Difference between revisions of "NG 900/9-3 Timing Chain Tensioner"

Revision as of 10:25, 23 November 2009

Overview

The tensioner takes up the slack as the timing chain and plastic chain guides wear. A spring pushes the tensioner against one of the chain guides inside the timing cover. A ratchet allows the tensioner to extend about 1 mm at a time until it reaches its limit. An indication of a loose timing chain is a rattling noise, especially before the engine has warmed up. The noise will be recognizable as chain rattle at idle with the hood open and may be loud enough to hear inside the cabin while driving. In some cases the chain may become so loose it hits the timing cover ("chain slap" or "death rattle").

The tensioner should be removed and inspected at least once after 100K miles, or any time the timing chain starts making noise. The timing chain extension is a measurable indication of the amount of wear on the timing chain and chain guides. Ideally the timing chain and guides should be replaced well before the tensioner reaches the maximum extension.

Information

References

Haynes Ch. 2A-6.9

Saab EPC 2-0300

Torque Settings

• Plug (spring), 16 lb-ft
• Housing, 47 lb-ft

Tools Used

• 3/8 Ratchet, 3" extension, 6" extension
• 12 mm socket (spring retaining cap)
• 27 mm socket (tensionner housing)
• 3/8 to 1/2 drive adapter for the 27 mm socket

Inspection

Access

The timing chain tensioner is located on the passenger side of the engine. The airbox, serpentine belt and upper idler pulley were removed to get good access with the tools on hand, and to see better. Removing the tensioner with all other parts in place is possible, but more difficult.

Fig. 1 - Timing Chain Tensioner Location

Close-up

Tensioner position behind idler pulley. The picture shows the tensioner housing with the off-center spring retaining cap at the end. The pulley was also removed because the pulley bolt did not allow enough clearance for the 27-mm socket used on the tensioner housing. A standard socket may be a better fit than the long socket shown below.

Fig. 2 - Timing Chain Tensioner Location Close-up

Removal

The 12-mm spring retaining cap must be removed first, otherwise the tensioner will extend fully while it is being removed! The spring and plastic pin come next. The tensioner housing is taken out last. It can take a fair amount of force to break the housing loose, then it can be unscrewed by hand, carefully to keep the tensioner pluger from moving.

Fig. 3 - Timing Chain Tensioner Retaining Cap Removal

Components

a - spring retaining cap

b - cap seal

c - spring inserted inside tensioner

d - plastic pin inserted inside the spring

e - tensioner housing

f - tensioner plunger

Fig. 4 - Timing Chain Tensioner Components

Extension Measurement

The tensioner range is from about 8 to 18 mm (9 or 10 clicks). Maximum extension on a normal older engine is probably between 11-15 mm. Mine was extended to the limit, which explained the chain noise from the timing cover.

Fig. 5 - Timing Chain Tensioner Extension Measurement

Wear Marks

After a little cleaning with a rag and a brush, marks can be seen on the back of the shaft, showing how the tensioner took up the slack as the timing chain stretched. 10-11 marks are visible, so the tensioner started at 7-8 mm and slowly extended to 18 mm over the life of the engine, before it could no longer keep the chain tight.

Fig. 6 - Timing Chain Tensioner Wear Marks

Reassembly

First the latch on the tensioner housing is pressed down and the plunger is pushed in to reset the tensioner. After that, re-assembly is in reverse order, tensioner housing first, tighten to 47 lb-ft, then the cap and spring with pin inserted. As the cap is screwed in, the spring tension pushes the pluger out to take up slack in the chain.