YM2000 revs uncontrollably
- Thread starter yanmardoug
- Start date
- Views: 5872
clemsonfor
Super Member
I never paid close enough attention? I know you can rev it with foot throttle past the set hand throttle position as i do that when i get to a thick spot.
OP
yanmardoug
New member
Checked the throttles and linkages, everything seems fine with that. It will be a while, but I'll open it up and check the rings when I get the chance. Thanks to all for your replies. When I discover more about this situation, I'll post an update. Meanwhile, I have more pressing issues with 2 other yanmars.
Domush
Platinum Member
Might want to consider pulling off the injector pump first. it's really easy (4 bolts and a cotter pin) and then you can tell if it's an injector pump/governor issue. When it's off, slide the governor slide back and forth, seeing if it's free and press in the injector pumps to see if the resistance is the same for each one. They should be really hard to depress by hand and spring back immediately.
The piston rings hypothesis sounds dubious, as if it were the rings and burning oil.. how would you ever shut it down as long as there was still oil in the pan and air to burn it with? You couldn't. It has hours of fuel in the oil pan and you didn't mention killing the air supply, so it should have grenaded, not come back under control on it's own.
Something to think about.
The piston rings hypothesis sounds dubious, as if it were the rings and burning oil.. how would you ever shut it down as long as there was still oil in the pan and air to burn it with? You couldn't. It has hours of fuel in the oil pan and you didn't mention killing the air supply, so it should have grenaded, not come back under control on it's own.
Something to think about.
Domush makes good points. :thumbsup: I could tell you in 2 seconds if it had a bad cylinder simply by listening to it turn over. You can too if you know what to listen for you have another one just compare them throttle OFF cranking and listen for the "hitch" in its getalong or not if they crank the same its probably pump. hth.
Id look at the pump 95% chance imho thats where it is since the linkage is ok, might tap on it see if it will free up.
I have my doubts its a down cyl you yourself pegged the reason - compression to fire it that and only 1 other cyl to run it on. 2 cycle engines are a different animal thats just my professional opinion known to be wrong a time or two.
Id look at the pump 95% chance imho thats where it is since the linkage is ok, might tap on it see if it will free up.
I have my doubts its a down cyl you yourself pegged the reason - compression to fire it that and only 1 other cyl to run it on. 2 cycle engines are a different animal thats just my professional opinion known to be wrong a time or two.
OP
yanmardoug
New member
Thanks Domush:
It has been a while since I worked on this toy last and so I had forgotten a couple of things. I agree that the rings theory is dubious but I couldn't think of anything more plausible until I went back out and looked at the tracor. Then I remembered that when I did have it running before I pulled the head, the crank vent was venting air and what appeared to be atomized oil and pretty high pressure was building in the crank case (unscrewing the filler plug allowed a very forceful release of pressure). So, while I had the head off, I also removed the crank vent cover (just above the injector pump), inspected that cavity and replaced the cover. It seems to me that I recall having seen somewhere that there is some kind of governor linkage behind that cover. I don't believe that I even inserted so much as a finger inside that cavity. Is it conceivable that removing and replacing that cover could have created this problem.
It has been a while since I worked on this toy last and so I had forgotten a couple of things. I agree that the rings theory is dubious but I couldn't think of anything more plausible until I went back out and looked at the tracor. Then I remembered that when I did have it running before I pulled the head, the crank vent was venting air and what appeared to be atomized oil and pretty high pressure was building in the crank case (unscrewing the filler plug allowed a very forceful release of pressure). So, while I had the head off, I also removed the crank vent cover (just above the injector pump), inspected that cavity and replaced the cover. It seems to me that I recall having seen somewhere that there is some kind of governor linkage behind that cover. I don't believe that I even inserted so much as a finger inside that cavity. Is it conceivable that removing and replacing that cover could have created this problem.
Domush
Platinum Member
The high pressure in the pan may be a blown head gasket. Do you have an overflow bottle on the radiator? That is the easiest way to look for blown head gasket, as it will blow bubbles in the overflow liquid. (sadly, I know this from experience)
Maybe car doc has a theory on this one, as I don't see any alternative beyond a blown gasket or a seriously worn set of valve guides. Worn rings would push a decent amount of smoke out the exhaust at all times and you haven't mentioned any.
Sent from my SCH-I500 using TractorByNet
Maybe car doc has a theory on this one, as I don't see any alternative beyond a blown gasket or a seriously worn set of valve guides. Worn rings would push a decent amount of smoke out the exhaust at all times and you haven't mentioned any.
Sent from my SCH-I500 using TractorByNet
Broken/worn compression rings or damaged/severely worn piston or deep scratches in cylinder wall is the only things capable of creating such pressure in the crankcase that I can think of.
The head gasket could be installed wrong possibly and a oil drain passage was uncovered near a combustion chamber. I believe these can be installed front to backasswards at least mine could be elifino?
OP
yanmardoug
New member
Domush and Car Doc: Thanks guys.
Given that I almost exploded this engine the last time I had it running, I am hesitant to try any diagnostics which involve turning the engine over; despite the fact that I doubt that it would start. The only way I got it started the most recent time was by pulling it. I don't believe that there should be nearly as much pressure build up in the crankcase as I was experiencing. I'm not certain (I was kind of in panic mode trying to get it to shut down) but I think that it was putting out a significant amount of black (or maybe blue?) smoke the whole time it was running on the occassion when it revved uncontrollably. When I get a chance I will check the pump and governor as that should be a pretty quick job. However, I've pretty much resigned myself to the idea that the safest approach to diagnosing this problem beyond that is going to be to take a look at the rings, especially the ones in the cylinder in which the diesel ran through into the pan most quickly. I assume that if diesel under no pressure will leak past the rings that quickly then compression could cause air to leak past them to create the pressure I was having in the crankcase.
Since there are no discernable lands in the tops of the cylinders and no apparent scratches or gouges in the cylinder walls, the only explanation for the difference in the leak down time between the two cylinders is that the rings in the more leaky cylinder are stuck or significantly more worn than those in the other cylinder (and why would the rings in one cylinder wear dramatically more quickly than those in the other?). Obviously, as I tear into it, I'll closely inspect the head, head gasket, and the top surface of the block.
All of that, of course, unless one or more of you can give me a better approach.
Given that I almost exploded this engine the last time I had it running, I am hesitant to try any diagnostics which involve turning the engine over; despite the fact that I doubt that it would start. The only way I got it started the most recent time was by pulling it. I don't believe that there should be nearly as much pressure build up in the crankcase as I was experiencing. I'm not certain (I was kind of in panic mode trying to get it to shut down) but I think that it was putting out a significant amount of black (or maybe blue?) smoke the whole time it was running on the occassion when it revved uncontrollably. When I get a chance I will check the pump and governor as that should be a pretty quick job. However, I've pretty much resigned myself to the idea that the safest approach to diagnosing this problem beyond that is going to be to take a look at the rings, especially the ones in the cylinder in which the diesel ran through into the pan most quickly. I assume that if diesel under no pressure will leak past the rings that quickly then compression could cause air to leak past them to create the pressure I was having in the crankcase.
Since there are no discernable lands in the tops of the cylinders and no apparent scratches or gouges in the cylinder walls, the only explanation for the difference in the leak down time between the two cylinders is that the rings in the more leaky cylinder are stuck or significantly more worn than those in the other cylinder (and why would the rings in one cylinder wear dramatically more quickly than those in the other?). Obviously, as I tear into it, I'll closely inspect the head, head gasket, and the top surface of the block.
All of that, of course, unless one or more of you can give me a better approach.
clemsonfor
Super Member
If it could suck the oil past that one bad set of rings, you would sound like you were running on one cyl once you shut your fuel lever down, It would only run on the one cyl oil was getting in. So if it sounded smooth your gov linkage must be stuck.
