Ford 300 Inline Six

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mayhugh1

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I'm plan to try my hand at building George Britnell's 1/5 (approx.) scale Ford Inline Six. This 300 cubic inch workhorse first appeared in the sixties and was used in Ford trucks for a decade. A shorter stroke version was used in passenger vehicles including the first car I was able to purchased new - a 1972 Maverick. In 2000, I rebuilt one of these engines in a '72 F-100 project truck that I used as a daily driver for a dozen years. The drawings purchased from George contain a lot of detail that will add realism to the model and challenge to its build. George documented his own build of this engine several years ago over on the 'other' forum.

After dealing with the pitfalls that can occur when trying to machine a complex crankshaft to fit an already completed crankcase, I decided to tackle it first. The Ford Inline six crankshaft is an interesting-looking 120 degree beast that's been replicated in this model. Its counterweight scheme isn't at all intuitive, but the engineers probably put all the lumps and bumps where they should be. The model's 8" long crank with its twelve tiny .312" journals will be one of the most difficult parts in this build. One of the photos shows a comparison of its SolidWorks model along side the Offy's crankshaft that tested my patience and machining abilities for several weeks last year.

The first step in its construction was to indicate a 9 inch length of 1-1/4" dia. Stressproof in my lathe's 4-jaw chuck so the ends could be center-drilled. Since I didn't have any material on hand, I purchased a length of 'ground and polished' 1144 from Speedy Metals. With the workpiece mounted between centers, I used my lathe's tailstock to zero out the measure of its end-to-end taper so I'd have a metric to track workpiece distortion during its various machining operations.

The workpiece was moved to the mill and clamped horizontally in the vise so a pair of reference flats could be machined on each end. These flats and a v-block were used to relocate the workpiece vertically in the vise so three additional center-drills could be added to each end for offset turning the rod journals.

The rod journals were roughed in using a center-supported four-axis indexing operation on my Tormach. Then with the workpiece set up between centers on the lathe, the rod journals and adjacent web walls were finish machined. The end-to-end taper measured less than .002" with the workpiece set up on centers in all three offset positions. These tapers were rough indicators of the initial mismatch errors in the end-counterbores. The taper measured along the main axis matched them to within a thousandth.

The crankshaft drawing specifies .312" for both main and rod journal diameters. I decided instead to target .328" for the rod journals and .375" for the main journals. The .328" was chosen because I happen to have a corresponding reamer for the rod bores. If a machining issue arises with the rod journals, the rod journal diameters can be reduced as needed to avoid scrapping the part.

The .375" diameter was chosen because of the availability of suitable ball bearings that I want to use for the outside main bearings. My plans include converting George's square bronze bearing design to round bronze bearings within the block and to replace the outer bronze bearings with ball bearings. Since I'm anticipating problems with the main journal machining, they may end up smaller with the inner bearings being machined to fit them.

The the rod journals and their web walls were finished using a Kennametal A2022N00CF02 grooving insert. This .087" wide carbide insert comes already bifurcated, and after a bit of lapping on a fine diamond plate it leaves a brilliant surface finish requiring little or no polishing. It's very important however to perfectly align its cutting edge with the lathe's spindle axis using a dial indicator. - Terry
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mayhugh1

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The journals were turned using side-to-side cutting motions and .005" depths of cut. The depths of these shallow cuts were set while simultaneously moving the carriage and the cross slide in order to achieve the best journal circularities and to reduce the chances of a dig-in due to workpiece deflection. In order to reduce this deflection, the spaces between the rod journal webs were packed with custom ground buttons held in place with lacing cord. All turning operations were done at 80 rpm and feeding was done manually. The finished rod journals wound up with .001" TIRs, and the four workpiece taper measurements remained at their previously measured values indicating a minimum workpiece distortion so far.

The workpiece was returned to the mill where the main journals and inch long ends were roughed in. Back on the lathe and between centers, workpiece deflection was now a major problem even with the rod journal packings. Light thumb pressure on the center of the workpiece easily created a .006" deflection - too much for accurate main journal turning. Some of this deflection was coming from the roughed-in ends which hindsight could have been done later.

I had some 1.250" i.d. seamless tubing on hand that I cut into a number of split pieces in order to stiffen the workpiece during turning. These snapped into place perfectly around the workpiece and were retained with hose clamps. These stiffeners reduced the center deflection to just over .001".

The main journals and their adjacent web walls were then finish turned. The measured TIR's were on the order of .001" with the stiffeners in place. However when they were removed, the workpiece relaxed, and the change in its shape caused two of the TIR's to increase to .004", and one changed to .003". Since the affected journals were still circular to within a thousandth, the increased runout was due to their centers shifting off the crankshaft's main axis. With the semi-finished crankshaft resting on v-blocks, it was apparent that the workpiece distortion had likely occurred sometime after finishing the rod journals and before the main journals were turned.

Next, the weird counterweight shapes were machined into the webs using the 4-axis step indexer still setup on my Tormach. After dealing with the frustrating machining errors on an uninteresting workpiece for so long, it was satisfying to finally see a crankshaft emerge. These operations removed a lot of additional material from the workpiece which added a bit more distortion and another thousandth or so to the main journal runouts. The TIR's of the inner journals were now at .005", .005", .0015", .003" and .0035". These runouts were high enough that if left uncorrected would create difficult fitting problems inside the crankcase, and the final result would most likely be an unsatisfying sloppy fit.

With the off-axis machining operations completed, the end spigots could be safely parted off with the help of a steady rest. I was finally able to measure the runouts with the ends of the crankshaft running in the ball bearings that will eventually be installed in the block. I was hoping the TIR's would improve, but they didn't change measurably.

During my Offy build I came up with a 'scraping' technique that enabled me to reduce the main journal TIR's of that crankshaft by slightly relocating their displaced axes. The journal diameters are reduced in the process, but since work on the crankcase hasn't yet started, this won't be a problem. With the crank resting between centers in the lathe and without any packings or stiffeners, the high areas of the journals were manually rotated back and forth against a razor sharp tool in the tool post. (I continued using the diamond lapped Kennametal carbide insert.) Working carefully while removing a few tenths at a time, the final TIR's were eventually reduced to .002". Progress was monitored with bluing and frequent trips between the lathe and surface plate where the TIR's were measured with the crankshaft running in its ball bearings. The relocated journals received blending polishings with 200g followed by 400g paper to bring them to a common .365"/.366" diameter. All journals then received a final polishing with 600g followed by 1000g paper. - Terry

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mayhugh1

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Although my project write-ups up to this point were done in realtime during the past two months while working on the crankshaft, I didn't make any realtime postings because I wasn't sure I was going to continue the build. The crankshaft looked very 'iffy' to me, and even George had commented about the difficulties he had experienced with its fitting inside his crankcase. If I wasn't happy with the finished part, my plan was to either increase the scale of the engine or to abandon the project completely.

Since I am reasonably satisfied with the final result, and it's likely that I'll be looking at it for the next year, I prettied it up some by masking off the journals and bead blasting the webs to remove the machining marks. Both ends received 1/16" keyways, and they were tapped with 8-32 screws. I've included a number of photos of the finished product. The block machining will probably begin next. - Terry

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Ghosty

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Terry, another one I will be watching, You do amazing work and incredible documentation of the build
Cheers
Andrew
 
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gbritnell

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Hi Terry,
It brings joy to my heart watching another one of my designs come to life. Like you I thought about increasing the rod and main journals but I didn't have any problems with the smaller size so continues on. When the day comes to
make the helical gears for the cam you're welcome to borrow my fixture.
 

awake

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Incredible work as always! And I have a special fondness for that engine; the first pickup I owned was a beat-to-near-death F100 with a 5-cylinder version of that engine. As in, it had 6 cylinders in it, but only ran on 5! Nevertheless, it hauled many a load of mulch and firewood before I finally sold it for $200 ... which was 4x what I had paid to purchase it!
 

a41capt

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Wow! Nice work Terry, and like others in this thread, I too had the pleasure of owning an early 80s F150 with a 300 six. A great engine, and thank you George for putting the effort into designing the model of this fantastic workhorse.

I’m watching with great interest Terry, the work on your crankshaft is nothing short of beautiful.

John W
 

Tim Wescott

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Incredible work as always! And I have a special fondness for that engine; the first pickup I owned was a beat-to-near-death F100 with a 5-cylinder version of that engine. As in, it had 6 cylinders in it, but only ran on 5! Nevertheless, it hauled many a load of mulch and firewood before I finally sold it for $200 ... which was 4x what I had paid to purchase it!
Hah! My dad had a friend who rebuilt engines. He had a story of an old Hudson that he bought and drove for a while. It had excessive vibration in the engine that he decided to fix. When he tore it down, he found a block of wood driven into one of the cylinder bores (and no piston, obviously), which looked like it had suffered from a broken ring.
 

splodge

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Great quality workmanship, will follow this with great interest...:)

Could I ask you , how I would go about purchasing drawings for this engine ?

Gary
 

mayhugh1

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Great quality workmanship, will follow this with great interest...:)

Could I ask you , how I would go about purchasing drawings for this engine ?

Gary
Contact George Britnell. He posts on this forum and in fact in this thread above.
 

splodge

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Thanks for the fast reply , I've been on the forum for many years and just quiet !..I follow all your builds , and I'm also a long way into building Ron's, offy 270.

Daft question maybe but how do I contact George Britnell directly ?

I'm still learning after all these years !

Gary
 

The_reach

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Thanks for the fast reply , I've been on the forum for many years and just quiet !..I follow all your builds , and I'm also a long way into building Ron's, offy 270.

Daft question maybe but how do I contact George Britnell directly ?

I'm still learning after all these years !

Gary
Would like to see your offy progress, im collecting materials for a half scale version
 

Scott_M

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Daft question maybe but how do I contact George Britnell directly ?
Hi Gary
Just hover over anybody's avatar and then click on "Start a Conversation" This will start what we used to call a PM "private message" directly through the forum.

Scott
 

mayhugh1

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Thanks for the fast reply , I've been on the forum for many years and just quiet !..I follow all your builds , and I'm also a long way into building Ron's, offy 270.

Daft question maybe but how do I contact George Britnell directly ?

I'm still learning after all these years !

Gary
You can send him a personal e-mail through this forum or he might contact you when he re-visits this thread.
 

splodge

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Thanks for the help folks, I will give it a go !

Would like to see your offy progress, im collecting materials for a half scale version
As for my Offy 1/4 scale is a nice size for me to work with, your going to need a large piece of aluminium for the crankcase in half scale !

Haven't any pictures of my progress , but can take pics , if you want to know anything...its a slow build for me but Rons build instructions are great , I assume you have it also..

Gary
 

Willyb

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Hi Terry
Great start on your Ford 300 six project. What are you using for media in your Bead Blaster? Really like the finish your getting. Looking forward to following along with your build.
Cheers
Willy
 

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