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Discussion Starter · #1 ·
Just got this tractor http://casecoltingersoll.com/showthread.php/42058-Case-446-78-bought-on-a-whim

Ran a bit off at first, but it turned out the plugs were mismatched and not tight. New plugs screwed in tight and it ran smooth. Then, after about 4 hours, running out of gas, turned the key to off, big backfire. Fueled up, started hard, ran weird, alternating from running to nearly stalling, like there was a fuel line problem. Then it pooped out entirely and I parked it.

Next day power washed it in preparation for working on diagnosis and repair. Noticed busted exhaust pipe, welded it. Had issue with wet condenser (see power-washing step earlier). Replaced condenser. Now it will start, after a lot of tries, run for a less than a minute--badly--then poops out.

Here is before and after video:


Where do I go from here?
 

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Considering you ran it dry I would check from fuel tank to carb. Does it have a fuel filter? The fact it ran on prior for 4 hours I'm guessing you dragged some junk the bottom of your fuel tank into the line. Either it's caught up in the needles in the carb or somewhere in the fuel line. That may be a good starting point.


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That looks like an intake valve is stuck open for some reason, lots of vapor being blown out of the carb! Maybe something got dropped into the engine while working on the exhaust?? That's not a P, so not likely to be a valve seat.__ If it's been a while since it ran last, it may just be stuck. I'd do a quick compression check, put some seafoam in the gas, and pour some into the intake while running, then let it sit for a few hours.
 

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I can't tell with certainty, but running it without the #2 cylinder baffle will make it run hot and increase the likelihood of valve problems.:think:
When I see an Onan missing the baffle I assume the owner has had engine problems or is unaware what problems it causes.

Jim
 

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Discussion Starter · #5 ·
Been working this through with a friend who is an automotive engineer, who works with a bunch of Onan fans, including one who used to work at Onan. Their diagnosis is that the engine needs a complete rebuild. They suggest repowering the tractor in the mean time, because I need it for work and that's the fastest way to get back up and running.

The problem is that I'm also pretty exposed already, having put out nearly everything I could afford for the tractor in the first place. My choices all seem to come down to spending as much as I spent on the tractor again, either to replace it with a new/used tractor, buy a repowering kit, or pay someone a ton to overhaul the Onan.

Really struggling with deciding what to do here. Is there any way out of this for under $1,000 that doesn't also involve a bunch of tools and fab skills I don't have?If not, what would you do in my situation?

I live in southwest Michigan. Is there anyone near me who could even work on this engine if I could afford it?
 

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I don't understand how, after running fine for 4 hours, the Onan fans conclude it needs a rebuild. Casenoob laid out the path i'd follow. Fuel related problem - work on the fuel line - tank, actual line, and carb. Incidentally, when shutting small engines down, i usually take them to slow idle for 20 seconds, before terminating ignition. Once you've solved the problem, switch to non-ethanol gas. It's a good tractor. Good luck with it.
 

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kwixon

I don't know what they used to diagnosis your Onan!
It was not smoking prior to running out of gas and sounded good, this is subjective on my part from what I see and hear on the video.
Did anyone do a compression or leak down on your engine? Rarely do I find an Onan requiring a complete rebuild unless it has thrown a rod.
Valve work, cam bearings, rings and sometimes pistons, broken cam gear ect. IMHO a compression/leak down would tell volumes regarding the overall condition of your engine. New Onans to me all get a good cleaning and checkout, most of them a good carb. cleaning, replacement of all rubber lines, fluids and filters, points filed and set, decarboned, tappet adjustment. IMHO verifiable diagnostics will lead you in the right direction, one would be amiss to go solely off the video.:think:

Thanks
Jim
 

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Well, it may well require a rebuild to be in A+ condition .. But, it doesn't necessarily follow that a rebuild is needed to get it into usable condition. I would certainly dig into it a little before condemning it. Compression check, leak down test, do those , pull the heads, examine the valves and bore, etc, then make a decision.
Onans often can be made very serviceable by rings, valve work and gaskets. Certainly under your $1k figure. More like $3-500.

gather some more info and revisit with us.

l
 
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