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Kohler M20 Twin cylinder, no spark with new ignition module


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07-27-17, 06:55 AM   #1  
Kohler M20 Twin cylinder, no spark with new ignition module

Bought this engine used, off a Ransomes rotary mower. I cannot get any spark out of it. The resistance from spark plug lead to the other spark plug lead is 14.8K. That seems to be out of the range of "22,000/42,000 ohms" specified in the service manual. The original ignition module tests at 30K but I get no spark from it either.

The service manual (page 8.2, Test #4) says "Module must have been 'fixed' to perform Test 4". Anyone know what this means? My test for spark was done with wire removed from module kill switch, one plug installed and the other held against block to observe no-spark.

If it's not the ignition module, what else could be preventing it from sparking? I'm a newbie at small engines. Could the flywheel magnet have gone bad?

Thanks for any suggestions, Rick

 
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07-27-17, 03:48 PM   #2  
Can you provide the model and spec # of the kohler?
Not sure how you are testing the mags but they should be tested separately and removed from the system. From the high tension lead to the stack/ground on the mag, 8k-20k ohms for most...but good ball park.
Check the air gap if mounted, should be .010 or the width of a business card.
Check your magnet by seeing if it will hold a large screw driver. They do but it is rare they fail.
I would need a wiring diagram to see how these are wired, could be a diode involved....

Marjbob and Cheese I think have a bit more experience with this so....


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07-27-17, 04:37 PM   #3  
Thanks BFHFixit for your reply. It's a Kohler M20 (the nameplate says M20S, not sure what the 'S' is for), Spec # 49500.

The ignition module on this engine serves both spark plugs -- unlike more recent Kohler twin engine models. So the resistance test I think is from the end of one spark plug lead to the end of the other. Or maybe I'm doing this wrong.

I've set the air gap to 0.14", using a feeler gauge, but I'm going to try the business card trick, maybe my gap is a bit too wide.

Rick

 
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07-27-17, 05:10 PM   #4  
I haven't messed with any of the M series kohlers in quite a while but best I recall, you unplug the kill wire and check for spark. If it has no spark and the plug is grounded and good and the air gap is correct, then the coil (module) is bad. I believe the ohm test is performed from the plug end to the metal laminations of the armature, not plug wire to plug wire. I could be wrong, been a while since I looked it up and I don't have my manuals right here with me.


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07-27-17, 07:21 PM   #5  
Ok so you have one coil/mag/ignition module for a twin...?
Seems you are using some manual or instruction for testing...Have you looked here it will only work with IE and you can simply accept the agreement and continue as guest. Once you find your manual it will tell you just who that engine was spec'd for and specific tests for that engine.
I also agree with cheese that the test is from the high tension lead to the "stack" lamination and or ground terminal.


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07-28-17, 07:16 AM   #6  
Thanks guys. I followed the link to the Kohler official parts and manuals; turns out I had the correct service manual for the M20S-49500. It looks like this is the basic engine; not built for a particular manufacturer. Here's a [URL="gravelymanuals.com/pdf/Kohler_M18_M20_Serv_Man.pdf"]copy[/URL

The flywheel magnet has no problem holding a large screwdriver. And I did reset the air gap using a business card. Still no spark.

I don't need much hooked up to test for spark, right? I had removed the flywheel (to re-glue a couple of the magnets on the back) so at this point none of the electrics are hooked up except the starter, the ignition module/coil and spark plugs. I'm thinking that the spark is generated simply by virture of the flywheel magnet moving past the coil and that I don't need to have anything else wired up.

I'm open to trying anything at this point. I'm heading off to work now but will work on this again this evening. Thanks again for your help.

Rick

 
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07-28-17, 10:26 AM   #7  
Make sure the coil isn't mounted upside down (flipped). I don't remember if you can do that on the kohler Magnums but you can on the commands and other engines and it doesn't work in that situation. It doesn't require any external electrical connection to generate a spark.


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07-28-17, 04:26 PM   #8  
You weren't getting spark prior to the work you did on the magnets. Is there a chance you glued them on in the wrong place?

 
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07-28-17, 04:53 PM   #9  
Cheese, don't think you can put the Kohler M20 ignition module on upside down. The bolt holes are offset so they would not line up in any other position.

 
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07-28-17, 05:00 PM   #10  
Thanks Marbobj. I think I put them in the right place, but who knows. But two things. First, your right that I was not getting spark before removing the flywheel. Second, I don't really understand magnetos, but I think the magnets on the back are related to the charging system (this engine uses a battery for the starter) and so they should not effect the ignition system. Or do I have this wrong?

 
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07-28-17, 06:03 PM   #11  
That's correct. Those are for the charging system. I'm not sure if they could influence the magnets providing the field for the ignition if mounted improperly.

Since you had no spark to start with those wouldn't matter. The module you have should provide spark if mounted properly. The module shown for that engine is a single connector for the kill. It's all pretty much a self contained ignition system if all the parts are good. Some of the two coil jobs get more involved with the kill circuit.

You might double check the grounding of the plugs. You disconnected the kill at the module, correct?

 
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07-28-17, 08:31 PM   #12  
The charging magnets won't influence the ignition components. If they weren't put in place in the correct polarity, they won't charge though.


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07-29-17, 10:13 AM   #13  
Well, I'm completely stumped. I now have 3 ignition modules: the original one (#1), the first new one (#2), and the second new one (#3). I purchased #2 off EBay and then complained to the supplier when I could not get any spark out of it. The supplier told me to keep it and they then sent me #3. Can't get a spark out of any of them.

They are all the same in appearance. Only difference is that #1 (the original) measures 30K ohms resistance from the end of one spark plug wire to the end of the other, while #2 and #3 show 15K and 14.8K ohms in that same test. The manual says this test should show 22K-42K ohms.

Yes, I removed the kill wire in all cases. When testing for spark, I install one plug and attach its lead. Then I attach the other lead to the other plug and hold it against the block to observe spark. The only indication I've had of anything is that I once felt some energy flow through my hand while holding the second plug to the block. But I think I need to see a spark if this engine is ever going to run again.

There's got to be some explanation -- surely all 3 modules can't be bad. Anyone have any idea what that might be?

Alternatively, where would be a good place to find a used Kohler M20 -- were these the engine on some popular garden tractor that I might be able to still find used somewhere? I need this engine for a sawmill I picked up a few months ago. It had a Kohler Command 25 on it, but had been left outside so long that the cylinders were so rusted as to be unrecoverable. This engine was intended to replace it, but it's not working out so well!

Thanks again for your help guys, Rick

 
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07-29-17, 01:46 PM   #14  
There are a couple of ignition coils that are connected to that engine. When I chase down the M20S number I get a 5258401 with two connectors on top. That number has been superceded by #5258402S. The coil you have has only the terminal for the kill.

The one you have may not interchange. Yours would be fixed timing. I believe a spark control box would provide variable timing. That may be what the second terminal provides.


Last edited by marbobj; 07-29-17 at 02:19 PM.
 
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07-29-17, 08:47 PM   #15  
Try checking it in the dark, if you are feeling the jolt, it's sending a pulse. Are you sure the plug is good? Is the engine turning slowly? If so, it may not generate enough to spark. That's a good engine and should hold up well pulling a sawmill, it is strong.


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07-30-17, 09:32 AM   #16  
In checking some other views of the module with the two connectors it appears the second is just a ground to the top plate. That being the case it leaves you with the single kill connector and it should give you spark with everything mounted and good parts.

It is unusual to have three bad modules. Is the new one a Kohler or a replacement part for a Kohler? Sometimes there's a language barrier .

 
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07-30-17, 08:15 PM   #17  
Okay, we're making progress, but I think I'll need a bit more hand-holding.

Took the engine to a guy down the road who buys and sells mowers, etc. He put a a spark plug tester on it and sure enough, it lit up on both sides. I'm guessing this means I'm getting a fairly weak spark, but hopefully it's enough to get this thing going.

So I brought the engine home, re-assembled the tin, put on the carb and intake manifold and exhaust manifold. The engine didn't come with a gas tank, so I gerry-rigged a line from a 1-gal gas can which I suspend overhead. I thought this would add some pressure to the fuel supply and help fill up the float chamber since I had previously removed and cleaned the carb.

A few minutes later, I notice that the bench top is wet with gasoline and then I notice that gasoline is sitting at the top of one of the spark plug holes -- the cylinder has filled up with gas! How the heck does that happen? Anyway, I've now hand-turned it over a few times to blow most of the liquid out of the cylinders. Also drained the oil out of the block, just in case it had been contaminated by gas (though didn't appear to have been). I'll leave it overnight for any remaining gas in the cylinders to evaporate and then try again tomorrow after work.

How could gas have got into the cylinders? Wouldn't it stop at the float chamber? Does this indicate some more significant problem? I've never seen this engine running, so I don't know where the last owner left it. In dismantling it, I only went so far as to pull of the heads -- everything looked okay to my untrained eye.

Thanks again for your help, Rick

 
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07-30-17, 10:32 PM   #18  
The float is stuck down, needle stuck open, something to that effect. It's not shutting the gas off when the bowl is full.


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