In The Shop: Blown Evo Cam Bearing

BLOWN EVO CAM BEARING

Replacing the Shovelhead in 1984, the Harley Davidson Evolution motor was produced until 1999. The Evo is known to be a very durable, dependable, and versatile motor. However, like the early Twin Cam and it’s nagging cam chain tensioner issues, the Evo also had a weak point inside its cam compartment.

Watch the FMH Multi-Hour Evo Top End and Cam Project

The weak component in the Evolution cam compartment is the factory INA cam bearing. This, stock, cam bearing is known as a partial complement bearing. This means, that the bearing has a cage that holds the needle rollers in place. Evos that were not properly maintained or had considerable mileage were susceptible to this cam bearings failure.

If installing a performance cam, the cam bearing must be updated. Also, it is important preventative maintenance to upgrade this bearing. If the bearing let’s go, catastrophic damage is inevitable. The bearing should be replaced with a Torrington or an S&S full complement bearing. These bearings do not have cages. They are full roller bearings. The Evo cam bearing is pressed into the right side case and supports the inside end of the Evos single cam shaft. If the bearing breaks apart, small, hardened, needle rollers can, not only, disperse throughout the cam compartment but can also drop into the crankcase.

Recently, we had a 1995 FLHTP In The Shop. The customer stated; when he was riding, the oil (pressure) indicator light came on and he shut the bike down immediately. Unfortunately for the owner, it was already too late. This motors bottom end had already been severely damaged.

Upon removal of the cam end cover, we were greeted by chunks of broken gear teeth, bearing rollers, and a broken breather gear. (Pics 1 & 2)

After further disassembly, we found:

•Broken cam gear (pic 3)

•Severely damaged cam (pic 3)

•Broken pinion gear (pic 4)

•Bent oil pump shaft

•Severely damaged oil pump (pic 6)

•.009″ pinion shaft run out

•Damaged right side crankcase @ cam bearing and breather gear locations. (Pic 5)

We stopped to have a conversation with the owner before further disassembly and inspection of the top and bottom ends. This may be one of those situations where it is better money spent to purchase a new motor or look into purchasing and freshening up another used Evo that is in better condition. Unfortunately, the cost of this repair can easily be as much or more than the motorcycles actual value.