A worm-drive circular saw is one of the more common power tools among both professional tool-users and weekend do-it-your-selfers. They are universally useful and have the tenacity to make most any construction or demolition project spectacularly simpler. Few users, though, understand the importance of regular maintenance, like lubrication.
Fortune, however, was kind to worm-drive circular saw users, and lubing your circ saw is a pretty simple process. A quick word of advice, though, before beginning this brief tutorial: always check your oil levels before using the saw. The oil level should never fall below the lowest threads in the tool housing, and, should that oil become thick or excessively dirty, flush the saw of the old oil and entirely relubricate it (*see below for flushing instructions).
The first and foremost step in getting that saw good and lubed is disengaging the tool, ensuring it has no power source to draw from, and resting it firmly (on its foot) on a sturdy, flat surface. Next, you simply need to reach and check the oil. To do this, use the tool’s wrench (the same one used to remove the saw blade) to remove the oil plug (this is the metal nut just above oil the reservoir that reads “oil level in operating position” on the right hand side of the tool). Add fresh oil to the oil reservoir allowing it to fill enough to spill out (a little) of the oil-hole at the arrow pointing up from the reservoir.
Next, you simply need to replace the oil plug and all will be right as rain with your worm-drive circular saw. Oh, and although you absolutely must use high-quality, high-speed oil (never, ever use motor oil), it is highly and always recommended that you use only Bosch or Skil lubricating oil in these tools. Using these lubes also offers the extra piece of mind in knowing that your tool is smooth and happy, and the simplicity of knowing exactly what to buy (Bosch lubricant: part number WD7LUB, Skil Lubricant: part number 80111). So, when lubing these Bosch and Skil saws, use only Bosch or Skil oils.
Now, if when checking the oil, the existing oil in the saw is ultra-dirty or thick, you will need to entirely flush the bad oil from the saw. To do this, immediately replace the oil plug, reengage the tool and allow it to simply run for about one minute to warm and loosen-up the existing oil. Remove the oil plug once more and invert the saw allowing the oil to drain completely from the reservoir.
Next, fill the reservoir with kerosene, return the plug again to its plugged position, reengage the tool and allow it to run for one minute. This will flush and clear-out the gear housing and reservoir of any residue. Remove the plug and invert the tool once more to entirely drain it of the kerosene. After ensuring you’ve drained as much kerosene as possible from the reservoir, refill it with the aforementioned Bosch or Skil worm-drive circular saw lubricant (fill it, again, to a bit of a spilling point at the oil-hole). Return the plug, and you have successfully lubed your circular saw and single-handedly enhanced its life and performance. Good job.