Im in possession of a Rossi Black Pixie .12 motor. Something i havent heard of in years. And nothing i know the specs of. Im helping out a friend who bought this motor used. I tore down the engine to find 3 ports intake and 1 exhaust. Head shims totalling 0.3mm. What shim clearance do we need to run 20 percent fuel? What glowplugs can work with this engine? Can a os#8 work? It came with an Odonnell 77 standard plug. Anyone know the oem needle settings? Any help would be appreciated.

If the motor is stock, the stock head clearance should be fine with 20%.

No idea about needle settings.

You want long standard plugs (everything BUT OS). MC59, MC8, Nova 5 or 6 something like that.

that's a good start !!!

Thank u. Anyone else can confirm this?

I'm not sure about the black head, but I have the gold head Pixie. Which was the 3 port; the black head was a 5 port. My real head clearance with no shims was .64mm. At this clearance I can run 30% with no shims. I believe the head clearence is a little excessive with no shims. I replaced the original carb with an OS speed tune carb. The engine runs great on higher % nitro. It won't idle very well when running 16% even with a hot plug.


Pass you soon...

I never measured the real head clearance before. But this is what i did. I put the piston at top dead center. Then rested the caliper on top the sleeve. And measured the distance to the piston. Then i did the same for under the head button to the glowplug.
I got 0.32mm and 0.36mm respectively. Is that good or bad? And this is not including the 0.3 mm shims.

i think needles setting were in the 4-4.5 range hsn 4lsn its been years since i ran one,which is kinda the norm for most engines.does any one if these were the last line or 2 of pixy i havent seen them in years

Thats odd... I used the same technique with my piston at TDC. My piston measured .96mm from the top of the sleeve. My button measured the same as yours. The 3 and 5 port must be different. I also apply a little heat to the engine crankcase to slightly loosen the pinch up to get a good measurement

Pass you soon...

Ok i will double check this.

Here is the method

Position the piston at top dead center. You will have to keep the cylinder firmly seated as you rotate the crankshaft to the TDC (top dead center) position. ABC engines will usually push the cylinder out of the crankcase due to the tapered fit. An easy way is to turn the engine up side down and press it firmly down onto a table top while you rotate the crankshaft.
The piston must be at TDC and the cylinder liner must be firmly seated into the crankcase to obtain the correct measurements. If it is not the final result will be incorrect.
Measure the distance from the top of the cylinder to the top of the piston using a good caliper. Be careful not to allow the measuring instrument to push the piston off TDC.

Now according to you, it measures 0.32mm

Now you must measure the distance from the portion of the head button that goes into the cylinder (squish band) to the surface where the shims seats (not the small chamber where the plug shows).

Let’s suppose it does measure the 0.36mm you said.

Now do the math...0.36 - 0.32 = 0.04

This means that to get the ideal real 0.40mm head chamber clearance for 16/20% nitro fuel, you should put a 0.36mm shim and you’re set.

AFM

ok from top of sleeve to piston is 2.38mm
from top of squish band to shim seating area is 1.86mm
from squish band to plug is 2.38mm
total shims removed 0.3mm

how does that work out?

Well it means that your real head clearance is the difference between
top of sleeve to piston 2.38mm, and top of squish band to shim seating area 1.86mm, which is 0.52mm.

It is a very large head clearance without any shims. With that head clearance you can use even 30% nitro, so the engine will have a lot of high end on 16-20% nitro.

Resuming. You don,t need to place any shims, weird as it sounds, but is the thruth according to your measurements. The distance from squish to plug is not considered when shiming an engine, unless head was modified from stock.

AFM