WD45 manifold question??

Double-check the mating surface, and see if it's actually flat. IF it's flat, then you're seeing core-shift... a flaw that occurs in casting when the plugs in the mold (that create the core) don't stay in position during the pour.

IF the surface isn't flat, then what you're seeing, is enough erosion on the end ports so that the 'ramp' of the port has a higher apparent position.

It is not unusual for these engines to exhibit erosion around the #1 and #4 cylinders- Thermal expansion causes the manifold to lose contact pressure against the gaskets on those ends, and when that happens, hot exhaust gases leak around the gasket, burning away the iron castings on head and manifold. Eventually, the iron 'burns' away, and the result, is that the port's apparent position and opening shape becomes distorted because of the missing metal.

Another issue that exacerbates the condition, is that the hardware corrodes away. If there's a washer with a nut holding a casting, and the washer rusts away, the tension goes away, and now there's no gasket pressure.

I had a particularly eroded cylinder head on a WD, but the rest of the head was in stellar condition, so I put the head in a vertical mill, and elevated the #1 end about 0.100" higher than the #4 end, then started planing off the manifold mounting surface until I got something that was reasonably flat... then I put a new manifold and hardware on. The end result, of course, was a manifold that if you looked really, really close, appeared to stick out of the #4 area more than the #1, and it did... but I had a flat, and secure seal that's been good ever since.

With these engines' performance envelope, the little change of port volume or geometry has no substantial effect on running character.

That's the theory. In real life, the engine is a thermal device, so when it warms up, things distort and deflect.

Although these engines seem to be simplistic in nature, the industrial engineering that went into their manufacture was brilliant. If you examine each part, you'll see that the machining operations for every piece are actually very minimal, and there are very few planes which rely on other planes in order to get proper fitment.

Here's an example:

In a typical V8 engine, the intake manifold spans from one bank of cylinders to the other, and also covers the pushrods and lifter valley. In order to properly seal against both cylinder heads AND close the valley, not only does the cylinder head port face need to be precisely angled and flat, the cylinder head needs also to be flat, and at proper angle to compliment the port face. Next, the manifold needs to have a flat plane, with proper angle matched across the top of the lifter valley AND the opposite bank. There's lots of complicated tooling required to make that happen.

Next, look at a cylinder head. In order for the engine to be balanced in operation on each cylinder, each combustion chamber needs to have the same shape, and proper valve alignment. That means the casting process needs to be perfect.

Compare that to how Allis did it:

the manifold bolts to a flat plane, and there's NO other dependancies.

The cylinder head is totally flat, with holes cut in it for valves.

Notice... the combustion chamber is (if you have Power Crater pistons) HEMISPHERICAL... that hemisphere is made on a lathe, with a radiusing attachment... so they're all essentially perfect. Couple that to a flat cylinder head surface, you've got an inverted hemi. Oh, and the valves... no fancy angles... once the head surface was cut flat, the machines drilled the holes perpendicular to that plane, and it was done.

Henry Ford didn't hold a candle to these guys... In my opinion, it's the epitome of simple, yet brutally effective engineering economics...

Sounds like it's time to get out the torch, and do some brazing.

It's been a few years since I skimmed a manifold, but I think I just used the mounting bolt holes, and put strips of metal between the manifold and mill table, and bolted it down. The iron wasn't hard, so it skimmed off easily. I have a 4" diameter Carboloy face mill, and I believe it may have been wide enough to do the whole thing in two overlapping passes.

Doug's suggestion of surface grinding works well, too. A guy could do it with a belt sander and a pair of sawhorses... the fact that there's no other dependant planes, makes it darned near impossible to screw up.

Beware of stainless. It can gall and seize like no other material. Use plenty of anti-seize goop.

Avoid titanium in there, too... it's so pricey that the Allis won't know how to run right.

The only concern I have with stainless studs, is that they're typically softer than plain steel, hence, they'll strain under the manifold's thermal expansion, and stretch. Allis probably didn't worry much about it back then, but my choice nowdays would be something that's rather elastic.

Keep a close eye on 'em, and don't be surprised if you get harrassed by the 'correct police'. ;-)

BTW... Nice brass!

You could've just kept mowing 'till you got to good iron. I think I've chewed over a quarter inch off one of mine, and it worked out fine.

Edited by DaveKamp - 25 Sep 2015 at 8:44pm

Sometimes, it's not about the destination, it's about what happens on the way.   

Or if he's like me, the milling machine needs a little exercise, and there's three other projects in the shop goin' at the same time, so it's a no-expense task.

Why do we work on these old tractors anyway... We could just throw the whole lot of 'em away and get new ones...

I echo the fact about the stainless steel studs-be very careful with them. The farm coop I was associated with years ago used stainless in the fertilizer business, not because they came apart easily after 10 years but because they twisted off easily after all those years and the boys found things quicker and easier to fix than when using mild steel bolts.

I'd at least use brass nuts on the stainless studs. There's no getting a seized stainless nut off a stainless stud. Been there, tried to do it. Stainless has its virtues, but it is not tolerant of acids. It should work here.

Been over 10 years ago but I bought a parts wd that wound up being a runner with the manifold leaking.  Took the mainfold to a local small engine shop and he smoothed it up on a flatbed grinder, over an 1/8 inch of material taken off in some places to get in all in the same plane.  About $30 if I remember correctly.  At the time, Mcmaster-Carr had the steel studs and brass nuts so I went with that option, all worked great till a bearing shelled in the rear diff and I haven't gotten back to it.

Wendell(OK/TX) wrote: Been over 10 years ago but I bought a parts wd that wound up being a runner with the manifold leaking.  Took the mainfold to a local small engine shop and he smoothed it up on a flatbed grinder, over an 1/8 inch of material taken off in some places to get in all in the same plane.  About $30 if I remember correctly.

The last manifold I had done ended up being so far out of square that the muffler wouldn't fit through the hood. Expect it depends on whom is operating the grinder

For the curious, here's how I ended up setting it for machining.


All installed, plus my homemade exhaust pipe bracket. After reading many of the discussions on mufflers, and doing some price checks, I opted to go with a stainless straight pipe. Used a bit of the 'red kind' to seal it up tight.  Thus far it doesn't seem offensively loud.


Fortunately the Correctness Police have no jurisdiction in this township. The hood got a quick coat of primer in hopes of staving off the rust for a bit. The manifold got a quick shot of manifold paint, which from previous experience should last until the next rain.

The exhaust pipe is a bit long, but the post driver usually clears the way.


Now, once I get the generator issue figured out....


-Aaron

Yeah, it'll bark a bit. I think I'd be more concerned about keeping rain out... need to put a stick on the can so's you can reach that high... ;-)