2006 Kubota L48 HST leak @ valve plate

[jhiller18405]

If anyone has insight it would be greatly appreciated, working on A 2006 Kubota L48 , It has a leak between valve plate and HST, this is the 3rd time its been split in 650 hours for same thing, gasket seems to walk around and then finally fails, Checked both surfaces with straight edge both are flat, Kubota said to use silicone, rather then gasket TA240-58190, Just doesn't sound like an answer. Really do not want to split this Tractor again.

 

[Murphyflyer]

Hi jhiller. My L48 has started to leak badly from the joint between the mid case and the hst. Have you fixed your leak? How did you do it?

 

[dfkrug]

Interesting problem. I like to use silicone in situations like this, even if you are forced
to use the gasket in there too, for clearance reasons.

I think what I would do is buy some new grade 12 metric bolts, and torque them to
spec, or a little beyond. I am surprised this is happening with the L48 as it has a
"mainframe" that takes a lot of bending stresses off the tranny cases.

Is there a chance these bolts were not torqued enough, or are from a bad batch?

 

[Murphyflyer]

I can get at two of the bolts at the bottom and checked them. They are tight.

 

[dfkrug]

The primary reason that I can see for a manufacturer NOT using silicone or some other gasket sealant
or gasket replacement, is it takes longer on an assembly line.

Leaks where you have them are more difficult than on most tractors, cuz you have to remove
the mainframe before splitting. With my old B21, you had to remove the mainframe AND the
separate oil sump below the tranny.

 

[Murphyflyer]

Has anyone tried Permatex 54540 hydraulic sealant? Can it harm anything in the system? I need to slow the leak until I finish the job I am on before I split the tractor.
I just looked at the specs for it. It is more for fittings.

 

[rScotty]

Has anyone tried Permatex 54540 hydraulic sealant? Can it harm anything in the system? I need to slow the leak until I finish the job I am on before I split the tractor.
I just looked at the specs for it. It is more for fittings.

Murphyflyer, I was following this thread and wondered how you were progressing. My hat is off to you for the many attempts to fix the problem. Your photo shows nice clean surfaces too.

In my experience, gaskets fail by "floating around" because the non-hardening sealer was assembled wet without giving it enough time to cure - or at least get tacky. That's even more of problem with silicone sealers because they are so slippery when wet. This may not be the problem you are having, but I wanted to mention it to help out the next guy.
I also suspect that a joint assembled with uncured sealer may never fully cure - which means that the gasket will never stabilize in one position.

With these non-hardening & silicon gasket sealers today, good practice is to LIGHTLY & EVENLY coat the gasket both sides and also both joint faces. I use my fingers a lot when doing that. The sealer is not much thicker than a coat of paint when I'm done applying it - especially onto a fiber or paper gasket. Then when the sealer gets tacky, stick the gasket lightly onto ONE joint face and then just let it sit there a while. Sometimes I'll wait until the entire gasket surface is cured before assembling. Curing can take hours, but in my experience it is better assembled cured than wet. There's probably some perfect cure point, but I don't know it. I err in the direction of too much cure than too little and it's worked for me. I then assemble it, give it about half torque, and let it set for up to a few hours. Then finish torquing it down later.

good luck, rScotty

 

[dfkrug]

I like to eliminate the paper gasket when I can. Sometimes the thickness of the
gasket is needed for clearance between members when they fit up. Some makers
use only a sealant, and no paper gasket.

I don't think all folks doing mechanical work are careful enough when applying
sealant. I clean both sides with acetone, after removing all traces of the previous gasket
and/or sealant. Oily surfaces are not your friend here.

I am a big fan of silicone, but the stuff ages in the container, so using old (> 6mo)
material is risky. I use a special gasoline-resistant sealant for 2-stroke engines.

 

[Murphyflyer]

I split my L48 yesterday and the gasket between the port plate and hst looks almost exactly like the pictures posted earlier in this thread. I am thinking of installing a new gasket and using Permatex Ultra Grey as well.

 

[jhiller18405]

We reassembled the tractor with silicone in place of the gasket. 450 hour and no signs of a leak.