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tecumseh no spark


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12-17-13, 08:04 PM   #1  
tecumseh no spark

7hp tecumseh snowblower. This is the older style, with the ignition device inside the flywheel.

Took it apart to replace the carb in the spring, figured I'd do a bunch of other stuff. Cleaned up parts, greased things, replaced the spark plug...

Once it was back together, I had no spark.
since then, I've:
-replaced the coil
-replaced the points
-gapped the points
-replaced the condenser
-replaced the coil again (three all told, including a brand new one)
-replaced the condenser (again)
all the while setting the gap to .020.

I tend to get a good strong spark at low speed, but as soon as the rpm goes up to running speed I run out of spark.

Finally, I took it to a shop. They said bad coil. I refused to believe it, paid them the $40 and left- only to find out they sheared off the key. Got a new key, problem persists.

I've bought a replacement engine now (going on 3' of snow on the ground) but I miss this one, and want to get it going.

Last week, I bought a whole new ignition thing- coil, points, body, etc all assembled. Installed it, gapped it, set the timing with my depth guage, and kicked it over. Started, ran crappy, but ran.

Then I put it back together to see if I could set the carb up, and the spark problem was back.

I've now torn it apart again, and gone over everything I can think of- and I just can not get a good spark at high speed.

What gives...?

 
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12-18-13, 04:20 AM   #2  
How were you determining you had spark at lower rpms and losing it at the upper range? It really sounds like a fuel/carburetor issue. As a rule, from my experience, if you've done and redone something with the same results, it usually turns out to be something else causing the problem.

However, if the spark was the problem you could replace the current ignition setup with an ignition module = no points and condenser. Then all you would need are good flywheel magnets (which never really fail) and a .010 air gap - module pickup to flywheel gap.

 
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12-19-13, 06:12 AM   #3  
The same way any sane person does- by removing the spark plug from the engine, plugging it into the plug boot, and grounding it- then turning over the engine to see if there's a spark.

I also have an inline spark tester, but I find in automotive use its unreliable, since it introduces an airgap prior to the spark plug

 
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12-19-13, 08:08 AM   #4  
From reading your posts I get the impression you believe you have the spark at lower rpms, but lose it at higher rpms. A possibility is the coil is at fault in not being able to saturate and discharge. Or the condenser may be draining too much from the coil, or the point gap may be too wide which gives you an advanced spark and poor coil saturation since the saturation occurs with the points closed = the duration of saturation is off.

If it runs good at the start and poorly in the upper range, I would still think in terms of fuel/carburetion.

 
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12-19-13, 10:20 AM   #5  
I'm also interested in how you determined it isn't getting spark at higher rpm. I'm leaning towards carburetor issues as well.


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12-19-13, 06:42 PM   #6  
I guess I wasn't very clear what I meant with lower RPM.


The engine will not start- or even kick over. If I turn the flywheel by hand, I can get a visible spark out of the spark plug if it is grounded and removed from the engine.

If I ground the plug and use the electric starter, I see no spark- if I let go of the starter switch, I might see two sparks in the last two revolutions of the engine... but nothing at higher rpms.

To be clear- I can spin the engine by hand faster than it is capable of creating a spark. I've gotten these same results with four different coils, three different capacitors (condensers), and three sets of points- in many different combinations... as well as a completely different ignition module consisting of all three components and its own iron core/aluminum body, off a different (running) engine, reset to .020 on this engine.

I suspect I'm missing something obvious- but I just can't figure it out.
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12-19-13, 09:21 PM   #7  
I see now. I saw where you got it running poorly and thought you meant it was cutting spark at high rpm. I'd lean toward condenser or coil then. It pretty much has to be one or the other assuming you've got the coil gap set properly (it's a pain to do on these engines).


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12-20-13, 05:29 AM   #8  
Well, as noted in several posts I've tried a handfull of coils and condensers- a mix of brand new and known working.

Is the coil gap something different than the points gap?
if so, is there a document or tutorial on setting it?

In my research I see lots of people saying to set a gap with a business card, but I suspect it's the gap between the iron core and the magnet- neither of which I can move here. Or can I? If so, this might be the thing I'm missing.

 
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12-20-13, 09:17 AM   #9  
The coil gap or air gap is the spacing between the coil pickups and the magnets on the flywheel. .010 inch will normally work for that on just about anything. That can be set using the business card as the gauge.

The point gap is the .020. That is the space between the contacts of the points when they are opened at their fullest. This can be critical because it affects coil saturation for spark discharge and the timing of the discharge, which is your ignition timing.

The condenser really isn't a capacitor.. The latter is used in a CDI (capacitor discharge ignition). The capacitor loads to capacity then triggers the discharge from the coil. This is pretty much what the points do with their opening and closing. When closed (grounding circuit) the coil saturates toward the ground. When the ground is cut (points open) the coil discharges and you get a high voltage spark for the spark plug.

In a point/condenser setup the condenser serves as a bleed off of excess voltage to protect the points from burning.

 
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12-20-13, 09:26 AM   #10  
I would leave the flywheel off to expose the points underneath. Take out the spark plug to make turning the engine over easier. Now turn the crankshaft a few times and measure the gap on the points.

Set that gap at .020 inch at its greatest point. Tighten down the points and clean them with acetone or any that doesn't leave a residue.

Now stick the rest of it back together and see where you're at.

 
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12-20-13, 09:33 AM   #11  
Unlike most other engines, this engine can't just be set with a business card. The coil is under the flywheel. Setting it requires special tools (dial indicator, 1/64th scale steel ruler). The process is described in the Tecumseh manual for L head engines pages 68 and 69. The condenser actually is a capacitor. Capacitors used to be called condensers years ago. With mechanics, the old term stuck.


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12-20-13, 10:59 AM   #12  
Cheese is right- the coil is under the flywheel, and the magnet is part of the flywheel. Good 70's design, I guess.

I've got a nice dial indicator, but not sure how I could measure this- and I'm fairly certain it can't be adjusted. I'll see if I can track down the manual, I assume its linked on this board somewhere

 
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12-20-13, 02:18 PM   #13  
The spark

The old flywheels had a hole in the face just for that purpose. You could drill a hole with a core drill but you would have to drill another one opposite side to balance the wheel. Just a thought. I guess about an inch to an inch and a half.
Sid

 
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12-21-13, 07:14 AM   #14  
I guess I'm just a bit slow; I'm using this manual, which seems to match my engine:
http://smallenginesuppliers.com/html...nformation.pdf

I've gone over the ignition chapter twice (pg 63 to 71) and I'm only seeing timing for adjusting the points in comparison to TDC by rotating the ignition assembly- I see no way of moving that iron core closer to the magnet- but I can potentially move the coil further up the iron shaft.

 
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12-21-13, 08:30 AM   #15  
I'm not understanding why you're wanting to change the relation of the coil to the flywheel magnets. A lot of adjustable coils/modules are adjustable towards the flywheel to use the coil in different applications and allow the locating of the coil relative to the magnets. If the coil you have isn't slotted at the mounting holes it isn't intended to be moved in or out.

The points are the critical component. The gap affects two things - the saturation time for the coil so at the breaking of the points the discharge can be at its greatest for the most efficient spark and the timing for the spark, which is critical for the running of engine. Some engines simply allow the gap setting to double duty for timing and saturation.

Others are setup with the points on a moveable base plate. for those adjust the gap of the points first, then time the breaking of the points relative to the position the piston is in the compression stroke. If you don't have timing marks on the engine crank, you may have to use the dial indicator I saw mentioned earlier or approximate the timing by locating TDC with a dowel against the piston through the plug hole and go from there.

Unless I'm missing something...

 
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12-21-13, 10:33 AM   #16  
The coil holes are not slotted for adjustment, but it is adjustable. Look at figure 4 on pg 64. The entire bracket has slotted holes. This is your adjustment. It's changes the point gap and the air gap. It's been a long time since I messed with one of these old engines. I don't recall how much the coil gap changes in relation, but it definitely changes the point gap. Anyway, if you aren't adjusting this properly, you don't know if it's set right. It's not just as simple as rotating the crank until the points open and set the gap.


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12-21-13, 11:00 AM   #17  
Marbobj-

I think I'm the one missing something, since I cant get this thing to spark at more than a couple rpms

I set the points to just open at .090 before TDC via dial indicator, as the book suggests, and as my first post explains I've replaced everything several times without luck- and the points themselves open widest at .020
I'm just completely out of ideas why it wont spark at this point.

Looking at figure 4 on page 64, I see the two bolt holes for rotating the assembly- but what isnt pictured is that the hole where the crankshaft passes through is machined to fit a lip on the block- this asembly can rotate, but not slide, so I cannot change the distance of the coil (or its iron core) from the magnet inside the flywheel... Unless the magnet in the flywheel can be adjusted closer to the coil.

 
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12-21-13, 04:04 PM   #18  
The slotted hole setup on P 64 is just a conventional point setup. Usually you see it more on larger engines. Motorcycles of those years have it a lot with battery coil/points. Cost effectiveness probably eliminated it on the small engines and the point gap took care of everything. Once the CDIs came in it was all a mute point anyway.

The slots are just for rotating the points on the ignition cam to adjust the timing. With the coil mounted on the base plate and rotated with the points it would maintain the focal point of the coil pickup to its exposure to the magnetic field at opening and closing of the points. There would be an advantage to that with the single pickup on the outside of the coil. The magnetic field is strongest at a single point and you would want that to pass the coil precisely for saturation. In the higher rpms it would all become more critical.

Coil air gaps are more a matter of the closer, the better without hitting something. The tolerance of the crankshaft bearings brings up the .010 gap as more of a standard. Using a business card is one thing, but using a sheet of paper wouldn't change the performance of the coil as long as the flywheel didn't strike the coil pickup.

In the case of this engine, I wouldn't get too excited about the air gap on the coil, I suspect it's fixed. The point gap is the critical setting. Then the timing by rotating the baseplate.

If you're getting spark the first couple of turns and you know for certain the spark is disappearing, it brings you down to the coil or condenser which is where Cheese pointed you. The points have to be clean and at least close to the .020 point gap. To get the engine to run properly, the point gap and timing will have to be set properly.

The .020 point gap through the air gap/pickup on the coil to the center of the magnetic field on the rotating flywheel magnets is the perfect alignment for the spark generation. From there forward, the introduction of the spark into the combustion chamber at just the right time determines engine performance as controlled by the ignition system.

 
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12-21-13, 04:26 PM   #19  
Just looking at this thing in another area. That engine has some type of brake with an ignition grounding inside the flywheel. I'd take a look at that and possibly disconnect it short term for testing purposes.

 
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12-21-13, 04:40 PM   #20  
the 'brake' is just a grounding thing- it grounds out the wire one of the points connects to, which kills the spark. It's been disconnected ever since I found out I'm arguing with a spark issue.


At this point it sounds like as long as the point gap is correct, and timing is anywhere close, I should be getting at least a consistent spark. I've tried a few different coils and a few different condensers, and now two sets of points, and a whole new assembly off another snowblower.

The only thing that's crossing my mind just now is that I have TWO flywheels- I would have told you yesterday I'm over 90% certain this one is from this engine, but it's entirely possible I screwed up at some point and the other one was off this engine. Would the magnet placement be different between flywheels when compared to the key?
I have to imagine the keyway in the crankshaft is identical based on where the nub for the point gap is, meaning all magnets would have the same placement- but I'll have to investigate this further.

 
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12-21-13, 04:58 PM   #21  
The brake is an engine brake to stop it from spinning. The ground is in it so the engine is killed and not trying to pull against the brake.


The placement of the flywheel key and whether the flywheel came from that engine wouldn't affect it generating a spark, if the diameter is the same on both. The running of it is another matter. What you need is a magnet moving in close proximity to the coil with the points opening and closing off the cam.

Did you wipe down the points with a no residue cleaner and make sure they are opening and closing fully?

 
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12-21-13, 05:04 PM   #22  
You're right, the air gap does not change. I was trying to remember how that system worked, but it does rotate around that boss in the center, only allowing adjustment in rotation.


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12-28-13, 11:12 AM   #23  
Well, I'm once again banging my head on this. I changed out the flywheel for another identical one I had, and wouldnt you know it, with the spark plug removed from the engine, at full starter power, it was getting a niceblue spark.

Installed the spark plug, tapped the starter, and it kicked over, ran for a moment, and sputtered out (carb needs to be set)

And then as if to mock me, the spark problem is back- anything faster than hand turning gives it no spark.

I'm out of ideas. Help?

 
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12-28-13, 12:35 PM   #24  
Check the condenser ground, make sure it is clean and tight. I think this one grounds through the case and mounting clamp. Also check to be sure the entire ignition plate is well grounded. If the condenser is filling up with a poor ground to discharge through, I guess that could cause this symptom.


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01-20-14, 08:38 AM   #25  
Well, after shelfing this for a while I cleaned everything with brake cleaner and it started right up. Thanks everyone for the help.
slapped it back on the blower and took it out for a spin-
Starting a new thread for my governor issue

 
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