Note: For seal type codes, see Table 2.


One of the main causes of black spark plugs is a rich air-fuel mixture. This means that there is an excess of fuel in the combustion chamber, which can lead to incomplete combustion and the production of carbon deposits. A rich air-fuel mixture can be caused by a variety of factors, including a faulty oxygen sensor, a clogged air filter, or a malfunctioning fuel injector. It is important to address these issues promptly to prevent further damage to the spark plugs and the engine.
black spark plug

Lubricant can be retained in the space between the main lip and the minor lip.
NBR


2. Oil seal structure and functions
Shaft Speed - Considering the speed that the shaft will be moving, the runout, the housing bore and the type of oil being sealed is vital to making sure you select an oil seal that will not suffer from abrasions or spiralling.
2. Metal Case

RS
Leather is probably the oldest of the lip materials still in common use, but the move towards mass production methods has seen a massive increase in the development of synthetic rubbers which lend themselves to accurate and repeatable injection and compression moulding. Nitrile (NBR) is still by far the most common elastomer for “normal” use, whilst Viton® (FKM/FPM) is rapidly replacing Polyacrylate (ACM) and Silicone (VMQ) for high-temperature applications. Viton® also has high resistance to abrasion and chemical attack making it a preferred elastomer. Recent developments in the use of PTFE for Rotary shaft seals has caused widespread interest particularly for high-speed shaft rotation or poor lubrication applications.
