Freshly rebuilt Kubota B6100 with magic expanding oil problem

SilverLakeFab · May 20, 2014

I am having trouble with the 1978 Kubota B6100 that was just rebuilt. I did a complete overhaul on the motor, and after running it for about 2 weeks this past winter, the rear main seal went on the engine, allowing engine oil to pour out of the starter when you ran the engine. From what I could tell, I had too much engine oil. My shop manual states that the machine should take 4.1 qts, and I was able to confirm that info with another web site, but it turned out to be wrong. According to my dip stick, my engine, when not running, is at 80% of the acceptable range according to the dip stick. I replaced the rear main seal, along with the two paper gaskets that hold the rear main seal flange, reassembled everything and put 3 qts of oil in the engine, which according to the dip stick is still spot on. After running for about half an hour, engine oil starts pouring out of the valve cover breather hose. Of course, I turned off the machine immediately, and checked the dip stick. When I pull out the dip stick, engine oil pours out of that hole. I honestly don't know what could be causing this. The oil filter is brand new, so that shouldn't be clogged, and everything inside the engine is brand new as well. Since the dip stick goes through the side of the bottom part of the engine block and straight down into the oil pan, how is it that I now have so much oil in the system that it floods out? Does anyone have any advice as to what to do with the little tractor to solve it's oil problem? From what I can tell, it's like I suddenly have more oil that I started with. Before pouring in the new oil last (2 days ago), the oil was allowed to drain thoroughly overnight. Ug; any ideas would be greatly appreciated.

Jim Nelson · May 20, 2014

It sounds like you have a bad seal in your hydraulic pump and are getting hydraulic oli into the crankcase. I had this happen on a B7200 I had.

SilverLakeFab · May 20, 2014

I hadn't thought of that, but it's a possibility. The loader that I have installed on the machine is a bit slow, so maybe that is the reason for that as well. It's totally worth a shot. I'll get the seal on the way and see what happens. Thank you for the help!

firemech · May 20, 2014

Also, check to see if your oil smells like diesel fuel. My previous B6100 (1983) started making oil at about 11,000hrs. It definitely was being caused by diesel fuel. I never did repair it but rather parted the tractor out; but my dealer said it could have been a seal at the back of the injector pump or injectors not sealing and leaking fuel by the rings when not running (probably not your issue with a fresh rebuild). My engine would make enough to start leaking out the dipstick in about 8 hrs

SilverLakeFab · May 20, 2014

Well, I'm going to cross my fingers that the seal on the back of the hydraulic pump will be the problem. That is a seal that I have not yet replaced. The seal itself is only about $6 ($14 with shipping), and that will only take me an hour or two to replace, so I'll give that a whirl first. I drained the oil on Sunday evening after experiencing the oil overflowing and just thinking that I had put too much in, and I didn't notice a diesel smell when draining, but I also didn't put my nose right up to the pan. I'll change out the seal on the back of the hydraulic pump and report back. Thanks again for the help!