How to Prep Your Ford 351 Cleveland Cylinder Heads

If you’re reworking factory iron heads for your Cleveland, there are all kinds of things you need to know. Have the heads Magnafluxed for cracks along with a close visual inspection before doing any machine work. Because some Cleveland head castings tend to crack, get this concern out of the way. Always install hardened exhaust valve seats so that your iron heads compatible with today’s harsh unleaded fuels.

As to porting: If you clean up the bowls and smooth out the high spots you wind up with a respectable street/ strip head, especially if you want a stock appearance. MPG Head Service has stamped-steel port plates, also known as port tongues, to get rid of that ugly exhaust fl oor rise on 4-barrel heads. This rise creates unwanted turbulence that interferes with exhaust scavenging. There’s not a lot you can do with this rise because you don’t want to grind off too much. Best you can do is make it a smoother ride for hot gases.

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This Tech Tip is From the Full Book, FORD 351 CLEVELAND ENGINES: HOW TO BUILD FOR MAX PERFORMANCE. For a comprehensive guide on this entire subject you can visit this link:

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Guides, Liners and Stems

When evaluating bare heads and deciding what to do first, a few things are immediatae priorities. Valve guides should always be replaced, whether you choose to use new guides or bronze liners. I know I will get arguments on this one, but bronze liners hold up better in the long term and they offer better oil control than iron or powdered metal guides. Complete replacement of iron valve guides is a matter of personal choice, but it’s also an expensive option because more labor is involved. The more affordable, less time-consuming option is bronze liners. What makes bronze liners a better value is their excellent lubricating qualities and therefore durability. Bronze liners are happy with chromed, non-chromed, and coated valve stems. All a machinist has to do is get stem-to-liner clearances healthy and you’re good to go.

 

Apply Prussian Blue to the new valve seat in preparation for cutting, which enables the machinist to see the cut and angle. A three-angle valve job is routine to improve flow and heat transfer.

 

Bronze liners are installed in existing valve guides. All the machinist has to do is machine the guides to size and drive in the liners. Of course it is more involved than. For one thing, headwork is not for the novice. It is for the trained, competent professional machinist with the right experience and equipment.

Installing bronze liners initially calls for reaming the iron valve guide to size. The machinist uses a reamer and less than 1,000 rpm for no more than five seconds per guide before checking size. Most machinists ream the guide dry in preparation for liner installation. Once guides have been reamed, use cutting oil and a ball hone to get a good crosshatch pattern. This cleans up the guides and prepares them for the bronze liners. Liners are driven in with a pneumatic driver at approximately 3,000 pulses per minute. Overpower the driver and you damage the liner.

It should take a machinist roughly five seconds to install each liner. Once the liner is installed and trimmed, a carbide ball is used to permanently install the liner. Because the carbide ball is .001 inch larger than the intended finish size (known as an interference fit), it presses the liner into place, coming out on the other side. Once the liners are installed, they should be honed to size one valve at a time. With each liner, check valve stem fit and movement using lubricant, then clean with solvent to remove any metal debris. Any debris left behind causes stem or liner damage. Be thorough in your clean-up efforts, then use plenty of engine assembly lube between the stems and guides when it’s time for assembly.

Another option is silicon bronze valve guides, which can be installed in iron or aluminum heads. If you’re going with bronze guides, they should be knurled externally for added security. Yet another option, though strongly discouraged, is knurling iron guides internally for oil control and stem clearancing. However, this is an approach with a limited lifespan and little benefit.

Valve stems should be inspected, measured, and dressed for proper fit and oil control just as you do with guides and liners.

 

Even new valve stems need to be measured and dressed to allow for thermal expansion and conservative oil fl ow. You want enough clearance to allow oil flow without starving guide and stem.

Valve faces are painted with red dye (or Prussian Blue) and ground to a compatible angle to the seats. High-tech cutters allow a multi-angle cut without having to change cutters.

This is a custom-made go/no-go gauge made from aluminum stock that measures 1.900 inches in length, which is what MCE uses to determine installed spring height.

Spring pressure must always be compatible with your cam profile. Too much pressure and you face excessive friction and wear issues. Not enough pressure and you’re looking at valve fl oat at high RPM.

Do not reuse valves. MCE, for example, specifies Manley stainless valves. Cylinder head work includes new valves, springs, retainers, keepers, and seals.

In recent years the trend has been away from umbrella valve seals and toward Teflon or Viton seals, probably because Teflon valve seals are more appropriate for racing and don’t offer long term durability. For street and racing engines, you want Viton valve seals, which offer extreme durability and oil control.

 

 

 

 

Valve Job

While you’re reworking heads, a multi-angle valve job improves fl ow and durability. You can perform a three-angle, five-angle, or radius valve job. Each varies in durability. First, you need to know how much valve face contact you want  with the seat. The more contact you have, the better your valve cooling and durability. However, you sacrifice flow with increasing seat contact.

For drag racing, as one example, you can get by with less seat contact (.060 inch) and better fl ow because power comes in short bursts and heat doesn’t have a chance to build as you see in road racing or extended highway driving. If your Cleveland is going to operate for extended periods at high RPM, you want more seat width (.080 inch) and heat transfer. Ford recommends .060- to .080-inch intake and .070- to .090-inch exhaust.

Most factory valve jobs are single angle with a lot of restriction. Engine rebuilds normally get a three-angle job (45-, 60-, 70-degree angle cuts), which is quite common for street performance applications. With a three-angle valve job, there’s a bottom cut that ranges from 50 to 70 degrees depending upon the head casting and port configuration.

Machinists normally begin with a 70-degree cutter just below the valve seat to improve fl ow. The 60-degree cut on a three-angle valve job, reduces restriction. The valve and valve seat get a 45-degree angle cut. Contact width depends on  what you want your engine to do. Normally, contact width is .080 inch.

A three-angle valve job improves flow significantly to where you can experience a solid 10- to 15-hp/torque improvement depending on technique and what is done port-wise. If you keep valve-to-seat contact around .060 inch for the intake valve, the news is even better. For cooling, minimum exhaust valve seat contact width should be .080 inch; however, this depends on how your engine will be used. Short blasts, such as in drag racing or marine use, can get away with a .060-inch contact width. Otherwise, .080 inch.

Should you go to larger valves during the machine work? This depends upon how much room you have for larger valves. Ford was mighty generous with Cleveland valve sizing at 2.09/1.73 inches. Valve shrouding becomes an issue if you try to go larger with factory iron heads. You also want at least .060-inch distance between intake and exhaust valves.

With original-equipment umbrella valve seals, expect to machine your heads for more modern Teflon or Viton valve seals. To accommodate Teflon or Viton valve seals, heads have to be machined at the valve guides to .530/.500-inch outside diameter. Another consideration is valve spring cups, which keep valve springs stable and reduce wear and tear at the head. Once your valve job is complete, make sure your machine shop checks each valve for freedom of movement before assembly.

Just about any high-quality, stainless valve works well in Clevelands. If you’re racing, use the lightest valve possible to reduce internal drag. Street engines can live with any high-quality stainless valve. When valves, guides, seats, and ports are machined and properly set up, it is time to check and mill deck surfaces to get a perfect mating surface. Milling deck surfaces, reduces deck thickness and combustion chamber size, which increases compression and makes valve-to-piston clearances tighter. This is why you should wait to do head work until the block is ready for mockup. You must know all the dimensions between the piston and combustion chamber. Heads need to be measured across and diagonally. If warping varies more than .003 inch in any direction beyond 6 inches, mill the deck .005 to .010 inch. Before milling, sonic check deck thickness and be sure you have enough deck. Keep in mind you may have heads that have already been milled. If you mill away too much, you have a doorstop.

If you’re working with Cleveland heads with bolt-fulcrum rocker arms, consider screw-in adjustment rocker arm studs and guide plates. This is a modification any competent machine shop can do. Pedestals are milled fl at the appropriate amount (thickness) to make way for guide plates and studs. Holes are drilled out and tapped for studs.

 

Written by George Reid and Republished with Permission of CarTech Inc