Im using a .12 .15 glow plug on my mds .40, it fits fine, and its the same length, put my plane shuts off, is this why? what the diff between car and airplane plugs

the car plugs have a higher heat range because car fuel has a higher nitro content. I would switch to an airplane plug, such as an OS #8 or I like the Hangar 9 performance plugs by McCoy.

you need a cooler plug with higher nitro. higher nitro means higher pressure and temperature, and more pre-ignition, so a cooler plug is in order. I've had a couple engines that would run for a couple seconds and then die on 30% nitro but were fine on everything else. turned out there was so much pre-ignition it was basically just killing itself. put a cooler plug in and added a head shim, ran great after that.

anyway, overall idea is correct though, plug is probably too hot. shim your head or go to a cooler plug. (just adding a second washer under the plug can sometimes make a big difference also!)

Hi!
There isn't such a thing as a ".12-.15 plug" or "Car and Airplane glowplugs"...only glowplugs!
Why your engine quits can have many reasons. Bad plug, tank and fuel lines leaking, carb not set properly, wrong fuel, too much nitro, too little nitro, worn out engine etc.

The more nitro/higher compression you have ...the cooler plug you must use.
For ordinary sport engines like OS 40-46, TT .40-46 and Magnum and so forth running on
0-15% nitro an OS 8 or Enya 3 is a good plug to choose. Higher nitro and you might have to try a cooler plug like a Rossi 5-6 glowplug or Enya 4.
But don't forget that this is a cut and try game...engines running on 0% nitro with high compression can still demand a cool plug like the Rossi 6 to develop max power.

Regards!
Jan K
Sweden

well, i got some os 8, those are the ones. Thanks anyways.

How old is your MDS 40?? The OLD black head engines that were imported by estes model rocket company were set up for low or NO nitro(high compression) most would simply not run on 15% or more nitro. If you have one of these engines try some 5% nitro... that and a good plug like the OS 8 you already have SHOULD yeild a good running sport class engine... some the engines also had air leak issues at the carb base and needles... once you can get it running take a close look at your fuel line for air bubbes.

John

ok. by the way how do you reach the fuel lines inside the fuesalage if you want to replace them?

That depends a lot on what plane that you have and how the fuel tank is secured inside? Was this a RTF plane that came with the tank installed? If not, you can remove the tank and fuel lines by doing the opposite of what you did when you installed them in the first place.

Ken

rtf

If there are only glow plugs, why does OS manufacturer so many different kinds with recommendations as to what engine they apply too?

Hi!
To suit different running conditions (not engines) when you want max power!
Thats why Rossi manufacture 8-9 different glowplugs.
"In the old days" it was mandatory to use Rossi 8 glowplugs in our F3D (6,5cc engines)pylonracing engines (running on 80/20 fuel) because of the high compression and high rpm (and lots of heat).
For just about every sport two stroke engine on the market the OS 8 and Enya 3 is the plug of choice, doesn't give the best rpm, but the best throtteling and reliability.

Regards!
Jan K
Sweden