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regulator-rectifier for ch18 Kohler

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Hello again to all!

I have an agco-allis 918 with Kohler ch18 engine.  I think it is about a 1994-1995 model.  Engine numbers long since rubbed off of the stupid sticker Kohler uses.  Anyway, voltage regulator is bad.  Went to a dealer that sells Kohler parts to get one, he tells me this one he has, number 41 403 10-S will work.  It looks way thicker and I tell him I don't think it will bolt up where my old, thinner one was, but he assures me it will.  Well, it will not!  My old one has a number on it, it is        4 173.  My engine does not have the sam module for spark advance, it is a fixed timing engine.  Is there a new regulator that will fit?  Or if not, can I bolt the one I got anywhere on the engine to make it work?  Not many options for mounting other than the original place.  It is in the plastic shroud and then has a ground wire running to it from the metal that the shroud bolts to.  Anyone have any info, advice, or ?  This is my winter tractor so not in a hurry to get it going, but I do need it to charge the battery for next winter.

Thanks for any info!


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You have a spec 62513 CH18 engine.

The original part number was 25 40303-S; now part number 25 403 37-S.  You have the wrong part.  

The regulator is designed to be in the engine blower air stream for cooling; it has small fins on the side that mounts into the blower housing.  

It should look like this:


(Note the pins are bent in the pic, they should be sticking straight out.)

I'd get the correct part.  Depending on the size of the fins on the one you bought and the charging load, it might overheat and fry the internal components.  Regulators designed to be mounted in "open air" usually have much bigger cooling fins.  

I made a parts manual for the spec 62513 CH18 engine from online screen shots.  It's available in the "Downloads" forum:


I prefer to look up the part numbers myself rather than relying on today's "parts guy".  

PS - Did you check the AC voltage from the stator?  Should run around 30 amps if I remember correctly.  


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Bill, the number you gave in your reply for what should be the correct part looks just like the one I bought, with the three pins under it.  Mine has the three pins protruding out the side more, and looks more like a part number 25 403 10-S.  What are the differences?  The one I bought, and the one you give the number for, won't fit in the pocket in the shroud and when pushed down into it the wires cannot be hooked up.  I can get pics of the thing if that will help.  I don't understand what the different regulators do differently, I assume they all put out 12 volt ac current.  What am I not seeing?

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I checked a little more at OPE Engines for part numbers.  For part listing 25 403 37-S, the regulator you bought (41 403 10-S) is referenced in the "replaces" part listing numbers ( as is the original 25 403 03-S and some others),  A pic from the web site for part 25 403 37-S. 



The regulator pic I included in my first response had the leads damaged - they were all pushed down.  They should be straight out to more easily attach the connector.  Other pics of the regulator before I bent the leads back to straight:



Here's an installed pic of it after the leads were bent back:


As long as the protruding part of the metal case is the same size and the distance between the mounting holes is the same, the connector would slide on without a problem. 

If you still are having problems, post some pics of what you're dealing with.  I'll measure the distance between the mounting holes if needed.  


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The protruding part of the case is longer on the new one, about 1/16 of an inch, which is why it doesn't fit.  I am wondering if I put two washers under the regulator to space it up some if that would be ok, it will allow air to escape around it and also maybe crud to get in.  If I do that, the wires will then hook up.  I see on your pic that the blower housing does not have a lip that comes up around the regulator as it sits on the housing.  Mine has a lip that sticks up about 1/8 inch all around, making in effect a deeper pocket for the regulator.  If the regulator did sit all the way down in the pocket, the pins would then not stick above the lip enough to get the wires hooked up without bending them pretty sharply outward.  

Do you think the washers spacing it out will work ok?

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46 minutes ago, steve-wis said:

Do you think the washers spacing it out will work ok?

I think spacing it out with washers would be OK. 

Or trim the plastic blower housing so that the new regulator fits (including the side of the lip so the wires can be connected.

The blower housing in my pic above is not a Simplicity OEM original spec 62513, it's one I picked up to convert the engine to a "chopper screen" setup.  You wouldn't think the hole would be that different between blower housings,  but they are.  Here's a pic of a spec 62501 blower housing (before I replaced it with the one above):  IMG_4623.thumb.jpg.baecf043a47cace60d813ff99b1dd673.jpg

It has no lip at all!


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Success!  I went back out to take pics and shoved the new one into the hole again.  This time I noticed that it wasn't hitting at the bottom on the fins, but around the ends of the regulator.  The old one was shaped a bit different on the ends.  I opened up the end of the hole a bit and sure enough it went in.  I now have it installed.  Sitting not running with key on, 12.1 volts at the battery.  Start it up and I have 14.3 volts.  Assume this is about right.  If I turn on the headlights with it running they don't dim with the engine slowing down so I guess it is covering the demands for voltage.  I did need to bend the pins just a little to get the wiring harness to hook up.

Thanks for the help!  Now I have to do some carb work, then it is ready for next winter.  Going to take out the high end jet and open the hole a few thousands so I don't have to run it with a third choke in the winter.

Thanks again!


Edited by steve-wis
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