Piston 2 or 3 bent or by design. d950

[JerryMT]

I said "Perhaps..."

My thought was that the compression testing meter probably has a very small orifice for GAS (as in solid, liquid, gas) to pass through. Liquid being much more viscus than a gas, might offer enough resistance to flow that the orifice would for practical purposes be blocked, and with no place for the oil to go quickly, the cylinder could become hydro locked.

It might take a few more revs during cranking to reach max pressure but oil wouldn't be solid enough to not transmit pressure. The compression testers that I am familiar with don't have an orifice in them. Orifice's by themselves slow the response and I doubt that they are used but I won't say that no compression tester has them.

 

[Henro]

It might take a few more revs during cranking to reach max pressure but oil wouldn't be solid enough to not transmit pressure. The compression testers that I am familiar with don't have an orifice in them. Orifice's by themselves slow the response and I doubt that they are used but I won't say that no compression tester has them.

EDIT: Sorry, I thought you were the OP of the thread.

I do not know. It was just a thought. BUT my guess is the connecting rod [of the OP's tractor} bent the first time the piston came up, IF it was bent due to a hydro lock situation. If the piston did not hydro lock on the first turn, it should not on later turns, it seems to me. But like I said previously, this is just speculation by a non mechanic.

A further thought would be, is there a chance it [the OP's connecting rod] was bent when in the possession of a previous owner? I forget what he reported above, but will look back after posting this reply.

 

[GeoHorn]

JerryMt,

Since you are so insistent upon precise terminology…

Viscus: An internal organ of the body, specifically one within the chest (as the heart or lungs) or abdomen (as the liver, pancreas or intestines). "Viscus" is the Latin word for "an organ of the body." The plural of "viscus" is "viscera.

My previous comment was simple to understand for anyone who has serious experience working on engines. Diesels usually do not have the same piston-to-head clearance that gasoline engines do and putting oil …even minute amounts…into the cylinder and cranking the engine can result in bent rods.

But if you have sufficient viscus….. go for it and see how you make out.

 

[JPB7745]

I used to work for a turf dealership who sold equipment for golf courses and the Jacobsen turf-cat mowers had the D950 engines in them. We were sent to the Kubota plant in Atlanta for class on them and had to do a complete rebuild of the D950. I don't remember why but It did stick with me that the #2 piston had a longer stroke than the #1 and #3.

 

[JerryMT]

JerryMt,

Since you are so insistent upon precise terminology…

Viscus: An internal organ of the body, specifically one within the chest (as the heart or lungs) or abdomen (as the liver, pancreas or intestines). "Viscus" is the Latin word for "an organ of the body." The plural of "viscus" is "viscera.

My previous comment was simple to understand for anyone who has serious experience working on engines. Diesels usually do not have the same piston-to-head clearance that gasoline engines do and putting oil …even minute amounts…into the cylinder and cranking the engine can result in bent rods.

But if you have sufficient viscus….. go for it and see how you make out.

I did not use the word "viscus". The term I used was viscosity which is defined as : the property of resistance to flow in any material with fluid properties (Meriam-Webster)

 

[Pau7220]

Did someone leave CNN on?????





Let's go Brandon!!!!!

 

[lugbolt]

These are indirect injected engines. When you pour oil into it, most of it sits in the prechamber for a bit. By time you get the glow plug back in, some of it has dripped down into the cylinder. If you're lucky a valve will be open and it'll blow it out. If not, it'll make a half stroke and, well, it won't compress oil....something's gotta give (usually the rod, though I've seen broken crankshafts too). You put, 7 or 8 cc of oil into the engine, piston is 3/4 the way down the cylinder on the intake stroke. Put the glow plug back in, hit the key, there is enough inertia from the weight of the crank flywheel and accessory drive such that you may not even know it happened. That is exactly what happened in my case. Never even knew it but sure enough got a weak/smoking cylinder afterwards.

also putting oil into a diesel cylinder is not a good idea on account of it being a compression-ignition engine. It can try to start, it will run on oil. So if you are doing a compression test, because the engine can ignite the oil, it throws your readings way off. I actually destroyed a gauge doing this...

Did some Daihatsu stuff-, the morons who built/designed the motor actually put a vent from the valve cover directly to the intake manifold, that ran kinda downhill. If you filled the engine too quickly while doing an oil change, the valve cover area would fill up, some of it would overflow through the vent and into the intake. I had to replace several crankshafts, and lots of rods due to this issue. I caught a couple of them before oil got into the intake, and learned what was causing it.....worked with the manufacturer and they changed the vent tube shape such that it has a bend in it which must face upward (toward the top of the motor) so that when an oil changer pours it in too fast, it will run out of the fill hole long before it ever overflows through the vent.

I have been through this. It doesn't take much to cause bent rod. Remember, I learned the hard way on almost everything that I know, which may not seem like much. Maybe it isn't but hopefully it's enough to help y'all. Or maybe the rod was already bent. Regardless, it's gotta be fixed. When I see a bent rod I assume that the piston crown is compressed, the pin can be compromised as well so I always recommend checking the integrity of the cylinders (round, no taper, within spec), if ok then replace the rod, piston, pin, and rings and hope the crank ain't twisted. It's not common with kubota as it is with Diahatsu.

 

[JerryMT]

These are indirect injected engines. When you pour oil into it, most of it sits in the prechamber for a bit. By time you get the glow plug back in, some of it has dripped down into the cylinder. If you're lucky a valve will be open and it'll blow it out. If not, it'll make a half stroke and, well, it won't compress oil....something's gotta give (usually the rod, though I've seen broken crankshafts too). You put, 7 or 8 cc of oil into the engine, piston is 3/4 the way down the cylinder on the intake stroke. Put the glow plug back in, hit the key, there is enough inertia from the weight of the crank flywheel and accessory drive such that you may not even know it happened. That is exactly what happened in my case. Never even knew it but sure enough got a weak/smoking cylinder afterwards.

also putting oil into a diesel cylinder is not a good idea on account of it being a compression-ignition engine. It can try to start, it will run on oil. So if you are doing a compression test, because the engine can ignite the oil, it throws your readings way off. I actually destroyed a gauge doing this...

Did some Daihatsu stuff-, the morons who built/designed the motor actually put a vent from the valve cover directly to the intake manifold, that ran kinda downhill. If you filled the engine too quickly while doing an oil change, the valve cover area would fill up, some of it would overflow through the vent and into the intake. I had to replace several crankshafts, and lots of rods due to this issue. I caught a couple of them before oil got into the intake, and learned what was causing it.....worked with the manufacturer and they changed the vent tube shape such that it has a bend in it which must face upward (toward the top of the motor) so that when an oil changer pours it in too fast, it will run out of the fill hole long before it ever overflows through the vent.

I have been through this. It doesn't take much to cause bent rod. Remember, I learned the hard way on almost everything that I know, which may not seem like much. Maybe it isn't but hopefully it's enough to help y'all. Or maybe the rod was already bent. Regardless, it's gotta be fixed. When I see a bent rod I assume that the piston crown is compressed, the pin can be compromised as well so I always recommend checking the integrity of the cylinders (round, no taper, within spec), if ok then replace the rod, piston, pin, and rings and hope the crank ain't twisted. It's not common with kubota as it is with Diahatsu.

I was able to find some data for the d950 Kubota engine. the Bore and stroke are 3 x 2.8 inches and the compression ratio is 18.1 this yields a combustion chamber volume of 1.093 cu in or 17.910 cc

These are indirect injected engines. When you pour oil into it, most of it sits in the prechamber for a bit. By time you get the glow plug back in, some of it has dripped down into the cylinder. If you're lucky a valve will be open and it'll blow it out. If not, it'll make a half stroke and, well, it won't compress oil....something's gotta give (usually the rod, though I've seen broken crankshafts too). You put, 7 or 8 cc of oil into the engine, piston is 3/4 the way down the cylinder on the intake stroke. Put the glow plug back in, hit the key, there is enough inertia from the weight of the crank flywheel and accessory drive such that you may not even know it happened. That is exactly what happened in my case. Never even knew it but sure enough got a weak/smoking cylinder afterwards.

also putting oil into a diesel cylinder is not a good idea on account of it being a compression-ignition engine. It can try to start, it will run on oil. So if you are doing a compression test, because the engine can ignite the oil, it throws your readings way off. I actually destroyed a gauge doing this...

Did some Daihatsu stuff-, the morons who built/designed the motor actually put a vent from the valve cover directly to the intake manifold, that ran kinda downhill. If you filled the engine too quickly while doing an oil change, the valve cover area would fill up, some of it would overflow through the vent and into the intake. I had to replace several crankshafts, and lots of rods due to this issue. I caught a couple of them before oil got into the intake, and learned what was causing it.....worked with the manufacturer and they changed the vent tube shape such that it has a bend in it which must face upward (toward the top of the motor) so that when an oil changer pours it in too fast, it will run out of the fill hole long before it ever overflows through the vent.

I have been through this. It doesn't take much to cause bent rod. Remember, I learned the hard way on almost everything that I know, which may not seem like much. Maybe it isn't but hopefully it's enough to help y'all. Or maybe the rod was already bent. Regardless, it's gotta be fixed. When I see a bent rod I assume that the piston crown is compressed, the pin can be compromised as well so I always recommend checking the integrity of the cylinders (round, no taper, within spec), if ok then replace the rod, piston, pin, and rings and hope the crank ain't twisted. It's not common with kubota as it is with Diahatsu.

Lugbolt makes some good points.

The procedure I found for Kubota recommended compression testing calls for removing all the injectors, attaching the compression gauge and cranking until max pressure is achieved on the gauge for each cylinder. If the pressure is below spec, add 1 ml of engine oil and repeat.

As far as combustion chamber volume, the Kubota d950 bore x stroke is 3.0 inches x 2.8 inches and the compression ratio is 18.1. This means the combustion chamber volume is 1.093 cu in or 17.910 cc. When you add the compression tester, the hose adds some volume to the system so there is some margin there. So you would have to add a lot of oil to the cylinder in order to hydrolock it by compression testing.

With out data to the contrary, it seems doubtful that the OP could have damaged the engine via a compression test however it can't be conclusively ruled out.

 

[Henro]

I was able to find some data for the d950 Kubota engine. the Bore and stroke are 3 x 2.8 inches and the compression ratio is 18.1 this yields a combustion chamber volume of 1.093 cu in or 17.910 cc

Lugbolt makes some good points.

The procedure I found for Kubota recommended compression testing calls for removing all the injectors, attaching the compression gauge and cranking until max pressure is achieved on the gauge for each cylinder. If the pressure is below spec, add 1 ml of engine oil and repeat.

As far as combustion chamber volume, the Kubota d950 bore x stroke is 3.0 inches x 2.8 inches and the compression ratio is 18.1. This means the combustion chamber volume is 1.093 cu in or 17.910 cc. When you add the compression tester, the hose adds some volume to the system so there is some margin there. So you would have to add a lot of oil to the cylinder in order to hydrolock it by compression testing.

With out data to the contrary, it seems doubtful that the OP could have damaged the engine via a compression test however it can't be conclusively ruled out.

This is very interesting. Only thing I can think to ask is are you sure you do not have the decimal place moved one position?

Don't have a horse in this race, but also put a lot of faith in experienced posters who actually work, or have worked for years, on Kubota tractors...

 

[JerryMT]

This is very interesting. Only thing I can think to ask is are you sure you do not have the decimal place moved one position?

Don't have a horse in this race, but also put a lot of faith in experienced posters who actually work, or have worked for years, on Kubota tractors...

You can run the numbers yourself. I ran them twice and got the same result. There is nothing magic about Kubota diesels. The fundamentals are all the same, just the execution is slightly different.

 

[Fordtech86]

This is very interesting. Only thing I can think to ask is are you sure you do not have the decimal place moved one position?

Don't have a horse in this race, but also put a lot of faith in experienced posters who actually work, or have worked for years, on Kubota tractors...

He is showing the volume in the combustion chamber (piston at TDC) not over all volume of the cylinder.

And this part not directly towards you, just to the general thread…

Going back through engine was already worn before this. 150 compression across the board, being a mower I would suspect possibly its dusted. Also the rod bearing failure did not happen during a compression test, that happened over time. End of that rod can overheat due to lack of oil supply and it can bend from compression forces over time and repeated overheating (of the rod end). You would be surprised at how long some engines can run knocking. On a mower it could be hard to tell with all the noise.

Just sounds like a rebuild in order, given parts are available.

 

[Henro]

You can run the numbers yourself. I ran them twice and got the same result. There is nothing magic about Kubota diesels. The fundamentals are all the same, just the execution is slightly different.

Your numbers are good as far as I can see. Actually would be a bit different probably since you do not account for whatever the amount of volume might be in the cylinder head. I have read here that kubota pistons come very high in the cylinder bore, almost flush with the block surface.

So if you did not put excessive oil in the cylinder in my mind it points to the possibility/probability of it being damage that occurred before you took possession.

 

[JerryMT]

Your numbers are good as far as I can see. Actually would be a bit different probably since you do not account for whatever the amount of volume might be in the cylinder head. I have read here that kubota pistons come very high in the cylinder bore, almost flush with the block surface.

So if you did not put excessive oil in the cylinder in my mind it points to the possibility/probability of it being damage that occurred before you took possession.

Actually my numbers account for whatever volume is in the combustion chamber because that is the way the compression ratio is defined. It is a ratio of the volume swept by the piston as it moves through it's stroke to the volume of the combustion chamber.
That was my point. The OP very likely didn't cause the damage by doing a compression check. He needs to fix the motor not feel guilty about causing the problem.

 

[Henro]

Actually my numbers account for whatever volume is in the combustion chamber because that is the way the compression ratio is defined. It is a ratio of the volume swept by the piston as it moves through it's stroke to the volume of the combustion chamber.
That was my point. The OP very likely didn't cause the damage by doing a compression check. He needs to fix the motor not feel guilty about causing the problem.

OK, I guess you are correct, as the compression ration would be stated for whatever the engine parameters were as built. My bad for not thinking this through completely.

Our conclusions are the same. IF he did not add too much oil to that cylinder.

Hope this helps him to feel better...