Timing Chain life?
Thread Starter
Instructor
Joined: Nov 2002
Posts: 131
Likes: 0
From: Tacoma Wa
Timing Chain life?
How many miles is a modern GM Timing Chain set good for? I know I put 175k miles on my 85 Corvette without it failing but curious as my curent miles are getting high.
Race Director
Joined: Dec 2000
Posts: 17,551
Likes: 26
From: El Paso Texas
They'll go damn near forever, but it's wise to change them at around 100K. Why?? Because you're losing timing advance. The sloppier the chain gets, the more the timing retards....which translates to a loss of torque and rough idle.
I changed the chain on my 84 at 135K. The car was instantly more responsive, idled much smoother, and had much better vacuum. My harmonic balancer had disintegrated and took out the timing cover seal, so I had to pull the cover anyway....figured it was a good time to change the chain. Very glad I did.
It's a big job, so plan on a weekend to do it. Took me about 8 hours at a leisurely pace.
I changed the chain on my 84 at 135K. The car was instantly more responsive, idled much smoother, and had much better vacuum. My harmonic balancer had disintegrated and took out the timing cover seal, so I had to pull the cover anyway....figured it was a good time to change the chain. Very glad I did.
It's a big job, so plan on a weekend to do it. Took me about 8 hours at a leisurely pace.
Race Director
Joined: Dec 2000
Posts: 17,551
Likes: 26
From: El Paso Texas
Originally Posted by 86z51-4+3
173687 and still going strong on my 86.idels fine
Try this. Remove the distributor cap. Turn the engine by hand until you reach the timing marks on the balancer. Stop. Rotate the engine the other direction until the rotor begins to move again. Note the timing mark reading. Take the difference and divide it by 2. That's how many degrees of timing you're losing.
If it takes 8 degrees to move the rotor, you're losing 4 degrees of timing advance due to chain wear.
Incidentally, if the chain ever does break, this isn't a clearance engine. Pistons and valves can and will collide. Not pretty.
Race Director
Joined: Aug 2000
Posts: 14,130
Likes: 7
Cruise-In II Veteran
I remember some years back working for a GM dealer,I believe it was suggested to have the chain replaced every 75K miles.I may be wrong about the mileage but it was around there.(more money for them too!)Yeah them chains can last a very long time,but they do stretch a little bit and after 100K miles its likely a little sloppy with age and mileage.
The gears also wear down,which increases slop.
Id replace an old one as a weekend project for preventive maint. down the road as a suggestion.
Just a side note,I tore down a 150K miles GM 3.1 V6 engine that has the metal timing gears and chain.Comparing the new set to the old timing chain and gears,I could visually see a big difference between the gear teeth.The new chain set was installed and felt tight on there while the old chain was loose on the sides before removal.It had alot of play in it!
The gears also wear down,which increases slop.
Id replace an old one as a weekend project for preventive maint. down the road as a suggestion.
Just a side note,I tore down a 150K miles GM 3.1 V6 engine that has the metal timing gears and chain.Comparing the new set to the old timing chain and gears,I could visually see a big difference between the gear teeth.The new chain set was installed and felt tight on there while the old chain was loose on the sides before removal.It had alot of play in it!
