Crankshaft rebuilding can be done yourself, though you need to understand how it works and why it is important to the engine. The crankshaft is necessary to keep the pistons rotating. The crank shaft will connect to the pistons with connecting rods, crank throws and crankpins. The most common ones use a four stroke cycle. In most instances, rebuilding the parts of the engine is much less expensive than replacing it and is frequently done when restoring or customizing a car.
Step 1 – Inspect
First, you need to inspect the old crankshaft to see what work needs to be done. Some of the main issues occur when the rods and bearings are out of alignment. You also want to make sure all the seals are properly functioning. Oil flow through the crankshaft is important and there are many factors that can cause issues within the crankshaft.
Step 2 – Disassembly
When you are taking the old crankshaft apart you need to make sure you put the bearing caps aside in the order that you take them off, as they will need to be put back onto their original places. This also applies to the rod end cap combinations. You can easily accomplish this by labeling a plastic plate and placing the pieces on the properly labeled section. This step is critical, as the caps have to be kept in order. It is not recommended that you use cardboard or paper, as fibers can attach to the caps.
Step 3 – Measurements
You will need to make several measurements on the old crankshaft. Use the micrometer and measure a main bearing race at the center. Write this number down and then turn the micrometer around the same bearing about 90 degrees and take another reading. If you subtract the two numbers it will give you the out of roundness. The taper is measured by measuring the side of the same bearing and then going to the other side and measuring that. The difference is the taper. You want to do this for all of the connecting rod journals and main bearing races.
Step 4 – Machining
If your measurements fall outside of the factory specifications you will need to have the crankshaft machined for undersized bearings. If the journals are fine then you can polish them yourself, but if there are problems with the bearings and you do not want to have them machined you will have to get a new one. It is also a good idea to have the older crankshaft x-rayed to see if there are any cracks. If your crankshaft is cracked then you will need a new one. A machine shop can quickly and easily remachine the bearings if this is needed.
Step 5 – Alignment
When you are installing the crankshaft back into the engine it is important that you make sure everything is aligned. Check that none of the bearings have shifted. You can add some prelube on the bearing caps to ensure they stay put. Make sure you replace the caps in the same order that you removed them.
Step 6 – Kits
If you are not confident in doing all of this yourself as I have just explained then there are rebuild kits available that provide all of the necessary tools and parts. They also provide step by step directions on what to do.