Leaking Powetech Genny Sump Pan

[travelite]

Folks,

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 have. I arrived at my bus some time ago 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:
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Vantare didn't mount the genny on a sliding tray. I'd like to disconnect the fore air springs, lift the front of the generator, and crib under the air spring mounts to gain access and clearance to all the sump pan bolts, but I need a very low profile jack. There's only about 3/4ths of an inch between the sump pan and the floor. Here's the low profile jack I found; it's a Mat Jack 1 (http://www.feldfire.com/15-Ton-Matjack-High-Pressure-Air-Lifting-Bag_p_501.html), max air pressure is 120 psi. It can lift 1.5 tons to a height of 2.5 inches. It's deflated height is 3/4":
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This past Friday I had a chance to give it 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:


FOR EXTRA CREDIT: Where are the main bearing caps?
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[Gil_J]

That generator looks like it's new!

Generally, these bags only run 10-15psi and should be configured in a way that when totally empty they are still supporting the generator. The bump stop appears to be under the oil pan. If so, I'd get rid of it and just make sure there are physical stops at the bags. If you don't change the stops, given this happened once, I'd install a 90 degree elbow on the drain fitting to make sure it can't contact the drip pan again. BTW, I see a red hose going through the drip pan. It doesn't appear to be sealed. If not sealed the drip pan is doing little to contain a spill.

What a great find in the Mat Jack. I have wondered the same before and thought the only solution would be a fork lift.

Main bearing caps would appear inserted from above. That is a setup I've never seen before. What is the bolt on the bottom for? It appears directly aligned with the center of the main bearing.

[Reagan Sirmons]

David,
I'm with Gil, how did you get the Kubota so clean?
The floor even shines.
Great work,
Pres

[travelite]

Thanks Guys,

The generator has only 600 hours on it; I plan to remedy that! I agree, the MatJack's are fantastic. They make them all the way to 70 ton capacity. Here's one (http://www.feldfire.com/22-Ton-Matjack-High-Pressure-Air-Lifting-Bag_p_505.html) that's sized perfectly to lift our buses; again, 1" deflated, max pressure 120 psi, max lift height 9.5 inches! Another great feature is when deflated they behave just like wood cribbing, totally stable and able to handle the load. The MatJack 1 made simple work of what I needed it to do. I can imagine using it for virtually anything - from lifting furniture to applying force to pressure activated adhesives.

Thanks for the insight Gil. I'll check the air springs for internal bump stops, that would be the best solution. Looking at the oil drain petcock, the ball valve is clear of the catch tray edge. It's the elbow threaded into the ball valve that made contact with the tray edge. I'll work on a better solution here. I definitely don't want any possibility of the quick oil drain assembly ever cracking the sump pan again. The red hose is the crankcase breather and it is sealed at the tray. This could have been a catastrophic loss of oil, which would depend upon the oil pressure cut-out switch to shut down the engine.

I've never seen the style of bearing cap assemblies that Kubota uses. It's clear that they end up with a very stiff block. Here's some snippets from the engine service manual showing the assemblies. I'd like to know the tolerance of the 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).

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[Joe Camper]

Lots of Vantare out there just like that. The frame for the doors on the quiet box is also welded in. If pulling the gen that makes that job real tight too. Eventually that drain issue got addresses by vantare but couldnt give u the year the oil drain was rerouted. Plastic air lines and push in fittings in the gen bay is also an area where u can make some big improvement get all that crap out while u r in there.

Looks luke u r having fun very good

[travelite]

Thanks Joe,

It's good to know that Vantare eventually fixed this issue.

I'll definitely get rid of the push to click fittings in favor of a brass compression fittings. If I ever need to remove the generator I'll lift it with my MatJack, bolt casters onto the engine mounts, and wheel it out! :)

[jetart]

wow - That seems to be pretty unique way to get the crank out of the end of the block like that. I haven't seen that before. Thanks for the pictures and diagrams.

[travelite]

Seems this engine design is known as a "Tunnel Crankcase" or "Barrel Crankcase". The design was used in prewar Bentley engines including the Lagonda V12, post war Aston-Martins, and Offenhauser engines. The bearing assemblies are known as "cheeses" or "discs". There's more information over on enginehistory.org (http://www.enginehistory.org/phpbb/viewtopic.php?t=493&sid=7219cdfaed6eeedc823994ca52fc8c9c). Enjoy! :)

[Gil_J]

I can see the added strength of the lower end of the block. I can remember when we built small block Chevy street rods. We always prefered the Corvette or truck blocks. This was because they had 4 bolt main bearing caps versus the standard 2 bolt caps. There must be some disadvantage seeing how few use this design.

[travelite]

Hi Gil,

I'm told that VM Motori and CMD (http://www.cmdengine.com/index.php/en/products/aeronautical-engines.html) use it in their aircraft Diesel engines. Lots of assembly and inframe rebuild disadvantages. The idea that the engine can be shorter, more compact is interesting. IOWs, the entire length of the crankshaft can be bearing surface area, no wasted space for counterbalance weights. That's not the case for this Kubota engine but for the big Maybach tank engines it was:

http://en.m.wikipedia.org/wiki/Maybach_HL230
http://en.m.wikipedia.org/wiki/Tunnel_crankshaft

[travelite]

Well, it took two days but I was successful in removing the old sump pan and installing a new one. If my physical dimensions were slightly different I would not have been able to complete this job - only someone with long lanky arms like me could have the reach and slenderness to get in there! A very difficult job... And, after its all bolted up and torqued what do I find out? Vantare's 3/8 NPT oil drain ball valve doesn't thread into the barely accessible sump ban bung! A quick call to Powertech reveals that the bung thread is metric and most likely straight and Vantare ran a NPT tap down it for a tapered fitting! Turns out the pitch on the metric thread is very very close to the 3/8 NPT as is the diameter such that you can get a seal once tapped. So, do I remove the entire thing and tap it on the bench or do I grease up a tap and contort myself into the small opening to do it in situ? :huh: I should have been a surgeon!

[jetart]

I wonder what the clearance is between the bearing cases and the block?

[Gil_J]

Why not get an adapter? I had this issue once before. The adapters exist but aren't always easy to source.

I would be reluctant to run a tap knowing I'd likely end up with some metal shavings finding their way into the oil pan.

[travelite]

Thanks for the nudge Gil, a little digging turned up this M16x1.5 (male) to 3/8 NPT (female) adapter. I'm in business again. :)

[travelite]

Folks,

My new adapter threaded in perfectly. So, for anyone in the same situation, rest assured that the factory drain plug in a Kubota sump pan is a standard 16mm 1.5 pitch straight thread. If you do the math, turns out the thread pitch on a 3/8" NPT is 1.41mm; hence, Vantare's success in re-tapping with an NPT tap and achieving a seal. (A cutting procedure that they most likely performed with the sump attached to the engine for an $8.00 savings in parts)! Yikes! :)

[Gil_J]

David,

I think the metric thread is also a straight thread, hence the washer. The National Pipe Thread is tapered. I'm stating both from memory, so take it for what it's worth.

[travelite]

Thanks Gil,

That's right, and in addition there's also a tapered metric thread. This is what concerned with this project. I had the straight M16x1.5 to 3/8" NPT fitting but I wasn't sure if the sump pan bung was straight or tapered metric and Powertech didn't know either. I wasn't at the bus to check so I bought the straight fitting and it turned out to be the correct one. (Finding a tapered metric to 3/8" NPT fitting would be more difficult). My local hydraulic shop, Asheville Hose, had everything I needed in stock. The plan is to come out of the sump pan bung with a 90 deg elbow then hang my ball valve off the elbow. This way the entire contraption is inside the containment pan with just the rubber drain hose hanging over the edge. With this arrangement there's nothing to make contact with the drain fitting assembly when the air is dumped from the air springs.

[travelite]

A friend suggested doing away with the fittings and ball valve and instead fitting a section of hydraulic hose with a JIC plug at the end. I had a section of hose made up today; it's a much better solution:

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