Chevy Astro 4.3 engine Timing Chain Life Expectancy


I have a 1991 Astro Van with 135,000 miles. It runs well and I would like to keep it. Is there an expected timing chain life?


Timing chains generally last the life of the engine. Timing belts typically last 60,000-120,000 miles.


[b]After 100,000 miles, a timing chain can begin to stretch. This can effect engine performance and fuel mileage.

To check for a stretched timing chain, remove the distributor cap if the engine is equipped with a distributor. Using a socket and breaker bar on the crank bolt, turn the engine one way and then the other while someone observes the disributor rotor. If the engine can be turned 5 degrees or more before the rotor begins to move, it indicates the timing chain is stretched. If the engine doesn’t have a distributor, remove one of the valve covers and observe when the valves move in relationship to turning the crankshaft.

If timing chains lasted the life of the engine, there would be no call for parts stores to sell replacement timing chain sets.



Most timing chain failures are due to lack of regular oil changes.
Usually they last the life of the engine.


You need to know what kind of timing chain that you have and whether or not it has a tensioner. A tensioner as roller timing chain motors have, will make the distributor rotation test ineffective.
That test is valid for a silent timing chain without a tensioner. If your motor has timing gears, they should last the life of the engine too.

The life of the engine is when something in the engine fails.

Learn what kind of cam timing drive that you have and then ask for advice from a dealer or two to know if it is prudent to change the drive as precaution.

Also, consider your starter, alternator, water pump, transmission, wheel bearings, crank seals, valve stem seals, crank and rod bearing inserts etc, etc. life expectancies too. I do not intend to be difficult but am trying to make a point. Drive and enjoy and keep your towing insurance current. A perfect life is not guaranteed.

A timing chain does not stretch. Its many bearing surfaces wear, effectively making the chain longer. Elongated might be a better word.


Different Chevy engine with more miles, but my '94 Blazer’s 5.7L is at 225K, and it’s still on the original timing chain. Runs smooth as a baby’s butt.

You typically don’t have to worry about chains unless you start hearing obvious rattle noises from the timing chain cover area.


[b]I guess I’m totally wrong on this subject. Even though I’ve replaced countless timing chains sets because the chain was either stretched and/or the gears were worn.



Timing chains are a great problem on some engines while rare on others. Small block Chevrolet engines with automatic transmissions with little stop and go traffic sometimes never need the chain replaced but in heqavy traffic and especially with manual transmissions the chain may not last 75,000.


Tester - would there be a tapping (or dooh, knocking) sound associated with the stretched timing chain?


Car makers have some timing chains that are braced with slides to keep them from vibrating. If yours is tight like that, it could last a very long time. The free slack can accelerate the wear.


The 4.3 is a Chevy 350 (5.7) with two cylinders whacked off. I suspect it uses the same timing chain. In years past, manufacturers have used plastic covered cam gears in an attempt to make the chain and gears run quieter. When this nylon cover flakes off the gear, the chain will slip and the engine will “jump time”. If steel gears are used, they seem to last forever in normal service…Chevy small blocks seldom suffer failed timing chains and or gears…The old Chrysler 318-360 engines would peel their plastic gears at around 130K miles if the car lasted that long…