I'm running the Losi Mach427 and I think it's dying. I know the compression is low. I can stick a finger in and turn the flywheel without to much effort. But, when it's running it runs very good and strong and it holds a tune. the problem I'm having is it keeps blowing out glow plugs. The first one looked burnt and distorted so I richened the top and bottom. The next two in about a tank each are broke in the coil a little way down. They don't look wet but not burnt either. It's plenty rich (or so it seems)and has a strong smoke trail. I'm wondering if an engine that's going out will do that? Or any other ideas you might have.

What fuel are you running, 20% or 30%?

20% use a hot plug like OS A3
30% use a medium/cold or cold like an A5

I have used OS plugs for a long time and they last so long that I change them about every gallon since they just won't burn out.

I'd try a different brand of plugs and then see what happens.

I thought the Mach427 took a long plug not a short OS plug! Are you sure you do not have a air leak as normally when the coil is breaking or getting distorted it has to do with running lean. How many gallons of run time do you have on it?

I'm running O'Donnells 30% and a McCoy MC-9 plug

Make sure you're using teh correct length plug like 46u mentioned and doble check fo leaks.

I still say try a different brand, the Mccoy users around here always switch to something else, they do burn out quickly.

Are you running O’Donnell race blend or the Ready To Run blend? I really like O'Donnell Race just wish I could get it around here!!!!!!!

Ya, we have the race blend here too, it's really good stuff.

The fuel is the race blend and the car has about 2.5 gallons through it. I'll check for an air leak but there is plenty of blue smoke .

With only 2.5 gallons on it should still be in good shape broken in properly and maintained correctly.

add 0.2mm shim to the head , the 427 head clearance is for 20% if you run 30% you need to add a shim to the head, this will probably solve your problems..

Good idea, didn't think of that. Thanks

Now to figure out where to get the shim?

use 1 of these.

http://www.horizonhobby.com/Products...rodID=LOSR1024


or use both :

http://www.horizonhobby.com/Products...rodId=LOSR1023

I am so use to STS engines coming with all the shims you need for what ever fuel you run. Let us know how it goes and good luck.

yeah i know..most of the engines come with heads shimmed to 20% ... not many have the shims for 30% from the factory except STS and a very few other. i can't wait ill i can get my hands on one of the MKII's

I'll order them tomorrow. Other than possibly burning up glow plugs what does an improperly shimmed head do to the engine itself?

It'll be a Rb Concepts engine for me next time.

Most of your higher performance engines come with enough shims to run 30%. Your sports engines normally do not and I guess that is what you have. Yes the STS D21T MKII will be my next engine but right now I am doing well with the STS D21B RBmods.

Itll actually give you more power ...shims are the way to retard the ignition , in full size cars or bikes for that matter the electronics take care of that ... with nitro engines wich don't have a outside ignition source they have to rely on the compression of the engine. because higher % fuel burns hotter so by leaving it the same as 20% it actually fires too early and it will rob you of a bit power...

All so can be done with glow plugs as well.

using plugs to get that same effect is not reliable... you should use the plug that your engine in combination with your fuel likes , some engines are happier with colder plugs then others , i know my STS 21T can't stand cold plugs , even with 30% it has a hard time starting, however go to a hot plug or a medium/hot plug and it will be fine...

now on the other hand my buddies 8ight who runs a Axe rossi engine with a turbo head , he runs cold or medium/cold plugs with 30%..

The LHS owner said low compression keeps fuel from reaching the plug causing it to burn out. It does seem to do it more when it's being run slow? Seems odd that would happen but might be true.

I know the compression is low so I'm going to install a new piston and sleeve and then shim it as well.

that may be the contribution of a lean low speed needle...

The main bearing coluld be failing. That's something to check if you start to burn plugs suddenly.