Remove the spark plug so it is easier to turn the engine over.2. To get started, drain the coolant and the oil, remove the exhaust pipe and header and get any parts that keep you away from the motor out of your way. The cam chain is less than $20 and is extremely easy to change any time you are checking valve clearance.As with any of the new-generation small four-strokes, we were impressed with the minimal amount of effort required to perform a top end rebuild.1. Thumper recommends changing the cam chain twice a year and the valves once a year for a YZ250F that is ridden hard. The company warned that the cam chain may be a weak point. However, a race team such as YoT routinely changes valves, pistons and cam chains, so they may never see problems that an average ownerwho leaves those same parts in play much longermight encounter.For expertise on engines that have been subjected to typical weekend-warrior abuse and maintenance, we turned to Thumper Racing. Most recently Dye wrenched for Chad Reed for both the Yamaha factory team and during his stint with Yamaha of Troy, but before that he wrenched for Steve Lamson, Tim Ferry and Brian Swink.
In fact, we had FMF Racing's Dave Dye show us the intricacies of the engine, and he felt it really had no Achilles' heel. The other reason is the Yamaha has fewer weaknesses to pinpoint.
Motionpro cylinder hone series#
Yamaha's YZ250F has existed for more years than any of the other 250cc four-strokes, so it is less of a mysteryone reason we left it for last in our series on small-bore four-strokes.
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