Mustang MonthlyHow To Engine
25 Engine Building Mistakes (Plus 2 More!)
Don’t screw up—build your Mustang’s engine for longevity and reliability!
Engines fail for two basic reasons: flawed parts or improper build technique (or both). Building an engine is not for the faint of heart, yet it is something you can do yourself if you take your time and pay close attention. There’s more to it than just replacing worn parts and popping pistons. Engines are precision internal combustion machines that mandate your closest attention from the teardown, cleaning, inspection, machine work, and assembly. And newer engines, like the 4.6L, 5.4L, and 5.0L modulars do not tolerate carelessness in any form. Miss important details in any engine build and it gets time-consuming and expensive.
We decided to put together a list of the most common engine-building mistakes in order to help you avoid errors that become expensive losses. And once you have read this article thoroughly, we’d like to hear from you to let us know what we have missed and what you have encountered building your own engines.
01. Settling Instead of Choosing
One mistake we see all too often is settling instead of choosing when it comes to engine, cylinder head, and block castings. We settle for a 4.040-inch over block and bore it to 4.060 inches, or we settle for a late-model 302 block when we wanted a properly date-coded ’65 289 block. Unless you are in a panic and need an engine right away, search the planet for the castings you want. Don’t settle for something you don’t want. Need a pair of 289 Hi-Po heads and have the cash? Search for them. We have the Internet now. They’re out there.
02. Installing Bearings Wet
We see this one time and time again, but there’s no reason to coat the backs of bearings with engine oil or assembly lube and we’re not sure why some builders do this. You want good bearing crush and security in saddles and connecting rods. Bearing saddles should always have a good crosshatch pattern and be bone dry for bearing security. Lube bearings and journal surfaces generously when it’s time to install the crank and piston/rod assemblies.
03. Link-bar Lifters
Link-bar roller tappets can be installed two ways—but there’s only one correct way. Install link-bar roller tappets with the link away from the block. Otherwise, they can contact the block, doing damage and shedding iron/steel particles throughout.
04. Using the Wrong Sealer
When you’re installing rocker arm studs or bolts that end in a water jacket, use a good commercial-grade Teflon sealer or Permatex’s “The Right Stuff” on the threads. Don’t overdo it. Some Teflon sealers will not seal rocker arm studs or bolt threads, which is when coolant gets into the engine oil.
05. Using Old Fasteners
Some engine applications, such as rod, cylinder head, and main cap bolts, should never be reused. Once a fastener is torqued to proper specifications, it becomes stretched and isn’t as effective in terms of clamping pressure when used again. If you are serious about engine durability, replace all of your hardware with ARP fasteners, which are aircraft grade and made to the highest standards. Always replace connecting rod bolts when rods are reconditioned during a rebuild. Never reuse the old bolts. Cylinder head and main cap bolts are available through Ford and through Summit Racing Equipment. Always chase threads to make them smooth and use a thread lubricant.
06. Not Using the Right Valve Seals
Engine builders have several options when it comes to valve seals. There are the good old-fashioned neoprene umbrella seals automakers have been using since the beginning of internal combustion. Umbrella seals are obsolete and not the seal to use anymore. Teflon seals have been a popular choice among racers for years. By far the best seal is the blue Viton valve seal, which requires the same machine work as Teflon seals. Teflon doesn’t last as long as Viton in street use, though it remains very popular.
07. Not Installing Hardened Exhaust Valve Seats
Unleaded gasoline has been the mainstream automotive fuel since the ’80s, yet a lot of us continue to perform engine rebuilds without much concern for exhaust valve seat wear. Aluminum cylinder heads are naturally already fitted with hardened steel valve seats. Old classic cast-iron cylinder heads are not. Tetraethyl lead was added to gasoline long ago to both boost octane ratings and provide lubrication for exhaust valves and seats. When lead went away, exhaust valve and seat wear escalated in older cars. When you rebuild, have your machine shop install all-new valves and hardened steel exhaust valve seats. If you really want to cover the bases, have both intake and exhaust valve seats replaced in the interest of longevity.
08. Poor Organization
Engine building success begins with organization, which not enough of us practice. Work bench clutter and accumulation create confusion and chaos, which are not what you need building an engine. When you knock an engine apart, dispose of anything you’re not going to reuse and promptly clean everything you’re going to reuse. Then, lay clean parts out in proper order and assess what passes and what doesn’t. Shop clutter is one of the quickest paths to disaster and engine failure. Maintain a clean and orderly working environment.
09. Not Checking True TDC and Degreeing the Cam
We see this mistake time and time again, especially in home garages. Never install a camshaft without knowing its true specifications. Never trust a cam card from a manufacturer because mistakes can happen anywhere. Cams get packaged in error and they don’t always get ground to the specifications on a cam card. Invest in a TDC indicator and a degree wheel from COMP Cams. Then learn how to read instruments and know what you’re installing.
10. Rolling Piston Rings On
Put 50 engine builders in a room and you will get 50 different opinions on how to assemble an engine. Rolling piston rings on can and will distort the rings. Not everyone agrees with this. Piston ring expansion tools put less stress on a piston ring because expansion is uniform. It does not distort compression and oil control rings. Oil wiper rings in the bottom groove must be rolled on because there’s no other way to do it and they are flexible. Position ring endgaps 45 degrees apart around the piston. Did you remember to check piston ring endgaps?
11. Not Using Rod Bolt Protectors
This is an error that will tighten the jaws of the most seasoned technician. When connecting rod bolts are not covered, you run the risk of scoring cylinder walls and crankshaft rod journals. Because rod bolts are very hard and crank journals/cylinder walls are soft iron, it doesn’t take much to nick the journal. Use rod bolt protectors no matter how careful you think you are.
12. Honing Without a Torque Plate
When engine blocks are bored, they are machined just shy of the planned oversize because we still need to finish-hone the bores for good ring contact and seating. When we finish-hone the block, each cylinder bore must be shaped the way it will be with the cylinder head bolted on and torqued to specifications. If you hone without a torque plate, cylinder bores will change shape when the heads are installed and torqued, potentially causing improper ring seating and loss of oil and compression.
13. Improper Seal Installation
Few things frustrate enthusiasts more than oil leaks from a fresh engine. Although it is common folklore that old cars just leak, that doesn’t have to be true. Classic engines leak because we don’t seal them properly. Gaskets are there to seal, which means you do not need a ton of sealer with them. You need perfect contact surfaces and a hair-thin line of Permatex’s “The Right Stuff” on just one side of the paper or cork gasket. Urethane/silicone gaskets require no sealer. Shaft seals require special care. The seal lip and spring must be pointed toward the inside of the engine. Pack the seal’s garter spring with engine assembly lube so it won’t pop out when you drive the seal in. Use generous amounts of lube on the seal lip and shaft for a lubricated startup. A dry seal lip on startup will tear and leak. If the garter spring pops out, the seal will leak. Use a very thin layer of sealer around the outside perimeter between the seal and engine.
14. Didn’t Check Pan and Pick-Up Spacing
How many engines suffer from low oil pressure and volume because pick-up and pan dimensions weren’t checked before the pan went on? Measure the oil pump pick-up to pan rail dimensions and pan rail to sump even if you’re installing a stock pan. The pick-up needs to be 1⁄4 to 3⁄8 inch from the pan sump for sufficient flow and pressure. Too close and you lose volume. Too high and you risk pump cavitation. Use a wad of putty between the pan and pick-up to ascertain pick-up to pan clearances if you’re not confident of your measurements.
15. Dog Gone Dog Bones
When you’re installing a spider-type roller tappet system, the word “UP” on the dog bones mean exactly that—UP. Yet untold numbers of these are found during teardowns with the word “UP” and the dimple facing down. Don’t make this mistake.
16. Using Excessive Sealer
Many an engine teardown has witnessed outrageous amounts of sealer to a point where it isn’t effective against leaks or it comes loose and blocks oil pump pick-ups and galleries. Gaskets are there to seal to begin with. They don’t need excessive amounts of sealer as a back-up plan. End gaskets, like this one, do not require sealer if you seat them properly.
17. Hot Cleveland Wedgie
Those building a 351 Cleveland listen up for this “heads up.” Side-by-side here are 351C combustion chambers. On the left is the open chamber common to ’70-’74 351C-2V and ’73-’74 351C-4V heads. The greatest insult is the ’73-’74 351C-4V head with the open chamber and large 4V ports, which offer poor low-end torque and a chamber with extremely poor quench prone to spark knock. What you want is the wedge chamber on the right. The best 351C head to go with comes from down under—the Australian head with 351C-2V ports and the smaller wedge chamber common to ’70-’72 4V North American heads. You get good quench and great low-end torque for the street. There are also excellent aftermarket heads for the 351C as well as the 351M and 400 engines.
18. Using the Incorrect Cam Lube
Flat tappet and roller cams call for different assembly regiments. Roller cams get engine assembly lube (slippery red stuff) on journals and lobes. Flat tappet cams get assembly lube on the journals and molybdenum lube (carbon gray gritty consistency) on the lobes. Never use molybdenum on cam journals or roller cam lobes.
19. Not Checking Journal Clearances Properly
Crankshaft journal to bearing clearances should always be checked with a micrometer and a dial-bore gauge to confirm bearing clearances. Although Plastigage is used with great regularity and success, it is suggested you lean to the side of accuracy and take no chances.
20. Piston Rings Installed Upside Down
When you’re installing piston rings, pay strict attention to instructions. Piston rings typically have markings and machining nuances that indicate which way they face. Get them backward and they will not seat nor function properly. And one more thing, oil wiper ring expanders must be installed where ends meet, but don’t overlap.
21. Rear Main Seals—Let’s Get It Right
When you’re installing two-piece rear main seals, stagger the seal gaps away from the main cap contact surfaces to reduce and even eliminate any chance of leakage. Use “The Right Stuff” on the seal tips.
22. Go With the Flow
If you’re building a 351 Cleveland and inclined to remove this coolant flow restrictor thinking you will improve cooling—don’t. This is the controlled bypass flow brass insert conceived by Ford engineers to reduce thermostat cycling and overheating. If you happen to be building a 351M or 400, this feature is cast into the block.
23. Doing It on the Cheap
When you’re building an engine, you can cut costs with three-piece pushrods. And if you’re building a stocker, you can probably get away with three-piece, thin-wall pushrods. But, are you a gambler? Gamblers take chances—but you shouldn’t. Spend the money and go with one-piece, 0.080-inch wall pushrods and sleep better.
24. Geared Up For Disaster
One of the quickest paths to engine expiration is using the wrong distributor gear for your camshaft. Iron flat tappet camshafts call for the use of a cast-iron distributor gear like this one. You can see the rough cast in the gear. Roller tappet camshafts mandate the use of a bronze, composite, or steel distributor gear. The most optimum distributor drive gear is composite because there’s less risk of damage to the cam and gear. And when you’re installing the distributor, get endplay and clearances right. Get it too tight and you will wind up with cam and gear damage—an expensive mistake.
25. Balance in Your Life
Plenty of money is spent building engines. Yet we do something foolish like reinstalling an old harmonic damper. Whenever you build an engine, never reuse the old damper. And if you’re going for high revs, put your money down on an SFI-rated damper in the interest of safety. The harmonic damper’s job is to act as a shock absorber for crankshaft twist and rebound. It softens the rebound as cylinders fire and work around the crankshaft. A bad damper can cause crankshaft breakage, or at least fail and come through your hood.
Two More (Consider This a Bonus!)…
+01. Did You Leave Something Behind?
Engine overheating can be epidemic, especially if you’ve tried everything, including a new radiator, water pump, thermostat, and even a high-capacity cooling fan. A hidden cause of engine overheat can be trash in your engine’s water jackets. Lazy engine disassemblers tend to knock core plugs inside the water jackets instead of removing them, hindering coolant flow. Slag and other cast-iron trash can block cooling passage and cause ugly hot spots that add up to a needle on “H.” Inspect all water jackets to ensure they are clear before assembling your short-block.
+02. Not Inspecting Parts Beforehand
Enthusiasts spend excessive amounts of money wastefully because engine parts are not carefully inspected before machine work begins. Remember—you get to pay for the expensive machine work even if the part is junk. Before having machine work performed, invest in non-destructive testing, such as magnetic particle inspection and pressure testing. This improves your chances of a successful build. A cracked cylinder head with port work and a valve job is nothing more than a doorstop and you get to pay for all of that expensive machine work.