rScotty
Super Member
- Joined
- Apr 21, 2001
- Messages
- 9,504
- Location
- Rural mountains - Colorado
- Tractor
- Kubota M59, JD530, JD310SG. Restoring Yanmar YM165D
OK. You are making progress. That leak needed fixing and now it is. Although the knock may seem louder now, we know that neither the knock or what is causing it has actually changed. So that's progress too - even if it doesn't sound like it.
For internal noises I've never had much luck sorting out which cylinder is making a noise. About all I've ever been able to do is what you have where you say it seems to be coming from the rear or the front of the engine. A stethoscope doesn't seem to work for me for pinning down the location of internal engine noises. I do as well just - or poorly - just walking around the tractor.
Hmm.... that reminds me. I was going to ask how difficult it is to take off the hood. If you have to start messing with the top of the back of an engine sometimes it's easier to take the hood off to get some working space.
As for isolating the cylinder.... I agree that's what you need to do now... no matter what the cause. The best way I know of to do that is to deliberately cause a cylinder to stop firing and see what effect that has on the knock. I don't think we know at this point if disconnecting the cylinder will make it knock more or less, but you have 3 other cylinders to compare with.
In the day's of gas engines we would simply short out a spark plug to do this test. For a diesel we usually scandalize the fuel flow to the injector. Same thing..
To know how to scandalize the flow, we first need to know if your engine is mechanical injection or common rail? With mechanical injection, each injector is fed by a separate line from the fuel pump. 4 cylinders = 4 separate lines. There may or may not be glow plugs with an electrical connection for each cylinder, but the injectors themselves are totally mechanical; no wires go to the injectors.
To "defeat" (sounds better than scandalize) an injector, you slightly loosen that pressurized feed line either at the injector or back at the pump. This makes for a major leak of diesel fuel but you keep the wrench on the nut and tighten it to stop the leaking while you think about the change in sound that happened when you loosened it up and that cylinder quit firing. i.e. the change in noise - or not - when that cylinder was taken offline. Do it a couple of times, keep a towel handy. If that injector is good, then taking it off line is going to make the engine run real ratty, but not affect the knock. And if the knock changed when you cut off it's fuel, then that cylinder's injector is suspect.
Now try one one of the known good cylinders. Does that make sense with what we just heard?
Alternatively, if your engineis the more modern "common rail", there is a common overhead line fed by the single line coming from the injector pump and each cylinder is connected to that pressure line. Common rail uses a computer to decide when to electrically open an injector's solenoid valve, so to communicate with the computer each injector will also have a signal wire connected to it.
Oh, again, don't be confused by wires to the glow plugs. Depending on the model of engine there may or may not be a glow plug and associated wire for each cylinder - the glow plug circuit is the same for both mechanically injected engines or common rail type. Not all engines have glow plugs.
The listening for a knock is the same for mechanical or common rail diesel. But for common rail type you don't have to loosen a nut to keep the injector from firing, you just unplug the signal wire for that injector.
There is one other way "old mechanic's trick" to keep a cylinder from firing. You can take off the valve cover and while the engine is running at as slow of an idle as you can get, you can slide a feeler gauge that is a bit thicker than your normal valve clearance right where you measure the valve clearance - which is usually between the rocker arm and the EXHAUST valve stem. This holds the exhaust valve open by a few thousandths of an inch - don't use more than .005" extra thickness... what you want is just barely enough to make it stop firing on that cylinder. You don't want to force the valve head to hit the piston... As you do this, that cylinder is still getting injected with fuel, but it cannot fire because holding the exhaust valve open that much keeps it from compressing. It's like you had a cylinder-selectable compression release. Instead of firing, that cylinder goes "phut, phut...."
Don't do it for more than a few strokes and listen for changes in the knock as before. You won't hurt anything if careful.
There used to be go/no go feeler gauge sets made with extra long long feeler gauges that were real good for doing this test. But you can stack some feeler gauges together if you are careful. The trick is in sliding the gauges into that gap while the engine is running. It's a knack.
Lastly, an injector not working right should cause that cylinder to run differently from the others... but end cylinders run differently anyway even when everything is right. So temperature is harder to figure out. I've never done this, but I'd look with a thermal imaging gun right at where each cylinder's exhaust enters the exhaust manifold. Before thermal imaging guns, we used a set of colored chalk marks that were heat sensitive to see if the manifold or head had "hot spots". Then we would debate whether or not we had learned anything, and if so..... what it might be.*
Or as Click and Clack used to say, "Do two mechanics who don't know what they are talking about know more or know less than one mechanic that doesn't know what he is talking about?
That part hasn't changed, check aviation supply for the temperature-sensitive chalk. It works best on air-cooled radials. Less well on tractors...
Good luck,
rScotty
For internal noises I've never had much luck sorting out which cylinder is making a noise. About all I've ever been able to do is what you have where you say it seems to be coming from the rear or the front of the engine. A stethoscope doesn't seem to work for me for pinning down the location of internal engine noises. I do as well just - or poorly - just walking around the tractor.
Hmm.... that reminds me. I was going to ask how difficult it is to take off the hood. If you have to start messing with the top of the back of an engine sometimes it's easier to take the hood off to get some working space.
As for isolating the cylinder.... I agree that's what you need to do now... no matter what the cause. The best way I know of to do that is to deliberately cause a cylinder to stop firing and see what effect that has on the knock. I don't think we know at this point if disconnecting the cylinder will make it knock more or less, but you have 3 other cylinders to compare with.
In the day's of gas engines we would simply short out a spark plug to do this test. For a diesel we usually scandalize the fuel flow to the injector. Same thing..
To know how to scandalize the flow, we first need to know if your engine is mechanical injection or common rail? With mechanical injection, each injector is fed by a separate line from the fuel pump. 4 cylinders = 4 separate lines. There may or may not be glow plugs with an electrical connection for each cylinder, but the injectors themselves are totally mechanical; no wires go to the injectors.
To "defeat" (sounds better than scandalize) an injector, you slightly loosen that pressurized feed line either at the injector or back at the pump. This makes for a major leak of diesel fuel but you keep the wrench on the nut and tighten it to stop the leaking while you think about the change in sound that happened when you loosened it up and that cylinder quit firing. i.e. the change in noise - or not - when that cylinder was taken offline. Do it a couple of times, keep a towel handy. If that injector is good, then taking it off line is going to make the engine run real ratty, but not affect the knock. And if the knock changed when you cut off it's fuel, then that cylinder's injector is suspect.
Now try one one of the known good cylinders. Does that make sense with what we just heard?
Alternatively, if your engineis the more modern "common rail", there is a common overhead line fed by the single line coming from the injector pump and each cylinder is connected to that pressure line. Common rail uses a computer to decide when to electrically open an injector's solenoid valve, so to communicate with the computer each injector will also have a signal wire connected to it.
Oh, again, don't be confused by wires to the glow plugs. Depending on the model of engine there may or may not be a glow plug and associated wire for each cylinder - the glow plug circuit is the same for both mechanically injected engines or common rail type. Not all engines have glow plugs.
The listening for a knock is the same for mechanical or common rail diesel. But for common rail type you don't have to loosen a nut to keep the injector from firing, you just unplug the signal wire for that injector.
There is one other way "old mechanic's trick" to keep a cylinder from firing. You can take off the valve cover and while the engine is running at as slow of an idle as you can get, you can slide a feeler gauge that is a bit thicker than your normal valve clearance right where you measure the valve clearance - which is usually between the rocker arm and the EXHAUST valve stem. This holds the exhaust valve open by a few thousandths of an inch - don't use more than .005" extra thickness... what you want is just barely enough to make it stop firing on that cylinder. You don't want to force the valve head to hit the piston... As you do this, that cylinder is still getting injected with fuel, but it cannot fire because holding the exhaust valve open that much keeps it from compressing. It's like you had a cylinder-selectable compression release. Instead of firing, that cylinder goes "phut, phut...."
Don't do it for more than a few strokes and listen for changes in the knock as before. You won't hurt anything if careful.
There used to be go/no go feeler gauge sets made with extra long long feeler gauges that were real good for doing this test. But you can stack some feeler gauges together if you are careful. The trick is in sliding the gauges into that gap while the engine is running. It's a knack.
Lastly, an injector not working right should cause that cylinder to run differently from the others... but end cylinders run differently anyway even when everything is right. So temperature is harder to figure out. I've never done this, but I'd look with a thermal imaging gun right at where each cylinder's exhaust enters the exhaust manifold. Before thermal imaging guns, we used a set of colored chalk marks that were heat sensitive to see if the manifold or head had "hot spots". Then we would debate whether or not we had learned anything, and if so..... what it might be.*
Or as Click and Clack used to say, "Do two mechanics who don't know what they are talking about know more or know less than one mechanic that doesn't know what he is talking about?
That part hasn't changed, check aviation supply for the temperature-sensitive chalk. It works best on air-cooled radials. Less well on tractors...
Good luck,
rScotty
