Why It’s Important To Replace Timing Belt Idler Pulleys

Don’t Risk Your Engine By Reusing Timing Belt Idler Pulleys

When performing a timing belt change, most shops recommend replacing the timing belt idler pulleys, timing belt tensioner, camshaft seals, and water pump. Many consumers wonder if that’s necessary. The answer is YES! Here’s why. The failure of a single idler pulley bearing can result in the destruction of an interference engine. Even in an non-interference engine, a pulley failure can leave you stranded and force you to pay all over again for a new timing belt and idler pulleys. Here’s an example of what can happen if you reuse the timing belt idler rollers or the timing belt tensioner.

This Subaru owner reused old timing belt idler pulleys

All timing belt idler rollers use a sealed bearing. The grease inside the bearing is designed to last the life of the timing belt, which can be 60,000, 90,000, or up to 110,000 miles, depending on the carmaker and the engine. Timing belts are cheap, but the idler rollers, tensioner, and water pump can really add to the cost. Here’s what happens if you reuse old timing belt idler rollers.

The bearing in this cog idler pulley burned up its grease

On the left you can see a cog idler roller with the grease seal removed. This idler roller is low on grease but the balls and cage still have some grease left. The cog idler roller on the right is one that should have been replaced when the timing belt was replaced. It ran out of grease, overheated, seized, and broke its retaining bolt. That produced belt slack, causing the pistons to hit the valves and destroy the engine.

They cog idler on the left has lost some grease. The cog idler pulley on the right lost all its grease, seized, and broke the retaining bolt, destroying the engine.

Idler seizes and breaks off and destroys the engine

Next, the idler seizes. In this case, as the inner race spun, it broke the retaining bolt. Once that happened, the cog idler ran into the tensioner located above it. The timing belt lost tension, the valves went out of time and the entire engine was destroyed.

Idler damages other components

As the cog idler let loose, it hit the tensioner and engine and ground off teeth on the idler and damaged the engine.

Notice where the valves contacted the piston. There were matching impact areas on each piston.

Timing belt idler replacement cost

The timing belt idler rollers and tensioner shown below cost about $200. This engine was destroyed because the owner opted to replace just the timing belt and not these other wear components. Remember, they’re designed to last the life of the timing belt, not the life of the engine.

©, 2020 Rick Muscoplat