Dewalt DW303 reciprocating saw

You will need to remove the blade holder then the 4 screws that hold the front cover on. You can go to DeWalt's service site using the link below and view or print a parts diagram which will help.
DEWALT ServiceNet

That sounds dangerous! Does it actually cut after you do that? It sounds like it has bad gears and wouldn't cut if you put pressure to the blade. On a dw303 it's likely not worth repair if that's the case.

Same symptoms happened with mine--pull out the battery and look at the connecting terminals--they may be misaligned due to dropped tool or using the tool to break off a cut. realigning the battery connections to marry the battery powered the tool up. However the terminals remain loose and lose continuity at any point .Certainly isn't a permanent fix. Unfortunately the terminals are part of the switch and it will have to be replaced.

The drive shaft for the blade is stripped or broken. take it back where you bought it.

Not sure what you mean by open but here is a parts diagram if you are trying to repair it.

DeWalt DW303 diagram

Open the yellow tab on the side of the blade guard and lift the blade out. Install a new on and close the tab. If the blade has been damaged, it may need to be pried off the locating pin at the attachment point.

To install blade into saw:
1. Loosen set screw.
2. Insert blade shank from the front between the reciprocating shaft and the blade clamp.
Locate hole in blade over pin on reciprocating shaft.
3. Tighten set screw. If the blade should break off and the shank does not come out of the clamp,
be sure the set screw is loose and eject the shank with a nail or pointed object.

Help Instructions, Repair Guides, Manuals & Troubleshooting Dewalt DW310K Heavy Duty Reciprocating Saw Kit... Is the Dewalt dw310 multi purpose saw available in 110 volts - posted in Reciprocating Saws ...
www.fixya.com/troubleshoot

go to Dewalt parts: http://www.toolpartsdirect.com

your missing a tooth on a large round gear in the gearbox.

when the gear on the engine rotates into the position where the little engine gear spins because there is no tooth to come into contact with the engine runs but the gearbox doesnt spin, hence no reciprocation, but engine runs.

if you bump the blade it will start going again, but when you cut it will stop offasionally in mid cut. you can repair this but stop using it the engine gear will be destroyed otherwise

I have a dewalt dw303 that you can use for parts, I need a new trigger or something the motor is dead and I found a new saw. go to craigslist.org, rochester ny tools section and look for dewalt dw303 that is my listing. for ten bucks ill sell you all the gears you need. i think it is close to the same model, i am sure it is the same gearbox.

try opening your gearbox, im positive that is what is wrong.