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B48m In A 448, I Hit Something Then Needed A New Coil

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#1 marlboro180 OFFLINE  

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Posted February 25, 2013 - 10:57 PM

So, a few days ago in a snowstorm ( errr, flurry ) I hit something in my driveway, a frost heaved rock that tripped the plow springs . The Normally stout running 448 went from running great, to a pair of gerbils running around in the motor. I thought at first the carb took a shot, but after diagnosing that, nope. Right cylinder just not running right, no power to speak of, exhaust smelled bad, ran funky after going over a bump or two.,..


So Sunday afternoon I spent going through things a bit, and just keep in mind I had this Onan running pretty darn well this fall.  What I did Sunday:


Set points to .021", they were worn down to .016,. cleaned 'em with the dollar bill trick.


Adjusted R  side valves to .005 , and .013.


Adjusted L side valves, actually exhast only,  to .013". I did not have the time to do the intake, as the intake manifold must be taken off to do this unless one has a special 3 knuckled wrench I think. But it was at .007 " anyways, so close enough anyways.


Put some new plugs in the thing, Autolite 437's, and ran it around for a bit even though it was still sounding doggy and had little power. Left head was running 235 F, and Right head at 110 F, hmmmmm



Popped the heads, and de-carboned them, nothing serious, just a light coating of carbon.


Put it all back together, and went back out to load test it. Still a dog, less so, but still a dog.Pulled her up to the shop, let her cool down and scratched my beard a moment......


This thing fires both plugs at the same time , Right????   Swap the plug wires  fool....


The dog of a cylinder came alive, and the other one ( lefty ) went weak.


Out came the coil, onto the bench and I got 4.3 Ohms between the + and - side, and 34K Ohms between the spark plug terminals. That, my frienss, is terminal.














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#2 Moosetales OFFLINE  


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Posted February 25, 2013 - 11:13 PM

Ouch. Glad you figured it out. I was up the road the other day throwing snow and all of the sudden I lost power. The throttle lever was up all the way but I had no power. I throttle her back and limped back to the garage. Once back I took a quick look around and slowly throttled her back up. Much to my surprise (and consternation) she fired right back up to full throttle. As you said....scratched my head and took another look. Come to find out, the throttle cable housing was slipping through the fastener and causing the cable to throttle down without moving the lever. I tightened things up and the problem was fixed. Of course I was sweating bullets as I had 12 inches of snow up my lane still to blow so I was grateful it wasn't anything too involved.

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#3 marlboro180 OFFLINE  

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Posted February 26, 2013 - 09:41 AM

Not sure why the rest of the post did not show up,  but here's the rest....


Yesterday my lovely bride was able to stop by our local Onan distributor and pick up a coil for me.  When I got home from work I eagerly went to work putting it into the 448. 10 minutes later, the 448 fired right up to her normal ways.  Once warm, just a tickle of the starter and she fires right off, and purrs down to a nice loping idle.


I took some temps at the heads and exhaust just to make sure things were going well, and the right and left were fairly nicely matched.  A good sign for sure.


Not being satisfied with just sitting there watching it run, running the throttle up and down.... I took off down the driveway and pushed back snowbanks just to make sure it ran just as well under load. I have to say it runs even better then I have ever had it running before. Smoother , quieter, and much more grunt. Pushed a  load of snow into the woods just because I could . :thumbs:  I pushed that pile up against a tree in an attempt to bog the motor, but all that happened was the loaded tires churned and churned while the motor hardly noticed.


A note about the coil- At first glance, the old coil did not look damaged to me , but once I had it out, there was a visible crack in the little raised black plastic box area between the epoxy bedded  terminals. I do not know if the shock of my hitting that rock was enough to do any damage, ( kinda doubt it, really) but it might  have been enough to do it in.  I'd say either way it was eighty bucks well spent for the new coil, as the 448 runs like a champ.   :dancingbanana:


We are supposed to get some more snow starting tonight, I say bring it on. :D


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#4 John@Reliable OFFLINE  


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Posted February 26, 2013 - 10:00 AM

Glad it was an easy fix!

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#5 superaben OFFLINE  

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Posted February 26, 2013 - 10:16 AM

Good diagnosis!  I guess the coil was just going out, and that bump gave the final umpf it needed to blow.  I've just never heard of that happening!


Ben W.

#6 marlboro180 OFFLINE  

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Posted February 26, 2013 - 03:02 PM

I think you are right about the final blow Ben, and I have to say I never heard of this happening either, dunno.