F-CAM for NB8C(BP) before M/C(early model) Mazda MX-5 Miata

Supported MIATA Model: NB8C before M/C

The cap shim size is available from 2.60mm to 3.65mm (every 0.05mm)

DurationTotal LiftHLABase Circle DiameterCam Diameter
Intake 25210.0mmw/ lifter33.0mm53.0mm
Exhaust 25610.0mmw/ lifter33.0mm53.0mm

Maruha's F-CAMs, thats' durations are equivalent for street and sports driving, feature the high lifts also suitable for sports drives.

(Picture 1)

Miata genuine camshaft
(Picture 2)

The F-CAM for NB8C before M/C

Picture 1 shows the MIATA brand camshaft for NB8C before M/C in cross-section, while Picture 2 is the cross-section of our F-CAM for NB8C before M/C.
Both cams have almost the same rotation diameter, although Maruha's camshaft has a smaller base circle and a 1.1 mm higher cam lobe that allows your MIATA to gain its power successfully.

The F-CAM for NB8C before M/C must be installed with a shim under bucket (SUB) which is free from valve timing adjustment procedure (Photo 1).
SUB is small and light enough to reduce your car's weight and takes advantage in stable performance at higher engine revolutions, while you need to remove camshafts every time to adjust shims (Picture 3).
As for your information, the MIATA brand Hydraulic Lash Adjuster (HLA) weights about 55 g, the MIATA brand valve lifter for NB8C with lifter shim is 47 g, and Maruha's valve lifter with SUB is 35 g.

(Photo 1)

Shim under buckets (SUB) with valve lifters
Above: valve lifters / Bottom: shim under buckets

(Picture 3)

Cross-section of Shim under Bucket (SUB) system

MIATA NB8C before M/C is only available to shim over bucket system that can be adjusted or be changed without removing camshafts (Photo 2), though it is not good for tuned-up cars because it is larger and heavier than SUB in addition to the chance of dropping from the valve lift at higher revolutions (Picture 4).

(Photo 2)

Shim over bucket with valve lifter
Left: shim over bucket/ Right: valve lifter
Shim over buckets are installed onto valve lifters. They tend to be heavier than SUB.

(Picture 4)

Cross-section of Shim over Bucket system

After installing high camshafts, the valve timing needs to be adjusted, while Maruha's F-CAM is free from valve timing control.
It is available for the MIATA genuine pulley with the precise knock-pin position for the desired valve timing.
Maruha's product helps you save time needed to adjust the timing.
When you change the engine system or have your own desired valve timing, slide cam pulleys must be used for valve timing control procedures.

The F-CAM for NB8C before M/C, sending more air/fuel mixture to the engine, can add more power to your car.
Instead of the MIATA genuine ECUs, when you use ECUs without air flow meters such as Freedom ECU, the car performance will be efficiently increased.
Furthermore, exhaust manifolds are the key to car performance enhancement.

In order to replace the MIATA's genuine shim with Maruha's SUB, the valve shim must be adjusted for the camshaft-to-valve clearance (Photo 3).
When the engine starts, the metal valve shims have thermal expansion.
Insufficient valve clearance causes poor valve timing or prevents the valve from closing completely.
If the valve clearance is too large, the engine will be noisy during driving. The rocker arm hits the valves.

(Photo 3)

Valve shim adjustment is necessary to have precise clearances.

You should measure the camshaft-to-valve clearance before removing the MIATA's camshaft from the engine in order to calculate Maruha's shim thickness for fixing the F-CAM.
Please measure the clearance for each of the two valves between the camshaft and the valve shim with a feeler gauge.
Repeat the procedure until you measure all valve clearances and record them.
The desired clearances will be brought by precise measurement of shim thickness.
Make sure to use a micrometer for measuring the genuine shim thickness or you cannot install the F-CAM in success (Photo 4).

(Photo 4)

Micrometer for measuring shim thicknesses

The next step is to calculate the approximate shim thickness of the F-CAM.
You will notice the desired gap that is 0.20 mm for fixing the camshaft.
Moreover, Maruha's inner shim is designed for 0.2 mm thinner than the MIATA brand shim's thickness.
The new shim, therefore, will be measured: (MIATA brand shim thickness) + (the valve gap measured - the desired gap 0.20 mm) - 0.2 mm = (the new shim thickness).
For example, if a MIATA's shim is 3.20 mm and a valve gap is 0.30 mm, the new shim will be calculated: 3.20 mm + (0.30 mm - 0.20 mm) 0.2 mm = 3.10 mm.
The F-CAM needs about 3.10 mm shim thickness.

The calculated thicknesses are not always equal to the actual desired one because of some errors from the desired thickness or because of different conditions of the shim arrangement procedures.
In order to avoid troubles, there is a way to adjust the shim thickness by means of shaving its surface.

For more information about the F-CAM line, please visit our F-CAM pages.

Enjoy cool driving with the F-CAM for NB8C before M/C!

・The product should be installed by a professional.
・Valve adjustment must be performed accordingly to that mentioned in the MAZDA MIATA maintenance guide.


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
E-mail: info@maruhamotors.co.jp