In the past, we showed you how easy is it to rebuild a set of overhead valve cylinder heads at home. However, when it comes to the more complicated cylinder heads in the Ford lineup (the Modular Two-, Three-, and Four-Valve overhead camshaft engines) the valvetrain might seem quite intimidating, and lead you to believe that you have to take them to a professional in order to work on them. While there’s no denying that there are a lot of parts involved, you can tackle 90 percent of the job yourself, and we’re going to show you how.
First and foremost, let’s talk about our specific use case — the 1996 to 1998 Mustang Cobra. This 4.6-liter Modular engine is a four-valve-per-cylinder dual-overhead-cam cylinder head design. While that might seem like a narrow production window, in fact, the “B-head” as it’s commonly known, was available on the 1993 to 1997 Lincoln Mark VIII and the 1995 to 1998 Lincoln Continental, which means the cylinder heads themselves are readily available and inexpensive in junkyards.
In the left image are the original intake valves and on the right are the exhaust valves. Notice the unique carbon buildup pattern on the intake valves. That's from the dual-intake-port design of the B-heads. A butterfly system (dubbed Intake Manifold Runner Control or IMRC) only opens the secondary port under WOT conditions, meaning both ports are not always active.
Getting Started: Disassembling The Valvetrain
The first step in any rebuild is the disassembly. If you’ve never worked on an overhead cam cylinder head before, this is where things can seem intimidating. The first thing to address is the secondary timing chain tensioner which needs to be compressed and locked in place with a pin.
Once that’s locked up, cracking the top cam girdle bolts seems easy enough until you realize they are also friction-fit on locating dowels which will require some persuasion to remove. Make sure you note which girdles go where, as there are four per head. Each has a unique part number cast into it which makes recording the location easy.
At this point, removing the camshafts is easy, but make note of the position (intake or exhaust) and which cylinder head (driver or passenger side) of each camshaft. If you do mix them up, not to worry, as each camshaft has its own part number. Also worth noting here is that while the cylinder heads are the same across the three applications mentioned above, the camshafts are slightly different in the Cobra applications (see sidebar for more details).
Since our valve seats are in good condition, we only had to lap the new valves into the head with a little rotational pressure.
With that out of the way, we get into some of the overhead cam-specific parts removal from the heads. Again, don’t worry, as the parts come right out. First, you have the cam follower, which is just a rocker arm, sitting on top of the lash adjuster and the valve. Once you have those set aside, the lash adjuster, which is like a ball-headed hydraulic lifter, pulls right out of the bore.
From there, you are left with just the valves and valvesprings to remove. The process is the standard affair, but you might need specialized tools here. We ran into the issue of our nice valvespring compressor not working on these heads because of the recessed location of the springs in the cylinder head. A quick visit to Amazon had a new compressor to us in 24 hours. The springs, locks, and retainers all come apart like any other setup, albeit in a much tighter space.
With bare heads, it’s time to determine whether the heads are good enough to rebuild as-is or if you need to take them to a machine shop to have the deck and or valve seats cleaned up. In our case, the heads were good to go, so we put them into the parts washer and cleaned them up in preparation for the rebuild.
With the cylinder head clean and the new valves lapped into place, we can now focus on rebuilding the rest of the valvetrain.
Getting The Good Cams
If you are searching for B heads in the junkyard or on the internet, if you just need the castings, or the valvetrain hardware, the 1993-’97 Lincoln Mark VIII, 1995-’98 Lincoln Continental, and the 1996-’98 Cobra are all the same. However, if you want performance cams, you’ll want the camshafts out of the Cobra. They utilize specific intake cams with additional duration, while they share the exhaust cams with the other applications. From our heads, the part numbers are:
F2LE-6A273-AF
F6ZE-6A271-AB
F6ZE-6A270-AB
F2LE-6A272-AF
Breaking down the camshaft part numbers, the exhaust cams are “F2LE” signifying they are the Lincoln parts designed in 1992, while the intake cams are “F6ZE: indicating a 1996 design specifically for the Cobra. The three numbers after “6A” indicate their position in the engine – intake or exhaust, driver or passenger head. The second two letters indicate engineering revision. “AF” on the exhaust cams indicate the sixth revision, while “AB” on the Intake cams indicates the second revision — which makes sense since these cylinder heads came off of a late 1998 Cobra, so they had the latest versions of the parts.
Using Good Valvetrain Parts To Rebuild
Since our heads and stock valvetrain appeared to be in great shape (save for the surprise at the end), but the valvetrain components are 25 years old, we decided to go ahead and replace everything. Thankfully, Melling makes that easy, as they have all of the components needed to rebuild the Cobra engine on the shelf. That’s no small feat in and of itself, but knowing that Melling has not only worked with the OEs on these parts, but actually supplied those parts in some cases, combined with the fact that all the parts are manufactured in the USA with premium materials, means we know they are top quality.
Melling manufactures everything we need to refresh this 25-year-old valvetrain. 32-valve engines require a LOT of parts to operate correctly. Fortunately, they aren’t as complex to disassemble and reassemble as you might think.
The first parts we installed were brand-new valves. The OEM intake valve (P/N: V1709) is a 7mm stem, 5.337-inch overall length steel valve with a 37mm (1.457 inch) head on it, with a 45-degree seat angle. Due to the design of the cylinder heads, the stainless steel exhaust valve (P/N V1908) is noticeably shorter, at 4.579 inches overall length, but with the same 7mm stem diameter. The head size for the exhaust valve is 30mm (1.181 inches) with the same 45-degree seat angle.
We tried to clean the carbon off of the factory intake valves, just to see if we could clean them up, but between the dual port design absolutely caking one of the intake valves, and the sheer age, using the new Melling valves was really a no-brainer. Since all of our valve guides were in great shape, we only had to lap the valves into the valve guides, and while 16 valves per head was a lot, there wasn’t much lapping required to get a solid interface between the valve and seat.
Here is a look at the new 37mm high-alloy steel intake valves and 30mm stainless steel exhaust valves before they were lapped.
Springing Into Action
Next up were valve springs. While ours were indeed 25 years old, what kills springs is compression cycles, not static load. We tossed them onto the Rimac and got consistent seat pressures in the 67- to 72-pound range. While that might seem low, in an overhead cam application, with much smaller, lighter valves, that is right in the OE spec.
We decided to do a little experiment and see if some aftermarket valvesprings we had would work on the B-heads. They were designed for a 1.64-inch installed height, but other than that, matched the physical specs perfectly. While they physically fit onto the heads, the shorter installed height of the B-heads results in incredibly high seat pressures making the answer a resounding “no.” The springs were rated at 100 pounds of pressure at the 1.64-inch height, and at the 1.46-inch installed height, we were well over 150 pounds of pressure on the seat. So while it might be tempting, make sure you use valvesprings designed specifically for the shorter 1.47-inch installed height during your rebuild.
Testing the old springs on the Rimac valve spring tester, we were seeing anywhere from 67 to 72 pounds of spring pressure on the seat. That falls within spec, which makes sense because these were low-mileage heads, but have been sitting in storage for at least 13 years. Fortunately, static compression doesn't wear out springs.
Modular Valve Locks And Retainers
When replacing valvetrain parts, it’s always smart to replace the valve locks and retainers. They are technically wear items and are inexpensive insurance when replacing springs. The Modular engines use a triple-bead lock design, and Melling offers steel replacement locks (P/N: VL-1804) and valve spring retainers (P/N: VSR-703). They are precisely machined replacements which should hold up in most performance applications.
The new Melling valve spring retainers and triple-bead valve locks are high-quality steel OE-style replacements. They work with any factory-style beehive springs.
Rocker Arms And Lifters — A.K.A. Cam Followers And Lash Adjusters
When working with Ford’s Modular engines, there are a few parts with unique names. Depending on who you are talking to, you might be using different terminology for the same parts. The first is the lash adjuster, or as Melling calls it (as do most people who are mainly familiar with pushrod engines), the hydraulic lifter (P/N: JB2271). These act like a standard hydraulic lifter, except, instead of sitting between the camshaft and pushrod, these sit at one end of the rocker arm and maintain zero lash between the rocker arm and camshaft lobe.
Like traditional hydraulic lifters, the Modular engines' lash adjusters use oil pressure to maintain zero lash in the valvetrain. Unlike traditional pushrod engines, however, the lash adjuster is a fulcrum point instead of being directly between the cam and rocker arm.
Next up is the rocker arm, or as it’s known in Modular-speak, the cam follower. Melling’s version (P/N: MR-929) uses an investment-cast body for strength, and high-strength, precision-machined steel roller and bearing to accurately transfer the cam lobe’s shape to the valve at the factory 1.8:1 rocker ratio. The end that rides on the valve is a proven slider-tip design. These rocker arms are robust units that will provide decades of reliability under the cams. Yes, under the cams, as the cam lobe sits atop the rocker arm, which is suspended between the lash adjuster and the valve tip.
While at first glance this might look like a traditional rocker arm, that center bit is what is in direct contact with the cam lobe, while the left socket rides on the lash adjuster and the slider tip on the right acts on the tip of the valve.
With all of the new valvetrain parts in place, it’s time to bolt the cams back into the cam towers. One thing to note here, is that Melling has all of the associated timing components required (cam sprockets, tensioners, timing chains, etc.) to completely overhaul the engine as well, but since we still need to pull the engine out of our 1997 Cobra to make some repairs, we saved that for another day. However, we did replace the factory cam thrust plates with the Melling cast-iron replacements (P/N: S803SP) as cheap insurance.
With everything in place, it’s time to replace the cams and bolt down the cam caps. Make sure you reinstall the caps in the proper orientation.
Not All Stories Have A Happy Ending
This story has a sad ending, however, as once we completed rehabbing the valvetrain of the first cylinder head, we tore into the second cylinder head to create a video on the process. Unfortunately we found one of the cam towers in the second head had a completely wiped-out bearing surface. The interesting thing about that was that the journal of the camshaft was fine, and from our understanding, the engine these heads came off of ran fine when the heads were removed (they were replaced with a set of class-specific cylinder heads).
While there are methods of repairing the cam towers that involve adding in a removable bearing, the cost of the associated machine work simply doesn’t make sense when you consider the current market value of a set of B-head castings. Since we have all the good parts, it makes way more sense to go to the junkyard and get a replacement casting from a Lincoln. Or, in our case, since we have a 1997 Cobra sitting in the driveway, just rebuild those castings. So much for just a simple head swap, but those are the breaks.
Regardless, we know that our heads will have brand new, high-quality Melling components and will hopefully give us another two or three decades of service before we even need to think about pulling the valve covers and replacing parts.
Unfortunately, when we pulled apart the second head, we found this wiped-out bearing surface on one of the cam towers. It’s repairable, as anything is, but it’s not a cost-effective repair considering the relative value (or lack thereof) of B-head castings.
