Mercruiser 7.4L - Replacing the Timing Chain


The timing chain needed to be checked, based on some of the research that I had done about the engine.  The particular version of this 7.4L / 454 C.I. GM engine is known as a ‘Mark IV’.  These engines used a timing sprocket that had nylon teeth.  Over time, the teeth could become brittle and crack.  So, I wanted to verify the type of timing sprocket and replace it as needed. Sure enough, the sprocket did have nylon teeth and should be replaced, based on the age of the engine.

I also checked the tension of the existing chain by measuring the deflection, as shown in the picture below.  The tension was in spec, but seemed to be a bit sloppy.  So, a new timing set was in order for this engine.  I chose to go with a high performance set, which should be tighter than a standard set.

Here is a picture of the old timing set removed and waiting for the new set.

The new timing set is installed in this picture.  The chain was really tight, but will loosen up some upon ‘break-in’.

Since the timing chain was the only item to be replaced on the engine block, it was time to start putting it back together. 

Click here to go to the Engine Assembly page .