Maruha / Heavy duty Timing belt

What is a timing belt?

Heavy duty Timing belt

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, nowadays the belt type is becoming more popular.
But the belt type can easily become elastic and suddenly break on the street.
Recently the engines are becoming more and more powerful, so some are adapted to the chain type for keeping the endurance.

When a belt breaks, camshafts stop rotating. 
But the crankshaft still rotates when the vehicle is moving. 
Then the piston hits the valves and in the worst case the engine becomes seriously damaged.

We would like you to understand that the timing belt is very important.

So important that it is placed into a timing case to be protected from other parts. However, it spurs on high-temperature in the case, 
and the quality of the belt's rubber changes.
In addition, there is an auto tensioner in Miata.

An auto tensioner has a mechanism where a roller always pushes the back of the belt with oil pressure or springs to keep a suitable belt tension.

This maintenance free system is easy for us (workshops 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. 
Belt vibration would cause engine trouble.


A timing belt is composed by mainly belt surface, rubber and core.

Belt surface
The belt surface protects 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.
And with tuning the engine becomes more powerful. The load and heat harm the timing belt more.

On the rubber part of the recent timing belt, usually H-NBR as STD is used.
Maruha's timing belt is not H-NBR as the STD level, but high strengthened H-NBR for racing engines.

Middle core
The core protects the belt from becoming elastic.
Glass fibers are used for STD belts, but more fine glass fibers are twisted to strengthen Maruha's belt.


The following is the data of the comparison of the STD belt with Maruha's heavy duty belt. 

  1. life on snap 3.5~4 times
  2. life on heat 2.5~3 times
  3. life on cogs 3 ~4 times
  4. 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 the another one is the belt cogs dropping into the tooth of the cam gears.
Maruha's timing belt is able to keep the correct valve timing with high performance.

Water pump

When changing the timing belt, please check the water pump too.
Because the water-pump is behind the timing belt it has to be exchanged simultaneously with the belt.
If you find water leaking from the water-pump after changing  the timing belt,
you have to do the same work again, it is wasting of money and time.




Maruha Motors Co., Ltd.
Ushizuma 2095-6, Aoi-Ward
421- 2106 Shizuoka city, Shizuoka prefecture
TEL: 0081-54-294-0076
FAX: 0081-54-294-1312