Originally posted by wtp
hi all,currently i using 25% fuel to break in the os-tr turbo ver.is there any need to add in extra shims between head clearance,or is there any tips to proper break in this gem.
There was a great post on the Nitro Engine Thread but it looks like its gone now.
The only way to see what your head clearance is is to take out the plug and insert a piece of solder in the head. It should be bent to poke under the head between the piston and head. Rotate the flywheel until it goes over TDC. Remove the solder and measure with a vernier.
For 20% Nitro 0.018" is good. Go to 0.022" for 30%
As the piston aproaches TDC the mixture is compressed and increases in temp. At some point the mixture will react with the glow plug and ignite.
For a colder plug this will be sooner rather than later. and later rather than sooner for a hot plug!!
So you need to balance the compression with the type of plug to achieve a the correct mixture burn.
A colder plug will give you better bottom end where a hot plug will be for high end power
Hope this helps