Ford 300 Inline Six

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One question, Terry: is that brass or bronze bar in the top picture ("Sanity checking...") the 0.875' diameter you mentioned and the same as the one in the lathe?

Just to confirm I understand.
 
The connecting rods were machined from 7075 aluminum. Since there aren't any sleeve bearings, the rod journals and wrist pins turn directly in the aluminum. The rods were machined integral with their caps in two-piece workpieces temporarily held together with the rod bolts. A few extra bolts were added to ensure the workpiece halves remained safely together after the rods were cut completely free of it.

The only 7075 material I had on hand required laying the rods out perpendicular to the material's rolled direction. I wondered if this orientation might compromise the rods' tensile strength, but I found an online white paper with experimental results showing less than a 5% loss in strength.

The rod machining was done in cookie sheet fashion with two batches of four rod/caps per batch. Workpiece preparation included care to minimize registration errors when they were flipped over for their second face machining. Each rod/cap pair was engraved with matching numbers to avoid mixing parts during assembly.

The rod bolts were protected during machining by temporarily modifying the cap design with extra added material. This additional material hid the bolts from the CAM software which would otherwise have cut them into chips. It was removed later in a separate setup.

After machining the top faces of the rod/cap pairs in each batch, the troughs left around them were filled with Devcon 5 minute epoxy and allowed to cure for several hours. This epoxy kept the rod/cap pairs safely attached to their workpieces during their bottom face machining. While still hot, the finished parts released cleanly from the Devcon after a half-hour oven bake at 225F.

A drip oil passage drilled through the top end of each rod should help with wrist pin lubrication. The assembled rods and caps were bead blasted before finally finishing the caps. A simple fixture helped with the consistency of these operations.
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The rods were fitted to the rod journals with the same bluing and scraping technique used on the main journals. Unfortunately, the crank's four inside rod journals had nearly the same .001" circularity errors found on the main journals. Since the rod journals don't turn a full 360 degrees inside the rods, their final fits were a bit closer. - Terry
 
One question, Terry: is that brass or bronze bar in the top picture ("Sanity checking...")
Hi Bob Terry mentioned he used SAE660 which I googled:
SAE660 or C93200 is a Leaded (Tin) continuously cast bronze and is a standard in the industry for light/medium bearing applications. Leaded (Tin) Bronze SAE660 or C93200 is suitable for various applications under medium loads.
Cheers, Dave.
 
Those conrods are tiny.. excellent work I like the epoxy technique as well 👌
 
Piston machining began with four workpieces turned from scrap-box drops of 6061. Each workpiece was a pair of piston blanks with a work-holding spigot between them, and both ends were faced and turned to the pistons' final diameter. In hindsight, the workpieces would have been more useful had the piston bottoms rather than the tops been at the ends of the blanks.

Several changes were made to the original piston design. They were lengthened to increase by a couple points the 5+ compression ratio estimated by my modeling. A third groove was also added to the two ring design to help with oil control.

During a downstroke, the piston's bottom ring is expected to scrape oil from the cylinder wall. Oil accumulated in the clearance space between the piston and cylinder wall tends to resist this scraping, and some of it will get by the bottom ring especially if the top ring is doing its job and completely sealing the combustion chamber. Some of the oil trapped between the two rings can find its way into the combustion chamber. Although a little oil is desirable for lubrication, too much will cause a smoky exhaust and plug fouling.

If a groove is cut around the piston just below the bottom ring, the scraped oil will be provided another evacuation path, and the bottom ring won't have to work as hard. Since a single downstroke will most likely fill this groove, holes drilled through it can direct the oil into the interior of the piston where it may even help with wrist pin lubrication. Oil control grooves aren't new, and I've used them on a few other engines. After a few calculations, though, I've realized the typically used eight drain holes may be woefully inadequate. For these pistons I used eighteen .050" holes.

A collet block and vise stop were set up on the mill to drill and ream the wrist pin holes through the eight candidate pistons. It was important that these holes be precisely perpendicular to the pistons' axes to prevent binding inside the cylinder and accompanying rod bearing wear. The blank was then moved back to the lathe where the three grooves were cut. An extra thousandth was also taken off the piston's diameter above the top ring. From the ring calculations, the widths and depths of the grooves were selected to provide .001" ring clearance and .006" behind each ring. The oil groove was .050" wide. After machining the pistons' interiors a rotary was set up, and eighteen equally spaced drain holes were drilled through the oil groove using a carbide circuit board drill.
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The wrist pins were machined from drill rod but not hardened. Their ends were drilled and aluminum rivets pressed in to protect the cylinder walls from scouring. The piston ring dimensions have been calculated, but they will be machined later. - Terry
 
Piston Rings Part 1.

I follow George Trimble's method when making my piston rings. The only change I've made to the process published in his original S.I.C. articles is to use a three hour 975F normalization rather than the 1475F he recommended. In addition, I light test each ring before it's installed.

My yields have typically been limited by circularity errors that show up in the finished blanks just before slicing rings from them. I use class 40 gray cast iron drops from a variety of sources accumulated over the years. I've measured circularity errors as high as eight tenths over portions of some of my blanks, and these errors have sometimes shown up days after being finished. Sometimes less than half of a blank passes my acceptance criteria of two tenths, and occasionally an entire blank was discarded. Once a ring has been sliced from a blank, it's nearly impossible to evaluate without being fully finished and light-tested. After harvesting rings from well-behaved portions of the blanks, my light-tested yields have typically been 80%-90%.

When starting a large batch of rings, I often prepare more than one blank. Even though only a dozen rings plus spares were needed for this engine, I prepared two blanks with enough total candidate material for some 60 rings. Starting with one inch raw material, the finished diameter of the blanks (and therefore the ring diameter) was .748". At a ring thickness of only .032" and .019" width, I was initially concerned with their strength and their tendency to break during installation. After a few tests though I found them to be quite flexible and very easily to install. George was also concerned about their fragility and increased the thickness of his rings to .044" and their widths to .031".

The candidate areas of the blanks were drilled/bored to their finished i.d.'s after being roughed down to .780" diameter. In order to help relieve any remaining casting stresses and minimize circularity errors, the semi-finished blanks received an eight hour 700F heat soak. This step isn't part of Trimble's process but seemed to improve the yields in my last two builds.

A day later, the blanks' o.d.'s were turned and polished with 400g paper to their final diameter plus/minus a tenth. After being allowed to 'settle out' over the holidays, their final circularities were checked using three quadrature measurements along their lengths. One blank showed no errors and had enough material for 30 candidate rings. About a third of the second blank showed errors approaching four tenths but had enough 'good' material for some 25 rings.

I began by slicing rings from the second blank. Flashing was removed and the inside corners of the parted rings broken using a 1/4" diameter hard ceramic file. The flat sides were then lapped for a .001" piston groove clearance using a simple shop-made fixture and 600g grinding grease on a glass plate. Fine finishes on these surfaces are important because their seal with the lower walls of the pistons' grooves is an important component of the combustion chamber's total seal.
The Trimble article recommends a straight radial break in each ring for proper contact with the spreader dowel in the heat treating fixture. Although 'good enough' results might be achieved by simply snapping the rings, I constructed a single purpose cleaver several years ago. Just before heat treating, each ring was cleaved and the running gap set to .004" with a diamond file. The gaps were verified inside a (spare) honed liner machined along with the original six block liners.

Since I (hopefully) had more than enough candidate rings from the first blank, I didn't slice any from the second finished blank.
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blank. - Terry
 
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Hi Terry !
. In order to help relieve any remaining casting stresses and minimize circularity errors, the semi-finished blanks received an eight hour 700F heat soak. This step isn't part of Trimble's process but seemed to improve the yields in my last two builds.

Can you explain more ?
Thanks !
 
Minh Thanh,
Well, I'm not sure what else I can add. Some cast iron is left with residual internal stresses after being cast and cooled, and these stresses can cause a part to distort as it's being machined and these stresses relieved. I don't know if it's true, but I've read that some machine manufacturers allow their castings to 'age' as much as a year before they're finally machined. I started heat soaking my ring blanks before finally finishing them in hopes of speeding up the aging process. My temperature and time probably aren't sufficient, but I figure the heat soak can't hurt. Although I have no firm evidence that it makes a difference, it did seem to help reduce the circularity errors in the rings in my last two builds. In addition to the heat soak, I also took advantage of the holidays and allowed the blanks to 'age' for nearly a week after the heat soak before slicing off the rings. After all that, a portion of one of the blanks wound up changing what I would call 'too much' after all. - Terry
 
Terry !
Thanks for sharing your experience !
I will try
Thanks !
 
Thanks for the description Terry but could you please provide some detail of the construction and operation of the Cleaving Device ?

xpylonracer
 
Thanks for a comprehensive description and photos, very useful.
I wonder whether the blanks would remain more stable if they were of more consistent section, i.e. without the significantly larger diameter and wall thickness at the chucking end.
 
"I light test each ring before it's installed."

Hi Terry,

How do you perform this light test, and what are you looking for?


Thank you for taking the time to post the progress of your builds.

Gary
 
Thanks for the description Terry but could you please provide some detail of the construction and operation of the Cleaving Device ?

xpylonracer
Xpylonracer,

As you can see from this view looking down on the cleaver, it is made up of two HSS cutting tools that slide in a slot. The ends of the cutting tools have been ground to 60 degree angles, and they have been shimmed to precisely align. The ring is placed in the cross slot and the top screw is adjusted so the top cutting tool is in contact with the ring's back face which is also in contact with the wall of the cross slot. This one time adjustment prevents the ring from twisting during the cleaving process. The ring is cleaved by turning the bottom screw which drives the bottom cutting tool into the ring. - Terry

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"I light test each ring before it's installed."

Hi Terry,

How do you perform this light test, and what are you looking for?


Thank you for taking the time to post the progress of your builds.

Gary
Gary,
I'm working on that right now and will post a Part 2 soon. - Terry
 
Thanks for a comprehensive description and photos, very useful.
I wonder whether the blanks would remain more stable if they were of more consistent section, i.e. without the significantly larger diameter and wall thickness at the chucking end.
Peter,
One thing I've learned along the way is that the workholding spigot needs to be solid and some distance away from the candidate ring material. If not, the lathe chuck, even a collet chuck, can distort the adjacent candidate material. Even though the machined blank might indicate perfect while chucked, circularity errors can show up after it's taken out of the chuck. - Terry
 
Thanks Terry.
I have machined thin walled tubular parts which had to be chucked for subsequent operations.
For those parts, I made a light push fit plug which would support the tube to prevent distortion when gripped in the chuck.
The plug was pushed out of the part after machining and could be re-used for the next part.
The parts were stainless steel. I'm not sure the process would work with cast iron and perhaps it's just not worth the fiddle!
Pete.
 
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