Installing a new engine in a vehicle doesn’t do much good if it’s not properly mated to the transmission. The transmission provides all the motive power for the vehicle. While the engine creates the power, the transmission sends that energy to the wheels via the axles/driveshaft. One of the most common engine installation errors happens during this process – failing to torque the flywheel.

Failure to Torque the Flywheel

You’ll have to disengage the old engine from the transmission to remove it from the car. When you drop the new engine in, you’ll have to reattach them. It’s a simple enough process, and is nothing more than doing the reverse of what you did to disengage them. However, there’s more that you have to do – you can’t just hand tighten the bolts, and you can’t “hammer down” and tighten them as far as you can, especially when it comes to used transmissions found on craigslist.

Flywheel bolts need the right amount of torque for safe operation. Too little torque and they’ll start to loosen, which is a bad thing that can lead to massive damage to the flywheel (requiring a replacement cost that your shop will have to eat in most cases).

Before you reattach the engine and transmission, make sure the torque converter is properly seated. The nub from the torque converter should be inside the face of the bell housing.

To torque the flywheel bolts properly, you’ll need a few things. First, and most important, you’ll need a torque wrench with the right settings and the correct socket size. Second, you’ll need the torque specs for the vehicle you’re working on. There’s no one-size-fits-all torque setting, and each manufacturer and model has its own specific torque settings. Find the specific ratings for the vehicle in question from the automaker or your shop’s manuals and adjust each bolt to the proper setting. Follow the recommended tightening pattern as well – never tighten bolts in sequence. Most automakers require some version of the star pattern.

NOTE: A word on torque wrenches – you’ll need the right type of torque wrench. Check the torque settings on the wrench and match those to the manufacturer’s requirements for the flywheel bolts. You shouldn’t use lb. ft. when it calls for lb. in. The same rule applies to flex plates used on automatic transmissions.