Crank Bearings and Seals Fits Stihl BR500 BR550 BR600 BR700

Crankshaft bearing and oil seal set that fits Stihl BR500, BR550, BR600 and BR700 backpack blowers. Four pieces: two crankshaft bearings and both crankcase oil seals. Replaces part number 9523-003-4301 for each bearing, and 9639-003-1585 (also listed as 9638-003-1581) for the seals; both sides of the crankshaft take the same size seal. Worn crankshaft seals are a common cause of lean running on backpack blowers. Air drawn in through a hardened seal lip bypasses the carburetor entirely, so the fuel mixture leans out under load and the engine runs hot. Left alone this ends in a scored piston. Because splitting the crankcase is most of the work on this repair, the bearing and both seals are normally replaced together at the same teardown. Pressure and vacuum testing the crankcase before final assembly confirms the seals are sealing and is worth the few minutes it takes.

• FITS STIHL BR500, BR550, BR600 AND BR700 backpack blowers. If your blower is bogging, running lean, or will not hold an idle after warming up, worn crankshaft seals are the usual cause - unmetered air gets into the crankcase past a hardened seal lip and the engine leans out. This is the bearing and seal set for that repair, and for any crankcase teardown on these machines.
• FOUR PIECES: TWO CRANKSHAFT BEARINGS AND TWO OIL SEALS. Replaces 9523-003-4301 for each bearing. The seals replace 9639-003-1585, also listed as 9638-003-1581; both sides of the crankshaft take the same size seal. Match any of those numbers off your old part or your parts diagram and you have the correct set.
• WHY THE BEARINGS GO - A backpack blower spends its working life near full throttle, which is harder on a crank bearing than intermittent saw work. A bearing that runs rough or hot takes the seal with it and then the piston, so replace both bearings while the crankcase is apart.
• DO ALL FOUR PIECES AT ONCE. Splitting a crankcase is most of the labor on this job. Replacing a seal and reusing a bearing with 400 hours on it means doing the whole teardown again in a season. Both bearings and both seals are in this set for exactly that reason - if the crankcase is open, all four go in.
• PRESSURE AND VACUUM TEST BEFORE YOU BUTTON IT UP. A new seal that is nicked on installation leaks exactly like the old one, and you will not know until the engine is together and running lean again. Seat the seals square with a driver rather than a socket, and test the crankcase to confirm the repair before the shroud goes back on.