Malkoff M91 Question

Hello All,

This is my first post. I had an old surefire 6p laying around that I wanted to upgrade in someway to make it more useful to me. I poked around on this forum and in other places and decided that it would be really cool if I bored out the surefire to take 18650s, buy an extender so I could run 2 batteries, and then get a malkoff m91 9-12 volt head to drop into it that would let me run the 2 18650s or if I wanted to I could theoretically run 4 cr123a batteries. The fit on the boring job is pretty tight (1 time around of standard white teflon tape will fit, but 2 seems to greater than the tolerance left from the machining), but it seems like it is very easy for the battery and head to become misaligned enough for the light to cut out with just a gentle tap on the light. I can tap it a few times until they line up again and then the light kicks on and is bright. Does this head not fit precisely on this body and its my hubris in frankensteining this thing together that is to blame? Or is this a common problem and everyone else just knows that you need such and such spacer or some other part that immediately fixes it? Thanks!

You need a magnet or spacer if you're using unprotected cells.
With spec that tight, you're not lining anything up by tapping it. That IS what often happens when a battery is just a little too short, though. Tap it, the light comes on, but if you move it around it may flicker, etc. I use a neodymium magnet with unprotected cells in a MD2 for that reason.

You could also use a fitting ring in the head with your M91.Check Malkoff's site. It pushes the dropin further back into the body. This is pretty common and works great

The voltage range on the M91 is much more than 9-12 volts now, as Gene is using a new driver. You can run this on a single 18650 with reduced output.

Start reading here...
https://www.candlepowerforums.com/vb/showthread.php?310739-Malkoff-M91/page26

Or even a primary 123 3 volt! Crazy

I think it is good to warn of potential risks of short circuit with unsecured magnets, and especially when the experience level of those asking is unclear.