How to increase HST relief pressure on a CK30

[dfkrug]

This thread has resurrected an issue I have with my Kioti's HST and HSTs
in general:
http://www.tractorbynet.com/forums/bobcat-tractors/165728-attacking-power-problem-ct225.html

This issue was talked about in other threads over the years, including this
one:
http://www.tractorbynet.com/forums/...7703-what-going-hydrostatic-transmission.html

How does one increase the relief valve pressure? This applies to all the
M27 tractors (CK25/30/35, Bobcat CT225/230/235) as far as I can tell.
It has been reported that the CT235 uses a RV set at a higher pressure
than the other Bobcat M27s:

For the CT225/CT230, KRAZK reports that the HST RV is 280kg/cm2 (3980psi)
while the CT235 is 300 kgf/cm2, or 4260psi.

From page 4-37 of my CK25/30 service manual, it is:
280 kgf/cm2, which is 3980psi

I am still waiting for a report on the CK35 RV spec. Anyone have the
service manual?

So....I went out and removed my Forward RV, which is fairly easy, using
a 8mm Allen-head wrench. See pix.

The cap has a bizzare straight thread that measures 13/16-14tpi. The
RV itself is hand engraved to read "280". The valve has a screw-adjustment
that is welded at the end to keep it from loosening or being modified. It
can be reset after grinding off the weld, screwing the adjuster in and
rewelding. If the 300 kg/cm2 valve has the same dimensions, then it can be
used instead.

Now, we just need a guinea pig to make this mod. I have not, as I do not
yet have a guage over 4K psi, and it is not high priority.

 

[bbse]

Looks like a plan. Where do you check the pressures at? I would definitely consider playing with this down the road. I am going to try to do the dealer thing but it looks like if I don't call them, they don't call me.

 

[dfkrug]

There are 3 plugs right under the floor mat immediately below the 3-pt
speed knob. The one on the left is the FORWARD test port. When I get a
guage, I will test the pressure. Too bad my CT230 is gone, or I would
do that one, too.

I wish all tractors were this accessible.

I was also wondering who is the manufacturer of this HST. I know that
the 3-pt hydraulics are made by Mita OleoDynamica of Italy.

 

[tinman955]

How much of an increase will help?

 

[dfkrug]

Any increase is going to help some. I am not as concerned about this
issue as some of the new Bobcat owners who have run into it. I was
very surprised when I could not spin tires in a few rare situations, but
those do not occur often. I do believe that DaeDong has made some
incorrect design decisions with this tractor; no other HST CUT I have owned
has done this.

 

[tinman955]

I hear ya on that one, thats why I ordered a new SST tractor so I dont hv this issue anymore

Glad to see you are working out the details on this subject, keep up the good work.

 

[Sabretooth]

I hear ya on that one, thats why I ordered a new SST tractor so I dont hv this issue anymore

Glad to see you are working out the details on this subject, keep up the good work.

Tinman think you might need name change a new SST:drool: just does not fit with tin name maybe Platinumman or Diamondman. I'm just trying to get a Boxblade for my Bobcat forget getting another new tractor and I can only imagine what my better half would say or do

 

[tinman955]

Tinman think you might need name change a new SST:drool: just does not fit with tin name maybe Platinumman or Diamondman. I'm just trying to get a Boxblade for my Bobcat forget getting another new tractor and I can only imagine what my better half would say or do

Trust me I didnt want to buy a another tractor already but I absolutly am done with HST's!! I kept my last tractor about 1000 hrs and 15yrs, it was a john deere 955 awesome tractor!!

I love my bobcat, just need more tractor and dont mind using a clutch. Sorry to be off topic guys, this a very important subject that needs to be addressed. I believe HST's have their place just not in my garage anymore.

 

[SunnyJim]

Trust me I didnt want to buy a another tractor already but I absolutly am done with HST's!! I kept my last tractor about 1000 hrs and 15yrs, it was a john deere 955 awesome tractor!!

I love my bobcat, just need more tractor and dont mind using a clutch. Sorry to be off topic guys, this a very important subject that needs to be addressed. I believe HST's have their place just not in my garage anymore.

No worries. For me its the opposite. I have to clutch as little as possible so HST is for me.

Everyone has to meet their own need or preference.

 

[Highbeam]

SST as in skid steer tractor or SST as in shuttle shift transmission?

 

[tinman955]

SST as in skid steer tractor or SST as in shuttle shift transmission?

Shuttle Shift Tranny

 

[williekioti]

I'm with you tinman, I too prefer the gear. Completely a personal preference though and I understand those that go HST for convienence. I'm a bit old school and like the keep it simple principle. Never had a problem with it not spinnin' a tire, bury the loader too deep and she'd dig her way to China......... ;-)

 

[tinman955]

Willie thats why im goin SST, I want the ability to pick the right gear and I want to put the most power to the ground. :thumbsup:

 

[tinman955]

So whatever happened to this thread? Sorry bout bringing it back up but unfortunately I might be buying another tractor that is a cab and they come only in a HST. So did anyone increase the relief setting of their HST for increased performance?

 

[bbse]

No, I still cannot get up that hill. I plan to fix the problem myself as soon as the warranty is up.

 

[Tim M]

Instead of grinding and rewelding I added a small shim to essentially compress the RV spring a bit (so I could easily go back) since I was planning to try and get it "fixed" under warranty. I took a thin flat washer(30-40 mils) and cut a slot so it could be slid in under the spring. I was able to get mine over 4000psi and I had plenty of pedal left. It made a considerable difference. Obviously one needs to BE CAREFUL! Do not do this without a pressure gauge.

Originally my pressure was at around 3700 psi if I recall. In the end my dealer got me a new RV under warranty and my pressure went up to right around 3950 psi. It did make a significant difference.

Tim

 

[dfkrug]

So did anyone increase the relief setting of their HST for increased performance?

I forgot that I started this thread, TIN.

Kudos to Tim for making an adjustment, and measuring the pressures,
before and after. I have been meaning to get a 10,000psi guage to
measure multiple HSTs.

I may be quite easy to intall the CK35/CT235 RV in a CK30/CT230 as
well. I don't imagine the part costs very much....

 

[Tim M]

At the time I did check the price was a lot more than I expected. I seem to recall a few hundred dollars.

Here is a picture of my original with the shim:

http://www.superxtune.com/public/RV_280.jpg

Tim

 

[Tim M]

So I just reread a few of the earlier posts.

At the time I was looking into this a few years ago the CK35 had the identical part number for the RV. (or so my dealer told me!)

Has Kioti bumped this pressure up to 4260 psi for the CK35?

Have they changed the HST internals of the CK35 to handle the higher pressure?

 

[dfkrug]

At the time I was looking into this a few years ago the CK35 had the identical part number for the RV.

Has Kioti bumped this pressure up to 4260 psi for the CK35?

Have they changed the HST internals of the CK35 to handle the higher pressure?

Nice job with the shim. I agree that over 50-75 clams, forget about
buying another RV.

My memory may be faulty but I thought there was a different part # for
the CK35 HST RV. Did someone check their service manual (CK35 or
CT235) for the specced HST pressure?

I don't know about any different internals of the CK35's gearbox, etc,
but if the CK35 has 5 more hp, it would be nice if it delivered more
HST pressure and/or flow. If the HST is exactly the same as the one in
the CK25/30, then the bigger engine is not wasted, however. It should
be able to go faster up hills in the high range.