Stalling an HST tractor

[Chain Bender]

I have a fairly new (135 hrs) Kubota 3200 HST. On several occasions I have stalled the tractor at around 1800 rpms while pushing into a sand pile or pushing brush.

Last week while pushing very light briars and vines my tractor started a very loud and RPM controlled knock. I checked all dummy lights and guages and everything was fine. I shut her down and checked the oil. It was full and clean. Checked the water in the radiator and it was full and not even hot. The block wasn't hot either.

I used my dad's tractor to pull my tractor out of the woods and up on my hauler. Took it to the dealer. Stopped by yesterday and they had it in a bay and running. It sure didn't sound like it was something they were gonna fix with just the hood up. No word on cause.

A friend of mine who has owned bulldozers for 40 years said that stalling an HST under a load can/will break the crank shaft.

Anyone have a response to the last paragraph?

Thanks in advance for your opinions.

CB

 

[orezok]

I've stalled my 7800 several times with a a tiller running at PTO speed when hitting a large root. Just fired it back up and kept going.

 

[nspec]

I find that very hard to believe. My money is on a problem related to the fuel delivery - either pump or injectors. Fuel problems or even air in the system often sounds like a bad knock. If you broke the crankshaft on a brand new hydro machine just by stalling it, I would be absolutely appalled at the manufacturer.

 

[Mickey_Fx]

I doubt you've done any engine damage due to overloading the trans. HST have internal pressure relief valves which bypass fluid when excessive pressure reached.

 

[Chain Bender]

Personally, I don't see the difference between stalling an HST or clutch transmission. Torque is torque in my mind.

On the fuel note, I had just added 5 gallons from a plastic container. But my fuel bowl looked good and I emptied it and didn't notice any debri or water.

 

[dynasim]

An HST naturally limits the torque that can be applied to any of the internal shafts because the torque is controlled by pump with a maximum pressure(set by a relief valve).

I stall my HST reasonably often(by pushing on stationary objects), and have never had an issue. The bigger issue with HST's is oil temperature, and if you stall for signficant periods of time, oil, and the safety valve, will overheat.

Hope its ok.

Chris

PS. With a clutch, you can get relatively large amounts of torque for very short periods of time(more than the engine will produce) because the engine has momentum.

 

[jinman]

Stalling an HST is something that happens often under normal operation. Stalling the transmission is not bad, but holding the transmission in the stall mode will cause it to overheat (oil heats up in relief valve) and it serves no purpose. If the transmission stalls, you need to use a lower range or less pedal deflection. If the tractor still stalls, then you are exceeding the ability of your tractor and should find a different method or talk to your dealer about a trade-up.

Stalling the transmission should not cause an engine to fail either unless the engine lugs down. Lugging the engine can cause lack of critical lubrication and tends to produce higher combustion chamber pressure and heating. This was hardly the case with your tractor since you said the engine was maintaining 1800 rpm while the transmission stalled. If your engine failed, it had nothing to do with the transmission in my opinion.

 

[namesray]

don't know if this holds true for a hst, but a friend told me once that he stalled his gear massey fergason at idle while pushing into round bales with 3ph spear (it was cold winter). started it back up and a bad knock in engine. diesel mechanic told him that rods bent. he said when stalling diesel at idle this can happen. always have some rpms when working it. i don't know how true that really is, but that is what my friend told me. i usually run my kubota b7800 at least 2000 rpms, usually 2300 no matter what. my dealer told me that you do a diesel no favors by idiling it or running it at low rpms when working it. hard on hyd hst pump and soots up engine. he said to run at higher rpms. i have and haven't had any problems with the 815 hours i have on that tractor. just some of my experiences for your info.

 

[pjbci]

Here is a possibility of what may have caused th knock. It could have stalled and kicked backwards enuf to restart th engine running backwards. Yes, a diesel will run backwards. I have never had it happen on a small engine but have had it happen to me with a caterpillar engine twice and an international once. Both engines knocked but were not damaged at all.

As far as the last paragraph is concerned....Not gonna break a crankshaft.

 

[DennisFolsom]

Last week while pushing very light briars and vines my tractor started a very loud and RPM controlled knock. I checked all dummy lights and guages and everything was fine. I shut her down and checked the oil. It was full and clean. Checked the water in the radiator and it was full and not even hot. The block wasn't hot either.

I used my dad's tractor to pull my tractor out of the woods and up on my hauler. Took it to the dealer. Stopped by yesterday and they had it in a bay and running. It sure didn't sound like it was something they were gonna fix with just the hood up. No word on cause.
CB

You mentioned that you had stalled it several times before at 1800 RPM. 1800 may not be enough power for what you were trying to do at that time. However, I find it hard to believe that would cause damage beyond the nuisance of stalling and needing to restart.

It sounds like you were only lightly loading the engine when the the knock started.

If I'm understanding correctly, the engine did not sound good when it was running at the dealer's afterward.

I'm betting that the problem is not the result of overworking the engine at 1800 RPM.

Good luck!

Let us know what happens.