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post #1 of (permalink) Old 01-02-2002, 09:15 PM
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Timing Chain? Verify my diagnosis...

I just acquired a Jeep cheap (a clean 86 Wag actually) with a swapped in 304, hasn't run in a year. Dry compression is near zero, wet will push 25-30 psi with a squirt of oil (in the 4 cyls. I tested) It cranks easy enough, although it is blowing back through the air horn. My hunch is timing chain. The distributer was moved by the previous owner so I can't use its position as a reference. Could it be anything else? Any good input appreciated.

76 CJ5,2.5" lift/Rancho 9000's,258/T-177/D300,HEI,Offy,Locked F&R
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post #2 of (permalink) Old 01-02-2002, 09:43 PM
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Re: Timing Chain? Verify my diagnosis...

If it's jumped a tooth or two, it's also stretched or the gears are worn. Here's an easy way to confirm:

1. Remove the Distributor cap.
2. Put a ratchet and socket on the crankshaft pulley bolt.
3. Have the 2nd person standing over the distributor looking at the rotor.
4. Start to rotate the engine CW with the ratchet to the timing marks on the pulley.
5. Stop rotation at the 10* BTDC mark.
6. Again, start to rotate the engine CW.
7. Have the 2nd person tell you EXACTLY when the rotor starts to move.
8. Stop the rotation of the crankshaft.
9. Look at the timing marks on the crankshaft pulley.
10. How many degrees did the crankshaft pulley move?
11. If the crankshaft moved more than 5.5 degrees, replace the timing gears and the timing chain.

IMHO, I replace the set at 4.5 degrees of movement as a preventative measure.
The number of degrees that the crankshaft pulley moves BEFORE the camshaft transfers the movement to the distributor represents the amount of slack in the timing gears or the timing chain. This slack is seen as a time lag by the distributor and the distributor acts accordingly and the spark to the plug is now delivered at the wrong time. It's best to have the whole mechanics of the timing train nice and tight

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post #3 of (permalink) Old 01-03-2002, 05:52 PM
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Re: Timing Chain? Verify my diagnosis...

Pop the valve covers, and look at the rocker arms.
Have a chop stick or small wooden (NO METAL) dowel rod for the #1 spark plug hole.

Crank the engine over BY HAND by the front crank bolt.
When the intake rocker arm for #1 starts to close,
1. Go slow! You are getting close...
2. Stick the chop stick in and feel for the top of the #1 piston to come up...

When the piston reaches Top Dead Center, Look at the balancer, see if it is at '0' (Zero).
If so, you have verified TDC.

Now, make a chalk mark on the balancer at TDC, and another one on the balancer right straight across from it.
Call the mark across from the '0' (Zero) the 'Odd' side mark.

Now, turn the crankshaft forward (never turn a crankshaft backwards on a good engine) 1/2 turn of crankshaft rotation.
This should be the end of the 'power' stroke.... and the exhaust valve should be beginning to open....

1/2 turn more should bring the piston back up to the top of the cylinder again at the top of the exhaust stroke.

Your exhaust valve should be almost all the way closed, and your intake valve should be starting to open...

Now, watch the intake rocker arm as you turn the crankshaft 1/2 turn again....

Did the intake valve close just as the 'Odd' Side mark you made on the balancer come to the '0' (Zero) mark on the timing
(Odd side mark straight across from the balancer timing mark...)

If it did, the cam timing is roughly correct....

That doesn't mean it couldn't have slipped a tooth or two... It just means the timing chain isn't broken, and moving the cam shaft roughly in the correct timing sequence.

Blowing back through the intake is a sure sign that in intake valve is 'Open' somewhere...

That could be stuck valve. (easy to fix. but requires pulling the head to fix correctly)
Bent rocker arms. (easy to fix, but why did it bend?)
Bent valves. (a little harder to fix. requires pulling the head, and maybe a new head depending on damage)
Broken timing chain. (rocker arms won't work at all, easy to fix if on valves are bent....)
Lifters stick in bore. (this will require some delicate diagnoses of the engine will be OK for service with out a rebuild)

Most AMC cams are flat as pancakes when we take them out...
All AMC V-8 engines don't have ANY oiling to the timing chain, distributor drive gear, or fuel pump eccentric.
This causes real problems.
I would advise an oiling upgrade before putting the engine back in service.
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