TSB For GT500 / GT350 Secondary Timing Chain Tensioner [Service Guide Attached]

I had this sent to me hot off the press but didn’t get the opportunity to go through it and post. This is a big deal and a major f*** up. Thanks for posting it.

We have seen a number of GT350 engines as well as a few GT500’s with broken off valve heads in the combustion chamber. I sensed it was due to defective valves, a supplier issue. This “customer satisfaction program,” not a TSB, has changed my view. It now looks as though a chain tension issue may have led to valves making contact with pistons and it just got worse from there.

What is difficult to understand is how this could take place years after GT350 engines were produced at the Niche plant. Was there a procedural change in the assembly steps that allowed this to happen, even if only randomly? Or even worse, was this related to a certain builder(s) not activating the tensioner(s)? Begs the question as to whether engine builders work on both GT350 and GT500 engine assemblies.

I just missed the window for this and am thankful but feel awful for any of you that are impacted by this one. I encourage any of you that might be affected to take a look (at the very least) yourself, using the linked pdf’s, to see if your tensioners are in the proper position.

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