Feeney Construction Log Page 6:
Valves and Rockers.

 

 

 

 

 

 

 

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In this chapter, we'll examine the machining of the Feeney's valves and rockers, plus the rocker post. Finally, we will try to buy some 1/32" diameter cotter pins (or split pins, if you would), and having concluded that a large pile of rocking horse droppings is more easily obtainable, we'll make them too!

  1. Some Notes on the Plans
  2. Machining the Valves
  3. Forming the Valve Seats
  4. The Rocker Post
  5. Machining the Rocker Arms
  6. Making Split Pins
  7. Seating the Valves

Some Notes on the Plans

In the plan set received with my casting kit, drawing FE-15-10 (Cylinder - 15cc) notes the valve seats are "0.468D x 45 degrees to suit valve FE-15-40". My plan set did not have this drawing. Instead, it had FE-10-40 (Valve 10cc) with valve heads of 0.375" diameter. Now apart from the fact that these valves would drop right thru the cylinder openings, if said openings were made to the 0.468" dimension there will be 0.032" clearance to the cylinder walls, and 0.062" between the valves, provided the valve stem guide holes are precisely symetrical about the bore axis. Recall that the guide holes were drilled from the top of the cylinder and even though the jig holding the cylinder for this operation was centered under the mill/drill, minor deviations are possible, or likely. Further, my bore is slightly smaller for resons explained in Part 5. The cylinder plan does not give the actual valve opening diameter, only the diameter of the chamfered seat. I decided to reduce the dimensions so there would be no great danger of a valve intersecting a cylinder wall. The openings are about 0.380" or so. The valve heads are 0.405". The chamfer is just enough to obtain a seal—I've no idea what this might be, and have no accurate way of measuring it.

Machining the Valves

Like the crankshaft, the Feeney's inlet and exhaust valves arrive sand-cast in aluminium bronze alloy. The casting sprue provides a way of arranging adequate workholding. In this photo, one valve has been held in the 3-jaw to machine the sprue to a stub suitable for gripping in a collet; the other remains as cast for comparison. Clean up the worst of the pimples on the stem before chucking. The stem is big enough that any slight ecentricity will be turned away reaching the final 0.125" diameter.

Here we see a finished valve in comparison to the "as cast" version. The first valve finished turned out to have a blow-hole cavity in the head. Even though it did not go through, it did not seem like a good thing to have. A quick email to Art had another pair on the way and I had a spare to play with. Turns out I needed it...

Aluminium bronze is tough stuff. A razor sharp tool with a generous nose radius (that will form the radius betweek stem and head) will help, but we need more. A female center in the tailstock would do, but the stem would probably deflect while we were trying to turn a concentric male center on the end, so that's out. The answer is a travelling steady, but your average travelling steady would be much too large for this job. Here we see my steady for small work. Instead of two fingers, it has one with a 90 degree notch in the end. The finger is shotted for adjustment and the attach point is above the lathe axis. The finger will wear quickly, but it's easily replaced.

As setup here, the steady leads the cut, so we must stop cutting before the finger hits the head. The finger can then be swung out of the way and the cut finished without support. This will not matter because (1): we are so close to the head, work deflection will be about zero, and (2): we are past the bearing length of the stem, so absolute precision is not needed.

After the stem is finished, the compound slide is set over 45 degrees to form the valve flank. Measuring the diameter at the narrow end of the taper is tricky, but the very edges of the vernier calipers can get a close enough reading and it's not that critical anyway. What is important is to get the best finish possible as this IS critical to achieving an adequate seal on the valve seat. Just turn slowly, and maintain a constant hand-wound feed from start to finish.

There's one more task we have to do before we are done with this setup. That's to face back the valve stem to length. The travelling steady is used to support the delicate stem during this process. Finally, a very, very light chamfer takes off the sharp edge. The stem as to be drilled, but we'll use a drilling jig for that. This shot also shows the notched end of the steady finger rather well.

In this shot, the flank is finished and we're ready to remove the valve, and face off the stub we've been gripping by until now. The head is supplied quite oversize, both in thickness and diameter. As the valve will seat on the 45 degree face, it does not matter if the head OD is not perfectly concentric with the stem. However, gripping the valve in a 1/8" collet gives good support and will not mar the stem finish.

Forming the Valve Seats

Next we come to the difficult task of "lapping" the head and seat. Now remember, this is the first time I've actually done this, so get ready for a laugh. We know that the process we use to finish cylinder bores is "honing" because we use a hone of some material softer than the surface we want to finish so that the abrasive particles embed in the hone/lap turning it into a cutting tool. I generally use aluminium when honing steel cylinders. But the valve seat IS aluminium so what are we going to use? Oh hell, lets just drop in a valve (the one with the blow hole), add some auto valve-grinding paste, and see what happens. What happens is the grit embeds in the head and cuts a nice groove in the valve! I could have—and did—predict this, yet did it anyway. Oh well, now at lest we know for sure. Obviously a different scheme is needed.

Here's my solution. It worked, but there's a better way. Bruce Satra details it in Pilgrim's Progress page 17, Vol 2, Issue 7 of SIC (back issues available). Bruce describes full-size, real-world practice where the 45 degree valve seat band is bordered by 30 and 60 degree reliefs used to control the seat width and valve height when seated. I knew the article existed and if I'd read it first, it could have saved a lot of trouble. Anyway, my solution was to glue some 600 grit paper to a dummy valve turned to have an included angle of 88 degrees (the dummy was fabricated with drill rod, steel, and Locktite—I'm not a complete masocist!) Not unexpectedly, the grit wore away quickly, but the backing paper remained, and proved soft enough to allow some diamond lapping paste to be embedded in it and the job got done.

Here's the tool in operation. It's being spun at about 150 RPM with lots of oil and no nore pressure that that provided by the quill spring. We are not trying to make a very big seat—just say 5-10 thou across. The test is to drop in a valve, close off all the holes like you're going to try playing the thing as a flute, and blow into it like a baloon—except in this case, noises are bad. When no air escapes, or only a very little, we're done. Final seating will be performed by an old but effective operation later.

Next time I'll do it the Satra way. This pic shows the stuffed valve; tough, hard aluminium bronze, lapped away by the soft aluminium valve seat which was itself, largely unaffected by the encounter! The stem has been cross-drilled #56 for the cotter pin. This was done by making a simple jig comprising a 1/8" hole drilled in a bar of steel, then cross drilled by rotating the steel block 90 degrees in the mill-drill vise to assure that both holes are on the same axis. The valve is poked into the hole and the #56 hole used to steady and center the fine drill. Go slow, withdraw frequently for chip removal, and take especial care when the drill is about to break through. The lip angle of normal drills is really too acute for brass/bronze and the drill will try to snatch up the work as it breaks thru. If you are not going gently, this can easily break a small drill and ruin your whole day.

The Rocker Post

The post that supports the rocker pivot pin is almost too simple to bother describing. It's a simple turning, milling (or filing) and drilling job. I mention it only because it provides an opportunity to correctly position the rocker pad faces with respect to the valve stem ends. I drilled all the head holes to the drawing dimension with three decimal places of precision using the mill DRO. When assembled, I found that the rockers ware about 0.020" aft of ideal positioning due to the rockers being a little shorter than the drawing dimensions, perhaps due to shrinkage after casting. This can be fixed by drilling the post offset from center to compensate. I won't bother as everything seems to work well enough, but it's not perfect. Shifting the rocker pivot off center is not a good idea as this would make for unequal lever arms.

Machining the Rocker Arms

As previously mentioned, the rockers are cast aluminium bronze. Machining consists of de-pimpling the rough castings with "riffler" files, filling or milling off the casting sprue, facing to width and drilling/reaming for the pivot, and finishing the two ends. One end gets a recess that forms a pocket for the 1/16" push rod (there is no provision for adjustment). The other is radiused 0.156" (5/32") where it will contact the valve stem end.

This had me a bit tossed until I hit on the setup shown here. I'm using a small rotary table, shop-made to the Model Engineer "George H Thomas" design. This table has a 0.250" reamed hole in the center, so I turned up a button with a 5/16" diameter on a 1/4" stalk and pushed this into the table center. The rockers were then mounted on a plate which was clamped to the table such that the center of the button was where the center of the 5/32" radius should be—or near enough. With the table centered under the mill, the rocker pad was milled by rotating the table and feeding in until the cutter was just kissing the inserted button, thus forming the required radius. Almost quicker to do than describe. The rocker itself was restrained against cutting forces by all manner of odd scrap bolted to the table as seen in the accompanying photos.

Making Split Pins

At one time, I'm sure you could walk into a hardware store ("ironmongers" they were called in my youth) and say "two one-thrity-second cotter pins please". Well let me tell you that progress has put a stop to all that nonsense! The Feeney valve springs are of the "hair pin" variety that I've heard termed "zero-rate". A detent in the top of the spring engages with a cotter, or "split" pin inserted through the hole in the top of the valve stem, holding the valve closed. A side effect of this arrangement is that the valve cannot rotate, so it only has to seat in one position. I guess the downside is that in not being free to rotate, there is no wiping action available to remove particles that might interfear with the seal. At any rate, with no commercial product available, I decided I'd have to make my own.

Cotter pins are made from half-round wire, so step one is to make some half-round wire. This requires a jig to hold the wire while it is ground or filed down. A simple V cut will suffice and if it is made to the correct depth, the jig can also be used as a gauge. If you draw this out, the depth of the V cut can be determined by CAD, or simple trigenometry if you're too lazy to fire up the computer.

I was (too lazy too lazy that is), and the answer arrives to us by way of the ancient Greeks as the hypotenuse of a right triangle whose other sides are 1/64" long (who needs computers?) Here we see a block of steel from the scrap box, set over at 45 degrees, squared up to the mill axis, getting a V groove milled to a depth of 0.023". Since we are milling down the flank of the V, this is another right triangle with both sides 0.023", so the down-feed required is 0.032". Funny, that's the wire diameter. Wonder if there's a trig relationship I don't know, or have forgotten involved here...

A length of 1/32" music wire is clamped in the block V (by a convenient screw in the case of my scrap box special) and filed down by stroking away from the clamping point until the file contacts the top of the block for the entire length. This provided enough half-round wire to make two pins. The wire could be anealed at this point, but I decided to leave it tempered, just in case this damn thing actually runs.

The pins are formed by bending lengths of the wire around a 1/16" mandrel to form a U shape, springing the ends together to poke them into a slightly oversize hole in a scrap steel bar, then, with the mandrel in place, hammering the pin down until it can go no further. When removed, a very neat looking pin results as seen here. I love it when a plan comes together, even if I did break a drill making the hole in the scrap bar!

Seating the Valves

Trial assembly time. The valves are inserted and the pins pushed through the valve stem holes. The hair-pin springs are inserted from the rear. First the detent is engaged with the cotter, then the ends are raised and pushed forward with needle-nose pliers until they snap into the tiny blind recesses drilled in the tops of the valve port tunnel. I tried the other way—holding the spring compressed while vainly attempting to insert the pin—forget it. Humans lack sufficient hands to do the job this way.

Now you can block off the plug-hole and blow into the bore. If air escapes, one or other valve is not seating. Find out which by closing off the ports. If the seat has been "lapped" adequatly, there's no point trying to fix it by more lapping. Besides, Bruce Satra says that the smaller the width of the seat band, the better. The seat needs to match its actual valve. I was stumped until Bert Streigler related how he used to seat new valves into Model A Fords: make a wooden dowel about the diameter of the valve head. Place the valve in position in the head, position the dowel over the valve head, then belt the other end of the dowel with a carefully calibrated hammer. In despiration, I tried it, and and to my surprise and delight, it worked just fine (note to self: trust whatever Bert says, regardless). After the requisite number of calibrated wacks, I could play the valves like a saxophone, and most importantly, turn blue trying to blow into the cylinder when both were closed. This thing may actually stand a chance of running after all!

 

Ruler

 

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