Please Identify this Tractor - WD Maybe ?

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There is another manifold with a rectangle cover plate that had something to do with kerosene.

The 'W' looking newer manifold has improved airflow and horsepower advantages over the older horizontal tubes type. One of the changes on the WD45 marketing for higher HP.

WD45 updates, dealer video : https://www.youtube.com/watch?v=1Viw0LBJClM

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When did they make the change ?

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Yes, the center photo shows what most will refer to as a WD45 manifold though it was used even after that with D17s and later too. Nowadays, it really is the only new manifold supplied as a replacement for all 201 and 226 CID applications. 

The WD had a straight gear shift lever from its introduction in 1948 up until late 1952 when the newer transmission was introduced with different gears and the curved shift lever.

Being from Kentucky, I am sure you have met "The Crack Doctor" AKA Ray's Crack Shop ; located on Hwy 210, between Campbellsville and Hodgensville, that guy can perform miracles with cracked, broken, and busted exhausts, intakes, and engine blocks.

In the 1980s, a friend had an exhaust manifold off of a Michigan loader that was broken in two pieces in the tube between flanges; my understanding is that those particular engines/manifolds were notorious for breaking in two.

We took it to a shop in Elizabethtown where they put it in an oven and slowly brought it up to heat for several days; ten or twelve days, if I remember correctly.

Prior to putting it in the oven, they sand-blasted it and bolted it onto a jig that had the same bolt-hole spacings as the engine.

Once the manifold had reached the peak temperature, those guys somehow welded it inside the oven, using Nickel rods.

After welding, it took just as many more days in the oven to slowly bring it down to normal temperature.

Once repaired, it lasted many more years and is still going strong. 

No, can't say that I have. I am a transplant from NY. I've been here in KY for 22 years now but have only had my tractors here from NY for 7 years since 2015. WD45 got a new manifold before coming here and the WD got 1 last year I bought online. I rarely get south of Radcliff with all the commuting I do into Louisville during the week for work. Seems like those old-time specialists are getting fewer and fewer. I can't even seem to find much local for radiator work or tire work which I do need soon.

The original manifold that my 1949 WD had on it. It was broken in 2 pieces at 1 time and Dad had JB welded it once which was letting go again plus the mating surfaces were badly eroded from running too long with bad gaskets. I finally got a good salvaged 1 online and now the WD matches with my WD45.

Welding ANY casting properly requires bringing it up to a high temperature, and Iron is a perfect example.  Cast iron needs to be ductile to survive welding, and a high-nickel rod brings ductility to the iron in the immediate welding area.  Frequently, the weld area is very ductile, but the remaining parent metal around the periphery, is not, and as the weld's Heat Affected Zone is cooling, it is shrinking (just as it expanded during the welding process) and the non-ductile periphery because stressed, and a new fracture appears.

Exhaust systems fracture for only two reasons:  They're not ductile, and they're heating and cooling.  We don't melt down fine wine glasses and twist them into coil springs for cars, but they make an impressive spring as long as they're not pushed past their limit.

Allis exhaust manifolds are, in comparison to every other engine manifold of the time, generally some of the best, and not just because A-C was a foremost wizard of foundary process, but also because they knew that something attempting to expand, was best to allowed to do so...  there's a little slack to allow linear growth in the 'log'.  This put the gaskets between under a fair amount of stress, and they tended to fail a bit, usually more on the #1 and #4 cylinders, due to the manifold wanting to 'bow' itself outward.  The end result was erosion from the end gaskets, seemingly most often at the #1 end... but a burned-away manifold can sometimes be skimmed flat with a face mill (or in my case, a single-point flycutter worked fine, too).

But all the tractors above are WD's.

The suggestion of a WD-45, is the curved shifter (though later WDs had them, and the angle-cut gears), and the lack of large cover on one side of the block...  the WD45's 226ci didn't have that cover that appeared on both WC and WD 201ci engines.