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CRF250 Although no specific service limit is advised in the Honda service manual, you should replace all the valves and springs at the same time as the piston. Honda recommends changing the piston every 15 hours, and in practice I estimate the valve train and piston to have a useable service life of about 30 hours. In fact the valve train usually wears out before the piston. The dangers of leaving the valves in place until the engine won’t start anymore, is that the valve seats will become damaged and require an expensive service of valve seat reconditioning. In a case like that, considering that new head is so inexpensive, it may be cheaper to buy a new head rather than fix the old one. Another problem that is rare for the CRF250 is a failure of the left side cam bearing. If the engine becomes particularly noisy at idle, or if there is a thick black residue of rubber present under the valve cover, then the cam bearing is worn and placing a greater side load on the cam chain guide. The rear tensioner chain guide is coated with rubber, which accounts for the thick black residue. |
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