Mechanics

TIMING CHAIN

1998 Nissan Altima

Engine Mechanical problem
1998 Nissan Altima 4 cyl Front Wheel Drive 80,000 miles

The lower chain broke while driving. Do the valves get bent when this happens? I have valve cover and the timing chain cover off. Is there a lower cover to get to the crank area? Thanks for any imput.
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Westcoast
September 16, 2010.



Yes, you can definitely bend valves if the timing chain breaks. To test for this, you need to do a compression check on each cylinder one at a time with that cylinder at TDC.

Here's the procedure for removing the upper and lower timing chains.

UPPER: 1. Remove the spark plug wires.

2. Set # 1 piston at TDC on its compression stroke.

3. Remove vacuum hoses, electrical harness, connectors, and harness clamps.

4. Remove the power steering pump, A/C compressor, and alternator belts.

5. Remove the power steering reservoir tank and reposition it for clearance.

6. Install engine support eye bracket at right rear of cylinder head, then support engine.

7. Remove upper right engine mount and bracket.

8. Remove the rocker cover.

9. Remove camshaft sprocket cover.

10. Wipe off the links of the timing chain next to the timing marks on the sprockets. Put paint marks on the timing chain, matching them with the timing marks on the cam sprockets and idler sprocket (see Figure 1).

11. Remove cam sprocket bolts, cam sprockets, upper timing chain guides (if equipped) and upper timing chain.

12. Support lower timing chain by using a suitable tool as shown in Figure 2 to avoid chain tensioner spring from coming out.

NOTE : This step is only to be applied when the lower cover is not being removed.

13. Remove the idler sprocket.

LOWER: 1. Drain coolant by removing the cylinder block drain plug and opening the radiator drain cock (Refer to MA section of the Service Manual).

2. Drain engine oil.

3. Remove the oil pan (Refer to " Removal" under " Oil Pan" in the Service Manual).

4. Remove the power steering pump and position it to the side. Remove the idler pulley and bracket as well.

5. Set # 1 piston at TDC on its compression stroke.

6. Remove the crankshaft pulley.

7. Remove the oil separator.

8. Remove the front cover.

NOTE : Engine may need to be lowered to provide clearance for the chain tensioner housing of the timing cover to clear the frame. Engine height may need to be adjusted when removing the cover.

CAUTION : Be careful not to tear or damage the cylinder head gasket.

9. Remove the following parts: ^ Lower timing chain tensioner (push piston in and insert a suitable pin into the hole).
^ Chain tension arm.
^ Lower timing chain guide.

10. Remove the upper timing chain (refer to " Removal of Upper Timing Chain" in this bulletin).

11. Wipe off the links of the timing chain next to the timing marks on the sprockets. Apply paint marks to the lower timing chain, matching them with the mating marks on the crankshaft sprocket and idler sprocket (see Figure 3).

12. Remove the lower timing chain and sprocket.

Ernest Clark
Sep 17, 2010.