This is a great topic! I'd like to thank everyone for shedding light on this for me.

Although I do have some more questions if someone can help...


Do all 0.12 engine manufacturers use the same size ball mill for the button?

If they do, do all chambers have the same milling depth?

Considering different bore/stroke ratios between manufacturers, would "compression testing" be a more accurate way to determine the number for head shims?

My thanks for any help,

Hi again

I got the pixy running great. now its the NS3's turn

I measured the head and its stock with 0.008" no shims and 0.010 shim added.

I use a C6 TGF plug with 16% nitro. I was thinking it might be better to reduce the shim by 0.004 for this nitro content and plug

What do you think?

Cheers

Ziggy yes on 16% you can drop to .014 Change to a number 5 plug

Vaportrail: there not all the same but very very close. unfortunatly static compression means very little , or should I say it is only a good indicator of what will happen when the engine is operation at slower speeds and off the pipe. Lots of CR is good at low speed however detonation can occur as it comes on the pipe. The pipe and the boost it makes has more to do with what CR you want to run than not.

Generally on a 12 engine .004 thousanths will change the Compression ratio about 3/4 to 1 point. I said generally.

Somone asked about plug fatigue the other day, plug fatigue can occur under high sustained RPM's this is where the plug stays shiney and the wire just fractures for no reason. This is why I have always run Mccoy MC9 or the new Odonnell plugs as they dont do this. When this happens it is usually not a tuning or head clerance problem. If you see the wire start to pull out of the hole this means that the engine is scavenging really hard and when this occurs the engine is making serious power.

Hi Motorman,

In the land down under, I haven't seen either the McCoy or O'Donnell plugs.

I'd be very interested in hearing your thoughts on about them compared to the usual Nova/RB plugs.
And maybe a recommendation for say, a Nova .12 engine . . . Turbo plug.

Cheers.

Hi Motorman

If shiming theory applies for all .12 engines can you shed me some light on the following???
S12 Sirio Evo 2 head shiming: I measured cylinder recess with piston at top and got 2.45mm, measured head recess and got 2.00mm, so we have a difference of .45mm.
To use the engine with 20 - 25% nitro, what is the ideal total chamber one should have? I've read that it should be around .55mm, is this correct?. The engine comes stock with two copper shims, one is .10mm and the other is .15mm, so i could just use the .10mm, am i right?
Glow plugs: What is the equivalent of O'Donnells 77 and 99 on Novarossi??, because that is the only plug available down here.
AFM

0.45 mm is 0.018" which is perfect for 20-25% nitro as I read it.

Measure the actual squish clearance using a piece of solder. Take out the plug and insert a piece into the head and turn over the motor by hand untill the solder flatens between the piston and head. Then measure the thickness of the solder.

Dont stick the solder in too far and through one of the ports and loose a piece inside the engine! (as I did!)

My Pixy had 2 shims which i removed completly to have 0.020" head clearance.

I just reduced my NS3 down to 0.014" and a C5TGF Turbo plug as Motorman suggested and it has a lot more low end power with no loss of top end and slightly cooler running.

Cheers

I'm a bit confused as to what constitutes a "Hot" Turbo plug.
The Novarossi site says they have a Hot range and a Cold range of plugs. Then, each of these "ranges" have various hot and cold filaments available.

The C.5TF is a cold body with a hot filament.
The C.5TC is a hot body with a hot filament.

I mean, wouldn't that make the C.5TC the hottest plugs of their kind?
Or did you mean the hottest of the Cold range?

Here in Oz at the end of January the ambient is likely to be about 30ºC and we'll be using 16% nitro in a Nova 3-port .12.

So, the question is . . . . which plug?

Placing stefans sarcasm to the side here is how to tell visually.

look at the plug from the bottom. the hot plug of the same range (ie5) will have a bigger hole or more clearence around the filament than the cold one.The smaller hole draws the heat away faster from the element on the sold one.
If its the long/short turbo variety the hole may be the same but the short one will be hotter than the long cold one. The extra plug depth draws the heat away faster on the cold plug.

Jus the facts man

I don't have the two types to be able to compare, but yeah, understand the physics.

Since you suggested that the hot plugs are barely hot enough, I'm trying to figure out why you would recommend the C5TGF to ziggy12345.

The C5TGF will be a long body/ hot filiment, yeah?
Whereas the C.5TC would be a short body/hot filament?

I'm presuming the C.5TC would be hotter than your recommendation.
What am I missing here?

I dunno why but when I lowered the head to 0.014" and used a C5TGF plug it goes like snot off of a stick!!

OK.
The question I'm trying to get an answer to is:

Would it go like snot off a greasy stick if you used a C.5TC?

[QUOTE]Originally posted by Taylor-Racing
OK.
The question I'm trying to get an answer to is:

Would it go like snot off a greasy stick if you used a C.5TC? [/QUOTE

That would depend on the consistancy of the snot. If its one of those sticky little bastards that you just cant flick of and end up wiping it on the underside of a chair.......

Now this is the problem, see . . most analogies really don't stand up to close scrutiny.

I did not recommend a TGF someone else did. If I made a recommendation it was just to use a 5
however a 5 cold is what I use. I believe stefan was referring to the number 5's as the hottest plugs of their kind. (generally an accurate statement) and yes the TGF is a cold 5, yes the TC is a hotter 5.
Personally I agree with Stefan and use the TGF. Heres why but it is my personal reason. The TC for me suffers harmonic failure in engines I build, so therefore I cant use them successfully unless its below 50 degrees on 30% max fuel.

Where can you get extra head shims?