Balance Gear Timing Tool 25-455-06-S Fits Kohler K301 K321

Balance gear timing tool that fits Kohler cast iron K-series engines. Replaces 25-455-06-S, and the earlier numbers Y-357, NU-10355 and 10355. WHAT IT IS FOR. The balance system uses two counterweighted gears that run opposed to the crankshaft counterweights to cancel vibration. They have to be installed in time with each other and with the crank. This tool is a toothed disc that meshes into both gears and holds them in the timed position while the crankshaft is fitted. FIRST - DOES YOUR ENGINE HAVE BALANCE GEARS AT ALL? This is where people go wrong. Balance gears were fitted according to the engine's SPECIFICATION number, not its model number. Two engines wearing the same model number can be built differently. They were generally specified where the engine was hard-mounted to the machine frame rather than on rubber isolators. On the K241 and M10 only a small number of spec numbers ever received them. On the K301, K321, K341, K361 and the M12 to M16 they are more common but still not universal - and some blocks were never machined for the stub shafts at all, which means they cannot be retrofitted. HOW TO CHECK. Drop the oil pan and look at the power take-off side of the block. Two counterweighted gears on stub shafts means you have them. An empty pair of bosses, or no bosses at all, means you do not and this tool is not needed. WHY TIMING MATTERS. The gears are intentionally out of balance. Timed correctly they cancel the reciprocating imbalance of the piston and rod. One tooth out and they add to it instead, which raises main bearing load and shortens the life of the engine. A NOTE ON THE GEARS THEMSELVES. They are cast iron, running out of balance on a single needle bearing. When the bearing or the shaft wears, they can break up, and a broken gear inside a running engine usually takes the camshaft and the block with it. If your gears have shaft play, address that before timing them back in.

• WHAT IT DOES - Holds both balance gears in their timed position while you slide the crankshaft in. Replaces 25-455-06-S and the earlier Y-357, NU-10355 and 10355. The factory description is 'tool, balance gear timing-disc'. Aluminum.
• CHECK THAT YOUR ENGINE ACTUALLY HAS BALANCE GEARS - This is the thing to establish first. Balance gears were fitted by SPECIFICATION NUMBER, not by model - two engines with the same model number can differ. On the K241 in particular only a handful of spec numbers ever had them. Drop the oil pan and look for two counterweighted gears on the power take-off side of the block. No gears, no need for this tool.
• WHY TIMING THEM MATTERS - The gears are deliberately out of balance and have to run opposed to the crankshaft counterweights. One tooth out and the system adds a vibration couple instead of cancelling one, which loads the main bearings rather than relieving them. The tool holds the timing marks aligned while the crank goes in, which is the only part of the job you cannot do with two hands.
• WHAT THE GEARS ARE KNOWN FOR - They are cast iron, they run out of balance on a single needle bearing, and when the bearing or shaft wears they can come apart. A broken gear in a running engine takes the camshaft and often the block with it. If yours have play on the shafts, deal with that now rather than timing worn gears back in.
• FITS KOHLER K301, K321, K341 AND K361 - Plus the M12, M14 and M16, on engines built with balance gears. The K241 and M10 are in the same family but only a small number of spec numbers received the gears. Check the block before ordering.