Tech Tips!

by Jonathan Teraji

The spark plug in your YSR has two primary funtions:
1. To ignite the air/fuel mixture
2. To remove heat out of the combustion chamber

Spark plugs transmit electrical energy that turns fuel into working energy. A sufficient amount of voltage must be supplied by the ignition system to cause it to spark across the spark plug's gap.This is called electrical performance.
Additionally, the temperature of the spark plug's firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called thermal performance and is determined by the heat range selelcted.
A spark plug cannont create heat! It can only remove heat. The spark plug works as a heat-exchanger by pulling unwanted thermal energy away from the combustion chanber and transferring the heat to the engine's cooling system. The heat range is defined as a plug's ability to dissipate heat. The rate of heat transfer is determined by:
1. The insulator nose length
2. Gas volume around the insulator nose
3. Materials/construction of center electrode
and porcelain insulator

The Gap of the spark plug is extemely important.Always check the gap on every plug before installation;plugs are not always pre-gapped at the factory. The correct gap for the YSR50 is: 0.020~0.024"(0.5~0.6mm).
Spark Plug Torque is often overlooked. It is most critical as it directly influences spark plug temperatures. A spark plug can only transfer heat effectively when it is fully seated on the cylinder head. The correct torque for the YSR50 is 18.0~21.6lb-ft (2.5~3.0kg-m)
The recommended factory plug for a bone stock YSR50, (not used in racing) is an NGK B7HS. For a modified street going YSR50 a B8HS, and for a fully modified racing YSR50 B9HS. On our race bikes we use an NGK B9HVX, which is a high performance platinum plug.

cold/hot plugs

Hot Type B7HS
Has a larger surface exposed
to the combustion gasses.
Dissipates heat slowly.
Firing end heats up quickly

Cold Type B9HS
Has a smaller surface exposed
to the combustion gasses.
Dissipates heat quickly.
Firing end does not heat up quickly
The insulator nose length is the distance from the firing tip of the insulator to the point where insulator meets the metal shell. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and/or fouling. The tip temperature must remain between 450C~850C. If lower the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. This can lead to misfire and fouling. If the tip temperature is higher than 850C the plug will overheat which can lead to pre-ignition detonation and big time engine damage.
Examples of Spark Plugs

That's it for now, shoot me some E-mail if you have specific YSR questions and I'll do my best to answer them as time allows, and/or suggestions for topics in "Tech Tips!" Remember this page is for you!

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