9 Rookie Engine-Building Mistakes And How To Avoid Them

Diesel mechanic repairing diesel engine of semi truck

Engine rebuilding is a complex job, and therefore, you will need to avoid mistakes as you go through the engine rebuilding process. To make your life easy, we thought of sharing a list of 9 rookie mistakes you could make when building an engine. Make sure that you don't commit any of these mistakes to stay away from trouble. 

Failing to take correct crankshaft measurements 

This is perhaps the most frequent blunder we come across. Your cylinder might be out of spec by as little as.003," and your crankshaft can be out of standard by as much as.0005" on Kohler K Series engines. Many clients have decided that standard-size components are what they desire based on the smoothness of the cylinder bore and crankshaft. On the other hand, your eye cannot discern a cylinder that is tapered by.004" or a crank journal that is out of round by.0005" (half a thousandth of an inch). An out of specification engine may not show any visible evidence of wear or damage.

If you want your rebuild to last as long as possible, use a micrometer to measure the bore and crankshaft.

Failing to use the proper micrometer 

Calipers are helpful for various tasks but not for measuring engine components. Your measurement will be thrown off if you move your wrist while counting. A micrometer is preferable because it is simpler to maintain perpendicular to the measured component and does not move until the thimble is turned. Using a micrometer takes experience, so be careful to fine-tune your method using recognized "standards."

Ignoring the valve seats that should be repaired 

If the surface of your valve seat is damaged, use a valve seat cutter to restore it. Many individuals believe that using a valve lapping compound would fix the problem. However, the valve lapping compound does not remove enough material to repair damaged valve seats. If you don't have access to a valve seat cutter, your local automotive machine shop may assist you. If you have more than one tractor, you may wish to invest in your valve seat cutting equipment.

Failing to check the end gap 

It's common for new piston rings to need some final adjustments. If you don't double-check your rings' end gaps once they've warmed up, the piston may seize in the cylinder. Before fitting the rings on your piston, be sure you drive the rings into the cylinder by themselves and use a feeler gauge to measure the end gap. If necessary, use a file to expand the opening.

Failing to check the flathead 

The more power your combustion chamber produces, the better the seal. Even if your engine has never blown a head gasket, you should use a feeler gauge and a flat surface to examine the flatness of your cylinder head. A glass countertop or a granite surface plate might be used for the flat surface. You should flatten the head if you can fit a.003" feeler gauge between any of the bolt holes. You may achieve this by sanding a flat surface with medium to fine-grit sandpaper, adding water, and running your cylinder head back and forth a few hundred times. It's much simpler and quicker than it seems!

Not having adequate rod bearing. 

Not inspecting the bearing clearance is apparent, and it's a relatively regular occurrence. A builder may believe that a crank checks to standard specifications—if it is tested at all—and that the clearance is OK. The worst thing you can do to a racing engine is overtightening the bearings, particularly on the rods, especially on a higher-rpm engine. When you spin them up, the rod stretches a little, pinching the bearing or not getting enough oil to keep it cool enough, causing the bearings to fail.

Installation of wet bearings

We see this a lot, but there's no need to use engine oil or assembly lubricant on the backs of bearings, and we're not sure why some builders do it. In saddles and connecting rods, you require excellent bearing crush and security. Bearing saddles should always have a lovely crosshatch pattern and be bone dry to ensure bearing stability. When installing the crank and piston/rod assemblies, thoroughly lubricate the bearings and journal surfaces.

Failing to use the correct type of sealer 

Use an excellent commercial-grade Teflon sealant or Permatex's "The Right Stuff" on the threads when inserting rocker arm studs or bolts that terminate in a water jacket. Don't go overboard. Some Teflon sealers cannot seal rocker arm studs or bolt threads, allowing coolant to enter the engine oil.

Using worn-out fasteners

For example, Rod, cylinder head, and main cap bolts should never be reused in an engine. When a fastener is torqued to the required specifications, it gets stretched and no longer provides enough clamping pressure when used again. If you're serious about engine durability, replace all of your hardware with ARP fasteners, which are aviation grade and produced to the highest standards. When rods are reconditioned during a rebuild, always replace the connecting rod nuts. Never use old bolts again. Bolts for the cylinder head and main cap are available from Ford and Summit Racing Equipment. Always use a thread lubricant and chase threads to make them smooth.

Failing to use the correct valve seals 

When it comes to valve seals, engine builders have a variety of alternatives. The good old neoprene umbrella seals that automakers have used since the dawn of internal combustion. Umbrella seals are no longer in use and should not be used. Seals made of Teflon have long been a popular option among racers. The blue Viton valve seal is the finest, and it needs the same machine labor as Teflon seals. Although it is still trendy, Teflon does not last as long as Viton in street usage.

Final words

These are the most common cookie engine build mistakes that you would probably make. Focus on these mistakes and make sure that you never commit any of them.

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