Thunderbird 840 Loader

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Thunderbird 840
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Thunderbird 840
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Thunderbird 840

This is a Thunderbird log loader parked by a tower where it works the 'hot deck' and also sorts and loads logs on trucks for shipment. Typically, the logs will be sorted to various grades and classes which are usually defined by a combination of size, length, ring count and limb size. Often they will be further sorted at the mill, or processing yard, but very often they are sorted 3 to 6 different ways right in the landing with a load of this and a load of that being shipped. The shipment of unsorted logs is called "camp run", which is a term that goes back to the days when loggers lived in logging camps and shipped whatever they produced for an average price. You probably can figure out what 'high grading' means in the context of a 'camp run' sale.

I can't put my fingers on the precise specifications of the T-Bird 840, however, I have found the specs on a T-Bird 838 loader which similar and perhaps just an older model. The 838 is an 85,000 lb machine perched on a Cat D6-H undercarriage (rollers and track chain). Power is a Cummins 6-CTA set at 1900 RPM for 230 HP. There are 4 pumps for the hydraulics. The main pumps are 57.5 GPM @ 3,900 PSI. These are open center circuits with one handling the stick and the left track and the other providing service to the main boom, the right track and the live heel. An override allows both pumps to be routed into the boom circuit to create a high speed boom lift. There are separate closed center circuits for the swing and the grapple control. The working level runs from 18 feet below grade to 28' above grade. If nothing else sets these 'made to be log loaders' apart from the 'converted excavators' it is the 4 pump configuration. That 4th pump runs the grapple so the grapple is 'hot' all the time. Converted excavators obtain the extra functions with a flow divider off of one of the main pumps which usually means that those 'tool' functions are either slow or don't work at all when a main function is engaged. With a dedicated pump, they are right on it all the time.

For more on the Keto 1000 processor see also Keto 1000 Processor

Dateline January 2002

This article was first written in 1997 when this loader belonged to the neighbors and was fairly new. It is sports a total of over 14,000 hours and has joined our collection of elderly machines. It is of an early 1990's vintage, and needless to say we now know more about it. It is now essentially an orphan as Ross Equipment who made them locally sold out to Madill who closed the line down in favor of their own Madill brand machines which have a lot of similarities.

Needless to say, we now know more about the machine as well. The 840 is indeed an newer version of the 838 with a little more reach (40 feet instead of 38 feet as with the 838) and more weight---over 50 tons. There is also an engine change. Instead of the Cummins 8.3, this machine uses the more robust Cummins L-10. The issue here is not more power. I'm doubtful if the horsepower setting on the L-10 is that much different, but the heavier engine doesn't have to work quite so hard. Indeed, it is usually operated at just a fast idle because if you open up the throttle it is so jumpy that you can't manage it.

Don't get me wrong, the C8.3 is a good engine and has ratings available from 150 to 300 horsepower. The L-10 which has since been discontinued by Cummins in favor of the M-11 is simply a larger engine.

All of these engines, however, represent the end of an era--the era being one of mechanically controlled and governed engines. This year represents the cut over to electronic/computer controlled fuel systems for further manage pollution and emissions issues. The classic designs with Bosch pumps or PT pumps as Cummins used on many engines for 50 years are now history.


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Thunderbird 840
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Thunderbird w/ Keto 1000
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T-Bird 840
Thunderbird 840 (before it was ours)

A digression is called for here to point out the difference between the log loaders and the excavators. A careful view will disclose that the booms are radically different. The excavator booms are configured for digging below grade. They customarily have a dog leg in them which gives them clearance over the machinery, but still allows the end of them to be lowered well below ground level. By contrast the log loader booms are usually straight and often lighter as they don't have to take the stresses inherent with digging. Next, notice the physcial placement of the hydraulic cylinders which control the stick (or dipper). On the loader configurations you will see this cylinder Under the boom and on the excavator it is on top of the boom. The reason is that a hydraulic cylinder is inherently more powerful when it is expanding than when it is contracting because when contracting its displacement is less due to the cylinder rod. since the primary digging action of an excavator is done with the stick it is very important that these cylinders be optimized for digging, but putting the cylinder on the bottom for the loader means that it will lift more.

You can see this if you look at the other machines such as the American 35 and the American 35A shown on this site. There are, of course, exceptions to the rule, at a review the cylinder configuration on the Drott 80 will give you a good laugh. Every cylinder on it is 'backwards'. It was obviously engineered as a digging machine and cobbled over into a loader. The Drott has some fuel economy, performance problems because of this too.

These T-Birds have a specially made high ground clearance car body so they can be used for loader logging. You can almost duck and run under the thing, which contrasts with the Hopto 900a which you have to park up on a block of wood before you can even crawl under it.


Automated processing of trees into logs is one of those ideas whose time has come. Shown above in the Thunderbird 840 with the grapple replaced by a Keto 1000 computer controlled processing head. This head is designed to pick up a tree, measure it, delimb it, and saw it into logs. The computer in the cab will even tell you how much wood you processed in a day.

As with many of the processor heads, the Keto is a Finnish product which comes to use from Canada. See Hakmet. There are several manufacturers of processor heads, but the Keto is unique in that it uses a set of tracks for driving the log through the system instead of spike wheels which others use. One of the issues with a processor head is fiber damage. Systems with spike wheels spike the log down the side producing spiked lumber (not a good thing). These processor heads come in a number of sizes, and need to be matched both to the timber size and to the size of machine on which they are installed. What you see here is a Keto 1000, the largest of the numerous Keto models. It opens to 39.5 inches implying that it will take a pretty good sized tree. It also needs a pretty good sized carrier. Here it is mounted on a Thunderbird 840 which is about the minimum. According to the manufacturer it should be on a 210 to 350 HP machine. The T-Bird has an L-10 Cummins set to around 250 HP, and we would rate it as 'adequate'. We considered installing one on the lighter less robust Link-Belt 4300 but decided that it was not a good idea. Bigger is better if you are working in large timber.

These heads are made with a flip up cylinder so they can be used for falling as well, however, we don't use it for that, as the Thunderbird is not armored for falling. If you have one set up for falling, you can use the single machine for 'cut to lenth' (CTL) processing. In this approach you fall the tree with the dangle head processor, thing pick it up, strip the limbs and buck it all at the stump. You then move the pieces to the landing.

Our approach is to fall with the Rotosaw where possible, or by hand where necessary, move the trees to a place near the landing, and then process them and dump the processed pile close enough to the road that the loader can reach it.

Orgins of Thunderbird equipment

A word is called for about the Thunderbird brand. There is a rich tradtion of manufacturing heavy equipment on the West coast and logging equipment in particular in the Pacific Northwest. While we think, for example, of Caterpillar being from Peoria, the company was formed by the merger of Holt and Best, both crawler makers based in San Leandro, California.

Hyster was born in Portland and made various logging attachments for dozers, particularly winches and double drum sets, in addition to making forklifts. The competition in winches, Carco is part of Pacific Car and Foundary -- now Kenworth etc. Skagit and Washington was legends in Pacific Northwest logging. Both made Drumsets for cable logging (donkies), and followed the technology into fully self contained towers and swing yarders. Alas, both Washington and Skagit have disappeared. Ross Equipment was a very large forestry related iron dealer in Portland. When they ran out of iron to sell, they decided to make their own. They bought the Danebo factory in Eugene which made carriages, and began manufacturing a line of yarders and hydraulic loaders. The Thunderbird 840 is one of the finest examples of their manufacturing work. Ultimately, though, even they recognized that domestic manufacture of hydraulic loaders was not cost effective. Their later models usually denoted with a 12nn in the model number were Korean excavators reworked into log loaders. Ultimately Ross disappeared and the Danebo factory was sold out and Madill bought the parts support. As I write this Madill is one of the few surviving local manufacturers of log loaders. They work making them in a factory in Kalama, WA, but have consolidated production in their British Columbia facility, and despite a good reputation, Madill loaders are few and far between here in the states. Presently except for the purpose built Madills, all tracked log loaders are after market modified excavators. I can't tell you with precision from when to when they were made, but I would put the Thunderbird name on equipment made in the 1980's and 1990's.

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