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I am beginning an engine build for my 1997 Z28 M6 street car. I haven’t finalized all my plans yet but it will be
- fuel injected
- naturally aspirated
- pump gas
- shooting for 450-500 RWHP while keeping strong low end torque.
I purchased an L94 (Aluminum block 6.2 L) long block that came from a dealer service center. Supposedly it has a bad camshaft but I’ll find out more as I disassemble the engine. So far I have taken off one cylinder head and found something interesting. There was a piece of steel that was clamped between the block and the head gasket. Obviously, it was there when the head was installed. I’m not sure exactly what it is but it’s brittle and magnetic. The sleeve wasn’t dented but the block has a dent and the head has a very slight dent. I’ll probably have to fill the dent in the block. It’s about 0.015” deep. Here are some pictures of the piece of debris.
If that engine came from a service center, then never go there for anything. Debris between the block and head? Really? Who does that? And that's not exactly a small, easily overlooked piece of debris, either.
I have no reason to believe that the service center removed the cylinder head. All the head bolts were still torqued. I’m pretty sure they just replaced the long block. The debris has likely been in there since it was first assembled. The crazy thing is it looks like the head gasket still sealed just fine. There isn’t any evidence of leaking through that area.
I finished disassembling the engine and found out where the piece of debris came from. It was a piece of the piston ring that must have busted off during assembly. You'll notice in the picture that part of the ring is broken away.
I found another issue on a different cylinder as well. I noticed some small marks on the top of the piston in cylinder #1 and then I found a scratch on the cylinder wall. (See picture) Hopefully it will clean up with an overbore. I'll measure the scratch depth before I do any machining.
So it looks like I'll be boring the cylinders out and putting new pistons in it.
Most of the parts for the long block have arrived. I still have some machining to do before assembly but hopefully will have the long block assembled in December.
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L92 Engine Build thread 
