RTV500 HST Shifting

[Jw5875]

Is that the screw and lock-nut on the end towards the front (front of machine) of the servo that is hard to see and almost under the back of the seat frame? (looks 1/4 " or metric??)

What increments to adjust, i. e. 1/8, 1/4/ 1/2 turn etc.?

I just did my 50hr. (actually 68hrs.) engine oil and trans/hydraulic oil change along with filters
and I have a lot more smooth shifting into gear and not so much "Bogging Down" now.

I might do some "tweaking" with the screw etc. if it is the proper one that you are describing.

JW5875

 

[timswi]

Ok, general question. Can anyone explain how the Polaris Ranger 400 has 29HP and the RTV500 has 15HP?..Inquiring mind (what's left of it) want's to know.

 

[mstordahl]

The servo is the little black valve just under the seat on the passenger side of the transmission. At the front of the valve (it sits lengthwise on the trans.) there is a flat head screw with a 14mm jam nut. That is the valve you want to check. Another couple things that came to mind as well...

1. How many hours are on the unit, and if you have changed the oil yet in the transmission, did you use the new Kubota Premium UDT? Reason I ask this is because the new oil is a thinner oil and works a lot better, like night and day on the ones that I have done. The kubota hydrostats are VERY picky as to what is run in them, and the oil that the Kubota engineers made is just for that hydrostats purpose.

2. Have you checked the maximum no load speed of the engine? This is VERY crucial to the 500 gas motor more than any, it has to rev to get its power. Making sure that the rpm is at 4000 plus or minus a hundred will make another world of difference. Of all the 500's that I have done an inspection on for low power, they all were below 3700 rpm. Trust me, that extra 4 or 500 rpm does make a big difference.

If both of those are good as I have stated, then you still need to adjust that servo screw to get it to "shift right". That will make it a whole new machine. Try about a turn at a time OUT, thats a good place to start, then fine tune it from there if you like. Any other questions, feel free to ask. I like to represent this product the best that it can, and it irritates me that the rtv's always seem to take a bad rep mostly from just not being set up right from the dealer. Its not acceptable in my books.

Matt

 

[timswi]

Thansk Matt,

I did the 50hr svc with Super UDT. Need to check the max RPM...I heard somewhere on this board that around 3750 was the max...4000 is correct?

Turning the screw out makes it more aggressive? 1/4 turn at a time?

Is there any risk of damage doing this?

 

[mstordahl]

Good about the fluid then.

The engine is good to 5000rpm from kubota, probly not supposed to say that, but that is where the rev limiter and data log are set in the computer. Anything over say 4500 is high, but they say it is good to 5000 without problems. Obviously they want to keep the engine reliable for the average person, so they limit the rpm down some. The spec in the book is to be at 3750rpm, but our factory training and the engineers have said that it was a mistake, and should be at 4000 to get the peak power.

No, turning the screw out makes the servo less aggressive. That is what you want, because you say yours will not back down on its own, you have to let off the pedal correct? So to do that, you have to back the screw out, which takes pressure off the spring on the servo piston. This makes it easier for the oil pressure in the hi side of the hydrostat to de-stroke the pump, which in turn slows your speed (downshift in simpler terms) and lets the engine stay in its peak power.

There is also nothing that you can damage with this. If you go out too far, the engine will rev up and not go anywhere. Too far in bogs the engine out and makes the hydrostat more aggressive, like what yours is doing.

Let me know how it goes.
Matt

 

[timswi]

Thanks Matt,

I'm going to change the servo settings a bit and see what happens...i can guarantee this isn't hitting 4K RPM's, but my Sun machine won't read it..Need to find another tach set up. Guess I need to get a shop manual to find the equivilant of the negative side of the coil, since there isn't one.

I'll see how that setting goes first.

What you're saying is that the early ones, like mine, were set up wrong from the get-go?

 

[mstordahl]

Not wrong, just that they learned after the units got out and were being worked on hills, they found that they had to increase the rpm some to compensate and get some more horsepower out of that little engine. If there is one thing that Kubota is known for, its there engines, so they didnt want to stick theyre neck out too much to begin with on the new model and engine. Its working out great now, so they know it will take a lot more and they are not being quite as reserved. Think of it this way, if 5000 rpm is the redline of this engine, 3600 (that most all are at from factory) is just 72% of maximum. Taking it up to 4000 only makes it 80%, still plenty safe. Basically, this little motor should have more in it for the future. Kubota always does this, they build a great engine and never really take it to its potential because reliability and economy are number one to them. Smart in my books, its what every sucessful engine builder has ever done.

 

[737pilot]

TIMSWI I want to personally thank you and all the members here for getting to the bottom of this underpower problem. It sounds like there is a fix and alot more power to the RTV500 than I thought. I know this is pushing it but if anyone could post a picture of the adjusment screws it would be a big help. I am confused about where the RPM adjustment is done and the servo adjustment. I hear you guys saying to turn up the RPM and I would like to know does that effect the IDLE RPM setting. I personally think the idle RPM is too high and would like it lower so it would be quieter in the woods but was told by the Kubota mech that it has to idle high for the HST to work properly. Thanks for any pictures.

 

[mstordahl]

Changing the maximum speed of the engine does not do anything to the idle speed on the 500. The idle speed on the 500 should be in the 1500 rpm area, a little more if it is in a cold climate to run good when cold. I will try to get some pictures posted for the people on here to be a lot more clear. The idle rpm by the way has absolutely nothing to do with the hst, just to how the engine runs in cold weather.

 

[mstordahl]

Here is a pic of the carb to show what screws you need to adjust for the idle and max rpm.

There is also a picture of the servo that you need to adjust. I circled it in yellow and then the red arrow is to the adjustment screw.

Matt