Engine Tips - Biggest Engine-Building Mistakes

Piston Rings Installed Upside Down

This one rears its ugly head the minute you fire the engine. Piston rings are shaped the way they are for a reason. Although it is a popular misconception that both upper rings are compression rings, nothing could be further from the truth, according to McAfee. He tells us only the top ring is the compression ring. It is modified (machined) at the top inside the ring groove to keep the ring from rolling down when exposed to hot gasses. This allows the ring to maintain sealing at the piston crown. The second ring is an oil-control element designed to meter oil up the cylinder wall. The more traditional oil rings in the third groove are oil scrapers. They carry oil down the cylinder wall and into the piston's interior for cooling purposes.

Piston rings have chamfers to provide a specific function, and are made of certain materials, also to provide a specific function. That's why you don't want to install them backwards, nor in the wrong groove. Follow the manufacturer's instructions closely and always use a ring installer. Do not roll rings into grooves (even though everyone does it). It is impossible not to warp piston rings when you roll them on because they are not spring material. They will remain warped.

MCE Quick Tip:

Always use a piston-ring installation tool. No exceptions.

Not Enough Connecting-Rod Side Clearance

This one can stop you cold. Connecting-rod side clearances don't get the attention they deserve. Remember, rod journals are the hottest spot in your engine short of exhaust valves, stems, and seats. Oil temperatures in this area can run upwards of 400-450 degrees F. This is why rod side clearances are critical to engine survival. They should be 0.015-0.025 inch. Rods become a throwaway at 0.028 inch side clearance.

Not Measuring Piston-Ring Clearance, End Gap, Side, Back . . .

It's easy to overlook piston-ring clearances. Most people think it's a matter of checking end gaps and popping those little guys in place. But did you know you need to check piston-ring side and back clearances? Checking these clearances and making sure you have at least 0.002-inch clearance in back and at the sides prevents ring bind and breakage.

Line Boring The Block

Although shops widely recommend line boring when bearing saddles are out of alignment, you need to avoid line boring whenever possible. Line boring puts the crank and cam closer together, which causes slop in the timing set and irregular valve timing. Unless you are dealing with an expensive block or a matching number block you want to keep, avoid line boring.

Laying A Crank On Its Side

Absolutely never lay a crankshaft on its side-not even for a few minutes. Crankshafts should always be stored standing straight up or hanging from a storage fixture. Laying a crank on its side will cause permanent damage.

Not Enough Pushrod-Hole Clearance

Pushrods should never rub the cylinder head, yet a lot of them do. Minimum pushrod clearance should be 0.060 inch.

Not Checking Cylinder-Head And Block-Deck Warpage

We learned the hard way how important it is to have a machine shop check for block-deck and cylinder-head warpage. When MCE Engines was doing our Summit Racing 331 Stealth engine project, the brand-new Ford Racing Sportsman block's deck was 0.017 inch out, which means cylinder heads and intake manifold would have wobbled. McAfee cut the deck, removing a 0.017-inch irregularity that would have created serious problems later on. All blocks and heads, old and new, must be checked for warpage and poor initial machine work before machine work begins.

Faulty Rear Main Seal Installation

Rear main seals should never leak, yet they do when not properly installed. When installing a two-piece rear main seal, the seal lip should point inward towards the front of the block. Seal end gaps should be located not at the main cap parting lines, but slightly away from them with a small dab of sealer at each gap. Use sealer between the seal and block grooves. One-piece seals follow the same rule, with the seal lip pointed toward the inside, and sealer between the seal and block.

Improper Valve Lash

Jim Grubbs of JGM tells us valve lash gets set improperly most of the time because many people don't understand how it works. It's a good idea to follow firing order when you adjust valves to make sure none get missed. Every builder has their own technique. Some adjust valves in quarter crankshaft turns. Some go bank by bank-watching the intake valve open and close-then checking lash.

Although few of us use mechanical cams these days, especially on the street, valve lash is typically 0.010-inch intake and 0.020-inch exhaust depending on application. See the manufacturer's specifications for details. With the cam lobe at base circle (valve completely closed), the thickness gauge should glide between rocker tip and valve stem without binding. Check to see if valve adjustment happens with the engine hot or cold.

For most of us with hydraulic camshafts, follow firing order, watching the intake valves open and close one cylinder at a time. As the valve seats, jab the starter quickly one more time. It's a good idea to see if the piston is at top-dead-center. Loosen the adjustment nut or poly-lock until you can turn the pushrod with finger and thumb. Twirl the pushrod and slowly tighten the nut. Once you can't twist the pushrod anymore, tighten the nut 11/44-11/42 turn. In some instances, 11/44 turn isn't enough and you will have rocker-arm noise. Most of the time, 11/42 turn is ideal. Some manuals suggest 31/44 turn. In our opinion, that is too much and could cause valve-to-piston contact at high rpm if lifters pump up.

Distributor Drive-Gear Fit

Distributor-shaft drive gears should always be a pinch fit, meaning the gear should have an ever-so-slightly smaller inside diameter than the shaft. This is necessary because the distributor drive gear has oil-pump load to deal with outside of just spinning a rotor. A good pinch fit, coupled with solid roll-pin integrity, should keep you in the clear. Some aftermarket distributors offer a loose distributor gear-to-shaft fit, or at the least a slide-on fit. This is unacceptable and could cause major engine damage if the roll pin fails.

Nitrous or Supercharging Without Proper Planning

Nitrous and supercharging can be costly mistakes if you don't do your homework beforehand. If you're contemplating quick, cheap power gains (nitrous-oxide injection), you must first know what's inside your engine. Cast or forged aluminum pistons? Cast pistons? Forget it. Forged? Good-you are cleared to proceed to the next step. What is your engine's compression? Don't know? Then you better check now.

When manufacturers assure you 100, 150, 200 bolt-on horsepower increases by touching a button, sacrifices will be made elsewhere. Your engine will not live as long. Nitrous introduces your engine to a violent jolt of extreme heat energy hammering the piston crowns, rings, and lands. Rod bearings also take a pounding with nitrous.

The same rules apply to supercharging, which isn't quick, nor is it cheap. It's just more subtle than nitrous, and mandates special care. Remember, there are no free lunches in the world of power. When you gain big one way, you make huge sacrifices somewhere else.

Not Checking Spark-Plug-Wire Resistance

Spark-plug wires get the same kind of attention rear axles do-not enough. If your engine is plagued with misfire or sluggish performance, check each of the spark-plug wires for resistance and external voltage leaks. If you see them arcing in the dark, or you have cracked and split insulation, they need to be replaced. Resistance to the flow of high-energy electricity will cause a weak spark or none at all. A spark-plug wire that shorts to ground (arcing you can see or not see) doesn't allow current to flow to the spark plug. If it shorts to ground, there isn't sufficient spark at the plug to get the job done. Borrow or buy a volt/ohmmeter and check your spark-plug wires for resistance from the distributor cap to the spark plug. While you're at it, inspect the distributor cap for cracking. No more than 4,000 ohms of resistance to current flow anywhere-including the distributor cap. Anything greater than 4,000 ohms of resistance is a throw-away.

Reusing Old Gaskets

Some types of gaskets can be reused repeatedly. Cork gaskets should be replaced every time you open the engine. Ditto for cylinder-head and intake-manifold gaskets. Reusing intake and cylinder-head gaskets is courting trouble. Can you afford to experience coolant in your oil? Why take chances? Replace the gaskets.

Applying Coatings To Head Gaskets

Today's cylinder-head gaskets don't need spray-on coatings or sealers. Install them dry and torque in sequence to proper specifications. Some head gaskets require a retorque after a full heat cycle; some do not. Read and follow the manufacturer's instructions to the letter.

Cheap is BAD!

Engines fail because of poor workmanship, but also when we choose to do it on the cheap. Cut-rate products are cheap because they aren't up to the same standards as the more expensive stuff. When you buy antifreeze that's a couple of bucks a gallon cheaper, there's a reason it's cheaper. It may have fewer additives, or lesser-grade additives, even though it's green like the higher-cost brands. The same can be said for engine oil, gaskets, seals, bearings, piston rings, pistons, hardware, valves, and the rest of it. Be smart and spend the money going in on better parts rather than suffer the consequences of engine failure later.