1/3 Scale Ford 289 Hi-Po

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Oct 24, 2007
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Central Texas
My shop time this past summer was spent modeling a Ford 289 Hi-Po engine. Its five main castings include the block, a pair of heads, the intake manifold, and a timing cover. Using workshop manuals and online photos for reference, I set out to build a 1/3 scale model of the popular 60's era muscle car engine.

A precise assembly of these five complex parts is a must, but the sources I was using left me with plenty of blanks to fill in. After a frustrating month of endless design and re-design, George Britnell graciously offered me his SolidWorks models of a nearly identical full-size 302 engine. He used these in another thread on this forum to 3-d print a quarter scale version of the same engine. It's fair to say that without his help my own project would have died on the vine.

SolidWorks has a powerful tool that's capable of scaling an entire finished model, and this is just what's required for 3-d printing. George's printer resolution allowed him to retain the rich detail in the engine's original castings, and he was able to print a museum quality model. Trying to replicate his results in metal on my Tormach however would require tiny and impractically long cutters and numerous setups with unreasonable machining times (or George's skill with a Dremel tool). So, I made modifications to the full-size engine's design to create a set of machining-friendly scaled models that retain much of the look and feel of the original engine.

Unfortunately, SolidWorks' scaling function doesn't scale the underlying sketches that make up the model. This means that design changes on the scaled model have to be made through the full-size version before it's scaled. With the complex filleting in the original castings creating the majority of the machining headaches, bouncing back and forth between the two models became insanely difficult. So, I decided to start again and created yet another set of 1/3 scale models based upon George's originals.

My models for the block, heads, intake manifold, timing cover, crankshaft, and camshaft are nearly complete. I have a running virtual assembly that includes rods, lifters, and pushrods and a camshaft driven from the crankshaft through a sprocketed timing chain as well as a distributor driveshaft driven from the camshaft through a custom helical gear set. What isn't yet complete is a block oiling scheme although the distributor has been angled around the crankshaft for a distributor-driven oil pump that matches what was done in the full-size engine .

During modeling, partial tool paths were generated using my CAM software so I could test the aging software and computer resources against the models' complexity. The block's lifter valley and the top surfaces of the intake manifold will likely tax my ability to generate the high resolution tool paths that I like to use.

The intake manifold's internal fuel and coolant passages need more work, and all the models will receive minor tweaks along the way. I've developed a bad case of computer burn-out, and I need to start making chips to keep up my enthusiasm for this project.

Material for the major workpieces has been rounded up. The engine will be machined from 7075 aluminum which is a considerably harder alloy than 6061 and capable of durable bearing surfaces and superior finishes. A 3" x 6" x 72" chunk of this was purchased 25 years ago from a building demolition site for just $35. It's now back inside my shop and being sawed into workpieces.

Before anyone asks, I'll gladly share what documentation I end up with after the engine is finished. Please don't ask me for George's original models since they're not mine to share. - Terry
Nice 3D modeling work.

Quite a challenging engine to build, so say the least.

I think the power of 3D modeling shines when you get into complex designs like this.

At 1/3 scale, most of the modified filleting can be safely machined using quarter inch ball cutters. As a bonus, those little nuisance parts should be a little easier to handle compared with those in a typical quarter scale model. I just wish I'd thought ahead about the dimensions of my raw stock. The finished height of my modeled block is 3.000", but the raw stock for its workpiece was only 2.970" high.
The first step in preparing the block's workpiece was to machine the .625" camshaft bore completely through my sawed off chunk of 7075. A gage pin in this bore will be used later to reference all the block's machining operations. The bore was located and spot-drilled on the mill before being indicated and drilled in my lathe's four-jaw chuck. An eight inch deep 7/16" through-hole was pre-drilled using a long Guhring drill followed by a 19/32" aircraft drill. The bore was finished using a .625" reamer supported in a floating tailstock holder. While still in the lathe, the front surface of the workpiece was faced normal to the hole's axis.

Surface plate measurements revealed the hole's entry point was within .002" of its target, but its exit on the axis already lacking stock was off by .010". A length of 5/8" drill rod was lightly polished for a close sliding fit in the bore and used to square up the other five sides of the blank to within a thousandth or so of the camshaft's axis. This, of course, removed even more stock from the already short axis.

A pair of blind 7-1/2" deep quarter inch holes drilled on either side of the camshaft bore with an aircraft drill completed the block's workpiece. These non-critical holes will eventually connect the coolant jackets on each bank to the outputs of the water pump. They were drilled using a combination of my mill's quill and bed feed since my lathe didn't have enough swing to handle the offset needed in its 4-jaw.

Before re-tweaking the block's design to fit within the finished dimensions of the workpiece, I wanted to verify the modeled spacing between the cam and crank bores. I came up with this spacing using an online roller chain calculator for a 12/24 tooth sprocket pair and 37 links of 3/16" pitch chain. The sprockets were machined from 1144 so I could verify their spacing. I wouldn't normally make these parts so early in the build, but with an untested block design it was necessary for peace of mind. This in turn required finalizing the camshaft's mounting details.

The cam's front and rear ends will be supported by 3/4" o.d. sealed ball bearings, while its three inner bearings will just run inside the block material. The cam sprocket will attach to a pinned flange on the nose of the camshaft through three slotted holes that provide the adjustment for timing the valves to the crankshaft. While back in SolidWorks a few cosmetic details were added to the lower end of the block including freeze plugs, engine mounts, and an oil filter mount. Provisions for a dipstick and a faux fuel pump are still needed, and I'm also considering an electric starter.

After machining the sprockets, their spacing was measured with a simple fixture on my mill. It was then I discovered my rookie mistake. A closed loop roller chain can only have an even number of links and I had designed for an odd number. After studying my alternatives, I decided to stay with the current sprockets and reduce the spacing for 36 links. This sounds like minor re-work, but it severely broke my model which will now require days of rework. On the bright side, it was better to find my mistake now, and hey it looks like the block's going to fit inside the workpiece after all. - Terry

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Hi Terry
Looking good !
Was there a reason you don't want to use a 1/2 link ? 1/2 link at Mcmaster Carr

Thanks much for your reply. To be honest I wasn't even aware of half links. After reading your response, I went searching but couldn't locate any for 3/16" pitch chain. This chain which I found on eBay several years ago being sold for repairing a particular pocket bike engine isn't at all common. Many online roller chain calculators don't even recognize its existence. - Terry
Hi Terry
I saw this and thought wow that is big chain for a model It must be much bigger than I think.
Little did I know it was a typo. But that explains it :)
37 links of 5/16" pitch chain.

Is it already re-3D modeled for the shorter chain ?

I just googled and came up with a normal link and a offset link for 5mm chain which they also marked as 3/16” next to it
Fantastic work! Beautiful model & machining!
-Great memories as well! I rebuilt a 289 for a 1968 Mustang coupe I once had, great little engine.

What exactly were the differences in the "standard" 289 & the "Hi-PO" version? If I remember correctly (which I don't some most times..), it was just a change in the head design combustion chambers & a larger pulley driving the alternator.

Were there changes to the block as well?

Fantastic work! Beautiful model & machining!
-Great memories as well! I rebuilt a 289 for a 1968 Mustang coupe I once had, great little engine.

What exactly were the differences in the "standard" 289 & the "Hi-PO" version? If I remember correctly (which I don't some most times..), it was just a change in the head design combustion chambers & a larger pulley driving the alternator.

Were there changes to the block as well?

The intake manifold was also a high rise - something that will be an add-on in my model to save machining time. The air cleaners on the ones I've seen were also chromed cold air types. - Terry
The intake manifold was also a high rise - something that will be an add-on in my model to save machining time. The air cleaners on the ones I've seen were also chromed cold air types. - Terry

Was the "Hi-Po" a single plane manifold as well?

You know you're going to have to do the Cobra air cleaner & valve covers right?



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And we’re off and running on another terrific season of “What fantastic creation will Terry make next?” I’m already addicted to this season’s episodes!!!

Thanks Terry,
John W
Another serial to watch, Thanks Terry.
PS did the ford straight 6 get lonely
The changes needed to correct the timing gear spacing involved only the block and timing cover. I decided to not trim the bottom of the block to maintain the 50/50 crankshaft split I had across the block and oil pan after realizing the front and rear oil seal inserts will fill the pan gaps nicely.

In preparation for the block's bottom end machining, the main bearing scheme was finalized. In what will be a deviation from the original engine's design, sealed ball bearings will be used at the front and rear of the block, and the three center bearings will be bronze disks. I used this mains setup on my last two engines and it worked well. Although the three bronze bearings will require fitting, I'll be able to avoid a line boring operation and scraping five clamshell bearings. This scheme works well, and the oil pan hides the blasphemy. A downside is that the ball bearings will complicate the routing from the oil pump.

With its numerous angled surfaces, the block's machining will require many setups. I started with the easy bottom surface which required only a work-holding vise. The deep pockets between the block's webs were designed for 3/8" cutters to avoid the chatter that would have come from the long skinny cutters needed for a precisely scaled interior.

One of the photos shows the heart-breaking result of the block's very first roughing pass. The operation wound up offset from the camshaft axis by .200". I traced the error back to a surface plate measurement where I'd misread a '9' as a '7' on my height gage. Several weeks ago, the close-up vision difficulties I've been having in the shop were diagnosed as cataract related. Corrective surgery is scheduled in a few weeks, but until then a magnifying glass and flashlight have become my best friends.

After a few days of mourning, a new workpiece was prepared. This one was finish machined with zero excess stock on all surfaces in order to minimize the number of hands-on measurements I'll need to make before my surgery. The pucker factor was high while the operation was rerun, but the last photo shows my do-over landed in the right place. This build has had a rough beginning, and my confidence is in some serious need of rebuilding. - Terry


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