Author: swarf

There is a reason the Bristol Hercules was likened to a Swiss watch running at 3000 rpm. The gear train that drives the 14 sleeves is made up of 28 gears driven from another gear cut into the crankshaft. This image is of the full size engine with the gear case removed.

The first step in making the gears was to prepare all the gear blanks. There are four styles of gear in the train. The gears are 48 diametrical pitch and there are 7 gears of each style required. I planned to make  9 of each just in case. In each set of seven, two of the gears are silver soldered together in a later step. The gears are all made from 1144 stressproof.

It’s a simple turning job to bring the outside diameter to size, drilling and reaming the axis hole and turning a small hub on three of the styles, the blanks are then parted off.  The parted face was ground down to dimension on the surface grinder. The blanks are supported on magnetic 123 blocks so the small hub protrudes below.

The blanks are mounted on a gear cutting arbor, two at a time, which in turn is mounted in a 4 jaw chuck on the rotary table. A last word dial indicator running on the gear blanks was use to adjust the 4 jaw so the blanks run true. The gear cutter is positioned exactly on the horizontal center line of the blanks.  

I used the D2nc gear g-code generator, which I added to the program specifically for this build. I created the g-code to cut the gears with 3 passes using the constant volume modified algorithm which is kind to the tooling.

In this image you see the completed gears which go into making up the train, 7 sets of the 4 styles of gear. You can see the marks on some of the gears where I’ve used a stone to remove the burrs around the teeth. As I cut the larger gears in pairs, only one of them needed to be de-burred. I’ve covered the gears in ‘Fluid Film‘ to inhibit rust.

The full size gears have holes drilled in them to form spokes. I guess that was a weight control measure. As this engine will never fly and weight is not an issue, I plan to leave them solid.

To cut the gear teeth three different sized arbors were required and these were custom made for the task. Two of the three arbors are shown below. All are of the same style with the shaft long enough to gang several blanks together at the same time. The smallest gear needed the arbor shank reduced to eliminate interference with the gear cutter.

 

 

The cylinder heads on a sleeve valve engine are junk heads.  This means that there are piston rings on the head that seal the top of the cylinder instead of a head gasket. The term “junk head” comes from the “junk rings” in steam engines that seal the heads. As the ring in the steam engine was stationary, it could be made from the lowest quality materials hence the term junk.

In a sleeve valve engine the junk head acts as a static or false piston at the top of the sleeve, sealing it as it moves in its elliptical arc.

The heads, are made from 2024 grade aluminum. A 3 foot long 2-3/8 round bar yields 20 1.6 in long blanks. These were faced at both ends in the lathe. There was a lot of material to remove to create the “false piston” on the head so I milled the blanks using the circle wizard in D2nc which made short work of it.

Below the blanks are ready for the next operation of creating the false piston.

 

To turn the outside of the sleeve, I first turned a simple lathe chuckling arbor and cap. The cap compresses the sleeve blank onto the arbor using a 1/4-20 bolt.

Below you can see the arbor and sleeve side-by-side.

One hell of a lot of swarf later the 19 sleeves are ready for machining the bottom ring and cutting the ports.

The sleeves are made from StressProof 1144 steel. This is a nice material to work with, easy to cut with the main benefit of reduced warpage and distortion that needs to be minimized in the final part. A 2 inch diameter 6 foot long bar is cut into 3.7 inch long slugs which yields 19 pieces. One short of the 20 target but that still leaves some margin for a few mistakes along the way.

The first operation on the slug was to faced both ends on the lathe to its final length. These were progressively drilled out on the mill using the trusty ‘Silver and Deming’ drill set to 1.25. A drill will always remove material faster than any other tool in the shop.

The drilled blanks are then bored out on the lathe to 1.372. That leaves .003 for honing on the Sunnen to the final bore size of 1.375 later on.

The first operation on the cylinder blanks is is to drill and tap the six holes for attaching the head. These holes are used by the fixtures for cutting the fins, turning the eccentric band and for the base operations to align the head to the front of the cylinder.

On the mill I use an edge finder to locate the the center of the bore, first by finding the limits on the y axis and halving that dimension and then by finding the limits on the x axis  and halving that.

The bolt circle was first center drilled

and then drilled to depth,

and hand tapped.

I put in exactly 10.5 turns of the tap per hole. you can just make out the black reference mark on the left tap handle near the tap barrel. I use that mark to count out the turns to make sure all holes are tapped to required depth.

After tapping, I use a 400 grit stone to remove the burr raised by the tap, and stone the top of the cylinder to eliminate the burrs.

Rinse and repeat the above 20 times over and in no time at all you have the cylinder blanks ready for fining and outside profiling.

 

 

While its a 14 cylinder radial, the plan is to make 20 of each the heads, cylinders, sleeves and pistons.

The Cylinders started out as a six foot log of 2 1/2 inch 6061 aluminum. These were sawed into 20 x 3 1/2 in long slugs and a facing cut taken on each end in the lathe. Each slug  was then drilled out to 1 3/8 inch using ‘Silver and Deming’ drills starting with a 1/2 inch diameter drill and enlarging progressively a 1/4 inch.

Each blank was then faced to length, bored to .003 under size to allow for honing later on and the recess lip for the cylinder head mating cut.

         

I can’t believe its been a year since I’ve last updated the SVR build blog. In the year that’s passed I’ve been working slowly but steadily at some of the more tedious aspects of the build such as creating some required fixtures and roughing out blanks for the cylinders, heads, sleeves and gears. I took many photos along the way and will be posting those in the next few posts as I catch you up on the progress.

Two weeks ago in late April I traveled to Detroit where I spent the day at the NAMES model engineering show along with Lee Hodgson of Ageless Engines, Bruce Patterson and Mike Murphy who both assisted Lee in the model engine design and testing. We spent a large part of the day going over the porting design and port events on which I had done some work. Lee had seen some of the work I was doing and wanted to review it with Bruce and Mike. The outcome of that meeting is that I am moving to build a single cylinder rig as soon as possible to test some alternative port timing events which are different from those detailed in the construction drawings.

Another reason for wanting to construct the test rig is that later on I plan to run-in each cylinder/sleeve combination prior to installing on the engine and doing the first fully integrated run.

Its understandable that the scale model would have different events from the actual engine as the original was supercharged with a 6:1 rpm ratio impeller while the scale engine is normally aspirated and relies on piston cylinder vacuum for induction.

What an epic journey this has been for Lee who has spent over ten years designing and constructing this engine. While Lee does not have his engine running yet, he likes to quote Mike and say “We have the problem surrounded and are sure it will submit soon.”

 

The bearing housing sits at the front of the engine and contains the first bearing that supports the crank shaft and the propeller.

The front of the housing has a 3/4 inch radius.  I felt that is a bit big for a form tool so decided to cut this “old school”.

The initial radius was formed with a rough step cut using a X/Z feed chart that I first created in Excel.

The rough steps were covered in layout fluid making sure to get the fluid into the base of each step as this is the reference line for the completed radius.

Using a file on a slowly turning lathe, the steps are smoothed and the shape refined.

Once all the blue between two steps disappears , that point of the profile is at the correct depth.  Working steadily, the entire radius is refined.

I’m happy with the way the completed radius turned out in the image above.

The gear case is a straight forward turning job with a couple of radiused corners.

 

To cut the the largest radius on the edge, I used one flute of a 1/4 in radius mill held in a lathe tool holder as shown below.