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Full Version: First newbee mistake w/ generator on SpongeBob
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I had an unusual failure occur recently. I'm new to air bag suspended generators. I've never played around with the two pressure regulators feeding air to the fore and aft air springs, but someone must've. I arrived at my bus yesterday to find a puddle of oil on the floor under the generator. Seems I've been driving with very little air pressure in the front air bags. In addition, the rubber bump stop mounted to the floor of the enclosure and designed to support the engine sump pan had sheered off. This allowed the oil drain petcock to rest firmly against the enclosure tray. I guess over the miles the force and vibrations were too much for the welded on sump pan threaded bung. The weld attaching the threaded bung to the sump cracked and began leaking! The sump pan has to come off to repair the weld. Odd failure! I now know to pay particular attention to the pressure in those air bags and to make sure the resting rubber bump stops are in place and secured properly! This is my first mess-up with this bus! Sad

David, are there 4 bags for the generator?
Is there a gauge that shows the pressure?
Looks clean , even with the spill!
Interesting problem. A heads up for owners with air supported gennies or compressors (my 120 V aux...has manual airbags)
Suspect a blockage to the front bags... air reg or check valve? A leak would have to be large.
At first I thought... why have 2 regs? Use different diameter bags and one reg. which I thought was in my 450. (imagine, BlewBird had one up on Prevost).
Now .. thinking... There are 2 regs aft of the Aux. compressor that I don't know what they are for. One 35 PSI , and the other 55. Originally , I thought one was for the toilet but no.
Maybe there are 2 lines going to the genset. I will have to try to trace or test.
Thank you.

I wonder what BB did with the bags with the genset move?
This past Friday I had a chance to give my MatJack 1 a try. I disconnected the fuel pump and tied it out of the way; I removed the air hoses and air fittings from the top of the air springs; I then removed the two top bolts releasing the air springs from the engine support mounts. I plumbed the MatJack 1 with air via a pressure regulator and slowly lifted the front of the Kubota. I then packed cribbing between the engine mounts and the air springs for support. This gave me enough room to reach around the backside of the kubota to release all the sump pan bolts. After unbolting the oil pump strainer the sump came right out:

QUIZ: Where are the main bearing caps?

Looks to me it slides out the front or back of the engine. In picture six, it shows something that looks like a rubber seal around the area where the cap would be. Possible the bolt on the bottom holds it in place, and the "cap" is bolted to the crank before installation.
That's it Steve. Here are a couple of snippets from the engine service manual showing the main bearing assemblies. It's clearly a very stiff block. I'd like to know the tolerances of the bearing assembly fit to the engine block. The bolt coming up from the bottom cinches each assembly to the block. The manual says that each bearing cap assembly is of a slightly different diameter requiring that they be placed on the crankshaft in proper order. (Maybe a machinist here can shed some light on the tolerance of the fit).
Maybe you can contact the manufacturer and ask. I would assume(and you know what word meansWink) that they are very tight. I don't think you would want any movement in that area. Do you know what rpm the engine is operating at? I have built many engines over the years, but have not encountered anything like that. The old 356 Porche comes close with needle bearings but that it.
Main bearing caps(at least on car engines) are numbered and set to very, very close tolerances. Sometimes you have to "persuade" them on. Most times, removal is with persuasion.

I learned that this design is known as a "Tunnel Crankcase" and that it's a very highly regarded design dataing back some time to prewar Bentley engines including the Lagonda V12, post war Aston-Martins, and Offenhauser engines. The bearing assemblies are known as "cheeses". Seems Kubota really outdid the competition in adopting this design, and it's one reason why they run forever.
In addition to "Tunnel Crankcase" these engines were also known as "Barrel Crankcase", or split barrel. The bearing assemblies are known as "cheeses" or "discs". There's more information over on enginehistory.org. Enjoy!
wonder if the design is accommodating the all at once demand of the genhead when operator turns on an electrical demand. they dont powerup slowly like a kubota tractor. I picked up several night towers that run full speed all the time with more than 10,000 hours on them. both are being used by pop Warner teams for night time practice and run perfect one is a lister and one a kubota. I notice that Kubota makes different cranks and bearings for different applications even in the same engine version. you almost have to go the oem for parts. I never have rebuild one but ran parts for the mobil tec at my shop reuilding a Kubota/Bobcat. Tractor Kubota parts may not fit.

I like the jack but have a fear of compressed air for lifting. I would much rather use displaced hydraulic fluid. You have a clean rig there
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