The piston’s tolerance within the piston chamber is so tight that there is no space for the piston to slide to the top. The resolution is to heat up the piston chamber with a wool dryer or heat gun. This will increase or expands the chamber, allowing the piston to slide smoothly, while maintaining superior compression. Read full post at https://uberant.com/article/442655-quick-tips-to-get-your-vehicles-rc-nitro-engine-running