Oil pressure woes

[eserv]

You mean low oil pressure is ok?

I came back to post to change the eMail setting so I get notified (new), and I see your post about 6-7psi at idle is ok. Would you expound upon that?

Thanks

6 - 7 psi oil pressure on a B6100 at idle when hot is OK as long as it comes up when you are at higher rpm. There is no need for high oil pressure on these engines, they don't have hydraulic lifters or anything that need higher pressure. If you take it apart I'm sure you will find nothing obviously wrong inside. Of course there has been a loosening of clearances all over the place in there causing leakage of oil hence lower oil pressure than it once had. If it were mine I'd just run it and be happy that I bought a Kubota that is going to give me years of faithful service!
ED

 

[ipz2222]

I just reread the thread, you still haven't put a mechanicle pressure guage on it yet??? You need to know what the pressure is at higher eng speed. You don't have to have a tach, just rev it up some. I don't think you'll be able to see the cam plug with the camera going in thru the gov case, the cam is on the other side of the eng. I just cked the old thread I made and there are not any pictures in it. I know I put them in there when I made the post. Maybe they delete after some time.

 

[Sterno]

I just reread the thread, you still haven't put a mechanicle pressure guage on it yet???

Of course I did, that's where I got the numbers from.

Eserv, I do appreciate the info that it'll survive on 6-7psi but I'm an anxious little fella and probably have some kind of OCD. I gotta get to the bottom of this, checking the cam plug and replacing the oil pump. If that don't fix it it's time to split her in half and re-bearing the bottom end, and yes I'm fully aware of how crazy I sound.

I just can't help it, it's gotta be to spec.

 

[Apogee]

Sterno,

Per the Kubota WSM, spec is 28.44-63.99 psi. No idle spec or rpm is given.

The issue might be as simple as a weak oil pressure bypass spring. The oil relief valve is located directly below the oil filter on the front case and is assy # 15261-3607-0. Lots easier to change than a full rebuild to see if it helps. Heck, you could even just stretch the spring a bit to see if it changes things if you are planning on rebuilding it anyway.

Checking that front plug is something that I'd also be doing after the pressure relief spring. The reason is the 20 lbs of pressure at high rpm. That makes me suspicious...

If you haven't figured it out yet, Kubota parts are gold plated. Folks are recommending to leave it alone because the parts are so darn expensive.

Hope it turn out to be an easy fix.

Happy Holidays,

Steve

 

[z751-hy]

Sterno: I'm glad you're going to get to the bottom of this. I'll be watching, because I have same problem with my 2cyl z751. And its cold and I don't need to be operating until May 2013, so I won't be fixing mine first.
I have not taken a careful look, but a quikie look at my manual suggest I have to take out the radiator, take off the front of the engine to access the oil pump. Not doing that.
But you did say your original oil was gross, so maybe the intake in the sump is clogged. To me, it looks like the easiest next step, unless your pump is easier.

ESERV, if 6psi is ok at hot idle, is 11psi ok at 2800rpm? Before its warmed up, the psi is 5 to 8 higher, like 11psi idle, and 18psi at full. That's noLoad. I have not been able to see the gage when under load.

 

[eserv]

ESERV, if 6psi is ok at hot idle, is 11psi ok at 2800rpm? Before its warmed up, the psi is 5 to 8 higher, like 11psi idle, and 18psi at full. That's noLoad. I have not been able to see the gage when under load.[/QUOTE]

No, I'd want to see at least 20 psi at 2800 rpm when hot. The clearances don't get larger as the rpm does but the pump volume does, you should see a greater differential than that.

 

[z751-hy]

No, I am no where near 20psi, I think I'll look into Apogee's sugg about a weak oil pressure bypass spring. Hope its easy.

 

[eserv]

No, I am no where near 20psi, I think I'll look into Apogee's sugg about a weak oil pressure bypass spring. Hope its easy.

A weak spring would cause low differential. It would be regulating the pressure at lower than desired

 

[moog]

So have you replaced the oil pressure sending switch? What your describing is exactly what happens when the oil pressure sending switch goes bad. That would absolutely the first thing I would try before I done anything else.

 

[Sterno]

Sterno,

The issue might be as simple as a weak oil pressure bypass spring. The oil relief valve is located directly below the oil filter on the front case and is assy # 15261-3607-0. Lots easier to change than a full rebuild to see if it helps.

That was my first thought, unfortunately to gain access to the bypass valve requires removal of the front axle support! (not the best design)
At that point it's only a handful of bolts, 2 springs and a new gasket to pull the gearcase and check the pump & Cam plug.

I'll be sure to take pictures

 

[Apogee]

Depending on where you guys are located you might also consider trying 30 weight oil in it. It will help if the motor has excessive clearance. Just need to make sure the tractor is about 20 degrees F or warmer when trying to start it as the oil will be pretty thick at that temp. If you keep the rig in the garage, then it shouldn't be an issue.

**If you live in a really cold climate where the tractor sits outside, then I wouldn't advise doing this**

The thicker oil base stock will hold the oil pressure a bit higher.

Steve

 

[TyMarrs]

My two cents. I had the exact same symptoms last year on my '78 B7100, ~3000 hrs. Oil light coming on at idle when hot. Checked sending unit and gauge wiring - no issues. Installed mechanical gauge - showed 11 psi hot at 2800 rpm and 6 psi idle. Checked and cleaned oil pressure relief valve with no result. Changed oil and replaced filter with no change. Pulled gear cover and - surprise! - cam plug was missing. I found it in the oil pan.

Ordered replacement aluminum plug, gasket, and o-rings from local dealer. Installed plug with a brass drift and permanent loctite. Oil pressure after repair was 60+ cold at idle, 30 hot. 40-50 psi at operating speed. I installed the mechanical gauge on the dash for peace of mind.

Once you've eliminated everything else - crack 'er open and have a look!

 

[Countrymech]

My two cents. I had the exact same symptoms last year on my '78 B7100, ~3000 hrs. Oil light coming on at idle when hot. Checked sending unit and gauge wiring - no issues. Installed mechanical gauge - showed 11 psi hot at 2800 rpm and 6 psi idle. Checked and cleaned oil pressure relief valve with no result. Changed oil and replaced filter with no change. Pulled gear cover and - surprise! - cam plug was missing. I found it in the oil pan.

Ordered replacement aluminum plug, gasket, and o-rings from local dealer. Installed plug with a brass drift and permanent loctite. Oil pressure after repair was 60+ cold at idle, 30 hot. 40-50 psi at operating speed. I installed the mechanical gauge on the dash for piece of mind.

Once you've eliminated everything else - crack 'er open and have a look!

Excellent report!! I wonder why it pops out, is it that oil pressure can build up behind it, pushing it out? Yet the internal oil leak isn't the same as the oil gallery having a hole in it....still it can build some pressure. Just wondering aloud....I'll be on the lookout for this on my next engine rebuild.

 

[z751-hy]

Wow. Now I have 2 reasons to drain the oil, and remove the sump/cover/bottom. I'll be looking for that plug, and I can clean the sump intake.
I wonder if that plug comes out, how likely it is to just fall down.

I'll keep watching, because I won't be trying anything until April or May.

 

[Apogee]

I've repeatedly read about this issue. Too bad Kubota didn't put a threaded pipe plug in there instead. Something like this would solve the problem for good and still allow the oil gallery to be cleaned when rebuilding:

http://products.coburnmyers.com/viewitems/sockets/socket-pipe-plugs

Might be worth considering if it can be done without leaving metal shavings behind.

Steve

 

[Apogee]

Thinking about this a bit more, I wonder how often this really occurs. I remember reading more than once of rod bearings looking like new and the engine having had spun main bearings. I always found that odd because it's usually the rod bearings that go first. Unless the plug falling out causes the main bearings to starve for oil...

It would be interesting if nobody (or very few) had ever installed mechanical gauges that would help connect the dots of the front plug falling out and the resulting low pressure causing premature bearing failure.

Steve

 

[ipz2222]

apogee, you can't tap the cam and install a screw in plug, the cam is too hard. I tried that when I had mine apart. I made my own plug (solid) drove it in and then spot welded it in.
Someone else said he had only 1 personal experince with this plug being missing, but it happened enough for Kubota to put out a bullitin on it and there are several people here that have found it missing ,, me included.

 

[Apogee]

Where exactly does the subject plug reside? Is this the blind plug that goes in the nose of the cam itself?

I haven't yet pulled my engine down and would like to know its exact location. I was just looking at the parts diagrams and it was tough to tell, so figured it best to ask.

Would love to know from those who have found it missing.

Thanks!

Happy New Year,

Steve

 

[ipz2222]

The very center of the camshaft in the front. If it is missing , there will be a hole in the center of the camshaft. Youy can actually spin the eng over and see the oil shoot out of the hole.

 

[kubotasam]

The very center of the camshaft in the front. If it is missing , there will be a hole in the center of the camshaft. Youy can actually spin the eng over and see the oil shoot out of the hole.

I am pretty sure there is two plugs. One at each end of the camshaft. Kubota parts shows two required on the parts diagram.