Bottom end knock, also known as rod knock, is a common issue that can occur in the FA20 engine, often as they reach a higher mileage. This type of knock is caused by the connecting rod bearings wearing out and becoming loose, causing the rods to knock against the crankshaft.
There are several factors that can contribute to bottom end knock on an FA20 engine. One of the most common causes is the use of low-quality or incorrect oil. Using oil that does not meet the specifications for your engine can cause the bearings to wear out faster and increase the risk of knock. The Subaru recommended oil is 0W20, however many owners suggest 5W30. Either way, only a high quality, fully-synthetic oil should be use.
Another common cause of bottom end knock is a lack of proper maintenance. Neglecting regular oil changes and failing to check the oil level can also lead to bearing wear and knock. Subaru recommend changing the oil every 10,000 miles, however if the car is driven hard or tracked, then the change interval should be reduced.
Overheating can also be a contributing factor to bottom end knock. If the engine is running hot, the oil can break down, causing the bearings to wear out faster. This can also be caused by a malfunctioning cooling system, such as a faulty radiator or water pump. The Mishimoto low temperature thermostat is a great upgrade to avoid this issue.
Lastly, bottom end knock can also be caused by high-performance driving, such as excessive revving, high speeds, and hard acceleration. These conditions put a lot of stress on the engine and can cause the bearings to wear out faster. If you plan to track your BRZ or GT86 then we recommend a number of performance upgrades to the engine. Get in touch and we can talk you through the best options.
In conclusion, bottom end knock on an FA20 engine can be caused by a variety of factors, including the use of low-quality or incorrect oil, lack of proper maintenance, overheating, and high-performance driving. It is important to always use the correct oil, change it regularly and maintain your vehicle properly to avoid this issue. If you suspect that your engine has bottom end knock, it is important to have it checked out by a professional mechanic as soon as possible to avoid further damage.
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If your FA20 engines knocking, get in touch and we can advise on the best options. We can also supply freshly rebuilt engines and forged engines too.