Having problems with your coil not firing here is help, Tec Timing, Good Read

#1
First check flywheel keyway and see if it's shered or slightly shered this effects the timing. But if you have good points and condensor then check the coil with a ohm meter disconnect all wires and spark plug wire. put one lead on the end of the coil wire and one to the other end of one of the little wires coming out of the coil and it should read at least 4 and 1/2 ohoms then check the other little wire (your coil will have 2 little wires coming out of it and it should read 4 1/2 ohms also if not then the coil is defective. and when you connect one lead to one of the little wires and the other lead to the other little wire it should read 0 ohms.

Most of you that have a motor quit running after a while after it warms up only to start up again can mean the coil is old and shorting out inside the coil or one of the really fine wires inside of the coil is parcially melted and opening up when motor is hot. If none of you never saw the dinky little wires inside of a coil you would figure it wouldn't do Jack but that's the way it is. Most generally most engines that die after running for a little while it's a fuel problem in the carb causing that or the gas tank is not venting through the gas cap.

Anyway on these old tecumsehs with the internal coil and with magnets glued to the flywheel has to have a air gap and you can set it with a cut away flywheel that tecumseh sold or make your own or you can do it like I say below.

Check your ign spec.s for your type of motor and timing specs and air gap required for your motor


Timing is .090 B.T.C. for the HM80 tecumseh engine
Air gap is .012
Point gap is .020
You need a tecumseh dial indicator and a 1/64 scale steel ruler
Pencil and paper...

Set points first

Set timing next using large treaded screw on dial indicator offset lever for this engine if you don't have dial indicator take off head and measure slightly less than 3/32nds (which is .094) before top dead center. I go a little further than .090 to like maybe .100 and move crank clockwise to .090 to take slack out of engine parts.

Disconnect all wires from points and connect a lead from the ohm meter to the threaded point's post and the other lead to ground. When you rotate the crank clockwise to .090 the points should begin to open and the ohm meter should read infinite. If not lossen the stator bolts and rotate the stator to get the points to open at the right B.T.C. settings Then tighten down both stator bolts - Get this as accurate as you can.

This old of a motor like yours requires tecumseh cut away flywheel to adjust air gap since there is no other way to read the gap between the magnet and coil legs since it's all internal and you can't see it.

Pay close attention this is critical measuring and I found this on the internet form a fellow who helped me with reinstalling loose magnets and how to check north and south poles and I also found how to set the air gap with a piece of electricians tape Hats off to this fellow I'd be lost without him. Only I went one step futher and figured how to make the air gap adjustment.

The bolts that hold the stator on have a slot that is in a circle rotation Pattern however it has a small amount of up and down movement that's probably moves around maybe a couple of 64ths or so this is where your air gap lies. In essence we are walking the coil closer to the magnet surfface because if it's to far away there will be weak spark or no spark at all.

First establish a mark on the top stator plate near the bolt area use a small chisel and lightly tap to make a mark. Do the same for the Bottom stator plate near the bolt area and do the same or use a known point to but your 1/64th scale steel ruler from. Write down all of these locations to help in case you forget.

Second establish a chisel mark to the left of the crank - stator area on the starter housing plate flange lip like where the starter shroud bolt goes into the welded nut take a chisel and mark a area above that nut level across from the top stator bolt then mark a area on the starter housing flange lip for the lower stator bolt. Take a very accurate distance measurement from these two marks and "Write it down." This is for in case you happen to go to far and you can return to this measurement.

Do the same for the bottom stator bolt level across to the housing flange. and write down the distance between these two marks with your steel 1/64 ruler. I repeat write down any adjustment from here on for the top adjustment or bottom adjustment.

Now that you have marked the two spots on the stator and 2 spots on the housing flange. Now your ready to set the air gap.

Use a piece of electricians tape which is .008 to .009 ths. we need .012 Air gap so if we double the tape that's .016 to .018 and that's too thick so I used one strip. Just use what ever tape you can find to the desired thicknes you need for your type of motor. When you take the tape off the roll don't streach it cause it affects the thickness. Put this tape over the 3 legs of the coil.

Now very carefully put the flywheel back on straight as you can and not cocked from one side to the other has to be very straight cause the crank is tapered (I say that cause I had six magnets for a lighting coil.) maybe you just have 2 magnets anyway make sure the flywheel is as far back as it goes to be seated - you don't have to put nut on and torque down. Rotate the flywheel 2 revolutions and very carefully take off the flywheel.

Check the tape and if there is no rubs then we have to set the Air Gap

A- Lossen the top stator bolt and ever so slightly move it to the right say 1/2 of a 64th mayb a slight tap from a hammer will do it - measure that you went that much and write it down! and tighten the top stator bolt.

B- Now lossen the bottom stator bolt and move the same distance and write it down! and tighten down the bottom stator bolt. Doing it this way does not disturb the timing because it's equal - (if you move say 1/64 on the bottom instead of 1/2 of a 64th the timing will increase to .100th and thats bad.)
C- with the electricians tape over the 3 coil legs carefully put the flywheel back on and seat then rotate the flyweel 2 revolutions and carefully remove.

Now if you see a very slight drag mark on the tape you have established your air gap. if not repeat the above moving the stator towards the flywheel magnets. After this check your timing again and if off a little loosen bottom stator bolt move stator counter clockwise to increase B.T.C. settings or clockwise to decrease B.T.C.

I had a mess when I took my flywheel off 3 magnets knocked loose and bad coil I replaced the coil and fixed the magnets and had spark but when I set the timing and moved the stator I lost the air gap and lost fire. I used this tape and measurement movements on the stator and established air gap and was my setting ended up at .092 B.T.C and it's tuff to get it this close 2thousands is finer than frogs hair.
I put it all back together and held the coil wire next to the head and give the starter a pull and and there was fire everywhere and with a sharp snap. I must of pulled the starter a dozen times admiriing my work like a little kid. I beat the system and so can you..... like my ole lady says I don't handle defeat to well...

Threw a Rod
P.S. My engine started on first pull hmm.....
 

Oldsalt

Well-Known Member
#2
Very good information, Thanks for your time in posting it. I gotta say that your comment on an engine running a few minutes and then quitting is often the coil. I know this to be the case and I believe a lot more people would be enrichened if they knew why ignition coils go bad. So here goes.

Those windings of fine wire inside the coil can short out and make the coil completely without spark, or worse as you point out, only work long enough to give a person hope that everything is gonna be OK. The usual and almost ONLY reason that the primary and secondary windings inside the coil decide to short is turning over the engine with the spark plug wire disconnected and hanging along side the engine. [Stopping the engine by pulling the spark plug wire or, sillier still, seeing how long a spark the coil will produce by holding the wire end near the head and slowly pulling it away until the spark quits jumping. Some think they are 'testing the coil', they aren't; they are testing the limit of the insulation between the primary and secondary winding of the coil]. The spark energy, generated by the magnet on the flywheel flying past the coil laminations, has to go somewhere. If it cannot simply jump across the gap at the spark plug [.035"] it will jump inside the coil windings. Typically burns a tiny 'carbon' trail that usually will not make the coil inoperative.....at that exact time. But the 'seeds of destruction' have been sowed. It will keep getting worse [carbon conducts electricity] until it jumps the spark there all the time and never across the plug gap.
 
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#4
Sowing the seeds of self destruction...

Very good information, Thanks for your time in posting it. I gotta say that your comment on an engine running a few minutes and then quitting is often the coil. I know this to be the case and I believe a lot more people would be enrichened if they knew why ignition coils go bad. So here goes.

Those windings of fine wire inside the coil can short out and make the coil completely without spark, or worse as you point out, only work long enough to give a person hope that everything is gonna be OK. The usual and almost ONLY reason that the primary and secondary windings inside the coil decide to short is turning over the engine with the spark plug wire disconnected and hanging along side the engine. [Stopping the engine by pulling the spark plug wire or, sillier still, seeing how long a spark the coil will produce by holding the wire end near the head and slowly pulling it away until the spark quits jumping. Some think they are 'testing the coil', they aren't; they are testing the limit of the insulation between the primary and secondary winding of the coil]. The spark energy, generated by the magnet on the flywheel flying past the coil laminations, has to go somewhere. If it cannot simply jump across the gap at the spark plug [.035"] it will jump inside the coil windings. Typically burns a tiny 'carbon' trail that usually will not make the coil inoperative.....at that exact time. But the 'seeds of destruction' have been sowed. It will keep getting worse [carbon conducts electricity] until it jumps the spark there all the time and never across the plug gap.
When I test for spark it's always with special spark plug that has the insulator and the little rod sticking out of it but it's made without the bent tang ( that you normally see with typical spark plugs) and the spark has to jump a required distance in order to show a good coil and it has a built on spring clamp to clamp it to the head and you put your coil wire on it to test. What it does simply let's you know if the coil is going weak or just about to give out on you - and your absolutely right about sparking the coil wire only the head - the high voltage in that coil really has no where to go to simply because the one of the little wires goes to ground and if you arc the coil wire to the head that's a double grounding that's bad news - that's asking for trouble at a later date. Your right that voltage has to escape by jumping the spark plug gap... period

Long story short "Never check spark with the coil wire only and arcing it out on the head" Plug that spark plug in and ground and then test...

One other thing most guys won't or can't figure out is reason a spark plug will spark shorting it out against the head with good spark and put the spark plug back in and it won't start well.....

It's because the plug has been exposed to a gasoline flooded motor and when they do get it started finally or with starter fluid the motor heats up the insulator on the inside of the plug with all of that raw fuel on it and gives it a shinny glazed coating. No matter how many times you watch the spark plug spark grounding it to the head and put it back in -it will never fire under compression.


When I see that glaze on the insulator I either run the plug through a spark plug cleaner that bead or sand blasts it clean or just plain buy a new one. God only knows how many gas fouled spark plugs mowers I repaired because they said they saw it spark while it was laying on the head...
 
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#5
A little more inf. to bring the expert out in you...

On these old motors the magnets are glued on to the flywheel - do your self a favor and re-glue them with JB weld - JB weld is non magnetic and works great just make sure you mark each magnet with a little paint on the top say like magnet A and magnet B and mark the same on the flywheel surface A and B so you won't mix up the magnets Tecumsehs fire with the north pole magnet first and then the South pole magnet last. multi 6 pole magnets for the charging coil are n.s.n.s,n.s.n.s.n.s.n.s.

If you get one out of sequence - then all bets are off and it won't charge nor fire. Anyway clean the magnet with sandpaper and the flywheel surface with sandpaper. You'll see exactly where the magnet goes anyway because the metal surface will show the little square where it used to be anyway because the metal will be shiny and the rest of the fly wheel will have surface rusted. This expoxy glue Tecumseh used does not hold up for ever and if you reglue them now you won't regret it and or your customer will be glad you did it too...

What I do is put jb weld under the magnet and place it exactly where it is supposed to go and clamp it down and let the jb weld ooze out and then put more jb weld on the surface of the flywheel around the magnet and up the all sides of the magnet about half way up or less on the magnet will do it - so now you got jb under and around it on the flywheel surface and up the sides of the magnet to lock it in securely and then let set for 24 hours.

Remember don't dare mix up the magnets. If you take your flywheel off and the magnets are knocked loose you can use a screw driver and put it on next to the magnet and hold a compass next to the screwdriver and if the magnet is north the red end of the needle will point towards the screwdriver. If the oppositte end of the needle points to the screwdriver then you know your working with a south pole magnet. In the direction that the flywheel moves while running the North pole magnet is used first then the south pole magnet so it has to be in sequence as N.S. to work....

It's a rare thing but sometimes magnets can loose their magnetism and result in weak spark but if you notice about equal pull when you try to take the screwdriver off of either pole magnet odds are they are ok to use...


Whew that was a long story short...

Threw a Rod
 
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#6
Tecumseh hints on motors that want to stop running or run rough

Make sure the kill switch wire is not grounded or shorting out causing it to die.

Check is there spark at the spark plug when it's laying on the head and visually see spark jump... Remember if a spark plug has been in a gasoline flooded engine it will never fire under compression even if you see spark.

if you have points and condenser check the gap on the points - condensors can go bad and nothing will work so might replace that before investing in a expensive coil.

Unhook all wires from coil and use a ohm meter put one end on the spark plug wire and one on the little wires coming out of coil and it should show maybe around 4 1/2 ohms and put the lead on the other little wire coming out of the coil and it should read the same.
sometimes coils short out inside of the coil because one of the really fine wires is partically melted and opening up when the motor gets hot and the motor will die and sometime will fire up just fine when cooled off only to quit running again when the motor gets hot again.

If you took the stator off then you will have to re-time the motor at the correct BTC settings. it may be firing to late and if it was firing to early it will buck the motor while you try to start it and jerk the rope out of your hand...

Check and see if the flywheel is cracked around where the crank shaft goes through it - that can cause a problem usually caused by inproperly torqed flywheel nut and the flywheel wobbled on the crank shaft and cracking the flywheel, also check both or all of the magnets with a screw driver - when your around 1 in or 3/4 in near the magnet it should pull it hard against the magnet if not it is weak and effects strong fire from the magneto... Also check if the key way is not sheared or partially sheared this greatly affects timing. Sometimes you can have the wrong keyway installed so check if it's the right one. There are a couple of different style's of keyways... Also make sure the flywheel is torqued back on to correct specs this can effect the way it runs if not tight enough it will wobble on the shaft. Make sure there is a concave washer behind the flywheel nut that helps keep the nut tight most motors flywheel nuts torque to 30 - 33 foot lbs for light frame motors and 35 - 40 foot lbs for medium frame motors but check your engine specs for your torque settings.

If you have spark and the motor dies after a while - check and see if the carb bowl is on correct and not turned to the point of not letting the float going all the way down like it's supposed to. the lowest point of the bowl is where the lowest point of the float rests against - if the bowl is spun around where the highest point of the bottom of the bowl hits the float when it comes down then your not getting a correct fuel level setting to run on.

Check if the gas cap is venting, check if the high speed jet is functioning properly and not corroded with grime and the hole is free and clear and not screwed in to tight causing it to run too lean. Check the float setting when it's closed to make sure your getting the bowl filled up to the proper level. Check for binding linkage on the governor rods and check the throttle shaft for binding or loose shaft bore's also check and see on certain models the butterfly on the throttle shaft can be installed upside down causing flutter in the way it runs... I've discovered in getting used engines most folks don't pay attention on how it goes back together or put the wrong parts in - like wrong keyways put in or even put keyways in backwards so beware and watch for governor rods put in the wrong holes and carb linkage put in the wrong holes on the throttle can disturb the way your engine runs...

Some things are obvious whats wrong how about electrical tape wraped around the coil wire because the outer covering is damaged. Coil wires get old and can break internally and cause weak sparks but also check for frayed wires any where you can and check and see if all screws and nuts and terminals are clean and tight. Any descreptancys can disturb the magnetic field for maximum fire power and weak wires will disipate voltage to the spark plug. If you have cracks in the coil wire then heave it...

Before taking any tecumseh stator off do this - Always accurately measure from 2 known points on the motor shroud housing and 2 known points on the top and bottom of the stator with a 1/64 steel ruler before you take any tecumseh stator off so you can reassemble without disturbing the timing settings...

Never let gasoline stay in your carb or gas tank for more than 30 or 45 days or it will break down and start to turn into varnish and plug all your jets up and it causes a bad running motor right off the bat.
always just let the motor run out of gas or just drain the carb and gas tank before storing the engine without use for a while or I'll guarantee you - you will be overhauling your carburetor for sure...

On one last note I've discovered on some motors besides tecumsehs when checking the points to open so you can check your BTC settings - you can't use a ohm meter because it grounds all the time and is useless when trying to use a ohm meter - anyway so the way to beat that one is to put someting real thin like a rolling paper for cigarettes in between the points and give it a slight tug while rotating the crank and when the paper comes loose and the points break imediately check the BTC settings and you can't go wrong doing this way but that depends on most of you on what ur smoking...
 
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buckeye

Well-Known Member
#7
Great info!!
This would be great for the tech section.
Thanks for a well explainedand very understandable explanation.
I have this one bookmarked.
 
#8
On one last note I've discovered on some motors besides tecumsehs when checking the points to open so you can check your BTC settings - you can't use a ohm meter because it grounds all the time and is useless when trying to use a ohm meter - anyway so the way to beat that one is to put someting real thin like a rolling paper for cigarettes in between the points and give it a slight tug while rotating the crank and when the paper comes loose and the points break imediately check the BTC settings and you can't go wrong doing this way but that depends on most of you on what ur smoking...
Just a note here on this point: The book says to remove the terminals off the points and isolate them so you won't read to ground until the points are closed.

A rolling paper would work, but if you're replacing points and condenser anyway as part of a rebuild, you've already got the wires disconnected. Good info and I know it's an old and still worthwhile post. :thumbsup:
 
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