GM 3.6 timing chain issue question

While browsing online for a replacement work car I noticed a lot of gm SUVs with the 3.6 for cheap, all claiming to have timing chain problems. A little googling tells me this was common. My question is on these engines does a failed timing chain ruin the engine? If the answer is "sometimes" is there any way to tell if the engine was destroyed without tearing it down? Can the timing chains be replaced in the chassis or does the engine need to come out?

In order.

Depends on "failed".  When the chains stretch enough they will set fault codes for cam timing.  If you ignore this long enough the primary chain will jump time.  The only times I have seen timing chain issues lead to internal engine damage were in engines chronically run low on oil to the point where the pickup sucked air a lot. No timing chain engine enjoys running with no oil pressure, and the damage could be more attributed to being run without oil than to chain issues.  (Kind of like the distinction between dying in your sleep, and falling asleep behind the wheel and having a fatal crash as a result)

If it starts and runs, it isn't destroyed.  I have had very worn chains jump time while hand cranking the engine to get to the correct orientation before pulling the chains off, somehow they stay in time when running.

Solid it depends on the chassis.  All longitudinal and some transverse can be done in chassis, some transverse the hood opening is physically smaller than the timing cover and you have to lift the vehicle off of the front subframe.

The vast, vast, vast majority of chains I have done - and I have done a lot of them - they were merely setting cam/crank correlation faults.  Almost always bank 1 because bank 1 sees the largest amount of effect from chain stretch.

Pete. (l33t FS) said:

In order.

Depends on "failed".  When the chains stretch enough they will set fault codes for cam timing.  If you ignore this long enough the primary chain will jump time.  The only times I have seen timing chain issues lead to internal engine damage were in engines chronically run low on oil to the point where the pickup sucked air a lot. No timing chain engine enjoys running with no oil pressure, and the damage could be more attributed to being run without oil than to chain issues.  (Kind of like the distinction between dying in your sleep, and falling asleep behind the wheel and having a fatal crash as a result)

If it starts and runs, it isn't destroyed.  I have had very worn chains jump time while hand cranking the engine to get to the correct orientation before pulling the chains off, somehow they stay in time when running.

Solid it depends on the chassis.  All longitudinal and some transverse can be done in chassis, some transverse the hood opening is physically smaller than the timing cover and you have to lift the vehicle off of the front subframe.

 

The vast, vast, vast majority of chains I have done - and I have done a lot of them - they were merely setting cam/crank correlation faults.  Almost always bank 1 because bank 1 sees the largest amount of effect from chain stretch.

Thanks for the very good explanation, it was very helpful. As far as removing the engine, what I'm looking at is a gmc Acadia, do you know if that can be done in the car, because I dont have a lift.

In reply to gearheadmb :

You are miles ahead if you drop the subframe with engine attached. There just isn't enough room against the passenger framerail to make it all work including sight lines for proper pulley alignment.

In reply to Ranger50 :

I'd like to say that the engines that do not have a giant torque bracket in front of the front of bank 2 are the ones you can do in chassis.  I honestly cannot keep the different models straight, they all blend in to "big truck" for me.  So far I have only had to drop two drivetrains out.

Seeing the marks was never a concern, aside from the bank 2 secondary chain to idler sprocket mark, which I always cheat on and paint the special colored chain link with a bright yellow paint marker so I can see it through the little access hole.

Coworker just got a quote of $7000 to fix the timing chain in his 2012 CTS 3.6 AWD.  I may offer to buy it from him and do it myself.  These are longitudinal mounted so likely an in car job.

I may be checking back for advice if all goes well.

This is a timely bump of this post...

I have a 2007 CTS 3.6 (RWD) with only 82000 miles that I suspect has jumped timing on bank 2 ( misfires on 2,4 and 6).

I was 2.5 ish quarts low on oil.

If I remove the valve covers, will I be able to tell if it has jumped a tooth (or more)?

In reply to gsettle :

No.  There are no useful timing marks.

You check if it's jumped time with a lab scope watching the cam and crank signals vs. a known good pattern, or watching the cam phasing with a scan tool.

If the cam timing is off, it WILL set codes for this, even if it's only off by a little and it drives fine.  (Usually bank 1 because that sees the most effects of chain stretch)  With misfires on one bank and no cam codes, I'd be looking at seeing if there's a blown fuse for the injectors/coils on that bank, or if the fuel trims are way wonky to suggest an exhaust restriction.

I'm going to offer to fix my coworkers car or buy it from him.  Feel free to offer any tips on a timing/phaser/water pump service.

Our 2010 SAAB 9-5 with the 2.8T v6 has been setting the cam codes so I am going to do the chains this spring.  After looking around the engine bay I am pretty sure the motor will have to come out which should be fun without a lift.