Urba Centurion Update - (Kubota diesel, 100+ MPG in mixed driving - Fall 2012 on)

[changzuki]

Originally Posted by BobS

Jerry
I see what you mean about Dottie. She, like I, skipped the gray stage. If you have a particular diet you are feeding her, I would love to get it in a PM. It, of course, would always carry the title "Dottie's Diet"..

BobS,
I pm'd you the "Dottie Diet". Hope it is useful for your pup.

If anyone reading this has an interest in the "Dottie Diet" I'd be happy to send it. If you can't bring yourself to pm me but would still like to have a copy of the "Dottie Diet", maybe ask BobS (if he's agreeable) and feel free to share with anyone..... Use at your own risk!

~CrazyJerry & Dottie

[changzuki]

Installation Success!
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After mulling over the options, the front four body-to-frame mounting bolts were removed and the body was jacked up off the frame. Two bolts around the each front frame horn, and two behind the front wheels where you'd normally find such attachment points.
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Must be getting old... In the past I'd have found a way to cram everything in place, but nowadays, bolts are removed and strategically placed to remember their original locations... And then there are the bathroom breaks....
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~CrazyJerry

[changzuki]

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Once the new transmission w/overdrive unit is actually in the car, it becomes apparent how much more space it consumes. The first shot below is the old three-rail 4-speed looking from the backside towards the bellhousing:
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This next shot is the new single 4-speed transmission w/overdrive unit looking from the backside towards the bellhousing:
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Wiring the overdrive unit is simple... If anyone makes it that far and needs clarification please let me know and I'd be happy to send you a drawing that takes the mystery out of the circuit.
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In spite of using stock Spitfire offerings, the shifter was shoved rearwards about a full inch. This caused problems with the shifter throw when going in to 2nd gear and especially 4th gear. The fix was to elongate the hole in the console, easy enough! Shifting from 3rd to 3rd overdrive and from 4th to
4th overdrive is just a flick of a switch away! The switch is located dead-center on top of the shift knob. It does not require the clutch to be depressed when shifting into, or out of, overdrive. It's pathetically easy - the ultimate in lazy!
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~CrazyJerry

[changzuki]

The maiden voyage with the newer 4-speed with overdrive was very disappointing. What was previously kinda fun, albeit with limited top speed, was now a complete garden slug - and it struggled just to match the previous 65mph limit.
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What happened?
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Was the extra weight partly the issue? Maybe the internal overdrive pump - even when not in overdrive?
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To add even more joy, the mystery vibration was still present and accounted for.
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As for the the overdrive itself, when the switch was thrown, the it engaged every now and then, or not at all.
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Since all the tools used for this job were still out and the stall was still setup, the thought of reverting Centurion back to Green Grand Prix trim was very appealing. The thought of pulling the engine yet again was not.
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So I walked to the front of the car and.......... :
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http://www.youtube.com/watch?v=455Dt6KsPuA

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~CrazyJerry

[nemo]

Sorry to hear you that your goals were not meet, yet.


Interesting read on j Type overdrive. This information was from a TR6. So it might be different.

J Type Overdrive Part I

The pump runs all the time that the mainshaft is rotating. However, if the OD is sent for direct drive, the pressure relief is set to a very low pressure (~20 psi) and the pump has the very easy task of pumping oil to the mainshaft for lubrication.

At normal driving engine speed of 3000 RPM, 3 X .033 or about 0.1 HP (about 75 watts) will be consumed. The OD might get a little warm but certainly will not get hot due to the pump energy. Note that this is not a precise calculation but probably has an error less than 25%, so it shows that the power consumed by the pump is negligible. There are other sources of power loss (heat) such as friction in all the bearings, bushings and thrust washers so the OD likely gets pretty warm if operated for an extended period.

By his calculations in direct drive the loss should be minimal. How do the gear ratios without the OD compare to the old transmission.

[changzuki]

Originally Posted by nemo

Sorry to hear you that your goals were not meet, yet.


Interesting read on j Type overdrive. This information was from a TR6. So it might be different.

J Type Overdrive Part I

By his calculations in direct drive the loss should be minimal. How do the gear ratios without the OD compare to the old transmission compare

nemo,
You beat me to that post - and a thank you as well. I have that article and there's another somewhere here in this disaster of a place where according to it, the choice of oil (a hotly contested topic) along with rpm and temperature can result up to approx 5hp being lost in this setup. If true, a Spitfire with 100+ ponies that might not noticed that, but in the right conditions that is a huge hit for a 17hp Kubota. The attraction to the Spitfire setup was, the fit with minimal modification, and, they are relatively inexpensive when compared to the alternatives some folks go for. In 30 years when there's no parts, etc to be found, I'll be slapping myself right?

The gear ratios in the 1500's 4-speed are nearly identical to the 1966 3-rail 4-speed (except 1st where the 1500's is a bit taller, less likely to pull out stumps)...

Getting ready to make a post that addresses the overdrive intermittent engagement issue. Mavis Beacon has me at about 9 words per minute, so I had to start a couple of hours ago!

~CrazyJerry

[nemo]

Spitfire

71 58@5200
72 48@5500
73 57@5000

But still triple what you have.


The only issue I ever had with the OD was the connections at the bottom of the switch being loose. Looking forward to the post.

[changzuki]

Originally Posted by nemo

Spitfire

71 58@5200
72 48@5500
73 57@5000

But still triple what you have.

Haha - thank you for that reminder! Posing in just a second, but today after working I did have time enough to remove and replace one of the engine mounts. The nut up inside the frame is rather...... challenging!

~CrazyJerry

[changzuki]

One reason the overdrive wasn't engaging is because the incoming voltage to the solenoid was low. The reason: discovery of a 1991 Service Bulletin outlining a catastrophic failure... So, I was running off the battery with no alternator on that maiden voyage... Read on...

The original Centurion's Kubota D750 was equipped with a dynamo to charge its battery. Small, light and quite simple it would keep the battery up but running accessories might prove challenging and unless one is willing to go fully led (save the headlights) you probably won't do much night driving.
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Also, if you are using one of these dynamos - dump it - I did! The bottom line is they will produce too much drag for something like a Green Grand Prix competition. These dynamos operate on the same principle as most motorcycles do: and it's not a very efficient way to charge a battery... For example, when the battery reaches maybe 14.1 volts or so, the voltage produced by the dynamo beyond that setting will be shorted to ground by the external regulator. That's right - shorted to ground - and regulating by dissipating the excess as heat! So in essence, the dynamo's 25 amp output (and drag from it) is continuous from the moment the engine is spinning it, until you shut it off. Not very Green Grand Prix record setting friendly if that's your goal.
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Also, the dynamo below (next to the Delco 10si) is of the "permanent magnet" design and when you spin it by hand, you'll feel the cogging of those magnets making it tough to turn. Night and day in this respect to the standard alternator.
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This is the one time I would trade off light weight (of the dynamo) for the heavier electro magnet (field type) alternator. While this standard type of alternator does use energy just to create a field, its ability to taper off voltage to a fully charged battery (by not producing any extra) makes for a free'er spinning unit. In the case of Centurion, you don't need electricity once the engine is running, so it makes sense to have a charging system that will taper output down to a trickle, and not continuously short the excess to ground..
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It's also easier IMO to incorporate an alternator cut switch on a standard type alternator than a permanent magnet generator.
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In an earlier post I mentioned Centurion used a "stock mid-eighties Delco 10-SI with a 12-SI fan, and is a single wire-to-battery circuit". This is a robust alternator that is inexpensive, easy to rebuild if necessary, and very common.
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After a long-term assessment of it, the time has come to ask if this selection is still a good one.
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The answer is no - at least not for the D750/D850/D950. The reason for this is I've recently stumbled over a 1991 Service Bulletin from Westerbeke Corporation. Apparently these little engines made their way into marine applications too and alternators such as the Delco I was using were one the alternators of choice.

The problem is the single lower mounting tab and where it attaches to the mounting boss that's part of the D750/D850/D950 engine timing cover. If this attachment loosens (possibly from vibration), continued use can cause the upper bracket to fail. Once this happens, the extra stress from the unsecured/loose alternator has been reported to break off the mounting boss. If the owner is lucky, then the entire front of the engine (timing cover) must be replaced. If luck is not with you, the busted metal will drop right into the sump and/or timing gears and then the problems multiply.
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The alternator replacement fix is fairly easy once you know what it is. And when you don't, there's endless hours on the internet doing some digging. There's a couple of compact alternators that have double (front and rear) lower mounting tabs that will straddle the Kubota's timing cover mounting boss and provide a very stable/reliable arrangement. Kubota has used an older style Nippendenso externally regulated alternator. I tried one of these 35 amp wonders but ultimately scrapped the idea since it was too difficult to decide on a suitable location for the regulator. Space for such items are at a premium with Centurion.
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A simpler and more elegant one-wire solution is available and it came on the gas sipping Geo Metros and Pontiac Fireflys. Delco supplies a part number but it's a Nippendenso unit:
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If you're using a Kubota D750/D850/D950 strongly consider trying to find (or make) the Kubota optional lower mounting bracket. The bracket will mount to the timing cover boss directly, and set the alternator a bit higher which makes removal of the oil filter a breeze! This higher position also gets the rear of the alternator a bit further away from the exhaust manifold so the alternator won't pick up as much of that heat. (My original reason for wrapping the exhaust manifold)..
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https://www.youtube.com/watch?v=phwiFsiqhoE

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Is it any wonder why fuel logs come soooooo slooowwww for Centurion?
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~CrazyJerry

[changzuki]

With the battery now held at a steady 14 volts, the overdrive was now working as designed and it was time to look into the sluggish performance of the D850 and hopefully even find this intermittent and very annoying vibration.
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Pouring over past notes/comments did lead to an idea. I had optimized the D850 with the old three-rail 4-speed and rear 3.27 differential for 50-52 mph. That was the target and the sweet spot. With the substiution of the single-rail 4-speed with overdrive, things were now out-of-whack. For example, where 50mph was 2414 rpm, the same 50mph was now 1931 rpm and that's a huge difference, especially considering horsepower output is now going to be less at 50mph w/overdrive engaged... The nearly 500 rpm drop represents approx 1/6th the 3000rpm advertised limit of this engine.
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On a modern diesel or gas automotive engine, this may not be a big deal but consider that the old school Kubota D850 is of the fixed fuel timing type. This can be a blessing or a curse. In a tractor or a genset where you just slide the throttle lever to the "rabbit" and leave it there, this fixed optimization can be very beneficial, however, in autos the accelerator foot becomes bored quickly and the engine must respond to its needs/wants/desires. This type of variable input works against a fixed fuel timing system like the Kubota's D850, so if you're going to play in this area, be sure you know what everything downstream of the engine is, what affect it will have on something like the rpm, powercurve, bsfc, etc, and then see if it's possible to even match the timing to the drivetrain and your driving expectations.
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This is very time consuming, and if caution isn't followed, can have negative consequences on both the engine and your wallet.
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The reason for going through this self-created pain is quite simply this:
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The above is not a fuel log, but a snapshot of where Centurion currently stands with her economy.
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~CrazyJerry