RTV HST Adjustments

Just a word of caution.

You're changing the Max RPM while the Max Torque stays the same, or does it? And the Max HP goes up with the increase rpm or just the RPM? Some unknowns without a dyno to verify actual output.

That being said the system was designed to work with a set rpm range.

I'd get everything working the best first with factory specs so you have a baseline.

And then start modifying the rpm for improvements.

Remember you are trying to fix a shifting problem. Get that out of the way first before trying for more HP and or Speed.

Every gain in one area can be a lose in another. Nothing comes for free.

My 2 cents.
 
SpudHauler:

I actually did not have a shifting problem with my 2010 RTV 900, but I did find the factory WOT setting was 3550+ rpm's (no load), which is what it's set at now.

I bought my unit this past summer with less than 50 hours, now has 65. I don't think they was ever any adjustments to the engine or HST. Now I'm assuming, since I never had a shifting problem, that my neutral screw does not need adjusting. I turned my servo adjusting screw out (CCW) 1/2 a turn from the factory setting.

At this point, without knowing what the tranny relief pressure is set at, my max rpm and max HST lever travel are synchronized. I still need to resolve the slack in the governor cable with engine rpm at idle. That is, I need to get the rpms to increase as soon as the HST lever begins to move forward.
 
TRIBUTE100 said:
SpudHauler:

I actually did not have a shifting problem with my 2010 RTV 900, but I did find the factory WOT setting was 3550+ rpm's (no load), which is what it's set at now.

I bought my unit this past summer with less than 50 hours, now has 65. I don't think they was ever any adjustments to the engine or HST. Now I'm assuming, since I never had a shifting problem, that my neutral screw does not need adjusting. I turned my servo adjusting screw out (CCW) 1/2 a turn from the factory setting.

At this point, without knowing what the tranny relief pressure is set at, my max rpm and max HST lever travel are synchronized. I still need to resolve the slack in the governor cable with engine rpm at idle. That is, I need to get the rpms to increase as soon as the HST lever begins to move forward.
Click to expand...
If it don't bogg the engine on take off at any point, and the engine torque keeps up with the trans torque. Then you will not really gain that much. But for the tweeker that you may be, you could relocate the hole for the "T" cable on either end to get more throw, and someone in this string had a good idea about a spring if you run out of cable length.
 
Now fella's If you have the time. And you want to really mess with things, you can remove the orfices (both of them) feeding oil to the servo piston (later models are already omitted). Then shim your charge relief to a pressure of about 85-90 psi. Now you will have more launching power, but most likely not enough engine. Engine bogg on take off and even sometimes on just aggressive acceleration. Also if you shim the springs for the AUX motor, it won't down shift until a higher pressure is reached. They do these things if you turbo your engine and actually get enough useful power from it. There is a vid out there some where showing a RTV laying a little rubber on take off. With something like 9 psi boost I think. Don't for get engine preformance, every RTV engine I rebuild needs the timing adjusted (always low) which could equal up to 3-4 HP and on lets say a 25 hp engine thats alot.
 
I see what you mean SpudHauler. I need to load up my bed with a bunch of weight, then get on my steep hill and see how it accelerates from a dead stop before I make additional adjustments. Thanks
 
AdamsRepair: Now most of that tweaking is above my backyard mechanic expertise, but adjusting the timing sounds intriguing. Is this an easy task ? If so, how.
 
TRIBUTE100 said:
SpudHauler,
I'm not sure where I picked up those other pressures I posted earlier.
Just found the relief pressure spec description in my downloaded RTV 900 Service Manual that I paid $10 for on site http://kubota.servicemanualvault.com/

"The relief pressure is set in between 25.5 to 26.5 MPa (260 to 270 kgf/cm2, 3698 to 3840 psi) when shipped from the factory. But, for the purpose of after-sales services, as it is impossible to reset the pressure precisely as set in the factory, its setting range is defined as a slightly wider range between 22.6 to 26.5 MPa (230 to 270 kgf/cm2, 3271 to 3840 psi)."

So based on this, it looks like the factory is setting that relief pressure between 3698 and 3840 psi.

I didn't want to have to take my unit to the dealer to have my pressures checked because of the hassle. I've never had shifting problems, once in a while I'll have to press on the brake. So, based on that, and since I only have 65 hours on my 2010 RTV 900, I was assuming my neutral adjustment on the servo was OK. I have no way of knowing what my relief pressure is set at. I'd like to think if I had the right gauges, fitting and tools I could do check it myself, but the procedure sounds involved on the relief pressure adjustment. My experience with any kind of dealer service shops has not been satisfactory. I may just drop by my local Kubota dealer and chat with the service technician to get a feel for their experience.
Click to expand...


Jumping back a few posts, I thought I'd share my lessons learned from DIY relieve pressure checking. If you are not comfortable with high pressure hydraulics, do not attempt this. Every component in the test line must be rated above the expected pressure. A hydraulic pinhole leak is not something to mess around with. It will mess you up. I will not describe every detail, because I assume you will be doing this with a WSM nearby.

First you need some calibrated, high resolution pressure gages. El cheapos from tractor store will not suffice. You are checking for target values, so the gages need to be calibrated, and they need to have adequate resolution so you're not guessing halfway between two marks. A digital gage would be better because you don't have to plumb a hydraulic hose into the system, and they usually include a filter to dampen minor pressure fluctuations.

The first challenge is removing the allen head port plugs. They are sealed with a thread sealant similar to lock-tite, so they usually feel like they are stuck. Be very careful, or you'll round out the recessed allen hex. I usually scrape around the edges with a dental pic to break away any corrosion between the male and female threads, and then soak with penetrating fluid and cross your fingers.

photo1_zps6656b08a.jpg


The allen hex is 6mm. I recommend a stubby impact version because they are less likely to twist off. I found a good set with SAE and metric sizes in 3/8" drive.

photo2_zpsd17ca951.jpg


I also recommend blocking the extension with another socket. This provides pure torsion to the plug and further eliminates the chance of rounding the recessed allen hex or twisting off the allen bit. You will have to play around to find the proper gadgets to block with. A socket seemed to work for the forward high pressure port plug.

IMG_0725_zps4163a7bc.jpg


If you are lucky enough to get the plug out without tearing everything up, then you will likely need an adapter for the next step. The plug is not a standard National Pipe Taper (NPT) plug. I believe it is British Standard Pipe Taper (BSPT). They are nearly identical, but differ by one thread per inch and the thread angle. I ordered a 1/4" BSPT to 1/4" NPT adapter, so I can install my hydraulic hose and pressure gage. Keep in mind, the adapter fittings must be rated for the expected pressure too.

IMG_0727_zpsf8c6a6d1.jpg


If you get this far, you are home free. Follow the remaining procedure in the manual and test your relief pressure.

Adjusting the relief pressure is not too bad, but be VERY careful. Minor adjustments could result in dramatic pressure increases which would not be good. Following the procedure in the WSM, remove the 10mm hex plug for the forward or reverse relief. Fish the check spring and relief valve out of the hole with a CLEAN magnet or needle nose pliers. Do not scar anything.

The valve is basically a preloaded spring trapped between two precision diameter seals. The preload force in the spring must be overwhelmed by the hydraulic pressure in order to unseat the seal. The trapping mechanism is a fine threaded fastener. One end of the fastener is a flathead screw forming the male threaded portion. The first seal freewheels/spins on this male threaded portion. The other end of the fastener is a female threaded collar, integral with the other seal. A 2.5mm allen hex acts like a lock nut.

IMG_0688_zpsc17181b3.jpg


IMG_0690_zps7ca81cb5.jpg


IMG_0689_zps9c921372.jpg


I only adjusted my reverse relief pressure. To protect the sealing surfaces, I cradled the valve inside a piece of garden hose sheathed with PVC. Clamp the seal most near the allen lock nut in the vice. Loosen the lock nut, turn the flathead screw, retighten the lock nut. It's that simple. I would recommend adjusting 1/16 of a turn, reinstall and test relief pressure. It's better to creep up on your desired setting than to overshoot.

IMG_0692_zps130c0fa2.jpg


IMG_0693_zps966cc2aa.jpg
 
Be real careful. (Quote me37250) ""The first challenge is removing the allen head port plugs. They are sealed with a thread sealant similar to lock-tite, so they usually feel like they are stuck. Be very careful, or you'll round out the recessed allen hex. I usually scrape around the edges with a dental pic to break away any corrosion between the male and female threads, and then soak with penetrating fluid and cross your fingers.""
Don't reef on the allen socket, use a steadily increasing pressure and hold it. Giving the sealant on the threads time to start to give up. A little heat from a propane torch helps. You don't need a lot of heat just warm the metal around the plug. Then slow and steady, but very hard pressure on the ratchet. I have rounded the allen plugs off B4, even cracked the valve body trying to remove the plugs. The newer models have straight thread plugs which are better but sometimes you need to strike them straight on with a flat punch bigger than the hex hole to free them up.
The allen screw on the relief valve in the pictures above is the jam nut. It is best to compress the spring to release pressure on the treads. then using a good flat tip and allen wrench, loosen the (Jam Screw) allen screw. Back it out far enough to be able to turn the flat tip end in or out, then set the jam screw. Put it back in and test the pressure.
 
I've read that using Valve Grinding Compound on the sides of the Allen head wrench or socket helps to tighten the fit for lessening the chance of slippage.
 
See my previous posts in this thread adjusting the cam lever assy, HST lever, servo screw, etc.

My next step was to resolve the slack in the governor cable and have the engine speed increasing as soon as the HST (lever) is applying torque to the transmission .

I decided to extend the engine throttle lever similar to member "me37250". I used some aluminum angle bar stock I found at Home Depot. Used size 3/4" x 1/2" x 1/16 and thought alum. would be lighter and angle would prevent twisting. I cut a piece just over 3", laid it on top of the throttle lever with 1/2 " angle side pressed firmly against the front edge of the lever and marked the holes from the bottom using a sharp mechanical pencil. Drilled out the 2 holes using a 1/4" drill bit on drill press. Temporarily mounted the alum. angle on top of lever with 1/2" side turned down and to the front. (sorry about the blurry pictures) Used 1/4" bolts (3/4" long) and nuts to secure. Found I had to grind down one side of one 6 sided bolt in order for each bolt to fit next to each other, but this is an advantage because you don't have to hold their bottom sides to tighten.

Alternately holding the throttle pedal and releasing, I found a spot on the alum. angle piece that allowed the throttle lever to reach both WOT and idle position, marked it and drilled a 1/4" hole as shown in picture. (That hole is approx. 15/16" O/C from the outer most throttle lever hole). Remounted the alum. angle and secured well using washers and lock washers.

CAUTION: After installing, I had to grind down the nut closest to the throttle lever pivot point so it would not interfere with the fuel shut off lever.

I connected the governor cable and adjusted it using the two 12mm? lock nuts on the closest bracket trying to achieve snug cable at idle position and WOT with pedal depressed. I started the engine, let it warm up, but it sounded like it was idling high. Got out my $14 laser tachometer (Ebay), and continued to adjust governor cable to achieve a final result of 1425 rpms at idle (spec 1300-1400) and 3350 rpms at WOT (spec 3200). I was satisfied with that result and will give it a test drive another day.
 

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We'll done! This is just another example of how different each machine is setup; my hole spacing was 2.25" from the outer hole to my new extended mounting point. I wonder if our HST levers move the same amount? The movement should really be described in degrees that the shaft rotates, but that's hard to measure. Maybe we chould try to measure the linear distance between the location of the HST lever rod mounting bolt when in the neutral position and then at 0.040" shy of full limit.
 
TRIBUTE100 said:
My Unit: 2010 Kubota RTV 900 (60 hrs)

Using SpudHauler's Instructions Here is what I ran into:

Checked and adjusted throttle cable and engine throttle.

Disconnected the HST rod, marked HST lever at full wide open.
Before reconnecting HST rod, started engine with rear wheels off ground, to confirm that wheels did not turn when the HST lever was in a self centering position. Reconnected HST rod and adjusted so HST lever was .040" shy of wide open. (prior to adjustment, lever was over 1/4" from full wide open)

Did not adjust servo adjusting screw.

Neutral screw: Mine has a large cap nut(over 17mm) over it and I did not expose it. I don't have any major shifting problems, sometimes a little stiff, but no complaints if brakes are applied.

Now the problem: With HST lever adjusted to .040" shy of wide open, started engine (wheels off ground) but could not get into gear (slight grinding). The .040" clearance adjustment would not allow the HST lever back to that "self centering (neutral) position. Went back and adjusted the HST rod to the 'sweet spot' where the wheels would not turn. But, that put the HST lever back to over 1/4" off the full wide open position.

Question: Does that indicate the neutral adjustment is off and the pressure must be adjusted at the dealers ? Also, since the HST lever is not reaching it's maximum forward (less .040"), am I not reaching the maximum power of the transmission ?
Click to expand...
It has just dawned on me........For the people that do the adjustments in this String and have Tributes problem with the lever not going to the .040" mark. The lever on the servo valve stem may have slipped due to a previous maladjusted linkage. Say if the rod was to tight and the lever bottomed out the valve, before the Cam lever assy. hit it's stop. Then the servo lever could have slipped. Being only held into place by a pinch bolt. Maybe the position of The Servo lever on the valve stem is throwing the stroke off.

I have to do "The adjustments" in this order. When installing a rebuilt tranny.

1 Accelerator pedal cable to Cam lever assy. Stop to stop. T cable an rod unhooked
2 Set HST rod at it's mid point.
3 Put Servo lever on Servo valve stem. Locating it where it will hook up to the rod with out much effort. Then tighten the pinch bolt.
4 Then put a mark on the valve body for full stroke.
5 Hook up rod to Servo lever and check stroke at .040" mark.
6 Now adjust throttle cable.
 
My dirt bike shifters use to slip around some time front shifting gears that's a good thing to check. Good information
 
AdamsRepair said:
Now fella's If you have the time. And you want to really mess with things, you can remove the orfices (both of them) feeding oil to the servo piston (later models are already omitted). Then shim your charge relief to a pressure of about 85-90 psi. Now you will have more launching power, but most likely not enough engine. Engine bogg on take off and even sometimes on just aggressive acceleration. Also if you shim the springs for the AUX motor, it won't down shift until a higher pressure is reached. They do these things if you turbo your engine and actually get enough useful power from it. There is a vid out there some where showing a RTV laying a little rubber on take off. With something like 9 psi boost I think. Don't for get engine preformance, every RTV engine I rebuild needs the timing adjusted (always low) which could equal up to 3-4 HP and on lets say a 25 hp engine thats alot.
Click to expand...
Edit Normal Charge pressure is 75=100psi But the higher you go with it, the longer the pump swash plate stays at full stroke as pressures rise. You don't want to add to many shims, 2 thick ones max. Because the shims and the fully collapsed spring won't let the poppet come out far enough to dump the volume of oil it needs to to regulate the pressure. (and that would be bad.) If you need more pressure you need a stronger spring. I was playing with this and added a very small light spring to the inside of the original spring increasing my charge pressure to 125 psi. I did this for trouble shooting purposes. It did increase the pulling power, and the shift points. But I'm sure it would bogg a stock motor. Because it also increases the HP control. They talk about in your WSM under transmission operation.
 
SpudHauler said:
Neutral Screw.

This is the screw I found out about after losing my servo screw adjustment.

So don't do like I did. Either leave the servo screw at the factory setting or make sure you know what the factory setting was before you adjust.

Now for this adjustment, you need to go to your local Kubota dealer and have them use their pressure gauges for the best neutal adjustment. AdamsRepair reports that adjustment can be off by as much as 100 lb difference when you try doing it any other way. Manual says 0 to 3 lbs difference between P1 and P2. So have the mechanics do this unless you have access to two low pressure gauges and the proper adapters for you machine.

After they adjusted the neutral adjustment bolt, and before removing the gauges, I would have them re-connect the HST Rod and check that it is adjusted for the best 0 to 3 lbs difference as well.

The mechanics reported that my neutral adjustement was off by quite alot, but as far as I know now, they didn't re-connect the HST rod and check that it was in the best adjustment for neutral.

Otherwise if you like trying things yourself you could do the following after the mechanics have adjusted the neutral bolt;

Warm up the engine and transmission, have the transfer case in 2wd, transmission in H gear, back wheels off the ground, no brakes applied not even the emergency brake, hold the fuel lever wide open so engine is running at full song and watch for wheels rotating.

You can’t use the accelerator pedal at all. Use the fuel pump lever or the manual throttle, if you have one, to increase the engine speed.

You may have to adjust on the HST rod to get no wheel movement. Loosen both locking nuts and adjust the rod for best neutral by turning in both directions until you find the middle point between a little forward rotation and a little rearward rotation. Some report better results when it's a little bias to the rear.

Hopefully you have found neutral and it's time for a test drive.
Click to expand...

Bump
 
I have not read through this whole post and maybe I should but this was the post that stood out to me and my situation.
Which is... when my buggy is in H and I pull the manual throttle wide open the buggy rolls backwards, the opposite happens when it is in R, it rolls forward. Likewise if it is in neutral on flat ground and I slowly ease the shifter into H I can feel the cogs in there rolling backwards, click click click.

My question is, can I just jack up the rear end, put it in H, hold the manual throttle wide open and adjust the aforementioned "neutral screw" until the tires quite spinning?
 
Alaska
What model RTV are you working on? this thread is for the old pre X model HST. on that model there is a condition called creep and is essentially the speed lever adjustment but on that model the lever had a neutral on the swash plate control lever. if it isn't in the neutral position the swash plates will cause the drive motor to turn in either a forward or reverse motion depending on the direction it is out of adjustment. there were some who modify this connection to a rocker peddle on the floor of the cab for forward reverse operation without gear lever change. i don't think this apply as is for the X model. BUT if your speed control lever on the HVT X model is out of adjustment it can cause a similar condition but only in one direction. if your X is creeping you need to adjust the speed control lever on the left rear of the HVT a little toward the front of the machine while the detent on the linkage is in neutral.
 
2016 x1100

I did do some adjusting on that lever when I went through the whole tamale, following your thread from earlier. It did not seem to have any effect, doing the same thing. Also curious that the tranny is spinning backwards in h and forwards in r.
 
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