fag paper . if you dont roll-your-own .
1 thousands of an inch can get you within 1 degree of timing .

Strobe marks On the primary side , if you got'em , can be used to dial in timing just a little bit closer than fag paper ,
or used after fag paper preliminary timing .
strobe timing can be used to confirm that both plugs are firing at the same time .
if they are off
the spark plug gaps can be manipulated by a thousands of an inch at a time to balance firing .
Opening the gap retards 1 degree .
Closing the gap advances 1 degee .
So you can compensate for the Magneto cam ring being a little eccentric by running
Slightly different spark gaps

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Originally Posted by quinten
the spark plug gaps can be manipulated by a thousands of an inch at a time to balance firing .
Opening the gap retards 1 degree .
Closing the gap advances 1 degee .
So you can compensate for the Magneto cam ring being a little eccentric by running
Slightly different spark gaps

Now that is quite a claim.

Is that “1 degree” at all rpm?


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Hi guys; still I cannot fire up the engine. Do not know why; I mean; I did not removed the magneto (HUNT). I did all the work with the mag in place and that is very complicated with the old pre units so cannot lose the timing...
If I do not have the gap right still would be some kind of sputtering or something after dozen of kicks I think.
Yes; these ones do not have crank marks.

So, If I have spark; flood the carburetor and have compression (not so much but last time that I rode this bike was exactly the same compression) the engine should does something but does not.

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you are skipping a step . Even though you do not think you lost piston position timing .
full advanced piston position needs to be verified before moving forward to magneto timing ,
Otherwise your timing Technique is just a guess .

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Originally Posted by triton thrasher
Originally Posted by quinten
the spark plug gaps can be manipulated by a thousands of an inch at a time to balance firing .
Opening the gap retards 1 degree .
Closing the gap advances 1 degee .
So you can compensate for the Magneto cam ring being a little eccentric by running
Slightly different spark gaps

Now that is quite a claim.

Is that “1 degree” at all rpm?
yes interesting...is that one degree per .001 of plug gap or just one degree overall?


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The comment about spark plug gap would be relevant to compression ratio, fuel type
RPM, mixture etc etc. It is not valid for adjusting timing on it's own.

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Hi Quinten; is a Hunt magneto; like the Fairbanks. Do not have that cam ring problem.; anyway; I do not see how the timing can be off if I only moved the points arm to sand it a bit to have spark...
I opened and closed the points gap. No any kickbacks due to the timing was not affected in theory.

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so you strobe your magneto at 2500 rpms on the right cylinder
and then you move it to your left cylinder and its 3 degrees off .
What you gonna do ?
1.Nothing you shouldn't have checked it in first place .
2. Take the Magneto apart and adjust the cam ring , taking it apart twice because you didn't quite get it right the first time.
or
3.open the sparkplug a 1/1000ths on one side , close it 1/000ths some the other ... and re-strobe
... there's no point trying to get to/to close , the spark plugs are going to erode anyway , but you gave them a fair start .
and the Baseline is from your strobe RPM .

the timing of each spark is partially a factor of each spark plug electrodes Gap .
( the time from Points opening and primary collapse ... to the voltage built in the secondary ... to jump the spark gap )
If both plugs have a same Gap ... the secondary winding does the same job on each side .
the potential form the plus side is equal to the potential of the minus side .
If the plugs have individual gaps , one side will fire sooner at a lower voltage . ( small spark gap )
one side will fire later ( the larger gap )
... the idea here is to synchronize the spark timings by allowing each plug gap to develop a slightly different voltage

Strobe timing uses RPM , but it's not done under load , so it does have it limitations .
each cylinder will go slightly down its own path under load .

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Sorry Reverb , I seem to be having two different conversations going .
i dont remenber what was wrong with your Magneto , its been about a year .
Bring us up to speed .
What do you think was wrong with it and what have you done to fix it .
the timing may have slipped a year ago , you may have had more than one problem and only fix one of them ?

I suggest going back to checking piston angle because that is the normal starting point .

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OK....Disregard everything I said about Lucas mags because you have a Joe Hunt (Fairbanks Morse type) rotating magnet magneto.

Except that correct point gap is still important and it does effect e-gap. I would also use a piece of white business card wetted with brake clean or carb cleaner to clean the points with after dressing them with abrasive and adjusting to the correct gap.

From what you mention, it sounds like there might be some doubt about the timing, but first I would want to be sure the wires are going to the proper cylinders. An easy check is to remove the plugs, reconnect them to the plug wires and then lay them on the cylinder head where you can see them spark. then kick it over and look at the spark. Blue is good, yellow and thin isn't as good but may still run.

Then put your finger over a plug hole and kick. The compression will blow your finger off of the plug hole. Carefully watch the plug from that side and note if the plug sparks at the same instant your finger is blown off of the plug hole. It might take a few tries to get the hang of it. If it seems off, you might just have the plug wires switched. Switch them and try again. If it still seems off, your timing probably did get changed somehow and will have to be reset.

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sorry Reverb , my mind is mixing up magnetos .

its a hunt magneto .
with wasted spark .
pre unit t100 , magneto is in the magneto hole ? , not hanging off the timing side ?
does magneto have advance ?

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Hello guys; thank you for your time.
There is nothing wrong about this magneto is just that I had no spark so removed one of the points sanded cleaned now I have spark but motor is dead.
Is a 5t speed twin; last time that I ride on it was 3 months ago, due to seems I have a fissure or like that under the gbox and I did not find it yet so is not good now, to use it to ride long distances (really leaks there)
Anyway; the magneto has a new coil and new condenser; as mentioned moved the points to sand them and clean after; due to I had no spark; after that I have spark.
As mentioned; spark is not the problem; the problem hence I asked about if the difference in gap is something that the engine could no fire up; is that the motor is there like dead; no noise nothing. I kick and kick and nothing.
A mentioned; I have spark; flooded the somewhat new AMAL 626 and have compression; not too much but have it (the same compression that had when I rode it last time). No kickbacks no matter the gap that I checked with the points because I do not see a way that I have the timing off only removing one of the points.

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when was the last time the mag was timed ?

it takes 20 minutes to make a down-hole timing-stick
and another 10 minutes to use it to check the timing .

It's all done with the back wheel propped off the ground
from the primary side ...
the old school method is decidedly low-tech ( the only Custom Tool needed is a stick )


.

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...as mentioned, the bike was in use 3 months then parked due to that big leak.
How in the World alone and automatically will be off?
Anyway; I put TDC then low the pistons with the stick method. Put a paper on the points with the pistons 5/16 down TDC. Then measured the max gap at 0.12 inches.

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Originally Posted by reverb
Anyway; I put TDC then low the pistons with the stick method. Put a paper on the points with the pistons 5/16 down TDC. Then measured the max gap at 0.12 inches.

What?

Are you trying to not set the timing?


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...I did not removed the magneto.

-Happens that if I over flood the carburetor, the engine wants to start but does not.

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Originally Posted by reverb
Then measured the max gap at 0.12 inches.

which part of the magneto uses 0.12 inches . ( 3.0 mm)

the points gap is 0.012 " ~ 0.015" ( 0.3 mm)
the spark gaps are 0.018 "

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Geez, maybe he just misplaced a 0 , I do that on occasion....and English is not my second language, lol


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