Originally Posted by spurgear
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.
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).
Letís 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 youíre set.