Robert,
Short of pulling off the intake to look at the camshaft while
turning the crank back and forth while watching the cam motion, there is
no easy or reliable way to determine timing chain stretch. There is a
method whereby a dial indicator is used on a valve retainer and the
engine is rotated two times in each direction, but you really need to
know what you're doing and have the tools to do that.
The very best way is to pull front cover and measure the timing
chain stretch with a straight edge and a machinist's rule or inside
calipers. The easy way to pull the front cover is to just undo the
eight front cover bolts. You don't need to bother removing the oil
pan. Pull the balancer and unbolt the water pump. It's not necessary
to remove the small water pump bolts, just the four large ones. Then
remove the four lower cover bolts and pry it away from the engine
starting at the top. There are dowel pins near the bottom of the cover
pressed in the block.
Once the cover is off, rotate the engine until all the slack in the
chain is on one side. Put your straight edge along the slack side of
the chain. Measure the distance between the straight edge and the chain
at a point midway between the two sprockets while applying pressure on
the chain itself. Maximum slack should be no more than 1/2 inch. Now
replace the chain and sprockets while you're in there. Pull the fuel
pump off to get it out of the way. Replace the front crankshaft main
seal also. The cam sprocket bolt gets torqued to 65 ft/lbs. The fuel
pump bolt and nut get 15-20 ft/lbs.
A double roller timing is the best. (Roller chain looks like a
bicycle chain.) Single roller is next and regular link chain like the
factory installed is the least desirable. I've seen a 1/2 slack on a
factory type chain after only 50k miles on a 403. Factory type chains
are complete junk in my experience.
There's a trick to getting the front cover back on. After cleaning
all gasket surfaces, glue a new paper gasket to the back of the cover
with Gaskacinch and apply Permatex #2 to the block side of the gasket.
Use a dab of silicone at each of the two front corners of the oil pan.
Start the cover in at the bottom first, using a small screwdriver to
lift the seal ears over the front edge of the oil pan as you set the
front cover over the dowel pins. Torque the water pump bolts to 22
ft/lbs and lower cover bolts to 50 ft/lbs. Don't forget to reinstall
the timing mark.
Grab your harmonic balancer and lay it face down with the key way
pointing straight up. The timing mark should be 16 degrees to the right
as viewed from the back. If it's not, the balancer has slipped and the
rubber is bad, which is unsafe. If the timing mark looks okay, check
the nose of the balancer. If a groove is present where the seal rides,
install a seal saver which is a thin metal sleeve over the balancer
nose.
Put a dab of silicone in the key way and grease the nose before
putting the balancer back on. It's preferable to use a harmonic
balancer tool to reinstall it, but in this case you can get away with
partially hammering it on with a block of wood, then use the bolt to
finish the installation. Don't try that technique on a Chevrolet V8
through. The balancer bolt gets torqued to 160 ft/lbs. I've socked
them on with an impact wrench many times in the past with no problems.
- -Scott Woodworth
