Servicing Engine Mounts
To help maintain cash flow in the slower winter months, many independent shops replace worn engines. This also helps squeeze some extra miles from a customer’s older, but basically sound vehicle. The replacement might be a new original equipment crate engine, a remanufactured engine, or even a used engine in good condition. Regardless of the type of engine being installed, it will likely require inspection and possible replacement of all rubber components including engine mounts.
Wear And Tear
Any rubber engine mount is a wearing or expendable part despite its appearance. While modern rubber components tend to endure extreme heat much better than older compounds, engine mounts still fail when exposed to ozone and high under hood temperatures. Rubber engine mounts will harden in most cases, which increases the engine noise and vibration transmitted through the chassis to the passenger compartment.
However, when repeatedly soaked with hot engine oil, engine mounts will soften and lose their mechanical strength. Since most powertrain mounts are simply two pieces of steel laminated together by a tough rubber compound, the mount tends to separate, which can allow the engine to shift in its cradle. Engine mount separation can cause “torque-steer” on FWD vehicles when power is applied to the drive train. In other cases, the engine might simply become dislocated, causing sticking throttles, clutch chatter, exhaust leaks and other operational complaints.
Transverse engines found in FWD applications generally suspend the engine with one large front mount and two smaller rear mounts located each corner of the engine bell housing. In some FWD applications, a “dog bone” or torque strut might be bolted between the engine and the front radiator core support to absorb engine torque.
The transmission is supported by a rear transmission mount attached to a removable frame cross member in conventional RWD applications. The same type of mount can also be located between the transmission and transfer case on four-wheel drive vehicles. Unfortunately, this type of mount configuration is usually ruined by hot oil dripping from the transmission or transfer case adapter. Some applications might also use a small torque strut that helps the rear transmission mount control engine torque.
Doing the Math
Component accessibility is a major economic issue when repairs are performed in a commercial setting. A conventional RWD platform provides an excellent example of why it’s cheaper to replace mounts when the engine is being replaced. One popular labor guide lists five hours for replacing both front engine mounts. Removing and replacing the engine requires 16.7 hours of shop time. Obviously, replacing the mounts in pairs will cost the owner approximately one-third as much as replacing the complete engine. But, since the engine mounts must be exchanged from the old engine to the new, replacing with new ones adds only the cost of the mounts to the repair order. As with any expendable, low-access component, it’s far less expensive to replace it during a major engine service.