Hi guys,

I bought an AP .15 and will probably break it in this weekend. The guy at the store gave me a long plug, and I pointed out to him that the instructions specifically say NOT to use a long glow plug; he took it back and gave me the Thunderbolt Heavy Duty Plug. Now, I'm no expert on these (hell, I'm posting in the beginner forum!), but the manual for the engine suggests a Thunderbolt R/C Short. My local LH stores don't seem to have that particular plug.

Will the one I have now pose a problem? If so, where can I get the recommend plug?

Thanks in advance!

Unfortuntely... I'm not familar with the Thundebolt plugs...

The reason for wanting the short plug is VERY important. You can get away with a short plug in an engine that specifies a long. A long plug in an engine that specifies a short is almost guaranteed to have the piston hit the plug.

If in doubt... get the exact plug specified. Don't accept a substitution that could damage the engine.

Someone else will probably be familiar with the brand of plug... and can tell you if its a short plug.

http://www2.towerhobbies.com/cgi-bin...ug&FVPROFIL=++

for pics of assorted plugs.

The only TRUE long one pictured is the McCoy. appx 7 threads

The O.S. 8 lists as a long... but has 5 threads...

The rest have appx 5 threads and don't list as short or long. (note the O.S. F has 5 threads and an extended portion that would stick into the engine further...)

I believe a TRUE short plug has 4 threads... (I don't have any, and can't find a pic of one to verify this....)

Good thing I didn't start it yet. YOur link didn't work for me, but it seems I have found it on Hobby People: http://www.hobbypeople.net/gallery/115535.asp

But damn, shipping is too much. [X(]

OUCH! that's just 3 to 3 1/2 threads! I can't even recommend trying one with more than 4 threads showing. And then only with no idle bar!

Do you mean with less than 4? I think I misunderstood missed entire last post.

Hi scubyfan,

An OS A3 will be perfect. It is a relatively short plug, and is also slightly hotter. I run this and 15% nitro is my OS 15LA with absoultly no problems. The smaller engines tend to like nitro more that larger engines and they run quite a bit better. 10-15% is about right.

Stefan

To be safe, take the head off the engine, and put in the plug. If the plug extends past the top of the combustion chamber, it's probibly too long, you usually want the plug flush with the inside of the head. Sticking in a very small bit is ok, as is being recessed a little.

You can stick an extra washer under the plug to raise it up if you need to run a longer plug in an engine designed for short plugs.

Most (but not all) .15 size engines take long plugs just fine. The OS LA, Mag .15, OS CV-A, Norvel, and Megatech .15's all take long plugs, they all have a thick enough head that it's not a problem.

But that doesn't mean the AP can handle a long plug with out getting in to trouble. Even if the piston doesn't contact the plug, an overly long plug increases compression which can make the engine tempermental. I don't know what kind of plug it likes, honestly.

However, a "heavy duty" plug is probibly a long plug, not a short. I know that's true with the K&B plugs I use, their heavy duty is the same length as their long.

From what I've seen, all the OS plugs are shorter than typical plugs. Why, I have no idea, but they are. So if you can't get an actual short plug, an OS is going to be the next best thing. If that's still too long, try adding an extra washer.

Hi guys,

I bought two Fox R/C Short plugs today. They are about 1 mm shorter than the previous plug, about 3 or so threads, so I thing they will be fine.

Will let you know if my engine explodes.

Thanks again!