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Discussion Starter · #1 ·
Got the deck on my 446 and finally got mowing but I'm having engine problems. Also I'm mowing some thick grass, this area I'm working on I mowed last fall and I'm just getting around to getting it knocked down for the first time. Several parts I have had to go over twice to get a good cut.

After about 20-30 minutes, the engine starts cutting out. The first time the left cylinder stopped firing and I crippled it back to the garage, let it cool off and pulled the cylinder heads thinking the worse that a rod broke but there was not mechanical noise or crunching. Didn't find anything wrong so I put the heads back on, torqued the bolts and it fired up just fine.

Headed back out and after 20 minutes or so, the same thing happened but not as worse in the sense that both cylinders were firing but if I put any load on it the engine would cut out and almost die.

I tend to think the of the worse when something like this happens but the overall feeling I have is that it's overheating as while I mowing in out in the open the entire front of the tractor is hot, even the dash tower is excessively warm.

When is does bog down, there is slight light colored smoke from the exhaust when the engine recovers after taking the load off it.

Right now my plan is to let it cool off and try it again in an hour. all engine sheet metal is in place, clutch fan is attached.

Not withstanding that, what could this be, carb problem? Gas? (I'm starting on the 2nd full tank since I got this 446 running)

Also this it the first time of really running it short of a few test drives and 30 minute tilling job, chances this 446 has been ran more in the last couple days than it has been ran the prior 5 years. Up to now I have no issue in any manner with the engine as when it runs it quiet smooth and has plenty of power.
 

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Discussion Starter · #2 ·
On the third try after it sat and cooled off for over 2 hours, it fired up and ran fine until suddenly just shy of an hour, the same thing happened.

Is this zebra just lazy and doesn't want to run for more than an hour? :sidelaugh:
 

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By chance, does this engine have the "old style" float in the carb? I had to replace mine several years ago because it would absorb the fuel and swell-up and stick. It was replaced with a brass float.
 

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Discussion Starter · #4 ·
geeco1 said:
By chance, does this engine have the "old style" float in the carb? I had to replace mine several years ago because it would absorb the fuel and swell-up and stick. It was replaced with a brass float.
It does but would that cause a ongoing issue once the float got saturated?

Mine comes and goes with the heat of the engine, once it cools off I'm good to go for another 30-40 minutes.

I think it might be the aftermarket vacuum fuel pump is the problem. When i got this 446 it was hanging off the side so I cut the hoses and tucked it all under the carb nice and neat. I'm beginning to think that the pump may have been put outside to keep it cooler. I have extra fuel hose, if I have time this evening i will move it back and see what happens.
 

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If you have the old foam type float then you need to upgrade it. Whether or not the float is contributing to the problem it will cause you problems until you fix it unless you only run ethanol free gas.

I doubt that the float is the issue at the moment, sounds more like an electrical problem. Have you replaced the points and condenser recently?
 

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Discussion Starter · #7 ·
Bart said:
If you have the old foam type float then you need to upgrade it. Whether or not the float is contributing to the problem it will cause you problems until you fix it unless you only run ethanol free gas.

I doubt that the float is the issue at the moment, sounds more like an electrical problem. Have you replaced the points and condenser recently?
I have a plastic float in the other Onan I have sitting in storage which I hate to steal it off that but I guess I should.

I haven't replaced the points or condenser, just cleaned and gapped the points.

Got it torn down now and I'm going to double check the valve gap and relocate the fuel pump to a cooler location. If that doesn't help I will swap the coil from the other Onan I have and go from there.

Now I'm trying to remember if it was missing one of the three screws that held the air cleaner on, if it fell into the carb then the engine ate it as I can't find it anywere in the carb or intake. I had the heads off yesterday so I know it's not in the cylinders or torn anything up. I suspect it's was already MIA as I do recall having the carb apart the first time and find a extra screw wedged in the choke butterfly (VERY lucky on that one!).
 

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Discussion Starter · #8 ·
Ugh, late night!

I rechecked the tappet clearance, seems the left side was off. Not sure why or if I messed up when I did it the first time.

One thing lead to another, had throttle cable issues as i found that the end were the cable attached was bent, had to take the levers off. re-ran the fuel pump lines and vacum line back over to the side of the engine instead of right on top of it.

Finally i go everything back togather and fired it up and it ran for a couple minutes and then died! Had no spark which I then gave up and went in for the night. This morning after coffee I had the idea to check the wiring since I hade the battery out messing with the throttle levers and found that knocked the hot wire to the coil off so all is good.

I will try mowing this afternoon and see if it behaves better.
 

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Discussion Starter · #9 ·
Did it again this evening. I'm fairly sure it's the fuel pump.

I put a new clear fuel filter on the line before it goes into the aftermarket vacuum pump, when the engine is cool, the filter fills half up with fuel, when it starts misfiring and stumbling after running less than an hour, there's hardly no fuel visible in the filter.

Either the heat is causing the pump to fail once it warms up or the the fuel level is getting lower in the tank after running and that the pump can keep up as long as it's not fighting gravity as hard.

I had an Onan carb pump on my B48 that I tried but it's needs new diaphragm and gaskets so it doesn't pump at all so I'm shopping for new fuel pump. I browsed on eBay for them and found the electric pumps but the price scared me since I'm a cheap-scape.

Any advice on getting a fuel pump, is it worth getting the Onan on the carb pump kit gaskets and diaphragm?
 

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Discussion Starter · #10 ·
Still having an issue so I'm going to confess something I did with a slighly different question.

If one re-used head gaskets instead of replacing them with new ones, could the engine be losing compression by blowing though a headgasket seal after the engine has been running at full thottle for say, 30-40 minutes? Once the engine cools off, the head gasket seal is restored and it's good to go for another 30-40 minutes? This is the only thing I can think of at this point.

Good news I guess is that the old fuel pump isn't bad but I do have a new Briggs pump installed including I ordered new head gaskets early this week. If the compression to the cylnders was being lost, would this also lose the vacum inpulse pressure to the fuel pump?

New head gaskets should be here to today so hoping this is the thing that will fix it. The 446 is cooling off in the garage waiting for the USPS mail to arrive.
 

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I'm of the mind to deal with the easy fixes first and my guess remains that you need to replace the condenser which often works fine until the engine heats up.

Also, the plastic float is going to cause you trouble until you replace it with a brass one--it's not a maybe thing, it WILL cause problems.
 

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Discussion Starter · #13 ·
All the metal tin is in place short of the exhaust heat shield that is on top of the left side exhaust which is there to protect the hood? both side metal plates are there.

I swapped the brass float from my other Onan engine with no effect, I swapped coil from it too with no result.

This weekend I will swap the condenser from other Onan and see what happens but one thing I starting to notice is that the engine is burning oil, esp yesterday when I pushed it hard tilling and I getting a lot of burnt oil deposits on the plugs. In cleaning the plugs, I'm seeing an improvement esp after running it hard and I noticed a white vapor that evaporated quickly from the right exhaust when I would try to restart the engine after shutting it off (almost as if unburnt fuel going to vapor and dissipating

Also, the new head gaskets came in yesterday and I put them on and torqued the head bolts which had no effect.

Almost to the conclusion that this engine needs rebuilt, the oil consumption is too high. After 2 hours of running, it's burning about a pint of oil which I'm watching very closely, so I think I'm going to swap in my spare B48 engine and see how it runs if I figure a solution for the exhaust since it's has the newer exhaust in front of the engine. That will give me the summer to rebuild this BF 16 hp.

There's not much more I can try at this point without tearing into the engine big time, I'm resigning myself to idea that I have a worn out engine.
 

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While the oil consumption is not a good sign I don't think it is related to the engine shutting down when it gets hot. In my experience, things that work well cold and develop problems when they heat up is because of an electrical issue.

You could do a leakdown test and that would tell you the condition of the engine. You might also want to make sure the breather is working properly as that can cause oil consumption issues.
 

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Discussion Starter · #15 ·
Bart said:
While the oil consumption is not a good sign I don't think it is related to the engine shutting down when it gets hot. In my experience, things that work well cold and develop problems when they heat up is because of an electrical issue.

You could do a leakdown test and that would tell you the condition of the engine. You might also want to make sure the breather is working properly as that can cause oil consumption issues.
How does one know if the oil breather is working? I'm getting a lot of oily smoke up into the air cleaner, I had the breather off when I adjusted the tappets and there wasn't much to it. Unlike the breather tube on my B48, the BF engine breather tube is a simple tube unlike the bigger tube on the B48 that has a fiber'ish thing in it to collect excess oil?
 

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You should be able to find information on servicing the breather in one of the Onan manuals. They should be cleaned periodically and there is a reed valve that may not be functioning properly. A faulty valve will allow crankcase oil to be forced up into the air cleaner housing where it will be fed into the carb and cause smoking as if the rings were bad.
 

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Here is a shot in the dark solution. When I bought my first Case tractor, a 1987 448, it did a very similar thing to what you are describing. I visited and joined the MTF site and asked about possible reasons that would cause this problem. I believe the thread was called "spontaneous shutdown" or something close to that.

A fine member by the name of Castoff gave me a detailed checklist to work through. It was a step by step electrical testing procedure that lead me directly to the ignition switch. I replaced the switch and never had the problem again. This may not be your actual problem, but it will lead you to any electrical issues that you might have.

Good luck. (I wonder what ever happened to that Castoff guy? :twisted: )
 

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e-boy
another thing.
the Bm and BG engines have a mesh screen inside the breather hose.
this helps keep the oil from reaching the air cleaner.
OF course i have the necc. parts for sale.
thank you. boomer (the used onan parts guy)
 
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