I tried different engine last week (Novarossi, Picco, Os) but I had some problem with the glow plug.

The spire of the glow plug seemed "squezzed". Why?
I put a new glow plug, after 20 minutes... the same. I tried other brand the same... same problem.

I tried differents glow plugs. Picco, Novarossi, Os, FX. What's the best?

Which kind of glow plug do you use for 1/8 on-road?

Waiting your answer

Depends on many factors. What engine? What nitro percentage? What head clearance? Are you running lean?

Nitro percentage 16%, Head clearance original, temperature engine 100-110°
Engine 1/8 on road: Novarossi Mito, Picco Emx, Os R2101. For each engine I had the same problem with the glow plug. Poor quality?

Which plug? You should run a 7 or 8 with these engines.

A bend in wire normally indicates a light plug, too high nitro, too high compression or to lean setting.

7 & 8 GP normally standard. 100-110deg tour running too rich. Don't know what you mean by spire. You skywriting on the ground? Blowing smoke? The GP black and wet? Or dry and grey? deformed coil, can be either rich or lean. But by temp you're too rich. Gotta learn to read your GP.

Spire, I'm sure he means coil.

Used glow plug nr. 7. I switched to 6 and 8 but I don't resolved the problem.
Yes the spring of the glow plug is the COIL. Sorry

I run OS RP8 plugs in both novarossi and OS engines. You mustn't use a novarossi or OS plug in a picco engine or a picco plug in a novarossi or os engine as the taper is different and you will damage the head of the engine!! I little bit of movement in the coil isn't a major issue as long as it stays shiny and slightly wet. If it goes dull or massively deformed then it is likely you are running lean or too tight on head clearance.

I think he means Celsius.

Thank for setting me str8. Spire(coil), deg(C). Tell me he's not in North America. Post a photo of GP give us a sample. We can read it for you. Spire(coil) wet, black soot, Dry, ash, deposits, any type of deformation. Manufacture of fuel and Nitro %. Temp at location. Give more info.

This is very interesting. Three different engines running at a "good" temp and the all of them deformed the glow plug coil.
As said before the first problem is that Piccos do not use an OS or Nova plug. Put a Picco plug on the EMX and one problem is solved.
What about the other two? Two engines with lower head clearance? Too lean or too rich setting with 230F?
Fuel? I think that is a good question.

Well, all I can say is you need to have a good long lasting combo of fuel, heat, and tune... I am no expert in the nitro engine world, but I have been running my picco Jlr red dot since 2012 on the same plug... I always pre-heat my engine to 200+ degrees before I start it, and only use 11% Byron race 3000 fuel, and tune it rarely after a pro racer buddy gives me a good tune... The pre-heating saves me a lot of headaches, and I mostly concentrate on racing..... I have seen so many others kill plugs just trying to get the motor hot, leaning engines forever, etc.... My pre-heater is the best tool I ever bought for my engine...

The only thing I can imagine is a too rich LSN and a too lean HSN. This can show a good running engine on the right temperature but at the end of the straight it will go too lean.

I run OS plugs in my Picco/Sonic engine. Thing is once you put one in you must stick with OS plugs.

I've never seen a glowplug wire that didn't deform after repeated use. These things happen when metal glows orange-hot and gets slammed with explosive shockwaves. A picture of the glowplug would help; it's possible the OP is noticing normal wear-and-tear that doesn't actually matter.