Piston Kit for Hilti DSH900 DSH900-X Cut Off Saw 54mm 412383

Piston kit for the Hilti DSH 900 and DSH 900-X cut off saws, 87cc, 54mm bore, replacing Hilti part number 412383. This kit does not fit the DSH 700 or DSH 700-X, which are 68.7cc saws with a 50mm bore using piston 412238. The two machines look very similar and share the DSH designation, so confirm the model on the machine plate before ordering. The kit contains the piston, two rings, the wrist pin and the circlips. Hilti catalogues 412383 as the piston and 412384 as the complete cylinder and piston kit. Cylinder scoring on a cut off saw is nearly always caused by masonry dust getting past a poorly sealed or neglected air filter rather than by wear, so inspect the filter, the filter housing seal and the intake boot before fitting new parts. Pressure and vacuum test the crankcase, fit a new cylinder base gasket, and break the new top end in at reduced load for the first few tanks.

• FITS THE HILTI DSH 900 AND DSH 900-X cut off saws, 87cc, 54mm bore. Replaces Hilti part number 412383. These saws work in concrete and masonry dust all day, and a scored piston is almost always the result of that dust finding a way past the filter rather than of honest wear.
• DOES NOT FIT THE DSH 700 OR DSH 700-X. Those are 68.7cc saws with a 50mm bore and their piston is 412238. The two machines look nearly identical and share the DSH name, so this is the mix-up to avoid. The DSH 900 takes a 14 or 16 inch wheel and cuts to 5.9 inches; the 700 takes a 12 or 14 and cuts to 4.9.
• IN THE KIT: the piston, two rings, the wrist pin and the circlips. Hilti catalogues 412383 as the piston and 412384 as the complete cylinder and piston kit, so if a parts list quoted you one of those numbers that tells you which you are being offered. This listing is the piston kit.
• DUST IS THE WHOLE STORY ON THESE SAWS. Before fitting a new piston, look hard at the air filter, the seal where the filter housing meets the intake, and the intake boot for cracks. A cut off saw pulls an enormous volume of air through that filter and anything getting past it goes straight down the bore. A new piston in a machine still drawing dust will score again within a job.
• DO IT ONCE. Pressure and vacuum test the crankcase before running fuel through it, since an air leak leans the mixture and scores pistons the same way dust does. Fit a new cylinder base gasket, clean the exhaust port, check the plug and gap it to .020 inch, and break the new top end in at reduced load rather than going straight to a full day of cutting.