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Question And Answer - Ask Anything

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Three-Valve Ford Spark Plug Madness

Mark Yunker; Omaha, NE: I have really enjoyed your articles on improving the S197 Mustang, especially the supercharger article last month. I have been reading some discouraging stuff about a problem with the three-valve heads and would love to get Car Craft's take on the spark plug removal issues. I know Ford has a TSB (technical service bulletin) out on this, but is this an issue? Also, what alternative heads are out there that correct this without breaking the bank, and how difficult would retrofitting 4V heads sourced from a Lincoln Mark VIII be?

Jeff Smith: Mark, the spark plug issue with the three-valve heads is very serious. The problem is with the design of the spark plug. Because there is very little room for the spark plug in the chamber, Ford extended the length of the ground electrode shield way past the end of the threads. This creates what Autolite calls a high-thread spark plug. If you look at the photo of the three-valve plug, you can see how far the ground electrode extends beyond the end of the threads. Since spark plugs are warrantied for 100,000 miles, they are often not removed until well beyond the end of the warranty cycle. The problem is that after this many miles, carbon collects between the extended ground electrode and the very small channel in the head leading into the combustion chamber. It can get so plugged with carbon that, when you yank on that spark plug hard, it breaks, leaving the shank in the head. Once this occurs, you have to remove the head(s) to remove the remains. Autolite's Technical Training Manager, Jay Buckley, recently completed a thorough YouTube technical training video that shows the very specific procedure Ford has created to remove spark plugs from a three-valve motor. I strongly suggest you watch the video (do a YouTube search for "How to change spark plugs on Ford three-valve modular engines--Autolite"). With this procedure, you should be able to remove the plugs without drama.

The first step is to work with a cold engine that has been sitting for at least eight hours. Remove the coils and wires and use compressed air and a nozzle to blow out any dirt collected in the spark plug wells. Using a thin-walled 9/16-inch spark plug socket, carefully loosen each plug no more than 1/8 of a turn. Next, shoot about 1/2 to 3/4 of a teaspoon of carb cleaner into each spark plug well. Loosening the spark plug slightly allows the carb cleaner to soak past the plug seat and begin to soften the carbon buildup on the plug. The next step is the most critical: Allow the cleaner to soak, preferably overnight. After soaking, use a beam-style torque wrench and carefully loosen each spark plug with no more than 33 ft-lb of torque. If you get to 33 ft-lb, stop and soak the plug again. Work the plugs back and forth carefully. You can hit the plugs with a second shot of carb cleaner, but if you have to soak them more than twice, you will need to spin the engine over to clear the liquid to prevent hydro-locking the cylinder. The key to this is to work slowly and carefully. Finally, use antiseize on the new spark plug threads and the shield area but be careful not to get any of the antiseize near the ground strap or it will immediately cause a misfire. It would also be a great idea to yank the plugs at 30,000 miles just to clean off any carbon and make it easier to remove them later. Yeah, it's a hassle, but it's a far better alternative than yanking the heads after the plugs break.

As for your questions about an alternative cylinder head swap, it appears you already have a pretty good cylinder head with the three-valve package. The early Lincoln Mk VIII four-valve heads look attractive, but from what we've learned talking with the guys from Modular Mustang Racing (MMR), there isn't a huge power advantage to switching to the Mk VIII four-valve heads. For a mild, normally aspirated street engine, MMR says you would be better off modifying the existing three-valve engine with classic induction and exhaust modifications. This is because you would have to invest quite a bit of money to convert a three-valve engine to the four-valve configuration and the power improvements may not justify the cost.

Fuel Pickups

Dave Sidle; Bryan, OH: Sometime back you wrote an article about a company that builds custom fuel pickups for stock tanks. I cannot find that info and wondered if you remembered who it was? Thanks for your time.

Jeff Smith: Holley originally offered these goodies, but they have since disappeared from the catalog. We then discovered that Walbro makes pickups that can be placed in multiple locations in the fuel tank for a constant supply of fuel for the pump. These are roughly 3 inches in diameter and are barbed for a 5/16-inch inlet hose. The pickups use a fine mesh 70 micron screen over the inlet, so if the pickup is uncovered, fuel still in the screen will help block air from entering the pickup, assuming that another pickup is still pulling fuel. These pickups are rated at 40 gallons per hour, so having three in the tank should offer more than enough capacity to feed a large pump, since even 80 gallons per hour is equivalent to sufficient fuel to feed 900 hp.

According to the Auto Performance Engineering (APE) website (, these pickups come in several configurations including with and without bleed holes. The bleed hole prevents the screen from blocking the inlet, but obviously it also bleeds a small amount of fuel. Without the bleed hole, it's possible that the screen could cover over the inlet and block flow. The pickups are also available in single inlet, a flow-through horizontal style, and a flow-through 90-degree inlet. APE sells these pickups for $26.00 apiece.

Modular Mustang Racing
39 Old Ridgebury Road
CT  06810
MAHLE Clevite
7670 Hacks Cross Road
Olive Branch
MS  38654
Honeywell UOP
Nitrous Pro Flow
4700 N.E. 11 Ave.
Ft. Lauderdale
FL  33334
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