INTRODUCTION - TIMING SYSTEM

3.2 JTS

Technical specifications

The timing system comprises a primary chain operated by the crankshaft ring gear which transmits the power to two intermediate ring gears each of which, in turn, controls a secondary chain that activates the inlet and exhaust camshaft ring gears for the respective bank.

The primary chain slides on two fixed guides and a moving guide that acts as a tensioner because it is connected to a hydraulic tensioner.

Special oil jets lubricate the moving timing system components.

The secondary chains are each guided by a fixed pad and tensioned by a moving pad thrust by a hydraulic tensioner.

Chain, gear and reference assembly for timing system

1. Reference at left inlet camshaft gear for left secondary chain

2. Reference at left secondary chain for left inlet camshaft gear

3. Reference at left exhaust camshaft gear

4. Reference at left secondary chain for left exhaust camshaft gear

5. Left secondary chain

6. Reference at primary chain for left intermediate gear

7. Reference at left intermediate gear for primary chain

8. Left intermediate gear

9. Reference at left secondary chain for left intermediate gear

10. Left intermediate gear window for left secondary chain

11. Primary chain

12. Reference at primary chain for crankshaft gear

13. Reference at crankshaft gear for primary chain

14. Crankshaft gear for primary chain

15. Right intermediate gear

16. Reference at primary chain for right intermediate gear

17. Reference at right intermediate gear for primary chain

18. Reference/window at right intermediate gear for right secondary chain

19. Reference at right secondary chain for right intermediate gear

20. Right secondary chain

21. Reference at right exhaust camshaft gear for right secondary chain

22. Reference at right secondary chain for right exhaust camshaft gear

23. Reference at right secondary chain for right inlet camshaft gear

24. Reference at right inlet camshaft gear for right secondary chain

Timing system crankshaft gear

The gear fitted on the crankshaft has the function of transmitting power from the crankshaft to the timing system kinematic chain; it has inverted teeth and works on the main timing chain which also has inverted teeth.

1. Main chain teeth

2. Crankshaft internal matching surface

3. Housing for key

Camshaft drive gears

The four camshaft drive gears, with the rear view (camshaft side) and the front view (timing side) for the individual gear illustrated in the diagram, incorporate the hydraulic actuators that allow the timing of the four camshafts (two inlet and two exhaust) to be varied continuously.

1. Ring gear

2. Camshaft bearing housing

3. Camshaft matching flange

4. Oil ports

5. Bolts

6. Timing sensor wheel

7. Camshaft gear fastening bolt housing

Idler intermediate gears

The two intermediate gears have the task of receiving the drive from the crankshaft by means of the primary timing chain and transmitting it to the camshaft drive gears by means of the secondary timing chain.

There are two toothed ring gears to carry out this function; the larger ring gear has inverted teeth and works on the primary timing chain (which also has inverted teeth), whilst the smaller ring gear has normal teeth and works on the secondary timing chain.

1. Main chain teeth

2. Bearing cover surface

3. Fixing bolt housing surface

4. Crankcase side bearing cover surface

5. Secondary chain teeth

Timing drive chains

The primary drive chain is made with inverted teeth and the gear on the crankshaft also has inverted teeth; the intermediate gear has inverted teeth for connection with the primary chain and a coil with standard teeth for connection with the standard type secondary chain.

A. Secondary chain

B. Primary chain

1. Rollers

2. Mesh

3. pins

4. Inner mesh

The timing chains have the task of transmitting the power between the various timing gears; they also have timing reference markings on the outer mesh.

Hydraulic tensioners

All the hydraulic tensioners are fitted on the crankcase or the head with a gasket in between that has the task of keeping an oil reserve inside the tensioner to ensure correct operation during starting.

Primary chain hydraulic tensioner

1. Pad

2. Piston

3. Reset

Secondary chain hydraulic tensioners

1. Pad contact housing

2. Piston

3. Reset