life of timing chain - 91 Suburban

Both as in if one goes replace both. Hard to tell the "normal" lifespan of the timing set or water pump. You could try to start it one morning and it could jump time with no warning. That's happened on a couple high mileage beaters I've owned. Some motors like the old Dodge 318 you needed to replace the timing set before 100K. Had a Dodge Dakota with a V6 that you could actually hear the timing chain chatter at an idle with 90K on it. Owned a Lincoln Mark IV with a 460 that slipped out of time at 130K with no warning. If you're lucky it will jump time when you're trying to start it otherwise if running it will bend and break stuff like valves, pushrods etc.. If you have the money, the skill, and some leisure time, I would change the pump and the timing set and belts at 190K.

Not to mention that if the chain breaks, it will scatter links through out the engine, which means pulling the engine to clean the pieces out of the oil pan, the galley etc. Years ago ford recommended chain and gear at 50,000 miles, seen some so stretched dont know how they kept running. GM liked a nylon coated cam gear, quiter, but the nylon would strip and then shred the chain. Most GM V-8 engines are not going to crash if the chain breaks, too much clearence on most stock engines unless high performance models with high compression., ie above 9.5:1..

Dont skimp on the timing set, buy the best you can get.

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