khh1955

This may not be the right forum for this question...but if anybody knows,it would be one of
you Extreme Speed guys!

I have a Diamond Dust with a .40 MVVS & grrt pipe,I run PM 15% heli fuel...and it blows plugs left & right.
I've been using OS A3 & A8 plugs (and others)...but haven't found the "Right" plug yet.

By the "Right Plug",I mean one that will last without losing alot in performance!

Any suggestions ?

Thx,
Kurt

Scorpion Racing

You may want to try the K&B 7310 HD plugs. That is what some of us in 424 here in Florida run. I had all kinds of burned out plugs till I switched to these. These are the same plugs the ducted fan guys used to use when the fans were popular. They have helped me stop blowing plugs so often.

Good Luck

Lomcevak Duck

My Feedback: (14)

I'm not the resident expert on plugs by any means, maybe bob27s will have a better hint for you. But if you're running several different plugs and blowing them all, maybe it's not the plugs, but rather another common factor.

Things to consider:
1) Are you sure you're not running too lean?
2) Are you maybe running too much nitro for your engine? (I don't consider 15% excessive, but I'm not familiar with this engine.)
3) If you're still blowing plugs, maybe a headshim to lower your compression?

cncswiss1

most of the mvvs engines are setup for zero nitro.. running 15% will need a lot of extra head shims..

If you want to stick with os plugs try the R5 from the car guys, it is OS's coldest plug.

the a5 is nice cold as well, just not as cold as the R5. and that K&B plug mentioned earlier is quite nice as well.

http://www.osengines.com/accys/glowplugs.html

combatpigg

My Feedback: (3)

If you can take a look at a combustion chamber from another hot .40 set up to run nitro, you can machine the stock MVVS head to match. Use an old glow plug to chuck the head into a lathe and take light cuts until you've opened up the chamber a little. A double bubble or trumpet shaped head are 2 types that work.
The Nelson plugs are the best I know of for severe duty and they sell special threaded blanks [heads tapped for their plugs] that you can adapt to your engine.

freakingfast

My Feedback: (3)

I no longer use OS plugs, the last batch of #8s I got were bad. The connection at the center tap lets go after one or two runs, several were DOA! As a test, I pulled some old/used #8 from old engines and they ran great.

I now use K&B 1-L (#7311) in place of OS #8 and the K&B HP (#7300) for high nitro like my OS 46 VX DF on 30%.(after 2 gallons I finally had to replace it, performance and idle were bad, the element was a dull grey.)
http://www.mecoa.com/acc/glowplug/glowplug.htm

Kurt, you may have other problems.
(A)Too much nitro for that engine
(B)The header is too short or wrong pipe for your setup.
(C)The fuel is foaming at speed. Use 1/4" thick Du-Bro's foam rubber UNDER and to isolate the sides of the tank, use in conjunction with an OS bubble less clunk. http://www3.towerhobbies.com/cgi-bin...0p?&I=OSMG5870 I've had fantastic results with this. Or you can go with the hassle of a bladder tank.

HighPlains

My Feedback: (1)

Since you are running low nitro fuel and blowing plugs, I would decrease the compression. Anything under 40% nitro is mild sport fuel.

evan-RCU

The problem is not the fuel and the MVVS funs fine on 10-15%. You will blow a plug by running lean. These motors lean out after launch so have it on the rich side before launch, the very rich side. I use Tower Hobbies plugs, great plugs at a cheap price and you don't worry about changing them.

BTW I DO have a Q500 MVVS turned around to rear exhaust and the GRRT pipe on a DD so I do know from experience with your specific set up.

freakingfast

My Feedback: (3)

What prop are you using Evan, maybe he's pulling too much prop.
Yes, some performance engines want too be so fat that they can barely stage on the ground just so it's not too lean when it unloads in flight.

evan-RCU

8x8 and 8x9 APCs

khh1955

Thanks for all the info...
perhaps at this point, I'll try it a little richer from the get go & see what happens!

Kurt

daven

My Feedback: (1)

Its all been mentioned above, but I'll try to consolidate it.

Burnt plugs are normally caused by a lean condition or over compression. If you are setting it rich on the ground, and it is still blowing plugs, you could either have an air leak in your fuel delivery or your fuel is foaming due to vibration. I would suggest a Tetra or Jett bladder style tank to eliminate fuel foaming as a potential factor. If you are still blowing plugs after installing a bladder tank, I would start shimming the head. Start with a .005" shim and go up from there until your problem goes away.

bob27s

My Feedback: (19)

If you are blowing all plugs, all of the time the aircraft is producing fuel foam.

Plugs blow primarily because of a lean condition.

Foam creates that condition when in flight, and there is little you can to about it other than to correct the fuel tank installation.

A bubble-free fuel system would be your best move.

khh1955

Thanks Bob,

I think I'll try running it richer from the get go next time...and
if I still have problems,I'll switch over to a bubble-free tank!

And I guess I'll put a bubble free tank on my list & order it anyway, just in case!

Thanks to everyone for all the suggestions!

Kurt

still4given

Don't forget to get the Bubble-jett Tanker. You can't fill a bladder tank with a regular pump. You will end up putting air in the tank.

Blessings, Terry

daven

My Feedback: (1)

Terry,

If you use a third line, I think you can fill the tetras with minimal air.

funflyerf4

My Feedback: (6)

Or just change the klunk in you tank to a sintered bronze filter and no bubbles will pass to the carb.


Frank


Dubro makes one and Jet power USA also sells them

jaka

Hi!
Having delt with MVVS pylonracing engines since 1992 perhaps I can help you.
First! Running 15% nitro ,if you use the old aluminium or black headed Q-500 MVVS engine is a no no without adding one or two 0.1mm head shims.
The newer Q-500 MVVS that can take 15% nitro is either gold headed or blue.
Second : Are you sure you run the short MVVS Q-500 pipe,No 3246?? The longer pipe is No 3248 and its used for lower rews.
Third: One of the best plugs to use is the Rossi No 8 plug. This was the stanbard plug to use in F3D pylon 15 years ago prior to the now used Nelson plug. As you understand the Nelson is way superior to any other plug but needs a special made head as it has 64/11" treads.

When glow plugs fail its mostly to do with either running too lean, too much nitro, To much compression or too big prop..All this means too much heat is generated!!
Get ride of one of these heat factors and you are in the right path.

kmtranmd

My Feedback: (71)

I agree that lean run is most often the cause of blown plug, no matter what brand.
But I also agree that some plugs are more easy to blow than others. Having said that, I stopped using OS 8 plugs because I think the elements in these are too easy to blow. I've had good success with K&B 1L until I had trouble finding them. Lately, I've been using OS F plug (the 4C plug) for everything including the Jett90L, Weston Magnum 50, OS 91 with pipe. When a plug goes bad, assuming not from lean run, I check the element. If element is distorted badly, I suspect it's from having plug too close to piston and causing too much heat buildup. I simply add extra plug washer to shim it a bit. Seems to do the trick most of the time. I can't recall having to replace plugs inside of dozen runs on any of my high rev motors. That's my 2 cents.