When a timing belt breaks in a Subaru engine, it stops rotating the camshafts in sync with the crankshaft, causing an immediate loss of proper valve timing. This results in catastrophic engine failure as the still-moving pistons collide with the now mistimed valves. To prevent severe damage, the engine must be shut off immediately if the belt snaps.
This article discusses the consequences of a broken timing belt in a Subaru, the urgent actions needed, typical repair costs, reasons for the higher failure rate, and provides key background details on timing belt function and recommended replacement intervals.
What Happens When a Timing Belt Breaks in a Subaru?
The timing belt is one of the most critical components in the engine of a Subaru. This ribbed belt connects the crankshaft to the camshafts, ensuring the proper timing and synchronization of the engine’s valves and pistons. When this belt breaks, it can lead to catastrophic engine failure.
The Immediate Effects of a Snapped Timing Belt
The moment a timing belt breaks in a Subaru engine, the connection between the crankshaft and camshafts is severed. This causes an immediate loss of valve timing. The camshafts will stop rotating while the crankshaft and pistons continue to move up and down. With the valve timing now randomized, the moving pistons will inevitably collide with open valves. The force of these collisions can bend valves, damage pistons, and even crack cylinder heads. To prevent this self-destruction, the engine will usually stall immediately when the belt breaks.
What To Do When Your Timing Belt Breaks
If you hear strange noises coming from the engine or smell burning rubber, your timing belt may have snapped. It is imperative to shut off the engine right away to mitigate damage. Coast your Subaru to a safe stop, and do not attempt to restart it. Even a few seconds of running with a broken timing belt can destroy the top half of your engine. The only option is to have the vehicle towed to a professional mechanic for repairs. Attempting to drive it further will likely result in a complete engine failure needing full replacement.
Repair Costs for a Severed Timing Belt
Due to the extensive labor and parts required, a broken timing belt is one of the most costly repairs on a Subaru. The repair bill can easily exceed $1000 in most cases. On some newer Subaru models with interference engines, the repairs can cost up to $3000 or more.
This includes replacing the damaged timing belt, tensioner, pulleys, bent valves, piston heads, and any other affected components. The exact cost depends on the extent of the engine damage. Preventative timing belt replacement is far more affordable, typically under $600.
Why Timing Belts Are Prone to Failure in Subarus?
Subarus are more susceptible to premature timing belt failure for a few key reasons. Firstly, their boxer engines have more dynamic loads and stresses on the belts compared to inline or V-configured engines.
Secondly, Subaru utilizes relatively long timing belt intervals of 105,000 to 120,000 miles on many models. The belts are more likely to degrade or suffer fatigue fractures with higher mileage.
Lastly, Subaru timing belt systems lack a piston interference monitoring system that could detect slippage or damage. Overall, proactive timing belt replacement every 100k miles is recommended for Subarus.
How Long Do Subaru Timing Belts Last?
The factory scheduled replacement interval is 105,000 to 120,000 miles for most Subarus. However, these belts often deteriorate and fail prematurely, especially when exposed to oil leaks or adverse driving conditions. Replacement every 90,000 to 100,000 miles is ideal for preventing failures.Belts older than 10 years should be replaced as rubber compounds degrade over time, regardless of mileage.
Will a Broken Timing Belt Destroy My Engine?
If the Subaru has an interference engine, a broken timing belt will almost certainly cause catastrophic engine damage. However, if the engine is a non-interference design, a snapped belt may not damage anything. Non-interference engines have sufficient clearance so the valves will not contact the pistons even with mistimed camshafts. The EJ251 and EJ252 are notable non-interference engines found in some older model Subarus. But the majority of Subaru engines are interference designs and will self-destruct when their timing belt breaks.
What is a Timing Belt?
A timing belt is a reinforced, toothed rubber belt that connects the crankshaft to the camshaft(s) in the engine. Its teeth mesh with gears on the camshafts and crankshaft, synchronizing their rotation and ensuring proper valve timing events in relation to piston movement. The belt is driven by the crankshaft and in turn drives the camshafts. It must withstand high rotational speeds and temperatures under the hood. The timing belt is essential for coordinating the precise timing of each engine cycle.
Summary
A snapped timing belt is an extremely serious issue in Subarus leading to engine destruction within seconds. But this dire outcome can be avoided with preventative timing belt replacement every 90-100k miles before age-related cracking occurs.
John Smith, a Los Angeles-based car specialist and automotive writer, boasts over 20 years in the industry. With a background as a master technician and a decade-long writing stint at notable automotive publications, John now shares his expansive knowledge on CarFinite, simplifying car maintenance for readers.