Great response Flashpilot, thanks! The list of potential equipment failures is impressive, and very helpful. My concerns about the effects of vibration transferred through the handlebars are now reinforced. And thanks too for the sobering anecdote about the exploding light. In my case, something like this could have serious consequences for a light unit mounted on the handlebars four inches from my hand, and with an end-cap pointed back only a foot from my upper thigh. Maybe I will start wearing full-fingered gloves in case I need to quickly remove a dangerously-overheating light.
What damage signs would you suggest I look for in a pre-ride inspection? Coil spring deformation seems an obvious one, and maybe cracks/disintegration in solder joints and circuit panels… but what else, surely not burn marks?
Vibration problems with the handlebar-mounted light continue. I obtained the Convoy C8 light you recommended, but maybe they have changed the switch mechanism since you purchased yours. My model changes mode with a light/quick single touch of the button. And out on the trail, it changes mode with each bump. It’s a great light though, and will make a very nice, inexpensive gift to a friend. I also purchased the Ultrafire A9-T60, a 2-mode light which I’ve not yet tested on a night ride, but will do so soon.
I have tried a couple of different methods of damping shock from the handlebars, namely: additional silicone padding and foam cell padding using 1/2” foam cell. Neither of these made a difference to the rattling I can hear from within the light, or to the involuntary mode shifts. The trails in Marin County are very rocky and my forks are rigid. Putting a pair of shock-absorbing forks on the bike would solve the problem, but I’m not going to do that.
So for me the quest continues to find a light that will function as I desire in high vibration conditions. The Ultrafire A9-T60 might prove to be satisfactory, but I won’t know until I’ve tested it on a night ride.
Also I will take your advice of carefully checking the equipment for stress-related mechanical failures. It seems that will be an important safety check to add to the list.
Here’s a few things to check, but please read to the end before disassembling your light:
Exactly which cells are you using? I wonder if they are to short to make proper contact with the spring ends. Its very unlikely but worth checking. When you shake the light, can you feel the battery rattling inside? If so, from top to bottom or width wise… or both? If its rattling top to bottom, buy longer batteries, or you can remove the battery tube and VERY carefully pull on the driver spring with needle nosed pliers to stretch it. Its a tough steel spring and not easy to stretch, so be very careful if you attempt this. You could easily rip the board its mounted to and yank the spring off, so be careful. If it rattles side to side, a wrap of electrical tape at the top and bottom of the cell will provide a tighter fit inside the tube.
Other things to check:
Remove the battery tube from your convoy. Remove the bezel, lens and reflector. These can be removed as a single assembly and be kept together to eliminate any dust from entering. Looking at the bare emitter, assure there is a small white plastic donut (reflector centering ring) surrounding the emitter. The emitter star board is mounted on a screw-in threaded aluminum piece we call the “pill”. The pill in this light has a hole to each side where it is tightened from the front and screws into the head. Take a pair of sharp needle nosed pliers, insert the points into the holes and twist clockwise to assure the pill is well tightened into the head. Make sure the plastic donut centering ring didnt fall out and reassemble your light.
The tail cap has the same 2-hole type design retaining the switch assembly. Make sure it is also tight by using your needle nosed pliers. If the clicky button still changes modes to easily, remove the 2-hole retaining ring and completely disassemble the tail cap. Remove the rubber tail boot and turn it inside out. You will see a rubber nub extending out that makes contact with the switch. Take a flat razor blade and remove aprox 1-2 mm off the nub to shorten it. Assure each spring end is clean and the inside of the brass plunger is also clean. You can clean it with a swap and rubbing alcohol, gin or vodka. Reassemble and try again. Repeat trimming the nub if necessary so that very little resting pressure is felt through the rubber tail boot. Ideally, the nub should just touch the switch but not exert any pressure.
More helpful info, thank you. My batteries are Panasonic NCR18650Bs. The fit is very solid inside the Convoy, with no side or lengthways rattling. With the UltraFire it is not quite so snug. About 2.25 wraps of electrical tape the batteries fixed that. I will try the tail boot trim you suggest on these lights and will let you know how it goes. There might be a couple of weeks’ time gap though, since it has finally (thankfully) started raining here in the Bay Area. The trails are wet now and another week’s rain is forecase. Once they’ve dried out I’ll get back on the mixed-surface bike.