One of the worst experiences in the world has to be spending all the time and money required to build a new race engine only to spin a bearing or have some other problem develop before it has even completed the break-in process. Building your own race engines can save you a lot of money (not to mention giving you the pride that comes from beating the competition with your own stuff), but race engines are too expensive for learning by trial and error.
Fortunately, many of the reasons for early engine failure are avoidable. All that is required is patience, attention to detail, and a few measurement tools that will help make your life a lot easier. In this article, we will describe how to properly install a crank into a properly machined block. This is the first and one of the most critical steps because everything-even the valvetrain-connects in some way to the crankshaft.
The most important part of installing a crank is making sure you have the proper clearance between the main bearings and the crank journals. The general rule of thumb is 0.001 inch of clearance between the bearing and journal for every inch of journal thickness. For a Ford Windsor with 3.00-inch mains, that works out to 0.003 inch of bearing clearance.
The first thing to do is to throw away the Plastigauge. Yes, it is simple and inexpensive, but it also isn't reliable enough. The Plastigauge may be OK for a quickie stock rebuild for your grandmother's station wagon, but it isn't accurate enough for racing. Instead, invest in a dial bore gauge and a couple of micrometers that can measure accurately to at least 0.001 inch. We sourced our mics for this project from Powerhouse Products. You can spend more on ultra-high-end measurement tools, but you can get a pair of quality micrometers (one that measures between 2 and 3 inches and a second that measures from 3 to 4 inches) along with a dial bore gauge for less than $200.
Now follow along as we build the proper foundation.
This Ford block may look like it's ready for the crank to be dropped in, but taking a few extra minutes to make some critical measurements can make the difference between a race-winning engine and one that doesn't make it through the break-in process.
Any contaminants, including dirt or small bits of metal trapped between the back of the bearing and the main housing bore, can change the bearing clearance. Although everything may look clean, be sure to wipe down both the main housing bores as well as both sides of the bearings with a lint-free rag and some lacquer thinner before installing the bearings.
All traditional V-8 engines have a thrust bearing to limit crankshaft endplay (movement forward and back). On a Ford, it is in the third main cap, as you can see here.
Here's a shot of a Chevy block. The thrust bearing is located in the rear main cap. Basically, the position is the only difference here. They both work much the same way.
For both Fords and Chevys, the upper bearing shell (shown here) lays into the block and has an oiling hole as well as a groove to help oil the entire journal surface. The lower shell is smooth and fits into the cap itself. Notice how the shell has a tang that only allows it to fit into the block one way. This also helps lock the bearing in place once the cap is bolted into position and keeps the bearing from spinning.