So you just spun a bearing in your motor and aren’t sure what to do. This write up will tell you what your options are. Before you can have any option, you need to determine the damage done or lack of damage done. And to be clear, throwing new bearings in it is NOT an option. I will explain why soon.
You need to disassemble your engine. Remove the head from the bottom end and then strip the block. Front case, crank, pistons, rods, everything needs to be removed. Once the block is stripped, we need to figure out if the crank and main journals are within spec. This is done by renting, buying, or borrowing a micrometer. You then mic out the journals. The specifications can be found in a Haynes manual. You need to check the cylinder bores too to make sure they are within spec and not out of round.
IF ALL MEASUREMENTS ARE WITHIN SPEC: Your block is still good and can be used for rebuild. Do a finger nail test. Use your finger nail and scratch each journal perpendicularly. If your finger nail catches, you need to take the block/crank to the machine shop to get the journal polished. If it passes and all the journals are smooth, no machine work needed. Even if your cylinder walls were within spec and not out of round, you need to hone them. You can have a machine shop do it or rent/buy a honing tool and do it yourself.
IF ONE OR MORE JOURNALS OR CYLINDERS ARE NOT WITHIN SPEC: Your block is going to need machine work in order to be usable. Even if only one journal is not within spec, the rest will need machined as well. For example, if all the journals but one journal on the crank is out of spec, all the crank journals need machined. Once the machine work is completed, you will need oversized bearings. Could be .20 over, .30 over, .40 over, etc. Ask your machinist. If your journals were fine but your cylinders were out of spec, the cylinders will need to be bored out. Once again, if one needs machine work, they all do. If your machinast bores them .20 over, you will need .20 over pistons and rings. Your machinist will tell you.
BLOCK AND OR CRANK MAY BE UNFIXABLE: even with machine work. Once you determine the machine shop will be needed, your machinist will be able to find out if its fixable. The damage done to the journals may be too much and too much material would need be removed to make the journals smooth and even. Again, your machinist will be able to figure out if its saveable or not. In most cases, your crank will be too damaged but the block will be saveable. If that’s the case, you will need a new OEM crank. Then the machinist will machine the block as much as needed and will tell you undersized bearings are needed. Your cylinders may also be unfixable. They may need too much material removed to be fix. The more material removed, the thinner the cylinder walls will be. On a 4G63, a .60 over bore is the absolute max you can go.
BUYING A NEW OR USED ENGINE: is always an option. If your old block isn’t usable, its the only option. If your block is fine or saveable, its obviously still an option. But then again, if you had the money to buy a new engine, you would have done so by now. If you end up deciding for what ever reason to get a used short block in running condition, you can still rebuild it. Rebuilding a running short block with no major issues and it great shape is by far a lot less of a hassle than rebuilding a short block that spun a bearing. You still need to take all the measurements and procedures mentioned above. Buying a used engine is a big risk. But the above info will tell you the shape of the engine.
REBUILDING A SHORT BLOCK: At this point, the short block is disassembled and journals are within spec either before or after machine work. The next step is very important. You need to thoroughly clean the block free of oil, rust, grit, metal shavings, etc. If you do not do this, you are just going to cause yourself to spin another bearing. This is why you cannot just throw new bearings in after you spin a bearing. Be sure to clean all the oil galleys throughout the block. There are long, bendable brushes you can buy to scrub and clean the oil galleys. Make sure you clean the oil pump and front case inside and out. When i rebuild a used motor, everything that comes off the motor gets cleaned. Every square inch of every part no matter the size or importance. I strongly suggest you do the same.
Next, you can start ordering the parts needed for the rebuild. Below is a list.
Main and rod bearings
Complete engine gasket set
Timing belt, all tensioners INCLUDING the auto hydraulic tensioner, and pulleys
Balance shaft elimination kit (BSEK)
Oil and filter
Copper spray for the front case gaskets
ARP head studs
ARP main studs
Once you get everything, you can begin assembling your engine. USE PLASTI-GAUGE WHEN INSTALLING MAIN AND ROD BEARINGS to verify there are no issues. This will determine if undersized or oversized bearings are needed. Rebuilding an engine will cost anywhere from $500-1000 depending on what parts you buy.