LT6 “Ticking” Service Bulletin

[John]

ADMIN UPDATE: Go to 4:52 AM (PST) post by GTPprix for the June 28, 2023 final TSB repair procedure. Thank you so much for GTPprix for his leading us through this entire learning process, culminating with the June 28th TSB in post # 192.

ADMIN UPDATE # 2 as of August 16th: With the absence of any new information and the simultaneous lack of any data that the ticking is causing any current nor long term reliability nor durability issues, this thread is TEMPORARILY closed. Anyone who has any new data, please PM “John” with it, for that new info could well be the precipitant toward this thread at that time being re-opened. THANK YOU.


Not a durability issue but one that GM wants listened to. We thank Gabed1 for brining this specific document to our attention.

Note most do not have the sound, i.e., neither mine nor two of our friend’s have it.

[John]

Sorry I do not. Every direct injection engine has a ticking sound. To me if your hatch is closed, if you can faintly hear it you are just fine, but if loud not fine. I just heard one that is clearly louder than the rest — and that owner (who just showed up) is taking it into the dealership.

[C8Zeb06]

Yikes! Hopefully they get to the bottom of this quickly!

[Abouttime]

Might be due to no hydraulic lifters?🤔

Mechanical lifters are notorious for noise; is it present as engine speed (pistons, wrist pin, etc.) or half speed (valve train)? Actually a slight valve tap in a mechanical lifter engine is okay; means the valves are fully closing, so no combustion blow by, as there is a little clearance between valve and tappet.

[John]

They noted in writing that this is NOT A DURABILITY ISSUE.

[AzDave47]

How do you get the audio clip to play? When I click on it all I get is a magnifying glass.

Also there are no mechanical lifters in this DOHC engine. The cam lobes act on the rocker pad that works directly on the valves.

[Abouttime]

AzDave47My bad on the lifters. But, could there be a higher tolerance on the cam lobe to valve clearance? Are we hearing to contact between the lobe and valve. I know in an older V8 I owned in the 1970’s you could hear the mechanical fuel pump lever contact as it ran over the fuel pump lobe on the camshaft.

Could this be similar? I know there was a lot of discussion on whether the z06 valve train would stay in tolerance via the use of shims.

[John]

IF we had contact between the lobe and the valve, GM would not have clearly stated that there are no durability issues.

[Phil1098]

AzDave47My bad on the lifters. But, could there be a higher tolerance on the cam lobe to valve clearance? Are we hearing to contact between the lobe and valve. I know in an older V8 I owned in the 1970’s you could hear the mechanical fuel pump lever contact as it ran over the fuel pump lobe on the camshaft.

Could this be similar? I know there was a lot of discussion on whether the z06 valve train would stay in tolerance via the use of shims.

Not at all what is going on. They check each lobe multiple times with computers and sensors. There are no shims and they have clearances designed and tested to stay within spec for 100K miles +.

[NA FURY]

IF we had contact between the lobe and the valve, GM would not have clearly stated that there are no durability issues.

Was this stated somewhere in certainty? The PIP states "No durability issues have been identified with this concern..." (emphasis mine). In the context of an open investigation, I'm assuming they phrased it that way for a reason.

[MGfoursixeight]

The LT6 does indeed have valve clearance shims and the spec for valve clearance is .006" to .010". There is a chart with shim sizes in SI if clearance is out of spec and requires adjustment.

It is worth noting that the procedure requires several special tools to remove/install the camshafts. Adjusting the valve clearance on a LT6 would be a fairly time consuming process. First you would have to measure and record the clearance for all 32 valves. Then if any are out of spec, R+I the camshafts and followers. From there determine which shims you have on the effected valves and go to the chart to see which size shim is required to bring the clearance with in spec.
Replace the effected shim(s), reassemble the head(s) and recheck the clearance to verify that all valves are with in spec.

[Abouttime]

Not at all what is going on. They check each lobe multiple times with computers and sensors. There are no shims and they have clearances designed and tested to stay within spec for 100K miles +.

Sorry, but I’m pretty sure they use shims. There are assembly videos that show builders using a tray of various shims.

[Italio]

My car has had this since I bought it definitely doesn’t sound like normal engine noise and only happens when the oil is up to temp…. Mine has been detected from cylinder 7 …. They are not 100% certain that this is not affecting performance or engine I’ve been dealing with this before any bulletins. I’ve also been told many times that they don’t know how to fix it so I don’t think they know exactly what the problem is.

[Phil1098]

Sorry, but I’m pretty sure they use shims. There are assembly videos that show builders using a tray of various shims.

I stand corrected, was thinking lifters. The measurement of the shims is like no other though to get 100k service intervals.

[Phil1098]

My car has had this since I bought it definitely doesn’t sound like normal engine noise and only happens when the oil is up to temp…. Mine has been detected from cylinder 7 …. They are not 100% certain that this is not affecting performance or engine I’ve been dealing with this before any bulletins. I’ve also been told many times that they don’t know how to fix it so I don’t think they know exactly what the problem is.

Is your car a Z06?