A timing belt is a very important part to drive the camshafts with a crankshaft.
In old vehicles, a chain type has been used however, nowadeys the belt type becomes more popular.
But the belt type can easily become elastic and suddenly snap on the street.
Recently every engine is becoming more powerful, so some are adapted to the chain type for keeping the endurance.
When a belt breaks camshafts stop rotating.
But a crankshaft still rotates when a vehicle is moving.
Then the piston hits the valves and in the worst case the engine receives very hard damages.
We would like you to understand that a timing belt is very important.
And with proceeding tunings, the engine becomes more powerful. The load and heat harm to the timing belt increase more.
On rubber part of the recent timing belt, usually H-NBR as STD is used.
Maruha timing belt is not H-NBR as STD level, but high strengthened H-NBR for racing engines.
The core protects the belt from becoming elastic.
Glass fibers are used for STD belts, but more fine glass fibers are twisted to be strength for Maruha belt.
The following is the data of the comparison of the STD belt with Maruha heavy duty belt.
A life on snap 3.5~4 times
A life on heat 2.5~3 times
A life on cogs 3 ~4 times
A life on wear 2.5~3 times
There are two patterns that cause the belt to become elastic.
It is the elasticity of the middle core and another one is the belt cogs dropping into the tooth of cam gears.
Maruha timing belt is designed against these two cases, and able to keep the correct valve timing with high performance.
So important that it is put into a timing case to be protected from other parts. However, it spurs on high-temp in a case,
and the rubber of the belt would change in quality.
In addition, there is an auto tensioner in Miata.
An auto tensioner has a mechanism where a roller always pushes the back of a belt with oil pressure or springs to keep a suitable belt tension.
This maintenance free system is easy for us ( work shops and dealers) but it is not so good for a high rpm engine,
because the belt starts vibrating at high rpm and the auto tensioner can not stabilize the belt.
According to the situations, belt vibration would be an engine trouble.
A timing belt is composed by mainly belt surface, rubber and core.
Belt surface is to protect from cam gears.
Generally Nylon material is used, but Maruha heavy duty belt is more strengthened with Nylon plus Kevlar,
and able to improve the endurance and reduce the wear-off.
The timing belt case that protects the timing belt sometimes causes heat damage to the timing belt with increasing temperature inside the case.
When changing the timing belt, please check the water pump too.
Because the water-pump is behind of the timing belt it has to be changed simultaneously with the belt.
If you find water leaking from the water-pump after changing the timing belt,
you have to do same work again, it is lost money and wasting of time.