Before i replaced teh bearing, one of my glow plugs broke within 2 minutes of running. I assumed it was the leaky bearing. After replacing the bearing, i popped in a new glow plug and it broke at about 1/2 tank. My HSN is 2 turns out. LSN is 1/2 turn out from flush. I use mc-59. 20% odonnel. Dynamite glow warmer. The performance is crappy and the tuning is odd, especially for 40 degree weather outside.

I run a medium plug in my 18TM, I actually run the traxxas heavy duty medium plug, have 2 gallons on it, with NO issues. I actually swapped to ceramic bearings in it a few weeks ago, not because it needed them, just for that added protection. Of course I also run a pullstart version.
Rod

Have you tried a different brand of plug?

A friend, last summer got a multipack and some of the plugs didn't even have a wire in them.

I've never been a big fan of the mccoy's.

The traxxas 3232 works well, also the os lc3.
The 3232 is a medium plug, and you may want to run a hot plug due to the cold temps (40's).

Maybe it's just a quality issue with the plugs. The wire may not be properly secured inside the plug.

What is the outside air temp? Are you storing your vehicle outside, in a garage? Keep your vehicle stored indoors and only take it outdoors when you are ready to run it. Going from a frozen state to glowing hot within a few seconds would put a lot of stress on the plug, maybe leading to some of the problems you're having.

before i replaced bearing, i fried the OS#8.

Sounds like you may be too lean, have you checked for air leaks?

When running in cold weather you'll need to wrap some alum foil around the head to keep temps up....could be that you're too lean because you're tuning by temp...and the head is not holding enough heat, giving you erratic condition

Cold air is much more dense then warm, leading to a lean condition.

Detonation may be causing the plug failures.

Try the OS LC3, they are hot, and longer than the #8,... oh yeah and richen it up!

well, my performance is pretty crappy at 3turns out on the HSN

F************************CK! the new glow plug crapped out on me, this time, it was less than a 3rd of a tank. Its not that i tune by temp, i tune by performacne, adn teh best performance is around 2 turns out. Also, i did the foil thing and it did birng up the temps.

Do you have a shim between the head and the block? If you have a shim, your engine is set up for 30% fuel. I run 30% in my engine, for what it is worth. Get a mccoy 8, Sure Fire 4, Traxxas 3232, or Odonnel 99. All are great plugs for this motor. These are medium plugs. Hot plugs will work also, like the McCoy 59, but most of the guys I know run medium plugs. Go back to factory settings and begin tuning again, this cold weather is murder on engines, very hard to tune either by performance or temperature.
HTH
Rod

After further research:

Tune for performance, then add/remove foil to get temps around 200-250f.

Pre-ignition can be caused by an exposed thread on the glow plug or a piece of carbon in the combustion chamber, a sharp edge or particle that heats up and ignites the compessed fuel mix before the plug would normally ignite the mix.

So, tear down the motor and check to see how much of the plug is sticking out into the combustion chamber. Instead of a long reach plug you may want a std length plug. To reduce or eliminate any edge (thread) of the glow plug exposed in the combustion chamber.

Clean the combustion chamber of any carbon residue.

Check the top of the piston and chamber for 'pitting' a sign of detonation.

The previous post made a good point about shims. Adding a shim will reduce compression. Too much compression is the cause of detonation. Detionation will cause severe damage.

Changing to a 'cooler' plug will retard ignition timing (if no pre-ignition).

Hope this helps, GOOD LUCK

sounds to me that you are too lean, when the weather turns cold the air is more dense and needs to be richened. Just remember that when its winter richen the hsn. going thru plugs and poor performance could also be a bad rear bearing. Someone said that you should check for pitting on the piston from predetonation, well it could also be pitting from the rear bearing coming apart. I have had to have the hsn out 4 turns in colder weather to make it run ok. Hope this helps

PULL THE HEAD OFF OF THE MOTOR WHEN YOU BLEW THE FIRST PLUG SOME OF THE METAL COIL COULD OF STAYED IN THE MOTOR AND NOW IT IS GROUNDING OUT THE NEW ONES YOU ARE PUTTING IN AND I RUN THE LC3 OS PLUG THAT IS WHAT THAT MOTOR COMES WITH AND 25% ROCKET SIENCE FUEL I HAVE A NEW TM AND OLD ONE THE OLD ONE HAS A GOOD 10 GALS. ON IT THE CARB. IS TOAST BUT IT STILL RUNS WITH A NEW CARB.

smoke is comming out of the head at 200 degrees, is that normal?

No, did you spill somthing on it? ...Fuel?

If you took it apart, did you use some type of cleaner on it?

probably fuel and wd40 or something. But i still dont understand why i get the best performance at 2turns out when the other guy has at 4turn out....Should i not worry about it? The temps are at about 210.