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Specialty Motor Cams Over Head Valve Conversion Story

The Stipe 327 Chevy OHV Model “A” Conversion
By Bill Stipe, Jr. Plymouth, Wisconsin

Top Half of Engine Assembled to BlockMy Dad gave me a 1930 Tudor Model “A” when I was in 9th grade. By the time I was a senior in high school I had fixed it up and was driving it all over the place. My friends kept telling me to put a V-8 in it and throw the four cylinders away, but my Dad always told me not to butcher up that car.

I had a book, Model A Ford Construction, Operation, and Repair for the restorer, by Victor W. Page. In the back were articles and pictures of speed products like HAL overheads, George Riley Co., R & R Mfg., Ruckstell, Miller, and Amber Super Valve in Head.

I wanted one of these so bad that I started to dream about how I could make one on my own. After starting my Tool & Die Apprenticeship in 1970, the year I graduated, I bought a Bridgeport Milling Machine in 1971 and started to make my overhead valve conversion for my Model “A” Ford.

I started with a 327 Chevrolet cylinder head, it was the closest head I could find that lined up with the Ford cylinders…if the chambers were spread 1” apart in the center of the head.

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Bottom Side of Cylinder HeadThe first thing I had to do was saw the cylinder head in two pieces through the exhaust gas heat riser port and weld this port shut. My Dad made a reciprocating hack saw using an old furnace stoker gearbox and other junk he had lying around, it was very handy.

I then fabricated a 1” wide x 1/4” thick steel band to join them back together. This would line up the head combustion chambers with the Model “A” cylinders. Also, a tube was added for the distributor mount (I used a Maytag washing machine agitator tube from Dad’s junk pile behind the barn.) The head was then welded back together using “Ni- rod” or nickel alloy rod.

Head Assembled on BlockAfter tack welding together, I used very short bead lengths, about 3/8” to 1/2” long, peening as I went. The head was preheated and post heated using an old kerosene space heater to heat the garage. I removed the sheet metal top so I could set the head directly on top of the fire chamber. I used my Dad’s Sears A.C. stick welder for all the welding. The valve cover had to be lengthened 1” and custom fit around the distributor tube, I oxyacetylene welded this.

The cylinder head was then milled flat using carbide cutters. The cylinder head’s push rod guide holes needed to be moved about a 1/16” and offset studs to align the rockers properly. I needed to drill and tap the head to feed an oil line to the rockers.

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Valve Cover, Head Spacer, Top of Cylinder Head from Top to BottomThe front of the cylinder head milled flat and bore cut with tapped holes to allow for an aluminum adapter to mount a modified early Ford V-8 water pump with an added ball bearing for the fan blades extra weight.


Engine Block with part of Water Jacket Weld OffThe block had to be milled down on the valve side to allow for attaching a 1/4” x 1” steel plate the full length of the block and welded flush with the deck. This plate blocks off the water jacket holes so oil can flow back down the old valve portholes. I also welded some extra pieces on the intake side of the head to seal this area.

Water PumpAll four exhaust valve guides need to be drilled out to 3/4” and the intake valve areas bored out to 1-1/2” diameter. Then press tubes in place to seal off water. Use sleeve Locktite to seal in place.

New and Old CrankshaftThe center cylinder head bolt/stud hole was the only one that could be used as is. The rest of the stud holes in the block had to be transferred, drilled and tapped into the block.

I made aluminum covers for the old block’s intake and exhaust ports. These unused ports must be sealed or oil will leak out. I added an oil manifold inside the block’s valve chamber area to feed the three main bearings and one to squirt oil on the timing gear. Drilling and tapping for a bulkhead fitting above the timing gear housing area feed this manifold.

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Push Rod, Lifter and Oil Pump from Top to BottomThe old oil pump slots were filled to direct the oil out the side hole of the block that was opened up to 1/4” pipe thread, this fed an oil filter manifold made from a newer Buick engine, with a bypass at 35-PSI. I dumped the bypass back into the valve chamber through the aluminum cover over number 3-exhaust port. The 35-PSI line feeds the main bearings and head.

I drilled 9/16” holes at the bottom of each rod area to modify the oil pan dip tray. The tappets were bored out to allow for an insert from Chevrolet lifters, this allowed Chevrolet Corvair push rods to be used.

I used custom valve springs to gain a little more pressure than the Model “A”, this will help over come the extra weight of the bigger valves, rockers, and push rods. The original Chevy springs are too heavy for the Model “A” cam.

I used Chevy 327 pistons in place of the Model “A’s” to lower my compression. The pistons staged below the deck by about 1/8”, but I still had to add a 5/16” thick aluminum tooling plate for a gasket to drop the compression even more. Model “A” rods were still used, but reworked to accept Chevy wrist pins.

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Head Assembled on  BlockThe cylinder head and block were hand lapped together with lapping compound until they mated perfectly. I sealed the 5/16” aluminum tooling plate to the head and block with high temp silicone, being very clean I spread the thinnest layer with a straight edged knife, you had to move quickly or there would be trouble.

After I filled the block with water, there were only two small pinholes in my welds that would bead up ever so slowly. I stopped them with leak stop after I started the engine. Wow, that was amazing!

I then made aluminum adapters for the intake manifolds to accept two 1-3/8” bore SU side draft carbs. I wanted a more modern distributor so I used a 1959 Ford V-8 and precision ground 4 lobes off to change it to a 4 cylinder, I machined the stem to fit the new distributor tube, then changed the centrifugal advance springs to advance sooner.

The crank was fully drilled for oil pressure and the rod dippers closed off. I did not counter-weight the crank and this I believe caused the bearings to eventually fail.

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Pressure Plate and Flywheel from Top to BottomI machined the flywheel to remove about 14 pounds, then drilled and tapped it for a 1955 Plymouth pressure plate and lengthened the input shaft on a 1955 Plymouth 3 speed transmission to fit. I made a custom shifter with an H pattern laid on its side; once you came out of first and hit second you could not get first or reverse again. I then adapted a 1946 Ford rear axle with 3.54 gears and made it an open drive shaft with a 4-link mount.

It took over a year to finish this project. The performance was unbelievable for a four banger; I had 15” aluminum mags with 10” wide rubber on the back and could get rubber in first and second with a little chirp out of third. I didn’t get to drive it more than 200 miles before the oil pressure started to drop, so I shut it down. It has been sitting in the barn for 28 years and I hope to get it running this summer. I made a counter balanced crank for it and plan to make a set of custom rods to lower the compression and eliminate the aluminum gasket, along with some other “secret” refinements.

Thanks to Dad for giving me that Model “A” and teaching me so many things in life, he’s going to be 93 years old March 24 2009. And thanks to Mom for putting up with my mess in the garage all those years! She just turn 87 May 7 2009.

Hope you enjoyed reading this as much as I did making it. Bill Stipe, Jr.

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