50mm Piston Kit Fits Stihl BR500 BR550 BR600 BR700

Piston kit, 50mm, for the Stihl backpack blower engine. Replaces part number 4282-030-2003, which has superseded to 4282-030-2005. Contents: piston, one piston ring, wrist pin and circlips. The engine is 64.8cc. Fits BR500, BR550, BR600 and BR700. All four are the same engine - they differ in fan housing, blower tube and rated air output, not in the piston, the ring or the valves. The BR700 belongs on that list and is usually left off. What does NOT fit: the BR350, BR430, BR450 and SR450 are a different 63.3cc engine and take piston 4244-030-2006. The FS130, KM130 and HT130 are 43mm. The FS90, KM90 and HL95 are 28.4cc. None of those will take a 50mm piston. The thing to understand about this engine before you rebuild one: it has a valve train, but it has no sump, no oil pump and no oil filter. The entire engine, valves included, is lubricated by the oil mixed into the fuel. Fifty to one, every tank. Running one on straight gasoline does not just seize the piston, it wrecks the valve train, and that is how most of these engines arrive on the bench. Valve clearance is 0.10mm - 0.004 inch - on both intake and exhaust, checked cold. The service manual calls for a check around every 135 running hours. Clearance that has drifted costs power long before it costs you an engine, so set it while the machine is open. The camshaft is gear driven, not belt driven, and the timing marks are painted onto the gear teeth. Line the marked teeth up with the crankshaft mark on reassembly. Piston kit only. Cylinder, valves, gaskets, crankshaft seals and the needle bearing are not included.

• 50MM PISTON KIT - Piston, one piston ring, wrist pin and circlips. Replaces Stihl part number 4282-030-2003, which superseded to 4282-030-2005. For the 64.8cc backpack blower engine.
• BR500, BR550, BR600 AND BR700 ALL USE THIS PISTON - All four are the same 64.8cc engine. They differ in fan housing, blower tube and rated air output, not in the piston. The BR700 is on that list too, which surprises people.
• NEVER RUN IT ON STRAIGHT GAS - This engine has a valve train but no sump, no oil pump and no oil filter. It is lubricated entirely by the oil in the fuel. Fifty to one mix, every tank, no exceptions. Running one on straight gasoline destroys the valve train as well as the piston, and that is what kills most of the engines that end up needing this part.
• VALVE LASH IS 0.10MM, INTAKE AND EXHAUST, CHECKED COLD - That is 0.004 inch, the same on both valves. Stihl calls for checking it around every 135 running hours. Lash that has drifted shows up as lost power long before it shows up as a failure, so set it while the machine is apart.
• THE CAM IS GEAR DRIVEN AND THE TIMING MARKS ARE PAINTED - Line the marked teeth on the cam gear up with the crankshaft mark on reassembly. Get it wrong and it will not start. Cylinder, valves, gaskets, crank seals and the needle bearing are not included.