My front door knob suddenly stopped latching when pulled shut and deadlock wouldn't turn without pressing door in tight. I thought I just needed to change position of strike plates. But when I unscrewed them, I found them very loose with the wood around the holes in jamb rotten with nowhere to put a screw. Also mortise very close to edge of jamb so very little wood to hold latch and deadbolt.

Don't think I want to replace entire latch-side door jamb for now. Don't have tools to mortise holes, etc. I don't have enough clearance for the kind you just install over jamb and the wood on jamb is pretty rotten so chiseling out wood for 48" steel plate probably not a good idea.

I can't use those smaller deadbolt/knob plates because the distance between deadbolt and knob is nonstandard 8 inches (and clearance issue as well).

I tried using longer screws hoping to get the strike plates attached to stud. But that has apparently already been done several times, so nothing there to hold screw.

So what is best way to fix this until I buy a new prehung door?

 

You just need to drill out the wood (where your screws need to go) and glue in some new wood. A 3/16" drill bit and golf tees is what I usually use. You could also buy a dowel and use that, then cut it off flush. The main thing us that it fits tight and that you glue it in with wood glue. Once it's dry you can reattach the strike plate, just drill a pilot hole for the screw first. This is an easy 5 minute fix... not counting the dry time for the wood glue.

 

Long before the internet, locksmiths were using aftermarket strike plates from a company called Don-Jo Manufacturing to improve strike plate security. (There's some new guys on the block now selling these humongous long strike plates, and sounds like this is what you found) Don Jo has some plates that conform to the commercial strike measurement of 4-7/8" long, whose screws will go above and below your wallowed-out holes, but not require a whole lot of additional mortising, if any; most doors have enough clearance for a surface-mounted plate that's 3/32" thick. Suggest the model 2SS or similar for your latchset, and model DBS... for the deadbolt. The screws supplied with these plates are usually quite a bit longer than normal, but even then, the plate for the latchset could use long screws as well because this is the plate that holds the door tight against the weatherstrip, so that the deadbolt will operate freely without binding.

Your local smithy can order what you need, or of course, they're probably available online nowadays.

Note: When using long (2-3" or more) screws that penetrate the first wall stud, take care not to over-tighten...if the builder didn't use shims right there at the strike plate area, and assuming there is some gap between the door frame and the stud, it's very easy to draw the door frame away from the door, increasing the door-to-frame gap. So as the screws snug up to the plate, just give it another 1/4 turn or so.

 

If you want to do this on the cheap, and you're close to a locksmith, they usually have leftover commercial 4-7/8" strike plates laying around. When we install electric strikes, the old plates accumulate in our shop until we have 2 or 4 dozen, then they're just thrown out. If they charge you more than 3 bucks it's hiway robbery...they'll probably just give you one. Most are brushed stainless steel finish, but hey, beggars can't be choosers...

 

Look for a product called Plast-Aid. It is a powder and liquid that when combined, coagulate and slowly hardens. As it hardens it becomes putty like. Before it fully cures, when it is putty like, put it in the existing screw holes. It will continue to cure and harden, effectively filling the holes. You can then drill new holes and put any size screw in.